part iii pre-feasibility study for masang-2 hepp · final report (main) chapter 16 project site...

PART III PRE-FEASIBILITY STUDY FOR MASANG-2 HEPP

Final Report (Main) Chapter 16 Project Site Condition

JICA Project for the Master Plan Study of 16-1 August, 2010 Hydropower Development in Indonesia

CHAPTER 16 PROJECT SITE CONDITION

16.1 LOCATION

The Masang-2 Hydroelectric Power Project (hereinafter referred to as “the project”) is situated approximately at 0°5’ to 0°10’ of the south latitude and 100°11’ to 100°15’ of the east longitude on the upper course of the Masang River.

The project is administratively located in Agam Regency (Kabupaten), West Sumatra Province. The project is located approximately 30 km northwest of Bukit Tinggi city, 100 km northwest of Padang city, the capital city of west Sumatra. Main structures such as intake weir, waterway and powerhouse are located in Palembayan Subdistrict (Kecamatan). Administrative map of Agam Regency is as seen in Figure 16.1.1.

Source: Agam Regency

Figure 16.1.1 Administrative Map of Agam Regency



16.2 TOPOGRAPHY

Physiographically the project site is located at the central Barisan system, which consists of a number of NW-SE trending block mountains. The Masang River originates from Mt. Marapi (El. 2,891.3m) and runs between these NW-SE trending block mountains. Around the project site the river flows to northwest, subparallel to Great Sumatra Fault System.

The major tributaries flowing into the Masang river are Sianok, Guntung and Alahanpanjang rivers. The project is sited between the confluence of Sianok and Guntung rivers, which is the most upstream of the Masang river, and the confluence of Masang and Alahanpanjang rivers.

In this pre-feasibility study, topographic survey was conducted at the Masang-2 project area to obtain topographic maps and cross sections of the following quantities.

Table16.2.1 Summary of Topographic Survey Conducted Survey Item Quantity Remarks

1. Topographic mapping on 1:10,000 scale 30 km2 Project area 2. Topographic mapping on 1:2,000 scale 4.0 km2 Main project structure sites 3. River cross section survey 10 km

16.3 GEOLOGY

16.3.1 GENERAL

The project consists mainly of a weir, sand trap, intermediate pond, connection tunnel, headrace tunnel, surge tank, penstock, and powerhouse. The geological investigations at the pre-feasibility stage were conducted to evaluate project site geology and seismic geology.

The section summarizes the geological conditions of the project site while Volume IV Supporting Report (2) details the results of the preliminary geological investigation and evaluations conducted at the prefeasibility study.

16.3.2 REGIONAL GEOLOGY

The regional stratigraphy of the project site, as shown in Figure 16.3.1, begins with the Carboniferous to Permian. These rocks and those of the Miocene intrusive rocks compose the bedrocks of the region. The Quaternary rocks, consisting mainly of pumiceous tuff and andesite from the volcanic activity of the Maninjau Volcano unconformably overlie extensively the older formations. The recent sediments, represented by alluvium, are of limited occurrence.

The major geological structure is the Sumatran Fault Zone (SFZ), also called Great Sumatra Fault System (GSF), one of the most seismically active zones in Indonesia. The SFZ, generally parallel to the Sunda trench, results from the partitioning of oblique plate convergence into normal convergence at the trench and represents right-lateral strike-slip faulting. According to Sieh and Natawidjaja (2000),



the SFZ, totally 1,900 km long, is highly segmented and can be subdivided into 19 major segments on the basis of its geomorphic and topographical expressions. The major segment of the SFZ in the proximity of the project site is the Sianok segment (0.7oS to 0.1oN), which, approximately 90 km long, runs from the northeast shore of Lake Singkarak along the southwest flank of the volcano Marapi around the project site.

Several local NE-SW and NW-SE fault systems are also distributed in the general area of the project site. The NW-SE fault systems, which are parallel to the SFZ, may be subsidiary to the SFZ

Source: Modified from Geological Map of the Padang Quadrangle, Sumatra, 1:250,000

Qal Alluvial deposits of silt, sand and gravel Qpt Pumiceous tuff and andesite of slightly consolidated glass, shards and pumice fragment Qmaj Andesite of Danau Maninjau caldera QTau Undifferentiated flows of lahars, fanglomerate and other colluvial deposits Pl Permian limestone rocks with some thin intercalations of slate, phyllites and quartzite Ps Permian metamorphic rocks of phyllite, slate and mica greywacke

Figure16.3.1 Regional Geological Map

16.3.3 SEISMICILITY

The project site is located close to the SFZ, one of the most seismically active zones in Indonesia. Accordingly seismic consideration needs to be conducted for structural design of the project. Seismic hazard assessment was conducted by using probalistic approach, local seismic design code and through review of some similar projects within Sumatra.



The design seismic coefficients obtained are summarized in Table 16.3.1. The design seismic coefficient through probabilistic analysis is consistent with that from Indonesia Seismic Map. They are both parallel to those of existing similar projects within Sumatra.

Accordingly in view of the type of structures under consideration, construction cost and the safety and environmental consequences of failure the design seismic coefficient for the prefeasibility study is recommended conservatively to be 0.15 for design of the weir and intermediate pond dike.

Table16.3.1 Summary of Obtained Design Seismic Acceleration Approach Design seismic coefficient Remarks

1. Existing similar projects 0.12 – 0.15 2. Probabilistic method 0.10 – 0.14 Cornell formula

3. Indonesia seismic map 0.12 – 0.13 Rock foundation 0.16 – 0.18 Highly weathered tuff foundation

16.3.4 GEOLOGICAL INVESTIGATION RESULTS

The geological investigation for the pre-feasibility study consisted of geological mapping, seismic refraction survey, core drillings, in-situ and laboratory tests. The quantity of geological investigation conducted is summarized in Table 16.3.2. The location of geological investigation is given in Figure 16.3.2.

Table16.3.2 Summary of Geological Investigation Conducted Survey Item Quantity Remarks

1. Geological mapping on 1:10,000 scale 25 km2 Project area 2. Seismic refraction survey 6,920 m Main project structure sites 3. Core drilling 460 m 12 boreholes 4. Field permeability test 92 sections 5. Standard penetration test 55 times 6. Laboratory test for foundation rocks 10 samples 7. Laboratory tests for construction material 10 samples

Source: JICA Study Team

(1) Geological Mapping

Geological mapping, as shown in Figure 16.3.3, indicates that three geological units are distributed in the project site; they are in the order of geological time from old to young 1) Limestone with some interbedded slate, 2) Greenstone and 3) Pumiceous tuff with some andesitic rock association.

The limestone is exposed chiefly along the Masang River valley and at the southern part of the project site. The rock, locally intercalated with slate and sandstone, generally strikes N120E and dips 45 degrees toward northwest. The limestone at outcrops is generally gray to dark gray, hard, highly fractured and highly jointed. The weir for Plan B, the intermediate pond dike and the powerhouse would be founded on the rocks.

The greenstone (serpentinite) is of limited occurrence, mainly in the southern part of the project site. The rock at outcrops is generally green to greenish grey, soft to extremely weak, highly fractured and sheared.



Pumiceous tuff with some andesitic rock association is extensively distributed over the hill slopes within the project site. The pumiceous tuff can be subdivided into two rock types, fine-grained tuff and tuff breccia. The fine-grained tuff, generally yellowish brown to brown and slightly consolidated, consists of silt to sand and contains glass and pumice. On the other hand, the tuff breccia, which underlies the fine-grained tuff is brown to greenish gray, semi-consolidated and includes lots of andesitic and basaltic fragments.

In addition, the recent alluvial and colluvial deposits are locally distributed in the project site. The alluvial materials contain a large quantity of subangular to rounded gravel and boulder of andesite.

(2) Seismic Refraction Survey

The interpreted seismic data indicate that four velocity layers underlie the project site. The inferred geological classification is summarized in Table 16.3.3 below.

Table16.3.3 Geological Classification of Seismic Units Seismic velocity (m/sec) Interpreted geological classification Layer thickness (m)Weir site B, ML-1 and ML-2

1. 300 – 450 Surficial deposits (talus, alluvial, etc.) 0.6 – 3.7 2. 820 – 1,400 Highly weathered/fractured limestone 0.6 – 14.8 3. 1,800 – 2,800 Moderately weathered/fractured limestone 10.0 – 90.0 4. >4,300 Slightly weathered/fractured limestone -

Weir site C, ML-3 and ML-4 1. 300 – 450 Surficial deposits (talus, alluvial, etc.) 0.2 – 2.5 2. 820 – 1,100 Highly weathered fine-grained tuff 1.9 – 21.8 3. 1,600 – 2,100 Moderately weathered tuff breccia 10.3 – 66.8 4. 2,200 – 3,600 Slightly weathered rocks -

Inlet area of waterway route (Plan B/C), ML-5 and ML-6 1. 360 – 500 Surficial deposits (talus, alluvial, etc.) 1.0 – 3.8 2. 880 – 1,500 Highly weathered fine-grained tuff 0.0 – 6.6 3. 1,700 – 2,200 Moderately weathered tuff breccia 15.0 – 36.0 4. 3,800 – 4,600 Slightly weathered rocks -

Intermediate pond dike site (Plan B/C), ML-7 to ML-11, L-5 and L-6 1. 300 – 500 Surficial deposits (talus, alluvial, etc.) 0.6 – 9.0 2. 700 – 1,100 Highly weathered/fractured limestone 1.0 – 11.9 3. 1,100 – 2,500 Moderate weathered/fractured limestone 3.6 – 53.0 4. 3,700 – 3,800 Slightly weathered/fractured limestone -

Surge tank and powerhouse (Plan A/B/C), ML-12 to ML-14 and L-3 to L-4 1. 300 – 500 Surficial deposits (talus, alluvial, etc.) 0.2 – 6.0 2. 700 – 1,500 Highly weathered fine-grained tuff 1.4 – 8.2 3. 1,700 – 2,500 Moderately weathered limestone/ tuff breccia 5.6 – 76.0 4. >4,600 Slightly weathered limestone -

Connection tunnel (Plan B/C), L-1 and L-2 1. 400 – 500 Surficial deposits (talus, alluvial, etc.) 1.0 – 9.3 2. 1,000 – 1,200 Weathered fine-grained tuff 0.9 – 6.2 3. 1,700 – 2,700 Highly fractured limestone/weathered tuff breccia 3.6 – 73.4 4. >3,300 Slightly weathered limestone -




(3) Boring Investigation and Field Tests

The boring investigation together with field permeability test was conducted to explore and evaluate the subsurface conditions of the project site. The results of boring investigation are summarized in Table 16.3.4. The results of field permeability tests are given in Table 16.3.5 below. The permeability in the foundation rocks is generally in the range of 1.0×10-5cm/se to 1.0×10-3 cm/sec; thereby indicating moderately permeable foundation rocks.

Table16.3.4 Summary of Boring Investigation Results Area Bore Location Geology Weathering/Fracturing Rock class

MW-1 Right bank 0-11.2m alluvial/colluvial 11.2- 50.0m tuff breccia

0-11.2m Completely 11.2-50.0m Highly

0-11.2m D 11.2-50.0m D/CL

Weir site A MW-2 Riverbed 0-4.8m alluvial/colluvial 4.8-20.0m tuff breccia


0-4.8m D 4.8-20.0m D/CL

MW-3 Left bank 0-9.8m alluvial/colluvial 9.8-40.0m tuff breccia


0-9.8m D 9.8-40.0m D/CL

Weir site B MW-4 Right bank 0-7.4m alluvial/colluvial

7.4-30.0m limestone

0-7.4m Completely 7.4-17.0m Completely 17.0-23.0m Moderately 23.0-30.0m Completely

0-7.4m D 7.4-17.0m D/CL 17.0-23.0m CM 23.0-30.0m D/CL

MW-5 Left bank 0-10.0m alluvial/colluvial 10.0-30.0m limestone


0-10.0m D 10.0-30.0m D/CL

Weir site C MW-6 Left bank 0-4.0m alluvial/colluvial 4.0-19.8m tuff 19.8-30.0m tuff breccia


0-4.0m D 4.0-30.0m D/CL

Intermediate pond site

MW-7 Right bank 0-4.0m alluvial/colluvial 4.0-30.0m limestone

0-4.0m Completely 4.0-7.8m Highly 7.8-30.0m Moderately

0-4.0m D 4.0-7.8m D/CL 7.8-30m CM/CH

MW-8 Riverbed 0-6.0m alluvial/colluvial 6.0-20.0m limestone

0-6.0m Completely 6.0-20.0m Moderately

0-6.0m D 6.0-20m CM/CH

MW-9 Left bank 0-3.0m alluvial/colluvial 3.0-40.0m slate

0-3.0m Completely 3.0-19.7m Moderately 19.7-40.0m Highly

0-3.0m D 3.0-19.7m CM/CH 19.7-40.0m D/CL

Headrace route MH-1 Plan A

0-10.0m alluvial/colluvial 10.0-19.7m tuff 19.7-69.0m tuff breccia 69.0-100.0m andesite

0-10.0m Completely 10.0-100.0m Moderately

0-10.0m D 10.0-100m CL/CH

Surge tank site MS-1 Plan A/B/C

0-0.5m alluvial/colluvial 0.5-28.5m tuff 28.5-41.0m tuff breccia 41.0-50.0m andesite


0-0.5m D 0.5-41.0m D/CL 41.0-50.0m CM/CH

Powerhouse site MP-1 Plan A/B/C 0-3.0m alluvial/colluvial

3.0-20.0m limestone


0-3.0m D 3.0-11.0m D/CL 11.0-20m CM/CH

Table16.3.5 Summary of Permeability Test Results

Area Geology Permeability (cm/se) Groundwater (depth-m)

Weir site A Alluvial and colluvial deposits 3.63×10-4 - 4.94×10-3 MW-1: 3.0m Weathered tuff breccia 5.22×10-5 - 3.51×10-3 MW-3: 15.5m

Weir site B Alluvial and colluvial deposits 3.76×10-4 - 1.51×10-3 MW-4: 5.0m Fractured limestone 2.28×10-4 - 2.07×10-3 MW-5: 14.5m

Alluvial and colluvial deposits 5.00×10-3 MW-6: No water Weir site C Weathered tuff 2.99×10-3 - 1.37×10-2

Weathered tuff breccia 7.55×10-4 - 2.01×10-3 Intermediate

pond site Alluvial and colluvial deposits 1.00×10-4 - 1.56×10-3 MW-7: No water Fractured limestone 2.95×10-5 - 4.59×10-3 MW-9: No water

Headrace route

Alluvial and colluvial deposits 1.45×10-6 - 2.85×10-6 MH-1: No water Weathered tuff 1.53×10-5 - 3.73×10-5 Weathered tuff breccia 2.16×10-6 - 2.42×10-4 Weathered andesite 2.85×10-6 - 2.36×10-3




16.3.5 GEOLOGICAL AND GEOTECHNICAL CONDITIONS OF THE PROJECT SITE

(1) Intake Weir Site

Weir site A – The site is located approximately 300 m downstream of the confluence between the Cuntung river and the Sianok river. The Masang River at the weir site shows U-shaped valley with a riverbed width of about 30 m. The geology of the weir site A, as shown in Figure 16.3.4, is composed of tuff breccia with alluvial and colluvial cover of about 10 m thick. The tuff breccia, especially its upper part was highly weathered into a poor quality of D class rock mass in Japanese Rock Classification Standard. Accordingly the weir foundation at the site will require deep excavation up to over 10 m deep to remove the overlying loose deposits and highly weathered tuff breccia or a combination of pile foundation to improve the bearing capacity of foundation rocks.

Weir site B – The site lies about 600 m downstream of the weir site A at the straight course of the river. The Masang River at the weir site shows wide V-shaped valley with a riverbed width of about 35 m. Figure 16.3.5 shows the geological conditions of the weir site B. The thickness of the surficial deposits is in the order of 1 to 7 m. The underlying limestone is exposed in the riverbed and at the right abutment. From field reconnaissance and core observation the limestone is generally very hard and strong, moderately to highly fractured and can be classified into D to CL class rocks from Japanese Rock Classification Standard. In addition, the permeability of the fractured limestone is in the range of 2.28×10-4cm/sec to 2.05×10-3 cm/sec and the limestone is thus considered to be moderately permeable rocks. Accordingly the foundation conditions at the weir are considered favorable with the weir structure founded in the limestone, however foundation treatment would be required to improve the permeability of the foundation rock.

Weir site C – the site is located further 500 m downstream of the weir site B. The Masang River at the weir site shows wide V-shaped valley with a riverbed width of about 30 m. The geology of the site, as shown in Figure 16.3.6, consists mainly of tuff, tuff breccia and limestone. The thickness of the highly weathered tuff and tuff breccia is over 30 m at the abutments. The underlying limestone crops out solely in the riverbed and is expected to be encountered at a depth of 35 to 40 m at the abutments. Because of poor quality of the weathered tuff and tuff breccia at the abutments, deep excavation or foundation treatment for the weir foundation would be required at the abutments.

(2) Intermediate Pond Site

The intermediate pond site is located at the lower course of a small stream, a tributary of the Masang River close to Kototinggi village. The width of the streambed at the pond site is about 5 m. The left abutment is a thin ridge and the right abutment is a mountainous hillslope.

The geology of the intermediate pond site consists mainly of limestone and contains intercalated thin shale beds, as shown in Figure 16.3.7. Alluvial and colluvial deposits as well as tuff locally overlie the limestone mainly along the stream valley. The thickness of these superficial layers is in the range of 1 to 4 m at the abutments and in the range of 1 to 6 m in the streambed.



The limestone is generally hard, moderately fractured and jointed and can be classified as CM to CH class rock in Japanese Rock Classification Standard. On the other hand, the interbedded slate is moderately to highly fractured and sheared and can be classified as D to CM class rock.

The limestone and interbedded slate at the intermediate pond site has moderate to low permeability with a permeability of 2.95×10-5cm/se to 4.59×10-3 cm/sec. In addition, no groundwater was observed during borehole drilling around the abutments, indicating that groundwater level around the abutments was very low.

Accordingly, the intermediate pond dike will be expected to be founded on the limestone, which is considered favorable in terms of bearing capacity. Leakage, however, would be likely to be encountered around the abutments and foundation rocks, especially from the right abutment of thin ridge.

(3) Connection and Headrace Tunnels (Plan B)

In Plan B it is planned to construct 1,060 m long connection culvert, 1,630 m long connection tunnel and 4,550 m long headrace tunnel along the left side of the Masang River. The connection and headrace tunnels will be located mostly in limestone interbedded with slate and locally in tuff and tuff breccia. No detailed geological data are available from the rock masses along the most part of the tunnel alignment at surface and at the tunneling depth. The geological conditions considered are based mainly on surface geological mapping and boring information obtained in the vicinity of the tunnel alignments, as shown in Figure 16.3.8.

As seen from Figure 16.3.8, the foundation of the connection and headrace tunnels is expected to mostly be CM to CH class sandstone and tuff as well as tuff breccia, and locally D to CL class rocks over several tens meters relating to the interbedded slate and highly fractured limestone. Consequently the general rock mass conditions are considered favorable from the viewpoint of tunneling and no major geological problems are to be expected during heading of the tunnels.

(4) Surge Tank and Penstock Sites

The surge tank and penstock areas are located at the left side of the Masng River immediately downstream of the confluence between the Masang River and the Alahan Panjang River. Here slope stability and foundation conditions are the major topics of the geological investigations. The boring investigation of MS-1 revealed that the tuff and tuff breccia, about 40-m thick, is highly weathered with a rock quality of D to CL class in Japanese Rock Classification Standard and the underlying moderately weathered andesite is moderately weathered with a rock quality of CM to CH class. The surge tank will be expected to be founded on moderately weathered andesite.

Similarly, the penstock will be located on the hillslope underlain by highly weathered tuff and tuff breccia. The rocks are expected to be D to CL class rock mass in Japanese Rock Classification Standard. For the foundation of fix points of the penstock the foundation tuff might be very poor with a rock quality of D class. If such foundation condition would be encountered foundation treatment



such as mortared rockbolts should be implemented to guarantee stable foundations.

(5) Powerhouse Site

The powerhouse is planned at the left bank of the Masang River. From field reconnaissance and boring investigation (MP-1), the overburden is about 1 to 3 m thick and the underlying limestone is very hard, highly to moderately fractured with a rock quality of D to CH class in Japanese Rock Classification Standard. The limestone, although highly fractured, is considered to have a sufficient bearing capacity for foundation support of the planned powerhouse.

Accordingly, because the foundation limestone is hard and strong and the overburden is thin, no major foundation problems will be expected. The limestone in the foundation area is suitable for the founding of the powerhouse.

16.3.6 CONSTRUCTION MATERIALS

The construction materials required for the construction of the project structures were fine and coarse aggregates, rock fill and impervious materials.

At the prefeasibility study stage the field reconnaissance (geological mapping) together with limited laboratory tests was carried out to examine the possible source, quantity and quality of construction materials.

(1) Sand

Sand materials were needed for the fine aggregates of concrete, grout and mortar. Riverbed deposits around the Dukuh (SS-1 to SS-3), around the weir site (SS-4) and close to the powerhouse site (SS-5) were inspected. The Dukuh sites are in operation by local people.

The alluvial deposits are predominately coarse sand with some gravel. The content of fines is zero to 2 % only. Table 16.3.6 summarizes laboratory test results of the samples. Especially the absorption values of the alluvial sands are high and should be verified in a later survey stage if the materials are to be used in concrete.

Table16.3.6 Summary of Laboratory Tests for Fine Aggregate Material Test Criterion SS-1 SS-2 SS-3 SS-4 SS-8

1. Specific gravity >2.5% 2.71 2.67 2.49 2.48 2.33 2. Absorption <3.0% 6.86 13.15 13.15 14.05 11.58 3. Soundness Na2SO4 12.0% 18.79 4.60 2.40 4.95 13.6 Mg2SO4 15.0% 4. Soft particle <1.0%


(2) Rock Quarry

Several potential limestone quarries (RS-1 through RS-5) around the project site were observed mainly as concreter coarse aggregate for the construction of project. Table 16.3.7 gives the results of



laboratory tests. As seen from Table 16.3.7, the index properties are satisfactory for concrete aggregates except for compressive strength. The low strength values of the limestone quarries were presumably due to weathering because these samples were taken from surface outcrops. The strength property should be confirmed at next investigation stage.

Table 16.3.7 Summary of Laboratory Tests for Coarse Aggregate Material Test Criterion RS-1 RS-2 RS-3 RS-4 RS-5

1. Specific gravity >2.5% 2.76 2.71 2.58 2.71 2.71 2. Absorption <3.0% 1.00 0.89 2.89 0.59 0.32 3. Soundness Na2SO4 12.0% Mg2SO4 15.0% 4. Abrasion <40.0% 25.1 32.3 5. UCS >500kg/cm2 182 141 163 255 372

Notes: 1) UCS = Unconfined compressive strength, 2) 1 kgf/cm2 = 98.1kN/m2 (kPa). Source: JICA Study Team

16.3.7 GEOLOGUCAL SUMMARY

The preliminary geological and geotechnical investigations conducted at the pre-feasibility study stage indicate that the topographical and geological conditions of the project site are suitable for the development of the project.

The mainly investigation results are summarized as follows:

- The basement rocks of the project site are Permian limestone rocks with some thin intercalations of slate. The limestone rock is extensively covered by Quaternary tuff and tuff breccia from the volcanic activity of the Maninjau Volcano.

- In comparison with the weir sites A and C the weir site B is more suitable for founding of the weir construction because at the site the overburden is shallow and the foundation rock of limestone is hard and strong enough to support the planned weir foundation.

- The intermediate pond site was favorable in terms of bearing capacity; however the permeability and leakage of the foundation rocks should be considered especially leakage from the right abutment of thin ridge.

- The planned connection and headrace tunnels would be expected to be founded mostly on CM to CH class rock masses. No major geological problems are to be expected at tunneling.

- Limestone quarry sites around the project site appeared available in quality and quantity as potential construction material sources but the strength characteristics should be confirmed at next survey stage.

- The project site is located in a region of high seismic activity close to the active Great Sumatra Fault, which is the major seismic source around the project site. The design seismic coefficient for the per-feasibility study of the Masang-2 project is recommended conservatively to be 0.15 for design of the weir and intermediate pond dike.



Figure16.3.2 Location of Geological Investigations



Figure16.3.3 Geological Map with Location of Sampling for Construction Materials

Final Report (M

ain) C

hapter 16 Project Site Condition

JICA

Project for the Master Plan Study of

16-13 A

ugust, 2010 H

ydropower D

evelopment in Indonesia

Figure16.3.4 Geological Section of the Weir Axis Alternative A

Final Report (M

ain) C


JICA


16-14 A

ugust, 2010 H

ydropower D


Figure16.3.5 Geological Section of the Weir Axis Alternative B

Final Report (M

ain) C


JICA


16-15 A

ugust, 2010 H

ydropower D


Figure16.3.6 Geological Section of the Weir Axis Alternative C

Final Report (M

ain) C


JICA


16-16 A

ugust, 2010 H

ydropower D


Figure16.3.7 Geological Section of the Intermediate Pond Axis



Figure16.3.8 Geological Section along the Connection and Headrace Tunnel Alignment Alternative B



16.4 METEOROLOGY AND HYDROLOGY

Meteorological Records and Hydrological Records are collected from Meteorological Climatological and Geophysical Agency (Badan Meteorologi Klimatologi dan Geofisika: BMKG), Research Institute for Water Resources Development under Ministry of Public Works (Pusat Penelitian dan Pengembangan Sumber Daya Air: PUSAIR, formerly DPMA), and engineering reports on various hydropower development projects. The location map of the stations is shown in Figure 16.4.1. The availability of data is summarized in Figure 16.4.2 and Figure 16.4.3. The catchment area of Masang-2 HEPP intake weir site is shown in Figure 16.4.4.

16.4.1 METEOROLOGICAL DATA

Climatic data such as air temperature, relative humidity, wind velocity, sunshine duration have been observed at the Tabing-Padang station, which is collected from BMKG. Pan-evaporation has been observed at the Lubuk Sikaping and the Tanjung Pati stations. Pan-evaporation data is collected from Masang-3 HEPP report.

(1) Air Temperature

The average monthly mean air temperature at the Tabing-Padang station in the period of 1971 to 2002 is summarized below.

Unit: ℃Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Mean26.3 26.2 26.4 26.5 26.6 26.3 25.9 25.7 25.7 25.8 25.7 26.0 26.1

As seen, the mean annual air temperature at the Tabing-Padang station is 26.1ºC on an average. There is a slight seasonal change ranging 25.7ºC in August or September to 26.6ºC in May.

(2) Relative Humidity

The average monthly relative humidity at the Tabing-Padang station in the period of 1971 to 2002 is summarized below.

Unit: %Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Mean81.1 81.3 82.4 83.0 82.6 81.4 81.6 82.2 82.2 83.9 84.6 83.1 82.5

As well as the monthly pattern of mean air temperature, there is no significant change of relative humidity throughout the year. The annual mean relative humidity in the period of 1971-2002 at the Tabing-Padang station is 82.5 % and there is a slight seasonal change ranging from 81.1% in January to 84.6 % in November.



(3) Sunshine Duration

The average monthly mean sunshine duration at the Tabing-Padang station in the period of 1971 to 2002 is summarized below.

Unit: %Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Mean53.1 57.4 53.3 55.3 59.5 61.7 60.9 55.4 42.9 41.7 40.4 50.7 52.7

As seen, the mean annual sunshine duration at the Tabing-Padang station is 52.7 % on an average. The maximum duration of 61.7 % and the minimum one of 40.4 % occur in June and November, respectively. Sunshine duration generally decreases with an increase of rainfall. The highest sunshine duration therefore occurs in June in the dry season.

(4) Wind Velocity

The average monthly mean wind velocity at the Tabing-Padang station in the period of 1971 to 2002 is summarized below.

Unit: m/secJan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Mean1.3 1.3 1.3 1.1 1.0 0.9 1.1 1.0 1.1 1.1 1.1 1.1 1.1

Mean annual wind velocity at the Tabing-Padang station is 1.1 m/sec ranging from 0.9m/sec in June and 1.3 m/sec in January, February or March. The wind velocity records collected from Masang-3 HEPP reports in the period of 1971 to 1989 are around 1 m/sec, but the others collected from BMKG in the period of 1990 to 2002 are around 0.1 m/sec.

(5) Evaporation

Pan evaporation records are available at the Lubuk Sikaping station and the Tanjung Pati station. The average monthly mean pan evaporation at the Lubuk Sikaping and the Tanjung Pati stations is summarized below.

Station Name: Lubuk Sukaping (1979-1985) Unit: mm/dayJan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Mean4.8 4.4 4.3 3.9 3.7 4.1 4.1 4.2 3.6 3.6 3.9 4.1 4.1

Station Name: Tanjung Pati (1975-1985) Unit: mm/dayJan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Mean3.3 4.1 3.5 3.6 3.6 3.5 3.6 3.9 3.6 4.1 3.1 3.5 3.6

The ruling factors of pan evaporation may be air temperature and relative humidity, namely evaporation rate varies season to season following to mainly the variation of humidity. As seen in the above table, the seasonal variation of pan evaporation is generally small throughout the year, because there is no great seasonal variation of relative humidity.



16.4.2 RAINFALL DATA

There are 13 rainfall gauging stations in and around the Masang River basin. The location map of these stations is shown in Figure 16.4.1. Also the data availability at these stations is shown in Figure 16.4.2.

The rainfall gauging stations are operated and maintained under BMKG. Monthly rainfall records are collected in Masang-3 HEPP and HPPS2, besides daily rainfall records are collected from BMKG in this study.

PLN formerly had own hydrological observation network (PLN-LMK Observation Network). Currently most of these stations have broken down, after regional office of PLN took responsibility for maintenance which the central office of PLN had taken.

(1) Monthly Rainfall Data

The monthly distributions of mean annual rainfall are illustrated below.

Manin jau : 3 ,199 mm (1969-1993)

0

100

200

300

400

500

600

Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec

Rai

nfa

ll(m

m)

Koto T inggi : 2 ,638 mm (1969-1993)

0

100

200

300

400

500

600


Rai

nfa

ll(m

m)

Su l iki : 2 ,440 mm (1969-2007)

0

100

200

300

400

500

600


Rai

nfa

ll(m

m)



Jambak: 3 ,797 mm (1969-1993)

0

100

200

300

400

500

600


Rai

nfa

ll(m

m)

As seen above, the annual mean rainfall at these stations ranges from 2,000 mm to 4,600 mm per year. It might be said that there exists little seasonality in the Masang River basin receiving rainfalls throughout the year.

(2) Hourly Rainfall Records

Hourly rainfall records are available at the Gunung Melintang, Maninjau, Sungai Talang Barat, Solok Bio-Bio, Muara Paiti, Patir, Puar Datar and Halaban Dua rainfall gauging stations.

Hourly rainfall records are collected to determine the rainfall pattern for the flood analysis. Hourly rainfall records of more than 50 mm were selected for estimating the characteristics of relatively heavy rainfall.

16.4.3 RUNOFF RECORDS

(1) Water Level Gauging Station (AWLR Station)

Only one water level gauging station has been installed in the Masang River basin. The station name is the Sipisang AWLR station located in the north of Palembayan town. The catchment area of the station is described as 458 km2 in the records from 1975 to 1992, and as 436.4 km2 in the records from 1993to 2008. On this study, the catchment area of the station is measured as 475km2 based on 1:50,000 scale map. Besides, the catchment area of Masang-2 HEPP intake weir site is measured as 443km2.

The Sipisang AWLR station is operated by the regional office of the River Bureau under the Ministry of Public Works (Balai Pengendalian Sumber Daya Air: BPSDA).

(2) Runoff Records

The daily runoff records are collected from PUSAIR in Bandung and the daily water level records are collected from BPSDA in Bukit Tinggi. The daily runoff records are available from 1975 to 2008 except in 1988, 1989, 1994, 2002, 2003 and 2004.

The average monthly mean runoff in the period of 1975-2008 is summarized below.



Station Name: Sipisang (1975-2008) Unit: m3/sJan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Mean22.4 20.0 21.6 23.8 22.5 18.7 16.8 18.1 20.6 21.4 27.7 29.2 21.9

As seen, the annual mean runoff at the Sipisang AWLR station is 21.9m3/s or 1,455mm in terms of the annual runoff depth, which is computed by dividing the annual accumulated runoff volume by the catchment area of the gauging station.

16.4.4 LOWFLOW ANALYSIS

(1) General Approach

The continuous long-term runoff data for a time period of more than 20 years at the proposed intake weir site is normally required for evaluating an optimum development scale of the project through power output computation. Further, it is highly expected that the runoff data should be of high accuracy because measurement on economic viability of project is highly dependent on the reliability of available runoff records.

On the Masang-2 HEPP, daily runoff records are required because the type of hydropower development scheme is runoff type.

As described in the previous chapter, the daily runoff records are available from 1975 to 2008 except in 1988, 1989, 1994, 2002, 2003 and 2004. Furthermore, the remaining observation years still include data-missing periods. Therefore, it is necessary to supplement the runoff records at the Sipisang station by infilling of missing data.

On the other hand, the monthly basin mean rainfall at the Sipisang station can be estimated for the period between 1973 and 1993. Thus the runoff data at the Sipisang station can be supplemented and expanded for the period of 1973 to 1993 by constructing a rainfall-runoff simulation model.

Along this line, the Tank Model Method is applied in this study as a rainfall-runoff model, the model parameters of which are calibrated by using rainfall and runoff records available in the period of 1982 to 1986.

Firstly, the reliability of the available runoff records at the Sipisang station for using calibration is evaluated by means of runoff coefficient and annual rainfall loss. Then lowflow analysis by the Tank Model Method is carried out to simulate 21-year long-term monthly runoff data at the Sipisang station.

Finally the daily runoff data at the Masang-2 intake weir site is estimated with 14-year simulated monthly data and 7-year observed daily data.

The outline of lowflow analysis is described below.



(2) Estimation of Missing Data

The observed rainfall records at all of the selected stations include several data interruptions. For the purpose of supplementing the missing rainfall records, the simple regression analysis on the monthly basis are carried out among the selected stations. Missing data at a station is supplemented by another station with linear regression equation which has the highest correlation coefficient.

(3) Test of Consistency of Rainfall Records

The method of testing rainfall records for consistency is the double-mass curve technique. Double-mass analysis tests the consistency of the record at a station by comparing its accumulated annual or seasonal precipitation with the concurrent accumulated values of mean precipitation for a group of surrounding stations.

The corrected rainfall is determined by the following equation.

)/( aCXCX MMPP ×=

where, CXP : Corrected rainfall at any time period at station x (mm) XP : Original recorded rainfall at any time period at station x (mm) CM : Corrected slope of the double-mass curve aM : Original slope of the double-mass curve

Test of Consintency ofRainfall Records

Estimation ofMonthly Basin Mean Rainfall

Monthly Runoff Records at Sipisang

Scrutiny of Runoff Records :( Reliability Check )

- Runoff Coefficient- Annual Rainfall Loss- Consistency of Records

( 1982 - 1986 )

Establishment ofRainfall - Runoff Simulation Model

( Tank Model Method )Calibration of Model Parameters

( 1982 - 1986 )

Supplementation & Expansion ofMonthly Runoff Records by Tank Model

( 1973 - 1993 )

Estimation of Long-Term Daily Runoffat Masang-2 Intake Weir Site

( 1973 - 1993 )

Daily Runoff Records( 1976, 1982 - 1986, 1991 )



The monthly rainfall records at the following stations are adjusted for the following periods.

Maninjau Station: 1979 to 1993

Suliki Station: 1988 to 1993

(4) Estimation of Basin Mean Rainfall at the Sipisang AWLR Station

The basin mean rainfall at the Sipisang AWLR station is estimated by applying the Thiessen Method using the corrected data. The records of selected rainfall gauging stations are divided in two periods considering data availability.

Case1 (1973 to 1986): Maninjau, Koto Tinggi, Suliki

Case2 (1987 to 1993): Koto Tinggi, Suliki, Jambak

The tables below show the computed Thiessen coefficients for estimating basin mean rainfall at the the Sipisang AWLR station.

Case1 (1973-1986)Maninjau Koto Tinggi Suliki

0.67 0.23 0.10

Case2 (1987 to 1993)Koto Tinggi Suliki Jambak

0.74 0.21 0.05

The estimated annual basin mean rainfall is 2,507mm.

(5) Evaluation of Runoff Records at the Sipisang AWLR Station

The Sipisang AWLR station is selected as a key stream gauge station for predicting the long-term runoff at the proposed Masang-2 intake weir site, because it is the only gauge located in the Masang River. The evaluated period of runoff records is determined to be 5 years from 1982 to 1986, because both rainfall and runoff records are available in this period for calibration of Tank Model parameters.

1) Relationship between Annual Basin Mean Rainfall and Annual Runoff Depth at the Sipisang AWLR Station

The annual basin mean rainfall at the Sipisang AWLR station is estimated for the period of 1982 to 1986. On the other hand, the annual runoff depth of Masang River at the Sipisang station is computed by dividing the annual runoff volume by its drainage area of 475 km2 for the same period as above.

The established relationship between annual basin mean rainfall and annual runoff depth at the Sipisang station is as follows.



YearAnnual Rainfall

(mm)Annual Runoff

DepthAnnual Rainfall

LossRunoff

Coefficient1976 2,207 1,375 832 0.621982 2,430 1,253 1,176 0.521983 2,314 1,233 1,081 0.531984 3,339 1,318 2,022 0.391985 2,615 1,449 1,165 0.551986 3,029 1,450 1,579 0.481991 3,030 1,326 1,704 0.441993 3,027 2,101 925 0.69

Average 2,749 1,438 1,311 0.53

The difference between the annual basin mean rainfall and annual runoff depth is the so-called evapotranspiration loss or annual rainfall loss.

The annual rainfall loss is analyzed for major rivers in Sumatra in HPPS2 as presented in Table 16.4.1. It is therefore found that the annual rainfall loss normally falls in a range of 700 to 1,500 mm a year which varies according to altitude, natural vegetation, seasonal distribution of rainfall, etc.

As seen above, the rainfall loss at the Sipisang station varies from 800mm to 2,000mm. From the hydrological point of view, the rainfall loss usually varies in a small range. Therefore it is estimated that rainfall data or runoff data has some errors. The basin mean rainfall is adjusted based on the following consideration.

The annual runoff depth is likely to be constant rather than the basin mean rainfall, with small variations of 1,200 to 1,500 mm. The observed record in 1993 is eliminated because it might contain errors due to malfunctioning of water level recorder.

Maninjau, Koto Tinggi, Suliki, Jambak rainfall gauging stations which are used for estimating basin mean rainfall are located outside the Masang River basin. This fact implies that the estimated basin mean rainfall might inevitably contain some error to some extent.

The estimated annual basin mean rainfall in 1976, 1984 and 1991 are thus adjusted such that the annual rainfall loss becomes 1,251mm, which corresponds to the mean annual rainfall loss in 1982, 1983, 1985 and 1986.

The adjusted relationship between annual basin mean rainfall and annual runoff depth at the Sipisang station is given below.



YearAnnual Rainfall

(mm)Annual Runoff

DepthAnnual Rainfall

LossRunoff

Coefficient1976 2,626 1,375 1,251 0.521982 2,430 1,253 1,176 0.521983 2,314 1,233 1,081 0.531984 2,568 1,318 1,251 0.511985 2,615 1,449 1,165 0.551986 3,029 1,450 1,579 0.481991 2,577 1,326 1,251 0.511993 - - - -

Average 2,594 1,343 1,251 0.52

2) Double Mass Curve Analysis

Based on the adjusted annual basin mean rainfall and annual runoff depth at the Sipisang station, the double mass curve is constructed as given below.

-

5,000

10,000

- 5,000 10,000 15,000 20,000

Accumulated Basin Mean Rainfall (mm)

Accum

ula

ted R

unoff

Depth

(m

m)

1976

1991

1982

1983

1984

1985

1986

As shown above, the annual basin mean rainfall and annual runoff depth are plotted on a straight line, satisfactorily showing the hydrological consistency ready for Tank model analysis to be discussed in the next section.

(6) Tank Model

1) Concept of Tank Model Method

The Tank Model simulation method is widely applied for estimating river runoff from rainfall data. The Tank Model Method has been successfully applied for low-flow analysis in various water resources development projects in Indonesia.

Basic concept of Tank Model

The basic idea of Tank Model is very simple. Consider a tank having a hole at the bottom and another hole at the side as illustrated below.



When the tank is filled with water, the water will be released from the holes as shown in the above. In the tank model simulation, it is considered that the water released from the side hole corresponds to runoff from a stream, and the water from the bottom hole goes into the ground water zone.

The depth of water released from a hole is given by the following tank equation.

HQ ×=α

where, Q : Runoff depth of released water (mm)

α : Coefficient of hole H : Water depth above the hole (mm)

Applied Tank Model

For the purpose of natural runoff simulation, four by four (4×4) tanks combined in series are used.

The top tank receives the rainfall as inflow to the tank, while the tanks below get the supply from the bottom holes of the tank directory above. The aggregated outflow from all the side holes of the tanks constitutes the inflow in the river course.

To effectively trace dry conditions in the basin, several modifications are made on the basic model. The model is firstly facilitated with a structure to simulate the moisture content in the top tank. This sub-model is composed of two moisture-bearing zones, which contain moisture up to the capacities of saturation. Between the two zones, the water transfers as expressed below.

)//(2 SSXSPSXPTCT −=

where, 2T : Transfer of moisture between primary and secondary zones (if positive, transfer occurs from primary to secondary, and vice versa) TC : Constant XP : Primary soil moisture depth



PS : Primary soil moisture capacity XS : Secondary soil moisture depth SS : Secondary soil moisture capacity

When the primary soil moisture is not saturated and there is free water in lower tanks, the water goes up by capillary action so as to fill the primary soil moisture with the transfer speed T1 as given below.

)/1(1 PSXPTBT −=

where, 1T : Transfer of the water from lower tank with capillary action TB : Constant

There are many tank model parameters such as hole coefficients of each tank, and height of side holes of each tank. These parameters cannot be determined mathematically. Therefore, these parameters are subject to determination through trial-and-error calculations comparing the calculated runoff with the actually observed runoff.

2) Input Data for Calibration Model

The applied model and simulation condition for calibration are given below. The period for calibration set from 1982 to 1986 because there are continuously rainfall records and runoff records.

Number of Tanks 4×4Calculation Time Interval 1 monthCalculation Period 1982 to 1986Observed Runoff at Sipisang Station 1982 to 1986Basin Mean Rainfall at Sipisang Station 1982 to 1986Monthly Average Evaporation at Lubuk Sikaping 1979 to 1985

The pan evaporation record at the Lubuk Sikaping station is applied. The pan coefficient of 0.7 is applied for estimating evapotranspiration in the basin. The average monthly pan evaporation is given below.

Station Name: Lubuk Sukaping (1979-1985) Unit: mm/dayJan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Mean4.8 4.4 4.3 3.9 3.7 4.1 4.1 4.2 3.6 3.6 3.9 4.1 4.1

3) Calibration Results

Through several trial-and-error calculations, the best coincidence between the simulated and observed runoff at the Sipisang station is obtained under the tank parameters as follows.



Hole Coefficient Height of Hole (mm)β α1 α2 H1 H2

Tank-1 0.300 0.350 0.350 15.0 30.0Tank-2 0.050 0.070 0.000 5.0 0.0Tank-3 0.010 0.030 0.000 2.0 0.0Tank-4 0.001 0.006 0.000 0.0 0.0

The rainfall-runoff relationship of the simulated runoff is examined compared with the observed runoff as summarized below.

Observed Simulated Observed Simulated Observed Simulated

1982 2,430 1,254 1,203 1,177 1,227 0.52 0.50

1983 2,314 1,233 1,143 1,081 1,171 0.53 0.49

1984 2,635 1,314 1,241 1,321 1,395 0.50 0.47

1985 2,615 1,449 1,400 1,166 1,215 0.55 0.54

1986 3,029 1,450 1,697 1,579 1,332 0.48 0.56

Average 2,605 1,340 1,337 1,265 1,268 0.52 0.51

Runoff Coefficient

Year

AnnualRainfall(mm)

Annual Runoff Depth(mm)

Annual Rainfall Loss(mm)

As seen above, the average runoff coefficient and rainfall loss of the simulated runoff are derived to be 0.51 and 1,268 mm, respectively. On the other hand, hydrological indices of the observed runoff at the Sipisang station are 0.52 and 1,265 mm. These derived hydrological indices are judged to be in the hydrologically reasonable range.

(6) Prediction of the Long-Term Runoff at the Sipisang AWLR Station

The tank model with the calibrated parameters in the above is applied to generate the monthly runoff at the Sipisang station dating back to the period of 1973 to 1993 by use of the estimated monthly basin mean rainfall.

The rainfall-runoff relationship of simulated runoff is summarized below.



Observed Simulated Observed Simulated Observed Simulated1973 2,213 - 1,188 - 1,025 - 0.541974 2,622 - 1,255 - 1,367 - 0.481975 1,882 - 990 - 893 - 0.531976 2,208 1,371 848 836 1,360 0.62 0.381977 2,215 - 1,010 - 1,205 - 0.461978 2,203 - 1,071 - 1,132 - 0.491979 2,061 - 866 - 1,195 - 0.421980 2,252 - 919 - 1,333 - 0.411981 2,797 - 1,403 - 1,395 - 0.501982 2,430 1,254 1,377 1,177 1,053 0.52 0.571983 2,314 1,233 1,159 1,081 1,155 0.53 0.501984 2,635 1,314 1,245 1,321 1,390 0.50 0.471985 2,615 1,449 1,401 1,166 1,214 0.55 0.541986 3,029 1,450 1,697 1,579 1,332 0.48 0.561987 2,674 - 1,410 - 1,264 - 0.531988 2,231 - 1,292 - 939 - 0.581989 2,122 - 963 - 1,159 - 0.451990 2,516 - 1,184 - 1,333 - 0.471991 3,030 1,326 1,538 1,704 1,492 0.44 0.511992 2,874 - 1,821 - 1,053 - 0.631993 3,027 - 1,646 - 1,381 - 0.54

Average 2,474 - 1,251 - 1,222 - 0.50

Runoff CoefficientYearAnnualRainfall

(mm)

Annual Runoff Depth(mm)

Annual Rainfall Loss(mm)

As seen in the table, the average runoff coefficient and rainfall loss of the simulated runoff are derived to be 0.50 and 1,222 mm, respectively. These hydrological indices are judged to be within the hydrological reasonable range.

(7) Daily Flow Duration Curve

For Masang-2 HEPP, daily runoff data is required for power output computation because the type of scheme is runoff type. Nevertheless, it is difficult to collect long-term daily rainfall and runoff data in Masang River basin and the monthly runoff records are supplemented and extended with Tank Model method. So the combination of daily observed runoff and simulated monthly runoff is used for setting the daily flow duration curve. The value of simulated monthly runoff data is regarded as simulated daily runoff in same amount.

The condition of data is summarized below.

Time Interval DailyObserved Daily Runoff 1976, 1982 to 1986, 1991Simulated Monthly Runoff 1973 to 1975, 1977 to 1981, 1987 to 1990, 1992, 1993

(8) Long-Term Runoff at the Masang-2 Intake Weir Site

The long-term daily runoff at Masang-2 intake weir site for 21 years in the period of 1973 to 1993 is estimated from the predicted long-term daily runoff at the Sipisang station by using the following equation. The flow duration curve as shown in Figure 16.4.5, is drawn by arranging the discharges in



descending order and assigning probabilities to each discharge.

)/( WDWD AAQQ ×=

where, DQ : Runoff at Masang-2 intake weir site (m3/sec) WQ : Runoff at Sipisang AWLR station (m3/sec) DA : Catchment area at Masang-2 intake weir site (=443km2) WA : Catchment area at Sipisang AWLR station (=475km2)

(9) Water Level Observation and Discharge Measurement

The field investigation of 3 month water level observation and 30 times discharge measurement was carried out from 2010 October 6th to 2011 January 7th by the sub-contractor. Location of the observation is at the Masang-2 intake weir site (St.1) and the Sipisang AWLR station (St.2). H-Q rating curve is established on the basis of observed water level and discharge, and hydrograph is established on the basis of observed water level and H-Q rating curve. Hydrograph is illustrated in Figure 16.4.6.

Consequently, the average water level is 0.75m and the average runoff is 23.85 m3/s calculated with H-Q rating curve. The Equation of H-Q rating curve is given below.

2)06.0(55.36 +×= HQ

where, Q : Runoff (m3/sec)

H : Water level (m)

The observed average runoff is about 15% of probability on the duration curve shown in Figure 16.4.5.

16.4.5 FLOOD ANALYSIS

(1) General Approach

Flood analysis is carried out to estimate the probable floods with various return periods as well as the probable maximum flood (PMF) at the Masang-2 intake weir site which are basically required for design of spillway and diversion facilities, and determination of dam height.

For estimating the probable floods, the unit hydrograph method is applied, which synthesizes the various probable runoff hydrographs from the probable basin mean rainfalls based on the relationship between unit of basin mean rainfall and its runoff, that is the so-called unit hydrograph. It is generally agreed that the unit hydrograph method is applied for catchment areas less than 3,000 km2.

In this study, the Soil Conservation Service (SCS) unit hydrograph, which is empirically developed in USA Department of the Interior is used, because no hourly flood hydrograph is available at the



Sipisang AWLR station to construct the unit hydrograph.

The general approach of flood analysis is outlined below.

(2) Rainfall Analysis

1) Depth-Area-Duration (DAD) Analysis

DAD analysis is carried out to examine the following relationships.

Relationship between rainfall depth and duration (DD Analysis)

Relationship between rainfall depth and area (DA Analysis)

a) Depth-Duration (DD) Analysis

Generally, heavy rainfall occurs intensively in a short duration and sporadically in a limited area. Hourly rainfall records exceeding 50 mm within 12 hours were selected for estimating the hourly rainfall hyetograph of heavy storm rainfall which might cause flood.

The rainfall duration of selected 63-storm rainfall is arranged. Among the storm rainfalls bigger than 50mm, 6-hour of rainfall duration covers 63% of all. Besides, 6-hour of rainfall duration covers 80% of all among the storm rainfalls bigger than 100mm. So, the design rainfall duration time is estimated as 6-hour, which represents the characteristics of the storm rainfalls in Masang River basin.



40 of selected 63-storm rainfall have smaller duration time than 6-hours. The average of the

40 storm rainfalls is estimated as the design rainfall pattern..

The design distribution of hourly rainfall is shown below.

Time (hour) 0 1 2 3 4 5 6Cumulative Rainfall Depth 0% 47% 78% 87% 95% 99% 100%Incremental Rainfall Depth 0% 47% 31% 9% 8% 4% 1%

b) Depth-Area (DA) Analysis

Generally, heavy rainfall occurs intensively in a short duration and sporadically in a limited area. Therefore the average depth of storm rainfall (basin mean rainfall) is likely to be smaller than the point depth of storm rainfall.

In general, relation between point rainfall depth and average area is expressed by an exponential equation given by the following equation.

]exp[0n

b kAPP −×=

where, bP : Average rainfall depth over an area A (mm) 0P : Maximum point rainfall at the storm center (mm)

A : Area in question (km2) nk, : Constants for a given area

The above equation is the so-called Horton’s Equation. Constants k and n usually vary according to the given rainfall duration such as 1 hour, 6 hours, 12 hours, 1 day, etc. These constants are to be obtained through rainfall analysis based on the isohyetal maps of various major rain storms occurred in the river basin in question. However, the exact determination of 0P is practically impossible, because it is very unlikely that the rain storm center

coincides with a rainfall gauging station.

To estimate the basin mean rainfall from the point rainfall, the area reduction factor showing the ratio of basin mean rainfall to point rainfall is introduced as expressed below.

0PfP ab ×=

where, bP : Basin mean rainfall (mm) 0P : Point rainfall (mm) af : Area reduction factor

If the Horton’s equation is applied, the area reduction factor under the given rainfall duration is given by the following equation.

]exp[ na kAf −=



However the available rain storm records in the Masang River basin are insufficient for reliable determination of the area reduction factor. The preliminary estimation of the design area reduction factor is carried out based on the following three approaches.

Firstly, the area reduction factor is estimated as 0.63 under the catchment area of 443 km2 for the Masang-2 intake weir site by applying the Horton’s equation assuming that constants of k and n are 0.1 and 0.25, respectively. These constants have been widely and empirically applied in tropical rain forest area.

A 443 (km2)k 0.1n 0.25fa 0.63

Secondly, the estimated design area reduction factors are examined in several other projects. The following design area reduction factors are based on the rainfall analysis using the observed rain storm records.

Project Name Catchment Area(km2)

Area ReductionFactor

Besai HEPP (D/D in 1990) 415 0.50Malea HEPP (F/S in 1984) 1,463 0.45Tampur-1 HEPP (F/S in 1984) 2,000 0.40Musi HEPP (F/S in 1984) 586 0.50Cibuni-3 (F/S in 1984) 1,000 0.41Masang-3 HEPP (Pre F/S in 1999) 993 0.50

Thirdly, the relation between the daily point rainfall and the daily basin mean rainfall around the Masang River basin is analyzed to estimate the area reduction factor of the river basin. The selected rainfall stations are the Payakumbuh and Maninjau stations. A basin mean rainfall derives from an arithmetic average of an annual maximum daily rainfall of a target station and daily rainfall of another station at the same day. The average of ratios between basin mean rainfalls and annual maximum daily rainfalls of target stations is estimated as the area reduction factor.

Usually, it is considered that the rainfall intensity in hyetal areas increases with the depth of point rainfall. However, the area reduction factor showing the ratio of area rainfall to the maximum point rainfall varies from 0.5 to 0.8 for the area rainfall amount. Further, the area reduction factor does not always increase with the enlargement of the point rainfall. On the other hand, the design area reduction factors examined in several hydropower projects varies from 0.4 to 0.5.

In due consideration above, the design area reduction factor is conservatively determined to be 0.50.



2) Probable Point Rainfall

Out of the available rainfall records around the Masang River basin, the annual maximum 1-day rainfall records are available at the Payakumbuh rainfall gauging station.The rainfall records at the Payakumbuh station have recording periods between 1951 and 1993 with some interruptions in recording.

The probable point rainfalls at the station with several return periods are estimated through frequency analysis using the Gumbel and Log Normal distributions as summarized below..

Gumbel LN400 263 319 291200 242 281 261150 233 266 249100 220 245 233

80 213 235 22450 199 213 20630 183 190 18620 170 173 17110 148 145 146

5 125 119 1223 106 100 1032 90 85 87

Return Period(years)

Probable Point Rainfall (mm) Average

The probable point rainfall is estimated as the average of the probable rainfalls by the Gumbel and Log Normal distributions, because the estimated frequency curves by the Gumbel and Log Normal distributions have similar shapes.

3) Probable Maximum Precipitation (PMP)

Generally three (3) approaches are used for estimating the probable maximum precipitation (PMP) as follows.

Meteorological (theoretical) approach in consideration of the upper physical limit of moisture source

Statistical approach which is empirically developed by Dr. Hershfield from the rainfall records in the United States of America

Historical approach by examining the historical maximum one over occurred in the area of interest

The available basic climatological data such as dew point, humidity, wind velocity in Masang-2 catchment area for the first meteorological approach are insufficient for the time being. Further, no historical rain storm records are also so far available.

Therefore, PMP is estimated by the simple statistical Hershfield method using a series of the



annual maximum daily rainfall records. This method is widely applied in the basin where rainfall records are available but other basic climatological records are hardly obtainable.

The Hershfield’s equation is expressed as follows.

nmnm SKXX ×+=

where, mX : Extreme value of 24-hour rainfall (PMP) (mm) nX : Adjusted mean annual maximum rainfall (mm) mK : Statistical coefficient nS : Adjusted standard deviation of a series of annual maximum rainfall

As seen in the above equation, PMP in question is assumed to be given as the adjusted mean annual maximum rainfall in question plus the Km times the standard deviation of a series of annual maximum rainfall in question.

The PMP is estimated by applying a series of annual maximum rainfall in the Masang river basin. The calculation process is as follows.

Computation of Statistical Parameters

The mean annual maximum rainfall (Xn) and its standard deviation (Sn) are calculated to be 96.1 mm and 47.1 mm, respectively.

Concurrently with the above, Xn-m and Sn-m are estimated at 91.6 mm and 38.2 mm, which are computed after excluding the maximum rainfall in the series of rainfall data. These statistical parameters are used for several adjustment necessary computing Xn and Sn.

Adjustment of Xn and Sn for Maximum Observed Event

The adjustment factors of Xn (fx1) and Sn (fs1) for the maximum observed rainfall shall be obtained from the Hershfield’s adjustment curves.

Applying the values of Xn, Xn-m, Sn and Sn-m, adjustment factors are obtained 97 % for fx1 and 89 % for fs1, respectively.

Adjustment of Xn and Sn for Sample Size

The adjustment factors of Xn (fx2) and Sn (fs2) for the length of record shall be obtained from the adjustment curves.

The obtained factors of fx2 and fs2 are 100.5 % and 101.6 %, respectively.

Statistical Coefficient Km



The statistical coefficient Km shall be obtained from the empirical Km curves. Applying the mean annual maximum rainfall at the Payakumbuh station (Xn) is 96.1 mm, the Km value is obtained to be 15.5.

Adjustment for Fixed Observational Time Intervals

Rainfall observation has been carried out on the daily basis at the Payakumbuh station. Since the recorded daily rainfall is computed based on the single fixed observation time interval (say 8 a.m to 8 p.m), the PMP value yielded by the statistical procedure should be increased multiplying by the adjustment factor (fo).

Applying that the number of observation units is equal to 1, the fo value is obtained to be 113 %.

Computation of PMP at the Payakumbuh Station

The adjustment mean annual maximum rainfall (Xn) is finally given as follows.

nXXn XffX ××= 21

In addition, the adjusted standard deviation of a series of annual maximum rainfall (Sn) is given as follows.

nSSn SffS ××= 21

The unadjusted point PMP (Xm) is computed as follows.

nmnm SKXX ×+=

Finally, the point PMP is adjusted using the adjustment factor fo as follows.

mO XfPMP ×=

As seen, the point PMP at the Payakumbuh station is estimated to be 852 mm.

4) Basin Mean Rainfall

Applying the design area reduction factor of 0.5, the probable basin mean 1-day rainfalls with various return periods as well as PMP at the Masang-2 intake weir site are estimated as follows.



PMP 426400 146200 131150 125100 117

80 11250 10330 9320 8610 73

5 613 522 44

Probable Rainfall(mm)

Return Period(years)

(3) Hydrograph Analysis

1) Unit hydrograph

Since no flood hydrographs are available for the present flood analysis, the unit hydrograph is developed by means of the SCS (Soil Conservation Service) synthetic hydrograph method. The SCS method was developed by analyzing a large number of basins with varying geographic locations. Unit hydrographs were evaluated for a large number of actual watersheds and then made dimensionless by dividing all discharge ordinates by the peak discharge and the time ordinates by the time to peak. An average of these dimensionless unit hydrographs was computed.

a) SCS Unit Hydrograph

The SCS unit hydrograph is derived from the flood concentration time and unit basin rainfall. The unit hydrograph is constructed for a unit rainfall of 1 mm.

The peak discharge of the unit hydrograph is calculated as follows.

pp tAQq /208.0=

where, pq : Peak discharge (m3/sec)

A : Basin area (km2) Q : Total volume of the unit hydrograph (=1mm) pt : Time to peak (hours)

SCS has determined that the time to peak ( pt ) and rainfall duration ( D ) are related to time

of concentration ( ct ) as follows.

3/2 cp tt ×=

ctD 133.0=



b) Flood Concentration Time

The flood concentration time is defined as the time of travel from the most remote point in the catchment to the forecast point. The flood concentration time can be estimated by the formula of Kirpich as follows.

385.077.097.3 −××= SLtc

where, ct : Flood concentration time (min)

L : Maximum length of travel of water (km) S : Average slope (=H/L, where H is the difference in elevation between the remotest point in the basin and the outlet)

c) SCS Unit Hydrograph Calculation

With a maximum length of travel ( L ) of 49km, the concentration time ( ct ) was found to be about 6.2 hours. With a catchment area ( A ) of 443 km2, the peak flow ( pq ) is found to be

22.3 m3/sec/mm.

A 443 km2

Q 1 mmL 49.156 kmtc 6.2 hoursqp 22.3 m3/s/mmtp 4.1 hours

2) Probable Flood Hydrograph at Masang-2 Intake Weir Site

The probable flood hydrographs including PMF at the Masang-2 intake weir site are derived by convolution of the probable basin mean rainfall, PMP with the design rainfall hyetograph and the unit hydrograph.

The base flow is determined to be 14 (m3/s) from the average rainy-season discharge records at the Sipisang AWLR station, and the rainfall loss is assumed to be 47 %.

The computed probable flood hydrographs as well as PMF are shown in Figure 16.4.7.

The probable design flood discharges with various return periods together with PMF are collected from various hydropower projects in Sumatra as presented in Table 16.4.2.

3) Creager’s Coefficient for Probable Floods at Masang-2 Intake Weir Site

Creager’s coefficient for probable flood is computed by the following equations.



ap ACQ )3861.0()02832.046( ××××=

048.0)3861.0(894.0 −×= Aa

where, pQ : Peak discharge of probable flood (m3/sec)

C : Creager’s coefficient A : Catchment area (km2)

The Creager’s coefficients corresponding to the various return periods and PMF for the Masang-2 HEPP are enumerated in the table below.

T Q C(year) (m3/s)

PMF 4344 92400 1493 32200 1341 28150 1280 27100 1198 25

80 1152 2450 1061 2230 959 2020 883 1910 756 16

5 634 133 537 112 456 10

Figure 16.4.8 and Figure 16.4.9 shows the relationship between probable flood peak discharges with return periods of 2, 20, 100, 200 years as well as PMF and catchment area for the Masang-2 HEPP and other water resources development projects in the whole Sumatra. The Creager’s curves are illustrated using the Creager’s coefficients of the Masang-2 intake weir site calculated in above. The probable floods at the Masang-2 HEPP are well plotted in reasonable range of design floods in Sumatra.

4) Probable Floods at the Masang-2 Regulating Pond Site

The time of concentration ( ct ) at the Masang-2 Regulating Pond is calculated as 0.17 hour with

the same method as the Masang-2 intake weir site. Probable floods at the Masang-2 Regulating Pond are estimated with the Creager’s coefficients of the Masang-2 intake weir site, because short time interval rainfall records like 10-minutes do not exist in Masang River basin.

A 1 km2

L 1.3 kmtc 0.17 hours

The results of flood analysis are estimated as follows.



PondT Q C Q

(year) (m3/s) (m3/s)PMF 4344 92 49.1400 1493 32 16.9200 1341 28 15.2150 1280 27 14.5100 1198 25 13.5

80 1152 24 13.050 1061 22 12.030 959 20 10.820 883 19 10.010 756 16 8.6

5 634 13 7.23 537 11 6.12 456 10 5.2

Intake

5) Probable Floods at the Masang-2 Power House Site

The Alahanpanjang River and the Masang River join together at the upstream of the Masang-2 Power House site. At the power house site, probable floods seem to be controlled by floods from the Masang River, because the catchment area of the Alahanpanjang River basin is smaller than the Masang River basin. So, Probable floods at the Masang-2 power house site are estimated with the Creager’s coefficients of the Masang-2 intake weir site as same as the regulating pond. The catchment area of the power house site is 919.5km2.

The results of flood analysis are estimated as follows.

PHT Q C Q

(year) (m3/s) (m3/s)PMF 4344 92 6281.3400 1493 32 2158.8200 1341 28 1939.1150 1280 27 1850.9100 1198 25 1732.3

80 1152 24 1665.850 1061 22 1534.230 959 20 1386.720 883 19 1276.810 756 16 1093.2

5 634 13 916.83 537 11 776.52 456 10 659.4

Intake

(4) Water Level Observation and Discharge Measurement

As mentioned in the chapter of lowflow analysis, the field investigation of 3 month water level observation and 30 times discharge measurement was carried out from 2010 October 6th to 2011 January 7th by the sub-contractor.

Consequently, the maximum water level is 2.01m and the maximum runoff is 156.61 m3/s calculated with H-Q rating curve in extrapolation. The Equation of H-Q rating curve is given below.



2)06.0(55.36 +×= HQ

where, Q : Runoff (m3/sec)

H : Water level (m)

16.4.6 SEDIMENT ANALYSIS

(1) General

Sedimentation analysis is preliminarily carried out to estimate the denudation rate in the Masang River basin. The sedimentation load is herein predicted based on the estimated runoff and the sediment discharge rating curve at the intake weir site. The rating curve is established based on the in-situ sampling records obtained through the field investigation conducted in the course of the study. The field investigation was carried out at the Masang-2 intake weir site and Sipisang AWLR station.

The sediment transport in the Masang River is judged to be higher than other rivers in the Sumatra. The denudation rate showing the expected average annual erosion rate in a river basin is generally influenced by the topography (soil condition, river gradient), deforestation of the land in the basin, rainfall intensity, etc.

In addition, the design denudation rates adopted in other water resources or hydropower development projects in Sumatra are collected for comparison purposes.

(2) Suspended Load Sampling

A total of thirty (30) suspended load samplings were carried out at the intake weir site where discharge measurements were taken. The samples were taken to a laboratory for further analysis. The sieve analysis results of samples are shown in Figure 16.4.10.

(3) Suspended Load Rating Curve

The laboratory analysis results of the samples show the total suspended sediment concentration which is the combination of both dissolved and undissolved sediment. The total suspended load is found from the following formula.

WS QCQ ××= 0864.0

where, SQ : Suspended load (ton/day)

C : Total suspended sediment concentration (mg/L) WQ : Flow discharge (m3/s)

Several results are considered unreliable because they show very low concentration or very high concentration. Therefore these unreliable results will not be used in the determination of the suspended load rating curve. The values of Qs are plotted against their respective Qw values to determine the suspended load rating curve. On the basis of the estimated sediment discharge at the intake weir site,



the suspended load rating curve is established as shown in Figure 16.4.11. The rating curve equation is given below.

7812.14615.5 WS QQ ×=

If the flow discharge Qw is known, the suspended load sediment Qs can be estimated.

(4) Total Sediment Load

The annual suspended load sediment yield is simulated by applying the above rating curve to the simulated daily runoff at the intake weir site. The catchment area of the Masang-2 intake weir site is 443km2.

Substituting runoff data, the average annual suspended load sediment at the intake weir site is estimated at 369,749 ton.

The density of sediment in appearance can be calculated by the following equation.

γγ ×−=′ )1( V

where, γ ′ : Density of sediment (ton/m3)

V : Void ratio of sediment γ : Unit weight of sediment (=2.65ton/m3)

Assuming a void ratio of 60 % in sedimentation, the density of sediment is found to be 1.06 ton/m3. Hence, the annual suspended load sediment is estimated at 348,820 m3.

The sediment load transport into an intake weir generally consists of suspended load and bed load. It is generally accepted that it might be difficult to accurately measure the bed load in a natural river. Usually, the rate of bed load transport is empirically estimated at 10 to 30 % of the total suspended load. The rate of bed load transport is estimated as 10% of the total suspended load, because 10% is usually applied in Indonesia.

Consequently, the mean annual sediment inflow volume into the Masang-2 intake weir is estimated to be 383,702 m3, which is equivalent to a denudation rate of 0.87 mm per year.

For comparison purpose, design denudation rates of various schemes around the project site are presented in the following table.



Project Name Project Stage Province Catchment Area Denudation Rate(km2) (mm/year)

Masang-3 Pre-F/S W. Sumatra 993 0.50Bt. Tonggar W. Sumatra 320 0.45Bt. Bayang-1 Pre-F/S W. Sumatra 84 0.70Bt. Bayang-2 Pre-F/S W. Sumatra 36 0.70Kotapanjang D/D Riau 3,337 0.50Kampar River Basin F/S Jambi - 0.50Upper Indragiri River Basin Jambi - 0.59Middle Indragiri River Basin Jambi - 0.53Merangin-2 D/D Jambi 1,309 0.34Merangin-5 Pre-F/S Jambi 2,597 0.70Lake Kerinci Jambi 1,053 0.72Source: Masang-3 HEPP, 1999.

As seen in the above table, the design denudation rates vary from 0.34 to 0.72 mm/year. The assumed denudation rate of 0.87 mm/year at the Masang-2 intake weir site might not be in the appropriate range.

Referring to the geology report in this study, there is place of gravel pit in the upstream of Masang River, and gravel extraction is seems to be carried out frequently. The samples of suspended load might be influenced by the gravel extraction. The gravel extraction might not be continuously carried out, so the design denudation rate of the Masang-2 intake weir should be estimated without influence of the gravel extraction in upstream. Nevertheless, it is difficult to estimate the volume of sediment yield from the gravel pit.

The grain size distributions of the samples are consists of mainly fine size grain smaller than 0.1mm, of which falling velocity is slow. It is estimated that the fine size grain has small influence to the sedimentation in the intake weir.

Consequently, the design denudation rate of the Masang-2 intake weir is estimated as 0.5mm/year which is the middle of design denudation rates in other projects. The design annual sediment inflow volume into the Masang-2 intake weir is estimated to be 221,500m3/year.

16.4.7 WATER QUALITY ANALYSIS

Water quality is important because it is linked to the availability of water for various uses. Specifically, for the Masang-2 HEPP it is important for the well being of hydraulic machinery, other equipment and hydraulic structures used in the project.

The laboratory test for water quality was carried out through the field investigation under the current study to identify the content of various chemical elements contained in the water in the Masang River. Water sampling is carried out three (3) times in total at the Masang-2 intake weir site. The samples were taken to a laboratory for further analysis.

The laboratory test results are presented in Table 16.4.3. The table shows that the pH of the water in the Masang River is around 8. It is therefore judged that the water in the Masang River will have no



adverse effect on turbine and metal for hydropower use, because adverse effect is expected to occur under the pH value smaller than 4.5.



Table 16.4.1 Annual Rainfall Loss of Various River Basins in Sumatra

No.

Sta

tion

Riv

er

Gau

ge ID

Cat

chm

ent

Bas

inA

nnua

l A

nnua

l A

nnua

lR

unof

fO

bser

vatio

nN

ame

Bas

inAr

eaM

ean

Mea

nR

unof

fR

ainf

all

Coe

ff.P

erio

dR

ainf

all

Run

off

Dep

thLo

ss(k

m2 )

(mm

)(m

3 /sec

)(m

m)

(mm

)

1Lh

ok N

ibon

gK

r. Ja

mbu

Aye

01-0

27-0

1-02

4,58

32,

685

175.

71,

209

1,47

60.

4519

72-1

993

2S

taba

tS

. Wam

pu01

-040

-01-

013,

870

3,09

920

6.8

1,68

51,

414

0.54

1974

-199

3

3Lb

. Sip

elan

duk

Bt.

Pan

e01

-055

-03-

0282

82,

250

28.4

1,08

21,

168

0.48

1973

-199

3

4Lb

. Ben

daha

raS

. Rok

an01

-058

-02-

013,

325

2,58

914

1.5

1,34

21,

247

0.52

1974

-199

3

5Tj

. Am

palu

Bt.

Kua

ntan

01-0

66-0

4-01

2,21

52,

211

77.6

1,10

51,

106

0.50

1975

-199

3

6S

unga

i Dar

ehB

t. H

ari

01-0

71-0

1-01

4,45

23,

239

310.

22,

197

1,04

20.

6819

75-1

993

7M

uara

Inum

Bt.

Har

i01

-071

-02-

011,

455

3,34

610

7.6

2,33

21,

014

0.70

1973

-198

7

8M

arta

pura

A. M

usi

01-0

74-0

1-01

4,26

02,

821

225.

01,

666

1,15

50.

5919

60-1

984

9B

anja

rmas

inW

. Tl.

Baw

ang

01-0

77-0

2-07

604

3,12

536

.81,

921

1,20

40.

6119

72-1

993

10K

unyi

rW

. Sek

ampu

ng01

-080

-01-

0443

82,

740

23.1

1,66

31,

077

0.61

1968

-199

3

11K

p. D

aran

gK

r. A

ceh

01-0

01-0

1-01

1,08

12,

012

33.1

966

1,04

60.

4819

77-1

993

12Tu

i Kar

eng

Kr.

Teun

om01

-205

-01-

012,

403

3,43

718

3.9

2,41

31,

024

0.70

1982

-199

3

13H

p. B

aru

Bt.

Toru

01-1

78-0

1-01

2,77

32,

843

128.

91,

466

1,37

70.

5219

72-1

993

14A

ir B

atu

Bt.

Indr

apur

a01

-141

-01-

0146

82,

887

31.3

2,10

977

80.

7319

73-1

993

15A

ir G

adan

gB

t. P

asam

an01

-165

-01-

011,

339

3,60

012

1.3

2,85

774

30.

7919

73-1

993

16D

espe

tah

A. M

usi

01-0

74-0

1-02

627

3,10

045

.22,

273

827

0.73

1974

-199

1

Sou

rce

: Sec

tora

l Rep

ort V

ol. 2

: H

ydro

logy

, Hyd

ro In

vent

ory

Stu

dy, J

uly

1997



Table 16.4.2 Probable Floods under Various Schemes in Sumatra

Catchment

No Scheme River Province Area(km2) 2 20 100 200 1,000 10,000

1 Tampur-1 Kr. Tampur D.I. Aceh 2,025 2,870 3,590 7,4702 Teunom-1 Kr. Teunom D.I. Aceh 900 2,300 3,120 8,3903 Aceh-2 Kr. Aceh D.I. Aceh 323 1,030 1,470 3,5104 Lawe Alas-4 Lawe Alas D.I. Aceh 5,705 2,500 4,250 12,5005 Peusangan-4 Kr. Peusangan D.I. Aceh 945 1,6006 Lake Laut Tawar Kr. Peusangan D.I. Aceh 195 500 810 940 1,6707 Residual Basin-1 Kr. Peusangan D.I. Aceh 106 360 530 600 1,0208 Jambu Aye Kr. Jambu Aye D.I. Aceh 3,890 1,939 2,331 3,800 4,8509 Rubek Kr. Jambu Aye D.I. Aceh 93 142

10 Residual Basin-2 Kr. Peusangan D.I. Aceh 128 320 480 550 94011 Lalang S. Belawan N. Sumatera 254 250 410 61012 Tembakau S. Percut N. Sumatera 171 140 230 34013 Lausimeme S. Percut N. Sumatera 106 180 280 30014 Helvetia S. Deli N. Sumatera 341 280 530 69015 Namobatang S. Deli N. Sumatera 93 250 27016 Baru S. Serdang N. Sumatera 671 470 750 94017 Pulau Tagor S. Ular N. Sumatera 1,013 430 820 1,07018 Karai S. Ular N. Sumatera 500 500 56019 Brohol S. Padang N. Sumatera 759 390 720 94020 Rampah S. Belutu N. Sumatera 423 180 290 37021 Renun A. Renun N. Sumatera 139 580 740 820 960 1,90022 Wampu S. Wampu N. Sumatera 1,570 2,97023 Limang S. Wampu N. Sumatera 959 300 94024 Sipan Sihaporas Sipan Sihaporas N. Sumatera 196 269 1,80025 Batang Bayang-1 Bt. Bayang W. Sumatera 84 59026 Batang Bayang-2 Bt. Bayang W. Sumatera 36 34027 Muko-Muko Bt. Antokan W. Sumatera 248 44 74 93 12028 Masang-3 Bt. Masang W. Sumatera 993 1,136 2,204 2,878 3,168 3,851 4,854 10,41929 Merangin-5 Bt. Merangin Jambi 2,597 1,970 2,460 5,30030 Lake Kerinci Siulak Jambi 916 590 1,538 2,177 2,464 3,102 4,092 13,34731 Batang Hari Bt. Hari Jambi 4,452 1,937 4,192 5,603 6,205 7,60132 Batang Hari (Alt.) Bt. Hari Jambi 3,825 1,664 3,602 4,814 5,331 6,53133 Kiri-1 Bt. Kampar Riau 1,187 2,537 7,27434 Kiri-2 Bt. Kampar Riau 552 1,44635 Kapoernan Bt. Kampar Riau 699 2,18136 Kotapanjang Bt. Kampar Riau 3,337 1,183 1,624 8,000 11,40037 Upper Sinamar Bt. Indragiri Riau 3,180 3,180 8,38338 Sukam Bt. Indragiri Riau 360 1,75539 Lower Kuantan Bt. Indragiri Riau 7,453 10,04740 Ombilin Bt. Ombilin Riau 1,078 118 175 211 26341 Musi (Intake Dam) A. Musi S. Sumatera 587 240 530 720 780 1,010 1,31042 Musi (Regulation Dam) A. Musi S. Sumatera 30 79 138 175 190 226 27743 Martapura Way Komering S. Sumatera 4,260 1,300 1,900 2,200 2,300 2,700 6,30044 Lematang-4 A. Lematang S. Sumatera 1,321 1,870 2,430 5,50045 Mine Mouth Steam Plant A. Lematang S. Sumatera 3,667 6,63646 Ketaun-1 A. Ketaun Bengkulu 449 500 800 980 1,070 7,140

Masang-2 Bt. Masang W. Sumatera 443 456 883 1,198 1,341 4,344Source: Hydro Inventory Study, Sectral Report Vol.2 Hydrology, July 1997. Masang-3 HEPP, 1999.

Probable Peak Discharge (m3/sec)Return Period (year) PMF



Table 16.4.3 Water Quality Analysis of Masang River

No Water Quality Parameter Unit Sample-1 Sample-2 Sample-3

Date 2010/10/25 2010/11/25 2010/12/25Weather Clear Cloud Cloud

1 pH 8.09 8.11 8.112 Temperature ℃ 25.4 24.9 24.93 Total Hardness mg/l 123.7 131 1264 Temporary Hardness mg/l 52.58 93 975 Suspended Matter mg/lit 136 299 2956 Total Solid mg/lit 261 327 3437 Ignition Residue mg/lit 0.08 0.07 0.078 Permanganate Value as O2 mg/lit 9.69 7.24 3.559 Carbonates as CaCO3 mg/lit 0 10.74 8.06

10 Bicarbonates as CaCO3 mg/lit 135.52 115 14111 Calcium (Ca) mg/lit 37.48 41.64 39.8912 Magnesium (Mg) mg/lit 7.34 6.57 6.3713 Sodium (Na) mg/lit 8.36 11.52 9.914 Potassium (K) mg/lit 1.96 2.77 2.815 Iron (Fe) mg/lit 1.579 0.72 1.2816 Manganese (Mn) mg/lit <0.02 0.69 0.0717 Copper (Cu) mg/lit <0.001 0.008 0.00818 Turbidity NTU 41 37 5219 Color Pt-Co-Unit 20 10 kol 10 kol20 Electric Conductivity µ/Cm 254 313 30321 Aluminum (Al) mg/lit 1.35 1 1.4222 Silica (SiO2) mg/lit 46.52 17.7 2223 Lead (Pb) mg/lit 0.008 0.42 0.4224 Arsenic (As) mg/lit 0.0024 0.002 0.002525 Ammonium (NH4) mg/lit 0.784 <0.02 <0.0226 Albuminoid mg/lit <0.1 <0.1 <0.127 Nitrites (NO2) mg/lit 0.002 0.003 0.00728 Nitrates (NO3) mg/lit 0.516 0.432 0.66629 Sulfities (SO3) mg/lit 0.155 0.072 <0.0230 Sulfates (SO4) mg/lit 17.65 21.03 21.931 Chlorides (Cl) mg/lit 7.77 8.09 7.8732 Phosphates (PO4) mg/lit 0.049 <0.002 <0.00233 Oxygen (O2) mg/lit 7.31 6.79 7.1734 Carbon Dioxide (CO2) mg/lit 1.73 - -35 P-value as CaCO3 mg/lit 0.052 <0.02 < 0.00236 M-Value as CaCO3 mg/lit 25 24.8 24.8



Figure 16.4.1 Location Map of Meteo-Hydrological Stations



Daily Rainfall Records

1969

1970

1971

1972

1973

1974

1975

1976

1977

1978

1979

1980

1981

1982

1983

1984

1985

1986

1987

1988

1989

1990

1991

1992

1993

1994

1995

1996

1997

1998

1999

2000

2001

2002

2003

2004

2005

2006

2007

2008

2009

1 Maninjau 52B 22-0052-02

2 Limau Purut 52C 22-0052-03

3 Padang Panjang 53 22-0053-00

4 Bukit Tinggi 54 22-0054-00 1961-

5 Baso 54A 22-0054-01

6 Padang Mangatas 54C 22-0054-03 1965-

7 Payakumbuh 56 22-0056-00 1920-

8 Koto Tinggi 56A 22-0056-01

9 Suliki 56B 22-0056-02 1923-

10 Kota Baharu 57 22-0057-00

11 Bonjol 58C 22-0058-03

12 Jambak 58F 22-0058-06

13 Lubuk Sikaping 59 22-0059-00

Source: BMKG

Monthly Rainfall Records

1969

1970

1971

1972

1973

1974

1975

1976

1977

1978

1979

1980

1981

1982

1983

1984

1985

1986

1987

1988

1989

1990

1991

1992

1993

1994

1995

1996

1997

1998

1999

2000

2001

2002

2003

2004

2005

2006

2007

2008

2009

1 Maninjau 52B 22-0052-02

2 Limau Purut 52C 22-0052-03

3 Padang Panjang 53 22-0053-00

4 Bukit Tinggi 54 22-0054-00 1961-

5 Baso 54A 22-0054-01

6 Padang Mangatas 54C 22-0054-03 1965-

7 Payakumbuh 56 22-0056-00 1920-

8 Koto Tinggi 56A 22-0056-01

9 Suliki 56B 22-0056-02 1923-

10 Kota Baharu 57 22-0057-00

11 Bonjol 58C 22-0058-03

12 Jambak 58F 22-0058-06

13 Lubuk Sikaping 59 22-0059-00

Source: HPPS2 Report, 1999. Masang-3 HEPP Report, 1999. BMKG

No. Station NameBMGID

HPPS2ID

RemarksHPPS2

IDStation NameBMGID

Remarks

No.

Year

Year

Figure 16.4.2 Availability of Climatic Records (1/2)



Daily Runoff Records

1969

1970

1971

1972

1973

1974

1975

1976

1977

1978

1979

1980

1981

1982

1983

1984

1985

1986

1987

1988

1989

1990

1991

1992

1993

1994

1995

1996

1997

1998

1999

2000

2001

2002

2003

2004

2005

2006

2007

2008

2009

1 163-01-01 28years

Source: Pusair Bandung

Daily Water Level Records

1969

1970

1971

1972

1973

1974

1975

1976

1977

1978

1979

1980

1981

1982

1983

1984

1985

1986

1987

1988

1989

1990

1991

1992

1993

1994

1995

1996

1997

1998

1999

2000

2001

2002

2003

2004

2005

2006

2007

2008

2009

1 163-01-01

Source: BPSDA Bukit Tinggi

Monthly Runoff Records

1969

1970

1971

1972

1973

1974

1975

1976

1977

1978

1979

1980

1981

1982

1983

1984

1985

1986

1987

1988

1989

1990

1991

1992

1993

1994

1995

1996

1997

1998

1999

2000

2001

2002

2003

2004

2005

2006

2007

2008

2009

1 163-01-01

Source: HPPS2 Report, 1999. Masang-3 HEPP Report, 1999. Pusair Bandung.

Air Temperature

196

9

197

0

197

1

197

2

197

3

197

4

197

5

197

6

197

7

197

8

197

9

198

0

198

1

198

2

198

3

198

4

198

5

198

6

198

7

198

8

198

9

199

0

199

1

199

2

199

3

199

4

199

5

199

6

199

7

199

8

199

9

200

0

200

1

200

2

200

3

200

4

200

5

200

6

200

7

200

8

200

9

1 Tabing-Padang 03106 22-0043-01

Source: BMKG

Relative Humidity

196

9

197

0

197

1

197

2

197

3

197

4

197

5

197

6

197

7

197

8

197

9

198

0

198

1

198

2

198

3

198

4

198

5

198

6

198

7

198

8

198

9

199

0

199

1

199

2

199

3

199

4

199

5

199

6

199

7

199

8

199

9

200

0

200

1

200

2

200

3

200

4

200

5

200

6

200

7

200

8

200

9

1 Tabing-Padang 03106 22-0043-01

Source: BMKG

Sunshine Duration

196

9

197

0

197

1

197

2

197

3

197

4

197

5

197

6

197

7

197

8

197

9

198

0

198

1

198

2

198

3

198

4

198

5

198

6

198

7

198

8

198

9

199

0

199

1

199

2

199

3

199

4

199

5

199

6

199

7

199

8

199

9

200

0

200

1

200

2

200

3

200

4

200

5

200

6

200

7

200

8

200

9

1 Tabing-Padang 03106 22-0043-01

Source: BMKG

Wind Velocity

1969

1970

1971

1972

1973

1974

1975

1976

1977

1978

1979

1980

1981

1982

1983

1984

1985

1986

1987

1988

1989

1990

1991

1992

1993

1994

1995

1996

1997

1998

1999

2000

2001

2002

2003

2004

2005

2006

2007

2008

2009

1 Tabing-Padang 03106 22-0043-01

Source: BMKG

Pan Evapolation

1969

1970

1971

1972

1973

1974

1975

1976

1977

1978

1979

1980

1981

1982

1983

1984

1985

1986

1987

1988

1989

1990

1991

1992

1993

1994

1995

1996

1997

1998

1999

2000

2001

2002

2003

2004

2005

2006

2007

2008

2009

1 Lubuk Sikaping BMG

2 Tanjung Pati P3SA

Source: Masang-3 HEPP Report, 1999

: Complite Data: Incomplite Data

No. Station NameDPMA

ID

No. Station Name

HPPS2ID

Remarks

Remarks

Remarks

Remarks

Remarks

Year

HPPS2ID

HPPS2ID

No.DPMA

IDStation Name RemarksHPPS2

ID


HPPS2ID


No. Station Name

No. Station NameManagement

Body


Bt. Masang - Sipisang

01-164 -00-01

BMGID

Remarks

HPPS2ID Remarks


01-164 -00-01

Year


01-164 -00-01

DPMAID

HPPS2ID

Year

Year

Year

Year

Year

Year

Figure 16.4.3 Availability of Climatic Records (2/2)



Figure 16.4.4 Catchment Area of Masang-2 Intake Weir based on

1:50,000 map

B. Masang

S. Guntung

B. Sianok

B. Masang

B. A. Alahanpanjang

Masang-2 Intake Weir Site

Masang-2 Basin 443km2

Sipisang AWLR station

Power House Site



Figure 16.4.5 Flow Duration Curve of Estimated Daily Runoff at Masang-2 Intake Weir Site

Prob

abili

tyEs

timat

ed R

unof

f(%

)(m

3/s)

0%78

.99

5%31

.32

10%

26.3

115

%22

.51

20%

21.4

325

%20

.29

30%

18.9

135

%18

.05

40%

17.3

545

%16

.73

50%

16.1

955

%15

.57

60%

15.2

965

%14

.55

70%

13.8

175

%13

.06

80%

12.3

185

%11

.48

90%

10.9

995

%10

.03

100%

6.32

Ave

rage

17.6

7

Mas

ang-

2 In

take

Wei

r Site

05101520253035404550

00.

10.

20.

30.

40.

50.

60.

70.

80.

91

Prob

abili

ty o

f Exc

eede

nce

Runoff (m3/s)



0.0

0.5

1.0

1.5

2.0

2010/10/1 2010/10/16 2010/10/31 2010/11/15 2010/11/30 2010/12/15 2010/12/30

Wat

er L

evel

(m)

Maximum Water Level2.01m 2010/11/26 6:00

Minimum Water Level0.55m 2010/12/23

Average Water Level0.75m

0

20

40

60

80

100

120

140

160

180

2010/10/1 2010/10/16 2010/10/31 2010/11/15 2010/11/30 2010/12/15 2010/12/30

Run

off (

m3/

s)

Maximum Runoff156.61 m3/s 2010/11/26 6:00

Minimum Runoff13.60 m3/s 2010/12/23

Average Runoff25.68 m3/s

Discharge MeasurementEstimated Runoff withH-Q Rating Curve

Figure 16.4.6 Result of Water Level Observation and Hydrograph Calculated with H-Q

Rating Curve



Figure 16.4.7 Probable Flood Hydrographs at Masang-2 Intake Weir Site

0

500

1000

1500

2000

2500

3000

3500

4000

4500

01

23

45

67

89

1011

1213

1415

1617

1819

Tim

e (h

our)

Discharge (m3/s)

PM

F40

020

015

010

080 50 30 20 10 5 3 2



Probable Maximum Flood

10

100

1,000

10,000

100,000

10 100 1,000 10,000 100,000Catchment Area (km2)

Floo

d P

eak

Dis

char

ge (m

3/s)

PMFC=92Masang-2 PMF

Return Period = 200 year

10

100

1,000

10,000

100,000


Floo

d P

eak

Dis

char

ge (m

3/s)

200C=28Masagn-2 200

Figure 16.4.8 Relationship between Probable Peak Discharge and Catchment Area in Sumatra (1/2)




10

100

1,000

10,000


Floo

d P

eak

Dis

char

ge (m

3/s)

100C=25Masagn-2 100


10

100

1,000

10,000


Floo

d P

eak

Dis

char

ge (m

3/s)

2C=10Masagn-2 2

Figure 16.4.9 Relationship between Probable Peak Discharge and Catchment Area in Sumatra (2/2)



Figure 16.4.10 Sieve Analysis of Suspended Load

0%10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

0.01

0.10

1.00

10.0

0

Gra

in S

ize

(mm

)

%

Inta

ke06

-Okt

-10

Inta

ke06

-Okt

-10

Inta

ke06

-Okt

-10

Inta

ke09

-Okt

-10

Inta

ke09

-Okt

-10

Inta

ke09

-Okt

-10

Inta

ke22

-Okt

-10

Inta

ke22

-Okt

-10

Inta

ke22

-Okt

-10

Inta

ke25

-Okt

-10

Inta

ke25

-Okt

-10

Inta

ke25

-Okt

-10

Inta

ke05

-Nop

-10

Inta

ke05

-Nop

-10

Inta

ke05

-Nop

-10

Inta

ke21

-Nop

-10

Inta

ke21

-Nop

-10

Inta

ke21

-Nop

-10

Inta

ke25

-Nop

-10

Inta

ke25

-Nop

-10

Inta

ke25

-Nop

-10

Inta

ke05

-Des

-10

Inta

ke05

-Des

-10

Inta

ke05

-Des

-10

Sip

isan

g21-

Des

-10

Sip

isan

g21-

Des

-10

Sip

isan

g21-

Des

-10

Sip

isan

g25-

Des

-10

Sip

isan

g25-

Des

-10

Sip

isan

g25-

Des

-10



y = 5.4615x1.7812

1

10

100

1,000

10,000

100,000

1 10 100

Runoff, Qw (m3/s)

Sus

pend

ed L

oad,

Qs

(ton/

day)

Adopted Not Adopted

Figure 16.4.11 Suspended Load Rating Curve



16.5 POWER SYSTEM CONDITION

Figure 16.5.1 presents data for the power system in the vicinity of potential sites as of 2011, 2019, and 2027, using the estimated indicators for power demand formulated in Chapter 3. In this figure, the figures in the circular symbols indicate the peak power (upper row) and base power (lower row, in parentheses) at each substation (bulk supply point).

The potential site located on the northern shore of Lake Maninjau is situated outside the 150kV loop system encircling Padang, another big consumption center. The nearest major demand center is Bukit Tinggi. However, Bukit Tinggi is connected to the aforementioned 150kV system, and the loop system is scheduled to be connected to the 275kV system at Payakumbuh and Kiliranjao in 2012. Connection to this system will presumably also resolve the problem of voltage drop at Payakumbuh and Padang Luar.

For this area, the forecast envisions base power of 121 MW as compared to peak power of 201 MW 1in 2019, and corresponding figures of 218 and 363 MW in 2027.

The power sources in this area able to make a direct contribution to base power are PLTA Maninjau (4 x 17 MW), which is connected to GI Maninjau, and PLTA Batang Agam (3 x 3.5 MW), which is connected to GI Payakumbuh. Considering the capacity factors2 of each source, the available power inclusive of this potential would be about 71 MW. This would make it difficult to secure the power for this system shown in the figure in its entirety.

Assuming improvement of the power supply and quality at Payakumbuh and Padang by connection to the 275kV system, and limiting the system scope of the base power secured by this hydropower source to the GI Simpang Empat - GI Maninjau section, the available power inclusive of this potential would be about 65 MW, and make it possible to secure most of the system base power required in 2027.

GI Simpang Empat is a bulk supply point on the northern end supporting the power demand in the far northern part of West Sumatra Province. It may be anticipated to become a source that is also required for eliminating the prospective problem of voltage drop in the distribution system connected to it.

1 The diversity factor was excluded from consideration. 2 Hydropower :60% is applied.



Year 2011

Padang Luar

Masang2

21.9

11.1 32.0

Simpang Empat

Maninjau

4×17MW

27.7

3×3.5MW

Ke Kota Padang Year 2019

Masang2

45.3

23.5 66.2

Simpang Empat

Maninjau

4×17MW

66.0

3×3.5MW

Ke Kota Padang

Padang Luar

(27.2)

(14.1) (39.7) (39.6)

Year 2027

Masang2

81.6

42.0 119

Simpang Empat

Maninjau

4×17MW

120

3×3.5MW

Ke Kota Padang

Padang Luar

(49.0)

(25.2) (71.6) (72.0)

Source: JICA Study Team by reference to RUPTL2010-2019

Figure 16.5.1 Power system condition around potential site (Masang-2)

Final Report (Main) Chapter 17 Plan Formulation

JICA Project for the Master Plan Study of 17- 1 August, 2011 Hydropower Development in Indonesia

CHAPTER 17 PLAN FORMULATION

17.1 BASIC CONDITIONS AND ASSUMPTIONS FOR OPTRIMIZARTION STUDY

(1) Original Scheme

The Masang-2 project site is located about 15 km north of Lake Maninjau and 90 km north of Padang city in West Sumatra Province. The Masang-2 scheme was originally formulated as a run-of-river type hydropower development project capable of daily peak generation. In the original plan, the peaking generation was considered possible by effect of a storage reservoir created by diversion weir on main stream of the Masang river. The original layout is as shown in Figure 17.1.1.

Source: HPPS-2 (1999) Sectoral Report Vol. 11

Figure 17.1.1 Original Layout of Masang-2 Scheme

Main features of the original scheme are as follows: • Average annual runoff: 25.5 m3/s • Reservoir Full Supply Level (FSL): El. 361.9 m • Reservoir Minimum Operation Level (MOL): El. 354.9 m



• Active storage volume of reservoir: 0.6 mil. m3 • Headrace tunnel (diameter x length): D3.9 m x 6,700 m • Penstock (diameter x length): D3.1 m x 500 m • Powerhouse, tail water level: El. 200.0 m • Power and energy generation, Max. plant discharge: 33.2 m3/s Average net head: 144.3 m Installed capacity: 39.6 MW Annual energy production: 256.1 GWh

(2) Alternative Powerhouse Site

Using the original layout as a basis for the current optimization study, site reconnaissance in the Masang-2 project site was conducted. During the preliminary review of the layout, it was revealed that the river bed elevation at powerhouse site on the 1/50,000 map available at that time is several 10 meters higher than the originally estimated tail water elevation. Also by the provisional rough measurement by a hand GPS device at the site reconnaissance, the river bed elevation seemed about 20 m higher than the tail water level indicated in the original design. Such higher river bed level at the powerhouse site unfavorably results in reduction of power output by more than 15%.

It is understood that the original Masang-2 powerhouse site was selected in initial phase of HPPS-2 on the basis of a temporary plan of the downstream Masang-3 scheme of which the reservoir FSL was set at El. 200 m. In the later phase of the HPPS-2, Pre F/S was conducted for theMasang-3 scheme and its reservoir FSL was lowered to El. 167 m to avoid submergence of vast farm land and populated town on the upstream tributary (Alahanpanjan river). The Masan-3 scheme is a hydropower project with 90 m high dam. However, its dam site is located within the natural reserve range. Implementation of the Masang-3 project seems unrealistic. In view of this situation, it is decided to shift the powerhouse site 2.3 km downstream in the current study. The planned new site is just below the junction of the Masang river with the Alahanpanjan river. By this shifting, the available water head for power generation increases by more than 50 m. Therefore, the idea of locating powerhouse on the original site is abandoned in the current study.

(3) Alternative Options for Intake Site

The original intake site (named Plan A) is located 500 m downstream from the junction of two rivers, i.e. Masang and Guntung rivers. Topographic survey works and geological investigations by the JICA team were started at the original intake site. However, it was revealed during the initial exploratory drilling that the original intake site is covered with weak volcanic sediment layer of more than 20 m thick at the river bed. Such thick and weak layer causes difficulty of intake weir construction and increase of construction cost.

To find more favorable intake sites, further reconnaissance was conducted along the downstream river course. In the reconnaissance, rock outcrop was found on river bed at a sharp bend of river in a range



of 0.5 to 1.0 km downstream from the original intake site. The rock outcrop was considered to have sufficient strength for supporting intake weir. This river stretch was selected as alternative intake sites (named Plans B and C).

(4) Flow Regulation Pond for Daily Peak Generation

In the original HPPS-2 plan, it was proposed to create a storage reservoir (0.6 mil. m3) on the main stream by a 20 m high diversion weir in order to regulate river flow for daily peak generation. However, the upper Masang and Guntung river basins are covered with volcanic materials. River slope upstream of the intake site is steep and the Guntung river bed is filled with big boulders and sand/gravel. The river water contains considerable amount of volcanic silt and sand due to ground surface erosion. It is foreseen that, even if a daily regulation reservoir is created on the main stream, it will soon be filled with sediments. For flushing of deposited sediments to recover the original storage capacity, the reservoir water level has to be lowered periodically down to reservoir bottom and much of inflow water has to be discharged downstream without utilizing it for generation. This means that generation operation has to be interrupted frequently for the sediment flushing operations. In addition, it is foreseen that if river bed boulders in the upstream reaches are washed out by flood flows into the reservoir, flushing-out of accumulated boulders from the reservoir is extremely difficult. Therefore, the idea of creating a reservoir (or pond) on the main stream is abandoned in the current study.

Instead of creating main stream reservoir, it is planned to build an intermediate regulation pond on the route of waterway utilizing natural creek or relatively flat land existing between the intake and the powerhouse. However, as the natural creek depression is not enough to create a large pond sufficient for daily flow regulation, it is necessary to excavate the hill ground around the creek.

(5) Restriction of Peak Generation Duration

The duration of peaking generation depends on daily load curve in the regional power system. The future daily peak load duration in Sumatra is estimated to be 4 to 7 hours a day. The power plant for longer peak duration and higher generation output requires larger water storage capacity of regulation pond.

In case of the Masang-2, land topography along and around the route of waterway is relatively steep and does not suite to build large storage pond. Closing of a small natural creek on the waterway route by embankment cannot make a pond having sufficient storage capacity because of steep terrain slope. In addition to the creek closing embankment, large scale excavation is required for creating a sufficient capacity pond. However, due to relatively steep terrain slope, scale of excavation becomes excessively large in comparison with the pond storage volume. In consideration of such topographic restriction, the peak duration time is fixed to be 4 hours a day for all alternatives. This duration is considered to be the minimum limit for the practical system operation.

(6) Penstock Line



Surface slope of the hill between surge tank and the powerhouse is not so steep. Construction of surface type penstock is relatively easy though anticipated base rock surface is deep. Most of forest cover is production forest. Environmental impact caused by penstock line construction seems less serious.

(7) Topographic Data

In the initial phase of the current study, only a map with scale of 1/50,000 was available for layout study. In the later phase, the following new maps prepared by local survey subcontractor of the JICA team were made available for optimization study.

• One 1/10,000 map covering whole project area (intake to powerhouse), made by photogrammetric mapping utilizing available satellite images.

• Four 1/2,000 maps respectively covering a 1.5 km stretch around the original intake site, a downstream alternative intake site area, intermediate pond area and a powerhouse area, which were all made by field survey works.

It is recognized that there are large elevation differences between the old 1/50 000 map and newly surveyed map. The elevation information indicated in the new maps is used for the optimization study. Therefore, elevation figures shown in the designs of HPPS-2 are revised on the basis of the new maps.

(8) River Runoff

Stream flow series of the Msang river is analyzed on daily basis in the foregoing Chapter 16. Long term average runoff (inflow) at the original intake site is estimated at 17.67 m3/s. Firm runoff (95% dependable inflow) estimated is 10.03 m3/s.

(9) River Maintenance Flow

If river water is fully diverted at intake weir to power waterway, the river just downstream of the intake weir becomes dry. To preserve natural environment of the downstream reaches, inflow at the intake weir needs to be partly released downstream. Rate of the required minimum downstream flow is decided to be 0.2 m3/s per 100 km2 of catchment area above the intake weir. This rate is applied to other hydropower projects constructed or being constructed in Sumatra. Since the catchment area of Masang-2 intake site is approximately 445 km2, the required minimum flow is decided to be 0.89 m3/s (>0.2 x 445/100).

Two large tributaries join the main stream within about 1 km stretch downstream of the intake site B. One of them is a right tributary Belukar river covering catchment area of 7 km2, which joins the main stream at immediate downstream of the intake site B. The other is a left tributary Banban river covering catchment area of 15 km2, joining at 1 km downstream from the intake site B. It is estimated that those tributaries drain water of 0.16 m3/s and 0.34 m3/s, respectively to the main stream on the 95% dependability. At least 0.50 m3/s comes from the tributaries in the 1 km stretch. This effect of



inflow is reflected on the requirement of minimum flow release from the intake weir.

17.2 SELECTION OF OPTIMAL DEVELOPMENT LAYOUT

(1) Alternative Layout Plans

Three alternative layout plans are taken up for optimization study. Layouts of them are shown in Figure 17.2.1.


Figure 17.2.1 Alternative Layout Plans of Masang-2 Scheme

Main features of each alternative plan are described in the following table:

Alternatives Main Features

Plan A • The intake site is identical to that in the original HPPS-2 layout. • Full Supply Level (FSL) at intake is El. 358 m. Tail Water Level (TWL) at powerhouse

is El. 142 m. • Gross head between the intake and the powerhouse is 216 m. • Adverse geology is encountered in the intake site. Depth of soft overburden is more

than 20 m at river bed. Concrete pile foundation is required in the intake weir and

Masang-2 HEPP Alternative Layouts

PLAN C PLAN B

PLAN A



intake structures. • Total length of headrace waterway (intake to surge tank, except pond) is 7.40 km. • Daily peak generation is made possible by a regulation pond created on small natural

creek by excavation. Pond storage capacity is limited. Plan B

• Intake site is shifted downstream by 0.5 km from the Plan A site. Geology at the foundation is relatively good. Lime stone rock is exposed in river bed.

• FSL at intake is El. 344 m. TWL at powerhouse is El. 142 m. • Gross head between the intake and the powerhouse is 202 m. • Total length of headrace waterway (intake to surge tank, except pond) is 7.24 km. An

upstream 1 km long waterway is cut-and-cover culvert. Underground tunnel works are reduced.

• Daily peak generation is made possible by a regulation pond created on small natural creek by excavation. Pond storage capacity is limited.

Plan C

• Intake site is shifted further downstream by 1 km from Plan A site. Geology at the foundation is marginally good. Rock is exposed in the river bed.

• FSL at intake is El. 333 m. TWL at powerhouse is El. 142 m. • Gross head between the intake and the powerhouse is 191 m. • Total length of headrace waterway (intake to surge tank, except pond) is 6.90 km. An

upstream 0.5 km long waterway is cut-and-cover culvert. Length of waterway is 340 m shorter than Plan B.

• Daily peak generation is made possible by a regulation pond created on small natural creek by excavation. Pond capacity is limited.

(2) Maximum Plant Discharge and Required Pond Capacity

In the development scale optimization study in the succeeding Section 17.3, the discharge of 32.0 m3/s is selected as the optimal maximum plant discharge. This plant discharge is also applied herein for all alternative layouts. It is noted that this maximum plant discharge is decided taking into account the restriction by the pond storage capacity. This means that the firm runoff is not fully used for peak generation and part of the firm runoff is used for off-peak generation even in drought time.

The required active storage capacity in the daily regulation pond is calculated by:

( )fQQTV −= max3600

Where, V = Required active storage volume in pond (m3) T = Peaking time (hours/day) Qmax = Maximum plant discharge for generation (m3/s) Qf = Firm discharge for generation = 95 % dependable discharge (m3/s)

(3) Design Input Data

Basic input data for designing each Plan are listed in the following table:



Design Input Data Description Unit Plan A Plan B Plan C

1. Catchment area above intake weir km2 443 444 4502. Average river runoff Firm runoff (95% dependable) (q)

m3/s m3/s

17.6710.03

17.71 10.05

17.9510.19

3. Min. downstream flow release from intake (qr) Inflow from tributaries in 1 km stretch Total min. river flow at 1 km downstream

m3/s m3/s m3/s

0.390.500.89

0.39 0.50 0.89

0.550.340.89

4. Firm discharge for generation (Qf) = q - qr m3/s 9.64 9.66 9.645. Daily peaking time (T) hours 4 4 46. Max. plant discharge (Qp) m3/s 32.0 32.0 32.07. Intermediate pond, active storage req’d (V) m3 322,000 322,000 322,0008. Intermediate pond, water surface area ha 4.0 4.0 4.0

(4) Designed Features

Designed features of principal facilities in each plan are presented in the following table:

Designed Features of Principal Facilities

Description Unit Plan A Plan B Plan C 1. Intake Weir (Un-gated concrete weir) Height (below overflow crest) FSL

ｍ

El. m10

358

10

344 10

3332. Connection Culvert (free-flow flume with

box shape) Internal section size (W x H) Length

m km

None==

3.75 x 4.15

1.06

3.75 x 4.15

0.723. Connection Tunnel (free-flow tunnel with

horse-shoe section) Diameter Length

m km

3.752.85

3.75 1.63

3.751.63

4. Intermediate Pond FSL MOL Drawdown

El. mEl. m

m

353.2343.2

10.0

339.9 329.9

10.0

329.2319.2

10.05. Headrace Tunnel (pressure flow tunnel

with circular section) Diameter Length

ｍ km

3.754.55

3.75 4.55

3.754.55

6. Penstock (underground inclined shaft type) Pipe diameter Length

m m

3.1696

3.1 692

3.1688

7. Powerhouse Type

Surface type

Surface type Surface type



Tail water level El. m 142.0 142.0 142.0

8. Generating Equipment Installed capacity (total of 2 units) Max. plant discharge Rated net head

MW m3/s

m

5532.0

191.7

52

32.0 178.8

4832.0

168.1

(5) Construction Cost

Construction cost of each Plan is estimated by applying the estimation basis described in Chapter 19. The estimated costs excluding contingencies are as follows:

Construction Costs Estimated for Each Plan Unit: US$ million

Description Plan A Plan B Plan C

1. Civil Works Intake facilities Water way Intermediate pond Penstock and powerhouse Sub-total

20.1842.0215.48

6.3784.05

6.91

41.34 15.05

6.25 69.55

7.4239.2812.85

5.4164.97

2. Mechanical & Electrical Works 47.63 45.50 43.193. Preparatory and Environmental Works 20.53 18.72 17.994. Engineering and Land Costs 31.08 27.39 25.87

TOTAL 183.29 161.16 152.02

(6) Power Generation Calculation

For each Plan, power generation calculation is carried out applying the flow duration curves derived from the 21-year low flow analysis (1973-1993) in Section 16.4. Daily average discharge duration curve applied is shown in Figure 17.2.2. Because there is no significant difference of the catchment areas of the three Plans (443-450 km2), the same river flow duration curve is applied for all three Plans.

Source JICA Study Team

Figure 17.2.2 Daily Average Discharge Duration Curve

0

10

20

30

40

50

60

0 10 20 30 40 50 60 70 80 90 100

Probability of exceedence (%)

Dis

char

ge (m

3/s)

Natural River FlowInflow to Intake

Masang-2: Plans A, B and C



All three plans are capable of peaking generation for 4 hours a day by the effect of intermediate pond having the storage capacity of 322,000 m3. However, due to difference of working water head, the Plan A is highest in generation output and the Plan C is lowest. The results of generation calculation are as follows:

Results of Power Generation Calculation

Description Unit Plan A Plan B Plan C

a. Maximum power output

b. 95% dependable power output (4-hour peak)

c. Annual average energy production

d. Plant factor (*)

MW

MW

GWh

%

55

55

255

53

52

52

240

53

48

48

225

53

Remarks (*) : PF= (c/8.76)/a

(7) Economic Comparison

All three Plans are operated by mixed generation mode, i.e., 4-hour peak and 20-hour off-peak generations. Benefits of the peak time power and energy are evaluated applying generation cost of gas-turbine power plant suitable for peaking generation. Benefits of the off-peak time power and energy are evaluated applying generation cost of coal-fired thermal power plant suitable for base load operation. Those thermal generation costs are explained in Chapter 14 and are summarized below.

• Gas turbine generation cost for peak time benefit: Power: 96.23 US$/kW Energy: 0.080 US$/kWh

• Coal-fired plant generation cost for off-peak time benefit: Power: 223.67 US$/kW Energy: 0.0417 US$/kWh

Total outputs obtained by the generation calculations are separated to peak time output and off-peak time output. The equations for separation, which are explained in Chapter 14, are as follows:

Output Power (kW) Energy (kWh/year)

Peak time output T

EP−

−=

24365/24

36524

)365/24( xT

EPT−−

=

Off-peak time output T

ETP−

+−=

24365/

36524

)365/(24 xTETP

−+−

=

Remarks: P = Peak output (dependable), kW E = Annual energy production, kWh T = Peaking hour (hours/ day)

Power and energy outputs of each Plan and their benefits are calculated in the following table. Construction cost of each Plan is annualized by applying the capital recovery factor (=0.1009) based



on discount rate of 10% and project life of 50 years.

Economic Comparison of Alternative Layouts

Description Unit Plan A Plan B Plan C

1. Power and energy outputs separated

Peak time: Power

Energy

Off-peak time: Power

Energy

kW

kWh/y

kW

kWh/y

31,100

45.4x106

23,900

209.6x106

29,500

43.1x106

22.500

196.9x106

26,800

39.1x106

21,200

185.9x106

2. Annual generation benefit

Peak time: Power

Energy

Off-peak time: Power

Energy

Total annual benefit (B)

M US$

M US$

M US$

M US$

M US$

2.99

3.63

5.35

8.74

20.71

2.84

3.45

5.03

8.21

19.53

2,58

3,12

4.75

7.75

18.20

3. Annual cost

Annualized construction cost

(Total cost x 0.1009)

Annual O&M cost (0.5% of total cost)

Total annual cost (C)

M US$

M US$

M US$

18.49

0.92

19.41

16.26

0.81

17.07

15.34

0.76

16.10

4. Net annual benefit (B-C) M US$ 1.30 2.46 2.11

The layout Plan B is most economical among the three Plans as the net benefit is highest. The second economical layout is Plan C of which the net benefit is about 86% of Plan B. The net benefit of Plan A is much less than those of Plans B and C.

(8) Engineering Assessment

The Plans A, B and C are further assessed from the engineering point of view as presented in the table below.

At the later phase of the current study, it was revealed that an IPP small hydro project (Guntung project) is in progress around the Masang-2 intake area. Its intake facility proposed is on the Guntung river located 1.2 km upstream of the Plan A intake site. Its proposed powerhouse site is located near to the Plan B intake site. The Guntung project having generation capacity less than 10 MW is under planning stage at present. Impact of this IPP project to the Masang-2 project is also evaluated in the same table.



Engineering Assessment of Each Plan O: Superior to the other Plans △: Relatively superior X: Inferior

Alterna- tive

Assess Point

Engineering Assessment Judgment

Plan A Technical • Access to the intake site from the existing road is about 0.3 km long. It is shorter than other Plans

• Adverse geology is encountered at intake site. Thick volcanic soft overburden covers the river bed at intake site. Base rock surface is as deep as 20 m. Costly concrete pile foundation is necessary for intake weir and sand trap.

• Due to the adverse geology, temporary river diversion for intake construction is difficult. Large scale excavation of right bank is necessary for constriction of temporary by-pass channel.

• If the Guntung project is realized, most of water of the Guntung river will by-pass the Plan A intake. Inflow to the Plan A intake probably decreases to 2/3 or less of the present estimate. This results in unrecoverable reduction of project economy.

X

Environ- mental

• It is necessary to procure partly the existing paddy fields on both banks for construction of intake facilities.

• River length where water flow diminishes due to water diversion at intake to power tunnel is about 8.5 km up to the junction with Alahan Panjang river. While the river water is not used by riparian people for farming and living, water release from intake to downstream river is required to preserve environment.

• Waterway from intake to surge tank is underground structure. Environmental impact to animals is minimized.

• All structures including intake facilities, waterway and powerhouse are located outside protection forest.

• Because of peaking generation, river water level downstream of powerhouse largely fluctuates, particularly in drought month. Warning system (siren, etc.) for riparian people will be required.

X

Plan B Technical • For access to the intake site, a new road from the existing road is necessary on the right bank. But, its length is only about 1.2 km.

• At the intake site, lime stone rock is exposed in river bed. This facilitates construction of temporary diversion facilities. Consequently, construction cost and time for intake facilities is reduced.

• The IPP Guntung powerhouse tailrace will be located between Plan A and Plan B intake weir sites. Even if the Guntung project is realized, there is no reduction of water flow to the Plan B intake.

• Connection culvert downstream of sand trap is open-air structure. By this, underground tunnel work on critical path is reduced. .

O

Environ- mental

• Large farm land is not in the intake weir site. Procurement of farm land is little.


△



Alterna- tive

Assess Point

Engineering Assessment Judgment

• Waterway from intake to surge tank, except connection culvert, is underground structure. Environmental impact to animals is minimized.



Plan C Technical • For access to the intake site, a new road from the existing road is necessary on the right bank. But, its length is only about 1.2 km.

• At the intake site, weathered rock is exposed in river bed. This facilitates construction of temporary diversion facilities. Consequently, construction cost and time for intake facilities is reduced.

• The IPP Guntung powerhouse tailrace will be located between Plan A and Plan B intake weir sites. Even if the Guntung project is realized, there is no reduction of water flow to the Plan C intake.

• Connection culvert downstream of sand trap is open-air structure. By this, underground tunnel work on critical path is reduced. .

△

Environ- mental


• Waterway from intake to surge tank, except connection culvert, is underground structure. Environmental impact to animals is minimized.



△

Plan A is environmentally inferior because the existing paddy filed is partly occupied by the intake facilities. The Plans B and C are environmentally more superior than the Plan A. From the environmental point of view, there is no significant difference between the Plans B and C.

Plan B is technically most superior because relatively sound base rock is exposed in the intake site and construction of the intake facilities is easy. Intake site for the Plan A is inferior since the foundation geology is bad. Rock exposed in the Plan C intake site seems to be in deeply weathered condition. The Plan C is therefore second superior among three Plans.

(9) Selection of Optimal Development Layout

Based on the foregoing economical comparison and engineering assessment, the Plan B is selected as the most optimal development layout for the Masang-2 HEPP.



17.3 SELECTION OF OPTIMAL DEVELOPMENT SCALE

(1) Selected Layout Plan

In the above Section 17.2, the Plan B was selected as the optimal development layout. The overall layout of the Plan B is detailed in Drawing M-010 and presented in Figure 17.3.1.


Figure 17.3.1 Selected Layout of Masang-2 HEPP

(2) River Runoff

As applied for generation calculations in Section 17.2, the catchment area at the intake weir of the Plan B is 444 km2 and the river runoff is 17.71 m3/s on average (Year 1973-1993). The river runoff in terms of 95% dependable runoff is 10.05 m3/s. For the river maintenance purpose, discharge of at least 0.39 m3/s is released from the intake weir to the downstream reaches. Net discharge of 9.66 m3/s is usable as the 95% dependable discharge for generation.

In a 1.2 km stretch downstream from the intake weir, the minimum river flow increases to 0.89 m3/s owing to inflow of 0.50 m3/s from relatively large tributaries. This minimum flow satisfies the widely applied requirement of 0.2 m3/s per 100 km2 of catchment area.

(3) Development Scale Alternatives

As mentioned in Section 17.2 (4) and (5), the daily peaking time is limited to 4 hours since there is topographic restriction in building large capacity regulation pond on the waterway route. Therefore, the Masang-2 scheme is designed for semi-peak generation even at the time of the firm discharge (95% dependable). If the pond capacity is large enough, peak generation output is increased and generation operation is limited to peak time only, i.e. no off-peak time generation at the time of firm runoff.

To seek the optimal generation capacity, four alternatives of maximum plant discharge are taken up taking into account the different water utilization factors (F). The F is calculated by Qave / Qmax where Qave is long term average flow for generation (=17.71 m3/s) and Qmax is maximum plant



discharge. Those alternatives are as follows:

Alternative Factor ‘F’ Qmax (m3/s) 1 0.45 39.4 2 0.50 35.4 3 0.55 32.0 4 0.60 29.5

(4) Economic Diameter of Tunnel and Penstock

Regarding the power waterway, smaller diameter tunnel (or penstock) is lower in construction cost but the generation output contrarily decreases due to increased head loss in waterway. Optimal (economical) diameter of tunnel (or penstock) is selected hereunder. By this selection, annualized construction cost and reduced annual generation benefit are combined for each tunnel diameter and a certain diameter at which the combined cost becomes lowest is selected to be the economical diameter of the tunnel.

Loss of head in the tunnel (or penstocks) is calculated for several different diameters combined with various maximum plant discharges. Reductions of generation output (kW and kWh) corresponding to such loss head is calculated. The reduced generation outputs are converted to reduced benefits by applying the same method as described in Section 17.2 (7). As to each different diameter tunnel, the annualized construction cost and the reduced benefit are combined to make a total of annual cost and annual loss of benefit. On the other hand, the construction cost of tunnel (or penstock) is estimated for each different diameter.

For the connection culvert extended along the river bank from the intake sand trap to the connection tunnel inlet, box shape concrete flume is applied. The culvert is constructed by cut-and-cover method. For the connection tunnel between the connection culvert end and the intermediate pond, standard horse-shoe section is applied since such tunnel type is economical because the flow in tunnel is free flow and internal water pressure is low. For the headrace tunnel between the intermediate pond and the surge tank, circular section is applied since flow in the tunnel is pressure flow and its internal pressure is relatively high. For the penstock line between the surge tank and powerhouse, surface type penstock is selected since the ground surface slope is not so steep and surface penstock is more economical than the under ground penstock. The penstock pipe is laid in open trench excavated.

Calculated results of economic diameters are illustrated in Figure 17.3.2. Selected diameters of tunnels and penstock and size of culvert are listed below.

Waterway

Max. Plant Discharge (m3/s) 39.4 35.4 32 29.5

1. Connection culvert (L = 1.06 km) Selected section size (w x h)

3.9 x 4.3

3.8 x 4.2

3.75 x 4.1

3.65 x 4.0

2. Connection tunnel (L = 1.63 km)



Selected economical diameter 3.9 3.8 3.75 3.65 3. Headrace tunnel (L = 4.55 km) Selected economical diameter

3.9

3.8

3.75

3.65

4. Penstock pipe (L = 695 m) Selected economical diameter

3.4

3.25

3.1

3.0


Figure 17.3.2 Economic Diameters of Tunnels and penstock

Required thickness of tunnel concrete lining is estimated to be 10% of the tunnel internal diameter. Penstock pipe just downstream of the surge tank is laid in horizontal tunnel of which excavation diameter is decided so as to make a 0.6 m wide gap between pipe surface and excavated tunnel surface. The gap is completely backfilled with concrete after installation of the penstock pipe.

(5) Design of Other Facilities

The intake weir is a concrete weir with height of about 10 m above the deepest foundation in the river bed. The weir has a 40 m wide ungated overflow type spillway of which crest elevation is equal to the Full Supply Level (FSL) of 344.0 m asl. A sand flushing sluice is provided on left bank side of the spillway near intake for flushing sediment deposited in front of intake entrance.

Intake structure is located on lest bank side of the weir. Trash rack with rake is provide at the intake entrance of which size is decided so that the flow velocity at the entrance is 1 m/s at the maximum. Incoming water at the intake is led to the sand trap facility located just downstream of the intake. The sand trap is a settling basin with rectangular cross section. The basin size is decided so that the flow velocity in the basin becomes 0.3 m/s at the maximum so as to settle sand particles larger than 0.5 mm. The basin is separated to double lanes by a center wall so that flushing of deposited sediment is conducted one by one without stopping water flow in either one of the lanes. At the downstream bay of the sand trap, a river outlet facility is provided for releasing the river maintenance flow of 0.39 m3/s. The downstream end of the sand trap is joined to the connection culvert.

2.0

2.5

3.0

3.5

4.0

4.5

5.0

20 30 40 50 60

Plant max. discharge (m3/s)

Econ

omic

dia

met

er (m

)Culvert, Connection Tunnel & Headrace Tunnel

Penstock Pipe



A small natural creek crossing the waterway route is closed by a dike to create the intermediate pond. The water diverted from the intake is stored in the pond for daily peak generation at the powerhouse. However, the creek valley is narrow and insufficient for storing the required volume of water. Therefore, it is necessary to excavate the ground around the creek to ensure the required storage capacity. Required active storage volume of the pond varies with the peaking time and calculated by the following equation.

)(3600 max fQQTV −=

where, V = Required active storage volume of pond (m3) T = Peaking time (hours) Qmax = Maximum plant discharge (m3/s) Qf = Diverted firm discharge (m3/s)

In order to always keep free flow state in the connection culvert and tunnel, the pond water level has to be lower than the sand trap water level by the head loss. The required water level difference depends on the head loss in connection culvert and tunnel. The head loss varies with the discharge in the culvert and tunnel. The full supply level (FSL) of the pond is decided taking into account the head loss at the maximum tunnel discharge being equal to the maximum plant discharge.

Storage Volume and Water Levels of Pond Description Unit Max. Plant Discharge (m3/s)

39.4 35.4 32.0 29.5 1. Required active storage volume MCM 0.429 0.371 0.322 0.286 2. FSL at Intake Weir El. m 344.0 344.0 344.0 344.0 3. Waterway head loss between

intake and pond

m

4.9

4.5

4.1

4.0 4. Water Level of Pond FSL MOL

El. m El. m

339.1 329.1

339.5 329.5

339.9 329.9

340.0 330.0

5. Drawdown m 10.0 10.0 10.0 10.0

The dike to close the creek is rockfill embankment with clay core. Storage volume ensured by closure of the creek with the embankment dike is about 0.14 MCM only. The required storage volume in excess of 0.14 MCM has to be ensured by excavation of the ground around the creek. Relation between excavation volume and resulted storage volume is shown in Figure 17.3.3. As seen in this Figure, huge excavation is required for ensuring the required storage capacity.

Figure 17.3.3 Excavation Volume vs Resulted Storage Capacity

0

1

2

3

4

0 0.1 0.2 0.3 0.4 0.5 0.6

Pond Storage Volume Ensured by Excavation (MCM)

Exc

avat

ion

Vol

ume

(MC

M)



A surge tank of vertical shaft type with a bottom orifice port is provided at the downstream end of the headrace tunnel before connecting to the penstock. Size of the surge tank is decided by up-surging and down-surging oscillation analysis. They are listed below:

Surge Tank Diameters and Water Levels Description Unit Max. Plant Discharge (m3/s)

39.4 35.4 32.0 29.5 1. Diameter of surge tank m 9.2 8.8 8.5 7.8 2. Highest up-surging WL Lowest down-surging WL

El. m El. m

361 315

361 316

361 316

361 316

Top of the tank is decided to be 3 m higher than the up-surging water level. Invert level of the headrace tunnel beneath the surge tank is decided to be 10 m lower than the down-surge water level.

Powerhouse is above-ground type concrete construction. A tailrace is a short open channel extended from the powerhouse to the river bank edge. Size of powerhouse is estimated on the basis of data of the other similar powerhouse projects. Capacity of generating equipment for each Alternative is calculated as follows:

Generating Equipment Description Unit Max. Plant Discharge (m3/s)

39.4 35.4 32.0 29.5 1. Max. head loss after pond 2. Rated net head 3. Installed capacity (total of 2 units)

m m

MW

15.7 176.4

63

15.1 177.4

57

14.1 178.8

52

13.9 179.1

48

(7) Construction Cost

Construction cost of each alternative is calculated on the basis of work quantities calculated for each alternative and unit prices referred to in Chapter 19. The results are in the following table:

Construction Costs Estimated for Each Alternative Unit: US$ million

Items Max. Plant Discharge (m3/s) 39.4 35.4 32.0 29.5

Installed capacity (MW) 63 57 52 48 1. Civil Works Intake facilities Waterway Intermediate pond Penstock and Powerhouse Sub-total

8.0246.4123.75

7.7085.88

7.4043.5218.85

6.9576.72

6.91

41.34 15.05

6.25 69.55

6.8339.5812.65

5.7064.47

2. Mechanical & Electrical Works 52.73 48.72 45.50 43.033. Preparatory and Environmental Works 21.30 19.95 18.72 17.984. Engineering and Land Costs 32.22 29.71 27.39 25.81



TOTAL 192.13 175.10 161.16 151.29

(8) Power Generation Calculation

Similarly to paragraph (6) of the forgoing Section 17.2, power generation calculation is carried out for each Alternative applying the same flow duration curve for the Plan B. Daily average turbine discharge duration curves of all alternatives are illustrated in Figure 17.3.4.


Figure 17.3.4 Duration Curves of Daily Discharges

The results of the generation calculations are as follows:

Results of Power Generation Calculation Description Unit Max. Plant Discharge (m3/s)

39.4 35.4 32.0 29.5 1. Max. power output 2. 95% dependable output (4 hours) 3. Annual energy production 4. Plant factor

MW MW GWh

%

63 63

242 44

57 57

241 48

52 52

240 53

48 48

238 57

(9) Economic Comparison

All alternatives are operated by mixed generation mode, i.e., peaking generation for 4 hours and off-peak generation for 20 hours. Benefits of peak time generation and off-peak time generation are evaluated separately as explained in paragraph (7) of the foregoing Section 17.2. Total generation output of each alternative is separated to peak time output and off-peak time output as explained in the

0

10

20

30

40

50

60

0 10 20 30 40 50 60 70 80 90 100

Probability of exceedence (%)

Dis

char

ge (m

3/s)

63 MW57 MW52 MW48 MWNatural river flow

River flow at intake

Daily average turbinedischarge



said paragraph.

Power outputs and energy productions of each alternative and their benefits are calculated in the following table. Construction cost of each alternative is annualized by applying the capital recovery factor of 0.1009.

Economic Comparison of Alternative Development Scales Description Unit Max. Plant Discharge (m3/s)

39.4 35.4 32.0 29.5 1. Installed capacity MW 63 57 52 482. Power and energy outputs Peak time: Power Energy Off-peak time: Power Energy

kW

kWh/y kW

kWh/y

42,40062.0x106

20,600180.0x106

35,40051.7x106

21,600189.3x106

29,500

43.1x106 22,500

196.9x106

25,00036.5x106

23,000201.5x106

3. Annual generation benefit Peak time: Power Energy Off-peak time: Power Energy Total annual benefit (B)

M US$M US$M US$M US$M US$

4.084.964.507.51

21.15

3.414.134.837.90

20.27

2.84 3.45 5.03 8.21

19.53

2.412.925.148.40

18.874. Annual cost Annualized construction cost (Total cost x 0.1009) O&M cost (0.5% of total cost) Total annual cost (C)

M US$

M US$M US$

19.39

0.9620.35

17.66

0.8818.54

16.26

0.81

17.07

15.65

0.7816.43

5. Net annual benefit (B-C) M US$ 0.80 1.72 2.46 2.45

Variation of the net annual benefit with the installed capacity is graphically shown in Figure 17.3.5.


Figure 17.3.5 Development Scale Optimization Result

0

1

2

3

4

5

45 50 55 60 65

Installed Capacity (MW)

Ben

efit

- Cos

t (M

US

$) 52 MW (4-hour peak)



(10) Selection of Optimal Development Scale

As seen in the above Figure 17.3.5, the annual net benefit (B-C) increases with increase of plant capacity. However, the benefit reaches the maximum at around the plant capacity of 52 MW (4-hour peaking mode). Further increase of the plant capacity results in reduction of the net benefit. Therefore, the 52 MW plant capacity by the maximum plant discharge of 32 m3/s is selected as the optimal development scale. A 52 MW peak generation for at least 4 hours is possible even in the drought year with 95% dependability.

Final Report (Main) Chapter 18 Preliminary Design


CHAPTER 18 PRELIMINARY DESIGN

18.1 DESIGN CONDITIONS

18.1.1 HYDROLOGICAL CONDITIONS

Long term low flow analysis for the Masang-2 project is conducted in the Section 16.4. The hydrological conditions related to the preliminary design are listed below:

Description Unit Intake Weir

Interm’t Pond

Power- house

Catchment area km2 444 0.9 920 Average river runoff m3/s 17.71 = = 95% dependable runoff m3/s 10.05 = = Design flood (200-yr flood) m3/s 1,341 15.2 1,939 Construction flood (2-yr flood) m3/s 456 5.2 659 Sediment inflow m3/yr 222,000 450 =

18.1.2 MINIMUM DOWNSTREAM FLOW (RIVER MAINTENANCE FLOW)

At the intake weir, river water except in flood time is fully diverted to the power tunnel. However, to maintain minimum flow condition in the river reaches downstream of the weir, the water of 0.39 m3/s at the maximum is released from the intake weir to the downstream river. This rate is decided so as to meet the criteria of 0.2 m3/s per 100 km2 of catchment area at the point about 1 km downstream of the weir site (444km2/100km2 x 0.2m3/s = 0.89m3/s). This criteria is already applied to the some other on-going or completed hydropower projects in Sumatra. In the 1 km downstream stretch from the weir site, relatively large tributaries having total catchment area of 22 km2 join the main Masang river. The required minimum river flow at that point is 0.89 m3/s. A natural flow coming from the tributaries is 0.50 m3/s with 95% dependability and this flow is combined with the flow (0.39 m3/s) released from the intake weir.

18.1.3 PLANT DISCHARGE

The generating plant is operated as a 4-hour peak and 20-hour off-peak generation mode depending of available daily river flow. However, as mentioned in Section 17.3, the maximum plant discharge is decided to be 32.0 m3/s taking into account the limited pond storage capacity. Any river flow up to this



rate is diverted to the power waterway at the intake. All waterway structures are designed for this discharge.

18.2 MAIN CIVIL STRUCTURES

18.2.1 INTAKE WEIR

The intake weir is located 1 km downstream from the confluence of Masang river (Batang Sianok) with Guntung river (Batang Guntung). This location is selected taking into account the following:

• Relatively hard base rock is exposed in the river bed and both abutments. Since the rock conditions are good, constriction of the intake weir and sand trap structures is easy and not costly.

• An IPP powerhouse of the on-going Guntung project will be located 150 m upstream of the Masang-2 intake site. Shifting of the intake to upstream site interferes with the IPP project.

The intake weir is concrete weir with un-gated overflow spillway. The crest elevation of the spillway is set at El. 344.0 m. This elevation is regarded as the Full Supply Level (FSL) for the power intake. As the river bed elevation at the weir is around El. 337 m, the height of weir above river bed is 7 m. This height is required to keep the water depth necessary at intake entrance.

The selected spillway overflow width is 40 m so as to suit the river channel topography. Overflow depth of the design flood (1,341 m3/s) is preliminarily estimated at 6.0 m, in which effect of high velocity approach flow in the upstream channel is taken into account. Design flood water level at the upstream side of weir is thus estimated at El. 350.0 m. The estimated rating curves are shown in Figure 18.2.1.


Figure 18.2.1 Estimated Discharge Rating Curve at Intake Weir

Masang-2 Intake Weir H-Q Curve

335

340

345

350

355

0 200 400 600 800 1,000 1,200 1,400

Discharge (m3/s)

Elev

atio

n (m

asl

)

Spillway crest El. 344.0 m

River bed El. 337 m

Intake Weir Tailwater H-Q

Intake Weir Spillway H-Q

200-yr flood= 1,341 m3/s



As it is foreseen that base rock surface is not deep, non-overflow section on both abutments is built with concrete. For required free-board of the non-overflow section, an estimated wave run-up height of 0.3 m, safety allowance for concrete dam of 0.5 m are taken into account. The top elevation (Z) of the non-overflow section on both abutments is decided at El. 351.0 m by the following calculation:

Z = Flood WL + 0.3 + 0.5 = 350.0 + 0.8 = 350.8 m say 351.0 m

A 5.0 m wide sand flushing sluice is provided on left bank side of the weir. Sill elevation of the sluice is set at El. 339.0 m at the weir axis in order to flush sand deposits accumulated in front of intake entrance. A concrete channel with steep slope is extended upstream to facilitate sand flushing operation. A service gate and a maintenance stoplog are provided in the sluice. Size of them is W5.0 m x H4.0m. It is expected that the sluice is capable of discharging 120 m3/s when the gate is full open under water level at FSL. Upstream river water level is lowered in short time and sediment flushing by natural flow is performed smoothly.

The river outlet facility is provided at the sand tarp downstream end. This location is selected so as to minimize abrasion damage on the outlet pipe and valves. It is foreseen that natural river water before sand trapping contains much abrasive sand. When the intake is completely closed, whole river water is discharged from the weir by overflow.

Design of the intake weir is shown in Drawing M-011.

18.2.2 INTAKE AND SAND TRAP

The intake is located on right bank side of the intake weir. Intake entrance structure is equipped with trash rack and raking machine. Depth of incoming flow on trash rack sill is decided to be as shallow as 3.0 m to minimize entering of sediment load in the river. Trash rack size is decided so that velocity of the incoming flow at the trash rack is 1.0 m/s at maximum. Since the maximum plant discharge is 32.0 m3/s, width of trash rack is 11.0 m in total of 2 entrance bays. Incoming flow is guided by double box type free-flow channels to the intake gates and then to the sand tarp. The intake gate is W3.8 m x H4.3 m of which sill elevation is El. 340.2 m.

The sand trap is double lane settling basin with rectangular cross section. By use of the double basins, it is able to drain sediment deposit in the basin one by one and to continue generation operation even during sediment draining.

The design flow-through velocity in the basin is decided to be 0.3 m/s at the maximum plant discharge. Particle size of sand to be removed is 0.5 mm or greater by applying usual practice. Dimensions of the settling basins are decided by the following equation.

uvhAL >

Where, L = Required length of settling basin (m)



Α = Coefficient to compensate turbulent effect in the basin h -= Depth of settling basin (m) v = Vertical settling velocity of sand particle varying depending on size (m/s) u = Flow-through velocity in the basin (=0.3 m/s)

The depth ‘h’ is decided to be 5.6 m to avoid submergence of sediment drain outlets during draining. The settling velocity ‘v’ for sand particle size of 0.5 mm is 0.07 m/s. Coefficient ‘A’ is estimated at 2. Thus, the required basin length is 48 m. To restrict the flow-through velocity ‘u’ to below 0.3 m/s, the required flow area is 106.7 m (= 32.0/0.3). As the basin depth is 5.6 m, the required basin width is 19 m in total, i.e, two lanes of 9.5 m wide basin.

The incoming water flow in excess of the flow capacity of the downstream connection tunnel is removed by spillage flowing over side walls of the basin. Top elevation of the walls is El. 344.0 m. The downstream end of each basin is closed by stoplogs so that the sediment draining can be done while continuing generation operation.

Sediment accumulated in the basins is periodically flushed through sediment flushing culverts (one for each basin) extended from the bottom of basin’s downstream end to the river bank edge. Size of the flushing gate is 1.5 m by 1.5m.

The river outlet facility consisting of 2 sets of pipe conduit and closure valve is provided in the wall on the river side in the basins downstream bay. To discharge water of 0.39 m3/s by each set, diameter of the pipe and valve is set at 0.3 m.

Total head loss in the intake and sand trap is estimated to be 0.2 m. Design of the intake and sand tarp is shown in Drawing M-012.

18.2.3 CONNECTION CULVERT

The connection culvert is extended from the downstream end of the sand trap to the entrance of connection tunnel. The culvert is box shape concrete flume with total length of 1.06 km. Flow in the culvert is free flow state. Top cover slab is provided to avoid entering of eroded debris or tree leaves into the flume. The culvert is constructed by cut-and-cover method. The size of internal section is W3.75 m and H4.15 m. The longitudinal slope is 1/1,200 to allow the maximum discharge of 32.0 m3/s. The maximum water depth (uniform flow) in the culvert is estimated at 3.75 m. Air space of at least 0.4 m is left between the flow surface and the culvert crown.

The culvert has to cross over the large creek (Aek Bamban) at the downstream end of the culvert. For crossing the creek, the culvert is constructed as a box type bridge supported by four vertical concrete piers spaced at 20 m. Just after crossing the creek, the culvert is jointed to the connection tunnel.



18.2.4 CONNECTION TUNNEL

The connection tunnel is extended from the downstream end of the connection culvert to the intermediate pond. The tunnel length is 1.63 km. Flow in the tunnel is free flow state. The selected tunnel section is standard horse-shoe shape since the internal water pressure is low. Its diameter is 3.75 m as selected as an economic diameter in the Section 17.3 (4). The required tunnel slope is 1/700 at the maximum discharge of 32.0 m3/s. The maximum water depth (uniform flow) in the tunnel is estimated at 3.38 m. Air space of at least 0.38 m is left between the flow surface and the tunnel crown. Total of water level drop between the sand trap and the pond is estimated at 3.9 m including outlet loss. At the outlet of the tunnel, an open channel with width of 12 m is extended down to El 329.4 m aiming at protection of the pond slope against erosion by tunnel outflow.

It is foreseen that, as the tunnel passes through relatively firm rock, heavy rock support such as steel ribs and thick shotcrete cover with wire mesh will be required only in short stretches for tunnel construction.

Route and typical section of the tunnel are shown in Drawing M-010..

18.2.5 INTERMEDIATE POND

The required active storage volume of the pond is 322,000 m3 as mentioned in Section 17.3 (5). The FSL of the pond is decided to be El. 339.9 m taking into account the water level drop in the intake, sand trap and connection tunnel at the time of maximum discharge.

The pond is created on a small natural creek by closing it with rockfill embankment and by excavating the ground around the creek. Location of the closure embankment is selected so as to maximize the storage capacity. To satisfy the storage volume requirement, it is necessary to largely excavate the ground around the creek. The water level drawdown in the pond is set at 10 m at the maximum in drought time. The water surface area required in the excavated part of the pond is approximately 2 ha.

The curves of pond storage capacity area including excavated part is shown in Figure 18.2.2.



315

320

325

330

335

340

345

350

0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7

Storgae Volume (MCM)

Ele

vatio

n (m

)

01234567

Wtaer Surface Area (ha)

MOL = 329.9

FSL = 339.9

Active Storage 0.322

Volume Area


Figure 18.2.2 Storage Capacity and Area Curves of Intermediate Pond

The pond water level varies on the daily basis due to water use for daily peak generation. The maximum drawdown will be 10.0 m, which will seldom occur in the drought year.

Sediment inflow for 100 years is estimated at 45,000 m3. The pond has a dead space sufficient in volume for storing whole sediment inflow for 100 years.

The creek closure structure is rockfill type embankment with central clay core. The foundation of the embankment is the weathered rock. Rock materials excavated for enlarging pond space are used for the embankment.

Aiming at slope stabilization on pond perimeter, horizontal drain holes drilled into hill slope around the pond are tentatively planned. Those drain holes will be effective to stabilize the slope at the time of fast drawdown of water level. Detailed slope stability analysis will be required in the future study.

Design flood inflow from the pond catchment is 15.2 m3/s (200-year flood). The other inflow from the connection tunnel is 32.0 m3/s at the maximum. An overflow type spillway is provided on the right abutment of the closure embankment. The spillway has a 25 m long overflow weir of which crest elevation is equal to the pond FSL (El 339.9 m). The spillway is capable of discharging 47.2 m3/s (=15.2 + 32.0) under 1.0 m overflow depth. The design flood water level is thus El.340.9 m.

For required free-board of the closure embankment (pond dike), an estimated wave run-up height of 0.35 m, safety allowance for embankment dam of 1.5 m and clay core protection cover layer of 0.25 m are taken into account. The top elevation (Z) of the pond dike is decided to be El. 343.0 m by the following calculation:

Z = Flood WL + 0.35 + 1.5 + 0.25 = 340.9 + 2.1 = 343.0 m



For emergency withdrawal of pond water in the future, bottom outlet facility is provided in a foundation culvert laid on the deepest foundation. The culvert having D-shape section (W2.2m x H2.5m) can be used as a temporary diversion facility during construction. A 0.4 m diameter steel pipe is laid in the culvert from concrete plug below clay core to downstream end of the culvert. A stop valve is installed at the upstream end of pipe and a service valve is installed at the downstream end of the pipe.

The pond structures are shown in Drawings M-013 and M-014.

18.2.6 HEADRACE TUNNEL

The headrace tunnel is extended from the intermediate pond to the surge tank. The tunnel length is 4.55 km. Flow in the tunnel is pressure flow state. The selected tunnel section is circular shape since the internal water pressure is relatively high. Its diameter is 3.75 m as selected as an economic diameter in the Section 17.3 (4).

At the upstream end of the tunnel in the pond, an intake tower is provided to accommodate a trash rack with raking equipment and a tunnel closure gate. The size of tarshrack is decided to be W5.5 m x H5.9 m so that the flow velocity at the tarshrack is 1.0 m/s at the maximum. The tunnel invert elevation just downstream of the intake tower is set at El. 322.0 m in order to provide sufficient intake submergence below the pond MOL for avoiding air suction into the tunnel. The tunnel invert level at the surge tank is set at El. 305.0 m to avoid air suction into the tunnel from surge tank during down-surging.

Total loss of head in the tunnel is estimated at 8.9 m at the maximum plant discharge. Losses due to friction, intake trash rack and tunnel bends, etc. are included.

It is foreseen that most part of the tunnel passes through firm lime stone except some short stretches passing weak rock. Heavy rock support such as steel ribs and thick shotcrete cover with wire mesh will be required only for such weak rock area.

Route and typical section of the tunnel is shown in Drawing M-010.

18.2.7 SURGE TANK

A surge tank is provided between the headrace tunnel and the penstock to avoid excessive pressure rise in the waterway system and to supplement or absorb water flow during transient operation of turbines. Simple vertical surge tank with a bottom orifice is adopted.

The size of surge tank is decided by provisional surging wave analysis. Selected diameter of the surge tank is 8.5 m. Estimated maximum up-surge level and the minimum down-surge level are El. 361.2 m and El 316.3 m, respectively. Top of surge tank is set at El. 364 m and bottom of surge tank (headrace tunnel) is set at El 305 m. Height of the tank is thus 59 m.



18.2.8 PENSTOCK

Surface type penstock is adopted taking into account site topography. A steel penstock pipe is laid in horizontal tunnel downstream of surge tank and then in an open trench excavated on hill slope down to powerhouse site. The pipe diameter is decided to be 3.1 m from the surge tank end to the downstream Y-branch as selected in the Section 17.3 (4). The Y-branch is located nearby the powerhouse, i.e. 25 m upstream from the powerhouse center. The two pipes after Y-branch to the turbine inlets have diameter of 1.8 m. The upper 190 m long horizontal part is embedded in the tunnel extended from the surge tank bottom and laid at El 304 m. Along the penstock pipe in the open trench, a stairway is provided for penstock inspection.

Penstock line is shown in Drawings M-015.

18.2.9 POWERHOUSE

The powerhouse to accommodate two 26 MW generating equipment is above-ground type and located on the left bank of the Masang river and at 300 m downstream from the confluence with the Alahan Panjang river. Normal river water level estimated from the field topographic survey is El. 141 m and river bank edge elevation is around El. 150 m.

The selected site is relatively flat and wide in topography and suitable for locating powerhouse and switchyard. Hard rock (lime stone) is exposed on the river bank wall at the powerhouse site. The foundation condition seems suitable for the powerhouse.

The powerhouse is a reinforced concrete building. Two units of main generating equipment and their auxiliaries are accommodated in the building. Machine erection bay and control/office bay are also included in the powerhouse. Tailrace is an excavated open channel extended from the powerhouse to the river bank edge. During construction of powerhouse substructure, insitu rock on the tailrace channel will be left unexcavated for the purpose of coffering. A 150 kV outdoor switchyard is located on east side of the powerhouse premises.

The tail water level for the generating equipment is provisionally fixed to be El. 142.0 m. The turbine setting level is set at El. 140.0 m. The water level of the design flood (200-year flood) at the powerhouse site is assumed at El. 149 m. The ground formation elevation around the powerhouse is set at El. 150 m. It is necessary to review the river water level in the future detailed study

The powerhouse design is shown in Drawing M-016.

18.2.10 PROJECT FEATURES

The principal features of the project are summarized in the following table.



Description Unit Principal Features1 Location West Sumatra Province2 Hydrology

Catchment area km2 444Average annual runoff at intake m3/s 17.7195% dependable runoff m3/s 10.05

3 Intake WeirType Ungated concrete weirFSL=Weir crest elev. El. m 344.0Height (overflow section) m 7Active storage volume None

4 Intake & Sand TrapIntake Type Horizontal inlet with screenSand trap type Double settling basinsMax. discharge diverted m3/s 32.0

5 Connection CulvertType Concrete flume with box section (free flow)Internal section size x Length m W3.75 x H4.15 x L 1,060

6 Connection TunnelType Horse-shoe section, free flow typeConnection tunnel, diameter x length m D3.75 x 1,630

7 Intermediate PondType Creek excavated and closed by embankmentFSL El. m 339.9MOL El. m 329.9Water surface area ha 4.0Gross storage volume MCM 0.50Active storage volume MCM 0.322Drawdown m 10.0

8 Headrace TunnelType Circular section, presuure flow tunnelHeadrace tunnel, diameter x length m D3.75 x 4,550

9 Surge TankType Vertical cylindrical shaftDiameter x Height m D8.5 x 59

10 PenstockType Surface typeSteel pipe diameter x length m D3.1 x 677Pipes after Y-branch D1.8 m x 17 m x 2 nos

11 PowerhouseType Above-ground typeBuilding structure Reinforced concreteTailrace Open ChannelTail water level El. m 142.0

12 Generating EquipmentInstalled capacity (total) MW 52Number of units nos. 2Gross head below pond m 197.9Rated head m 178.8Max. plant discharge m3/s 32.0Peaking oeration time hr/day 4Annual energy production GWh 240

Project Features in Preliminary Design of Masang-2 HEPP



18.3 HYDRO-MECHANICAL WORKS

The hydro-mechanical works comprise steel gates, stoplogs, trash racks, valves and penstock pipes. Their operation devices, hoists, hydraulic systems, raking machine, etc. are also included in the works. However, water turbines for generating equipment and their mechanical auxiliaries including turbine inlet valves are not included in the hydro-mechanical works.

The hydro-mechanical works preliminarily designed are described below.

Size, WxH (m) Q’ty Acting water head (m)

(1) Intake Weir, Sand Flushing Gate Type: Rope hoisted fixed wheel gate 5.0 x 4.0 1 11

(2) Intake Weir, Sand Flushing Stoplog Type: Rope hoisted slide panels 5.0 x 4.0 1 11

(3) Intake, Trash Rack With raking equipment 5.5 x 3.5 2 9

(4) Intake, Entrance Closure Gate Type: Rope hoisted fixed wheel gate 3.8 x 4.3 2 9.8

(5) Intake, Entrance Stoplog Type: Rope hoisted slide panels 3.8 x 4.3 1 9.8

(6) Sand Trap, Sediment Darin Gate Type: Motor drive spindle gate 1.5 x 1.5 2 9

(7) Sand Trap, End Stoplog Type: Rope hoisted slide panels 4.2 x 3.8 2 3.8

(8) Sand Trap, River Outlet Valve Type: Cast steel spindle valve φ0.3 2 5

(9) Connection Culvert, Inlet Gate Type: Rope hoisted fixed wheel gate 3.75 x 4.15 1 5

(10) Connection Tunnel, Outlet Stoplog Type: Rope hoisted slide panel 3.75 x 5.0 1 4.75

(11) Pond, Bottom Outlet Control Valve Type: Steel hydraulic valve φ0.4 1 40

(12) Pond, Bottom Outlet Maintenance Valve Type: Steel hydraulic valve φ0.4 1 40

(13) Pond, Bottom Outlet Conduit Type: Steel pipe laid in culvert φ0.5 1 40



(14) Penstock pipe Type: Steel pipe laid on trench φ3.1 1 Static 221

φ1.8 - 1.6 2 Static 221

(15) Powerhouse, Draft Tube Stoplog Type: Rope hoisted slide panel 3.5 x 1.8 2 14

18.4 GENERATING EQUIPMENT

18.4.1 GENERAL

Masang-2 hydropower project is run of river type with intermediate pond and has capacity of 4 hours peak operation and maximum output of 52MW, using net head of 178.8m and discharge of 32m3/s.

Vertical shaft type of Francis turbine (maximum output : 26MW), 3 phase synchronous generator (maximum capacity : 28.1MVA), oil supply system, compressed air supply system, water supply system, drainage system, switching device such as circuit breaker, control equipment, station service transformer and traveling crane are to be installed in the powerhouse.

HDWiz (developed by J-Power, based on existing hydropower plant data around the world) has been used for the designing of the electrical equipment.

18.4.2 UNIT CAPACITY AND NUMBER OF UNIT

Generally, for the turbine generator, a large unit capacity is said to be more economical merits of scale. However, optimum unit capacity of the turbine generator is determined in consideration of influence to the power system, development timing and transportation restriction.

Nevertheless, unit capacity and number of unit has been decided taking following items into consideration.

a. Influence of the unit capacity to the power system

b. Transportation route and weight restriction

c. The level of current manufacturing technology

d. The reliability and flexibility of maintenance and operation

e. Discharge variation between wet season and dry season

As for the subject A of the influence of the unit capacity to the power system, neither 26MW×2 units nor 52MW×1 unit will affect great influence to the power system in case of tripping of turbine generator because power system capacity of Sumatra is more than 3,600MW.



Therefore, there is not any special consideration to the influence of the unit capacity to the power system.

Regarding the subject b of transportation route and weight restriction, main transformer (1 unit option) of 60t is estimated the heaviest electrical equipment for the project. There is already existing paved national road in the suburbs of the project site and construction purpose road to be built to the project site. Therefore, there is no any special problem for the transportation. Necessity of reinforcement or replacement of bridge shall be examined in the next detailed design stage.

As per the subject c of the level of current manufacturing technology, both 1 unit and 2 units option can be made by electrical equipment manufacturer around the world.

Regarding the subject d of the reliability and flexibility of maintenance and operation, 2 units option has an advantage over because one of the unit can be operated in case of another unit is in stop condition such as fault or maintenance.

Finally, as for the discharge variation between wet season and dry season, there is not any serious problem during wet season. However, during dry season, turbine will be operated less than 30% rated output and consequently it will cause serious problem to the turbine such as cavitation and vibration. Therefore, 2 units option has a great advantage over the discharge variation.

According to result of the above comparison, 26MW×2 units has been determined for the Masang-2 hydropower project taking especially the reliability and flexibility of maintenance and operation and discharge variation between wet season and dry season into consideration.

18.4.3 TURBINE (1) Turbine Output

Rated turbine output at rated effective head of 178.8m and rated discharge of 16m3/s per unit can be calculated as follow;

Pt = 9.8 × Hn × Qt × ηt = 9.8 × 178.8 × 16.0 × 0.926 =̇. 26,000 kW where Pt : Rated turbine output per unit(kW) Hn : Rated effective head(m) Qt : Rated water discharge per unit(m3/s) ηt :Turbine efficiency(%)

(2) Type of Turbine

Generally, type of turbine can be determined by close relation between effective head and turbine output. Vertical shaft Francis type turbine can be selected taking Masang-2’s effective head and



turbine output into consideration.

(3) Runner Material

Stainless steel anti-corrosion type such as 13 chrome high nickels stainless steel is recommended to be applied for the runner material. Surface of runner and wear ring shall be coated (hard or soft) in case of water quality. Detailed coating method shall be specified in the next detailed design stage.

(4) Turbine Center Elevation

Turbine center elevation can be determined based on the draft head (Hs), which in turn, also can be decided by the cavitation coefficient of the turbine related to the optimum turbine specific speed (Ns). Hs can be calculated as -2.38m by using the above relation. Therefore, the turbine center elevation is 140.00m.

(5) Effective Head

Effective head can be calculated by gross head (192.9m) – friction loss of waterway. As a result of calculation, loss of head is 14.1m, effective head is 192.9m-14.1m=178.8m.

(6) Size of Runner

Designing of turbine runner is to determine the principal dimensions of the turbine and weight of the turbine. According to the study result, maximum diameter of runner is estimated 1.7m and weight of turbine is 4tons. However, the actual size of runner shall be offered from the turbine manufacturer in the next detailed design stage.

(7) Rated Revolving Speed

Specific speed (Ns) of Francis type turbine generally is between 70 to 300 m-kW. Ns 123 m-kW is obtained by calculating the relation between the effective head and specific speed previously adopted for similar projects. With this in mind, the revolving speed of the turbine is obtained as 500 min-1, based on the specific speed of Ns 123m-kW.

(8) Turbine Aeration System

Aeration piping system for the runner and draft tube shall be studied in the next detailed design stage.

(9) Penstock and Inlet Valve

One (1) line penstock is bifurcated into two (2) pipes for 2 units and connected to inlet valves. The Inlet Valve will be of the by plane Valve type with a diameter of approximately 1.6 m.



18.4.4 GENERATOR

A three phase alternating current synchronous generator with vertical shaft rated capacity of 28.1MVA and power factor of 90% lag is selected.

(1) Type of Generator

Type of generator can be determined by revolving speed and generator capacity and normal type is adopted for the Masang-2 project taking generator capacity and revolving speed into consideration.

(2) Rated Generator Capacitor

Rated generator capacity can be calculated from the rated turbine output, power factor and generator efficiency as follows;

Pg = Pt × ηg / p.f (kVA) = 26,000 × 0.973 / 0.90 =̇. 28,100kVA where、 Pg : Rated generator capacity(kVA) Pt : Rated turbine output per unit(kW) ηg : Generator efficiency(%) p.f : Power factor(%), lag

As the results of above calculation, the rated generator capacity is 28,100kVA.

(3) Insulation and Cooling Method

F class is adopted for insulation of the stator and rotor, and enclosed hood, air cooled type with water heat exchanger system is applied to the cooling system.

(4) Generator Rating

Principal specifications of the generator are as follows;

Rotation direction Counter clockwise from view of generator top

Rated revolving speed 500min-1

Rated capacity 28.1MVA

Rated power factor 0.90

Rated voltage 11.0kV

Rated frequency 50Hz

Excitation method Brushless excitation



18.4.5 AUXILIARY EQUIPMENT

(1) Oil Supply System

Oil supply system for the inlet valve operation purpose and governor operation purpose are installed at each unit. The oil supply system is composed of oil pressure pump( regular use, stand by use), oil pressure tank, oil sump tank, oil leakage tank and control board.

(2) Compressed Air Supply System

Compressed air supply system (regular use, stand by use) for the generator brake, oil pressure tank and general uses are installed at the powerhouse.

(3) Water Supply and Drainage System

Water supply system for the cooling of turbine, generator bearing, generator cooler and oil supply system cooler are installed at the powerhouse. Water will be taken from drafty tube by water supply pump, and then supply to the each equipment through strainer and sand separator..

Water drainage pit shall be prepared at bottom of powerhouse and leakage water shall be drained by water drainage pump.

(4) Parallel in Circuit Breaker

There are two connection methods between generator and power system. One is low voltage synchronous system (connection point is low voltage side of main transformer) and another is high voltage synchronous system (connection point is high voltage side of main transformer). Regarding connection method of the Masang-2, low voltage synchronous system is applied in consideration of generator capacity, improvement circuit breaker and simplicity of station service power.

(5) Control System

Regarding control system, one-man control system is applied for control of turbine, generator, main transformer, auxiliary equipment, transmission line and control board and it can be located at control room in the powerhouse.

(6) Station Service Transformer

Station service transformer for the auxiliary equipment power source for the turbine, generator, main transformer, lighting, ventilation shall be installed at lower side of main transformer and supply the power to the each equipment.

(7) Traveling Crane

Maximum capacity of main hook is determined by the maximum weight of installed equipment and generator rotor is the heaviest equipment generally.



Masang-2 hydropower project, the generator rotor of 47 tons is estimated the heaviest equipment.

18.5 OUTDOOR SWITCHYARD EQUIPMENT AND TRANSMISSION LINE

18.5.1 OUTDOOR SWITCHYARD EQUIPMENT FOR MASANG-2

(1) Main Transformer

One (1) transformer per one (1) turbine generator is desirable from the point of view of the operation. However, one (1) transformer per two (2) turbine generator shall be applied for the Masang-2 hydropower project taking into improvement of transformer’s reliability and reduction of construction cost consideration.

Regarding location, the main transformer shall be located at outdoor switchyard which is adjacent place of powerhouse. Three-phase transformer is recommended to be adopted and to be designed taking into transportation restriction, efficiency and installation space consideration.

Maximum weight of transformer (including trailer) is expected to be 100 tons and it can be transported to the project site.

Main specification of the main transformer is shown as follows;

– Rated Voltage ：Primary 11.0 kV ：Secondary 150 kV – Rated Capacity ：Primary 56.2MVA ：Secondary 56.2MVA – Rated Frequency ：50 Hz – Rated Frequency ：Outdoor type – Cooling method ：OFAF (Oil forced Air Forced )

(2) 150kV Outdoor Switchyard Equipment

150kV outdoor switchyard equipment shall be installed at adjacent of powerhouse same location as the main transformer.

There are conventional type and Gas Insulated Switchgear type, the conventional type which is economical advantage shall be adopted from the point of view of the installation space and construction cost.



150kV outdoor switchyard equipment consists of 150kV bus, circuit breakers, disconnecting switches, current transformer for protective relay/metering, voltage transformer for protective relay/metering, supporting insulator, stringing and steel structure.

Whole single line diagram including generator, main transformer, bus and transmission line are shown as follows.


Figure 18.5.1 Single Line Diagram for Masang-2



18.5.2 TRANSMISSION LINE

Source: JICA Study Team based on RUPTL

Figure 18.5.2 Reference between Location of Masang-2 and Transmission Development Plan

a) Voltage class applied

Judging from the rated capacity of the generator, it would be appropriate to have a voltage of at least 150 kV for system access.

b) System access point

In the study of system access, a selection was made of methods based on the existing and planned transmission facilities indicated in RUPTL. The relative merits of each access method were assessed from four perspectives, as follows. The Study Team made a relative assessment of distance and topography, but made assessments with respect to environmental factors (forested tracts, natural preserves, etc.) and system operation only when there were prohibitive factors.

Aspects Candidates

T/L Construction Environmental issues System OperationLength Topography Natural

conservationForest class

Resident imposition

1 Inc.(Maninjau –Simpang Empat T/L) (Along vicinity of Masang River)

◎ 34kms

◎ × －－－

2 GI Padang Luar ○ 80kms

○ － ◎ ○ －

3 GI Simpang Empat (Along vicinityof Masang River)

△ 100kms

◎ × －－－

4-A

dd Inc.(Maninjau –Simpang Empat T/L)

(Detour-route against Nature conservation(through protection forest))

◎ 38kms

◎ － ○ ○ －



5-A

dd Inc..(Maninjau –Simpang Empat T/L)

(Detour-route against Nature conservation(through non-regulated area))

◎ 54kms

◎ － ○ ○ －

6-A

dd GI Simpang Empat

(Detour-route against Nature conservation)

× 120kms ◎ － ○ ○ －

Evaluation : Good ◎→○→△→△△→× Not good

i) Transmission line construction

Considering construction of a transmission line extension to the three aforementioned candidates (Candidate 1 - 3), extension along the Masang River would offer the shortest distance to the 150kV Maninjau-Simpang Empat for the route (entailing the shortest distance or the shortest route for extension that can basically be confirmed by map). If the route distance for Candidate 1 is assigned the value 1.0, it is estimated that that for Candidate 2 (access to GI Padang Luar) would be 2.2, and that for Candidate 3 (access to GI Simbang Empat), 3.0. In addition, Candidate 1 would allow a more unified and simpler construction method than the other candidates because the route would pass through on the village side.

As for the topographical factors related to transmission tower construction, in the case of access to GI Padang Luar, there is a comparatively close road leading to Bukit Tinggi, and this would hold advantages for hauling materials and assuring a patrol route. At the same time, however, there is much undulation in the mountainous terrain, and this could make it difficult to take full advantage of this road. In the case of Candidate 3 (access to GI Simpang Empat), there is no straight-line route, and it was thought that the line would go down the Masang River, along the mountain on its northern side, like the 150kV transmission line feeder connection between Maninjau and Simpang Empat. This was given the highest rating.

ii) Environmental aspect

The prospective site of the power house is near the border between the regencies of Agam (Kabupaten Agam) and Pasaman (Kabupaten Pasaman), on the Agam side. The Masang River forms this border, but the river itself is in Pasaman. The shortest route would lie in extension of the transmission line from the Masang-2 power station along the Masang river to the village side. In this case, the line would cross the Batastinjaulau and Sinanggamaur mountains and the natural preserve along the Masang River. In reality, transmission line construction over this route would not be practicable.

Therefore, it was decided to add a route to the GI Simpang Empat that detours to avoid this natural preserve to the list of study subjects as Candidate 6. The Study Team also decided to add two other routes (one passing through the protection forest and another that does not pass through the protection forest), consisting of feeder connection to the Maninjau-Simpang Empat 150kV transmission line, for the zone study subjects as Candidates 4 and 5.



iii) System operation

Of the route zones for connection to the Maninjau - Simpang Empat 150kV transmission line, the table shows the increases in distance that would be entailed by the route through the protected forest area (Candidate 4), the route through a district without any forest-related constraints (Candidate 5), and the route for system access to GI Simpang Empat along the lines of Candidate 5 (Candidate 6). Once the line comes out on the village side in connection to the Maninjau - Simpang Empat 150kV transmission line, however, the terrain would be basically flat, and the transmission tower foundations and structures could be built virtually in line with the standard design. For this reason, selection of a route to the Maninjau - Simpang Empat 150kV transmission line free of any environmental constraints would presumably be preferable in the cost aspect to system access to GI Padang Luar (because the cost advantage would outweigh the extra line length). To make a comparison in respect of the supply-demand balance, it may be noted that RUPTL foresees a peak demand of 45.3 MW at GI Simpang Empat in 2019. If a feeder interconnection is made to the Maninjau - Simpang Empat 150kV transmission line with a maximum generated output of about 40 MW, most of this output would be consumed by GI Simpang Empat. Similarly, the 2019 peak power at GI Padang Luar is 66 MW, and most of the demand could be absorbed by this potential site.

To draw a comparison in respect of power quality, connection of the potential site to GI Padang Luar would merely decrease the power flow from GI Payakumbuh to GI Padang Luar. There is also thought to be no problem as regards voltage, because GI Payakumbuh (a 275/150kV substation) has a close electrical distance with GI Padang Luar. On the contrary, interconnection of a hydropower station in close proximity to GI Simpang Empat, which would form the terminal system, could be expected to improve the voltage at GI Simpang Empat. In this respect, feeder connection to the Maninjau - Simpang Empat 150kV transmission line would bring substantial benefits.

As for the type of transmission line and protection relay system, a parallel two-circuit line will be constructed for system access with GI Padang Luar. Judging from the rated capacity of the potential site, there would be no obstacles to the standard specifications (1 HAWK, 2 cct), and no problems as regards the protection relay system (distance or ground orientation). In the case of feeder connection to the Maninjau - Simpang Empat 150kV transmission line, the following three systems are conceivable.

Four-circuit line, pi feeder connection

Two-circuit line, pi feeder connection

Feeder connection

Because the four-circuit pi feeder connection would require a physical increase in the number of lines, it would entail a higher construction cost, but it would also enable construction without



modification of the current protection relay system on the Maninjau - Simpang Empat 150kV transmission line. The two-circuit pi feeder connection would reduce the construction cost by an amount commensurate with the two-circuit decrease, but could present difficulties in the aspect of system operation. Specifically, failure and suspension of supply between the potential site and the GI Simpang Empat 150kV transmission line would result in routing of the potential site output through GI Maninjau. This would not only be inefficient but also lengthen the electrical distance somewhat as regards the primary bus voltage (GI Maningua - GI Simpang Empat - potential site). This situation could require compensation for reactive power. Such problems are particularly liable to surface in the event of grid extension in the aforementioned northern terminal direction beginning from GI Simpang Empat. Feeder connection would result in three-terminal operation, and this would require a switch to a protection relay system that could protect the other terminals. Because the potential site and GI Maninjau could become the power source terminals, a carrier-type protection relay system would have to be installed, and this would complicate the power system operation somewhat. Operation of other terminals is not a part of system operation in Indonesia at present, and the installation must take account of factors such as an increase in the work load of system operators.

Therefore, in extension of the grid toward the northern end of West Sumatra Province as noted above, a single transmission tower would be built to specifications permitting the installation of four circuits. Initially, it would be possible to operate with a two-circuit line pi feeder connection or to construct a standard tower (with installation of two circuits per tower) and an additional transmission line in anticipation of grid extension toward the northern end, for operation as a four-circuit pi feeder connection. Naturally, if grid extension toward the northern end is not a consideration, there would be no problem with a two-circuit pi feeder connection. As for the type of transmission line applied for this feeder connection, it could be the same as the Maninjau - Simpang Empat line (1 HAWK, 2 cct).

Based on the above, an in-depth study was made of feeder connection to the Maninjau - Simpang Empat 150kV transmission line (both through the forest reserve area and through the area without environmental constraints) and GI Padang Luar system access, inclusive of the route zone1.

1 The objective of this study is not a rigorous search for a single answer but an examination of all the possible candidate sites,

unless a particular site offers overwhelming benefit and rationality.



GI Simpang Empat

GI Maninjau

Potential site

Masang‐2

GI Simpang Empat

GI Maninjau

Potential site

Masang‐2

GI Simpang Empat

GI Maninjau

Potential site

Masang‐2

Four-circuit line,

pi feeder connection Two-circuit line,

pi feeder connection Feeder connection

Figure 18.5.3 Types of Connection

c) Route zone

The figure below shows the route zone between the potential site and GI Padang Luar, and for feeder connection to the Maninjau-Simpang Empat 150-kV transmission line.


Figure 18.5.4 Route Zone (Masang-2)

i) Technical perspectives on transmission lines and transmission towers

There is an elevation difference of about 750 meters between the potential site and GI Padang



Luar. The straight-line route in the direction of Bukit Tinggi crosses the Ladangatas, Batasarik, and Galanggang mountains.

The selection of route zone was made with consideration of the terrain at both points and the area between them, the slopes on both banks along rivers (selection of fairly gentle grades of no more than 30 percent), and the up and down grades (of no more than 35 percent every 200 m). It was assumed that the northern or southern end of the route zone would be adopted as the practical route.

The route from the potential site to the Maninjau - Simpang Empat 150kV transmission line goes down to the village side, and the elevation difference is estimated to be about 100 meters. However, the maximum elevation en route would reach 550 meters, that is, a route across mountains for an elevation difference of just under 400 meters was selected. Here as well, the selection took account of the slope grade angles and the up and down grade angles, as already described. As far as possible, the shortest route was taken; after coming down from the mountain, the line would pass through an area of rice paddies before connection with the Simpang Empat - Maninjau line.）

ii) Environmental and social concerns

Selection of the route zone avoided natural preserves and other factors fatally blocking construction. Transmission line extension through a protected forest area would call for curtailment of the development area to the minimum requisite in this area. Full surveys and examination of the on-site topography would also be necessary. In addition, there is a possibility of passage through a timber industry forest, and the prospect of compensation would also have to be taken into account.

Although the zone apparently does not contain any plantations or other large-scale farming tracts, it does contain several villages. As such, construction of transmission lines in the vicinity of communities would require consideration of items such as land acquisition and blockage of sunlight. The existence of residential areas in the vicinity would also hold the possibility of consignment of transmission line maintenance to local monitors after the construction is finished. For this reason, the distance from communities must also be studied. There are no problems with detraction from scenery, because the zone in question does not contain any scenic districts.

In this pre-FS study, the Study Team considered a number of options for the route zone. In the future process of detailed route selection, a selection could be made of a route befitting the times. The cost calculation in this study adopted the Candidate 5 route, which avoids the natural reserve area (and goes through an area without constraints).

part iii pre-feasibility study for masang-2 hepp · final report (main) chapter 16 project site...

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