kawatech pre design2015

MOST-BMBF

joint project

Vietnamese-German Cooperation for the Development

of sustainable Karst Water Technologies

Pre-Design

for the pilot implementation of a hydro power driven water

pumping and distribution system

( )

Edited by Karlsruhe Institute for Technology (KIT)

Institute for Water and River Basin Management (IWG), Prof. Dr.-Ing. Dr. h.c. mult. Franz Nestmann

Institute of Concrete Structures and Building Materials (IMB), Prof. Dr.-Ing. Harald S. Mller

With contribution of KSB AG

Division for Hydraulic Services, Dr.-Ing. Jochen Fritz

Karlsruhe, 10.03.2015

Pre-Design

Page 2 / 127

Content

1 Introduction ...................................................................................................................................... 4

1.1 Background and objective of the document .......................................................................... 4

1.2 Summary of the planned pilot system for hydro power driven water pumping and distribution (Concept 1) ......................................................................................................... 5

1.2.1 Motivation and objective ......................................................................................... 5

1.2.2 Hydro power driven water pumping module at Seo Ho HPP for water conveying to Ma U ................................................................................................................... 6

1.2.3 System to distribute water from Ma U to the supply area Dong Van City ............ 10

1.2.4 Systems to distribute water from Ma U to the supply areas Sang Ma Sao and North Slope .......................................................................................................... 12

1.3 Overview of the measures described in the Pre-Design ..................................................... 12

2 Specification of measures .............................................................................................................. 14

2.1 Weir and intake structure ..................................................................................................... 14

2.1.1 Location and present state ................................................................................... 14

2.1.2 Description of measures ...................................................................................... 15

2.1.3 Materials and services ......................................................................................... 16

2.2 Sand trap ............................................................................................................................. 16


2.2.2 Description of measures to minimize water losses and to prevent flotsam entry into the headrace channel .................................................................................... 17

2.2.3 Description of measures to improve the sediment deposition capacity ............... 18


2.3 Headrace channel ............................................................................................................... 25




2.4 Intake pool ........................................................................................................................... 28




2.5 Penstock bypass to PAT-pump-modules ............................................................................ 39



Pre-Design

Page 3 / 127


2.6 Extension of power house and tailwater pool ...................................................................... 50

2.6.1 Location of power house extension ..................................................................... 50



2.7 Machinery and equipment ................................................................................................... 56



2.8 Pressure supply pipe ........................................................................................................... 60

2.8.1 Location ................................................................................................................ 60


2.8.3 Material and services ........................................................................................... 77

2.9 Distribution tank Ma U ......................................................................................................... 81

2.9.1 Location ................................................................................................................ 81

2.9.2 Functionality ......................................................................................................... 82



2.10 Distribution from the tank Ma U to the tank Dong Van City ................................................. 91

2.10.1 Location ................................................................................................................ 91


2.10.3 Materials and services ....................................................................................... 100

2.11 Storage tank Dong Van City .............................................................................................. 103

2.11.1 Location .............................................................................................................. 103

2.11.2 Description of measures .................................................................................... 104


2.12 Distribution from the tank Dong Van City to the existing network of Dong Van City ......... 112

2.12.1 Location .............................................................................................................. 112

2.12.2 Description of measures .................................................................................... 112


3 Summary of materials and services ............................................................................................. 119

4 Time schedule .............................................................................................................................. 126

Attachment A Isometric drawings of penstock bypass

Attachment B Isometric drawings of pressure supply pipe

Pre-Design

Page 4 / 127

1 Introduction

1.1 Background and objective of the document

September 2013 marks the beginning of the Vietnamese-German Cooperation for the Development of

Sustainable Karst Water Technologies (KaWaTech) funded by the Vietnamese Ministry of Science

and Technology (MOST) and the German Federal Ministry of Education and Research (BMBF). The

joint R&D-project is scheduled until August 2016.

On 19th of February 2014 the Vietnamese and German partners agreed on implementing a pilot

system for hydropower driven water pumping and distribution based on a novel technical concept

the so called Concept 1 (see Minutes of Discussion from 19.02.2014 and Reconfirmation Document

from 27.02.2014). The draft of Concept 1 contains the implementation of a hydropower driven water

pumping module at the existing Seo Ho hydropower plant (later referred to as Seo Ho HPP) to partially

high efficiency and robustness as well as by low operation and maintenance costs and effort in order

to enable a sustainable long-term operation. Furthermore, the draft includes the construction of a new

storage and distribution tank at Ma U as well as of new distribution facilities. Hereby, starting from the

tank, water might be distributed to the three supply areas Dong Van City, the villages around Sang Ma

Sao and the villages northeast of Dong Van City (see Fig. 1).

In line with the decision on the pilot implementation the partners also agreed on a task distribution as

well as on a preliminary implementation schedule (see Minutes of Discussion from 19.02.2014 and

Reconfirmation Document from 27.02.2014). In principle, the German partners are responsible for

developing the technical concept, the Bill of Quantities and the successive Pre-Design.

Furthermore, they are in charge for the development, testing and provision of the innovative

water pumping modules including their transport to Vietnam. In addition, they support the

implementation through expert monitoring with temporary technical accompaniment on site

and the accomplishment of capacity development measures. The Vietnamese partners are

responsible for preparing the Final Engineering Design as well as for the accomplishment and

financing of the successive construction and implementation works including the provision of

materials and transport to the construction site, custom duties and domestic transport for

materials delivered to Vietnam by the German partners.

The construction start of the system parts Seo Ho HPP Tank Ma U Dong Van City (see section

1.2.2 and 1.2.3) is planned for summer 2015. The implementation of the facilities to distribute water to

the villages around Sang Ma Sao and to the villages northeast of Dong Van City (see section 1.2.4)

could commence at the same time or at a later date.

The Bill of Quantities for the pilot implementation of a hydro power driven water pumping and

distribution system (later referred to as Bill of Quantities) was handed over for budget

planning of Concept 1 in June 2014 from the German to the Vietnamese partners. At the end of

October 2014 the German partners received the message via VIGMR that the financing had been

approved. The present document Pre-Design for the pilot implementation of a hydro power driven

water pumping and distribution syste (later referred to as Pre-Design) is based on this

document. However some sections of the present Pre-Design include comprehensive updates. For the

preparation of this present document additional field trips to Dong Van in July/August 2014 and

November 2014 and laboratory investigations were carried out by KIT.

Pre-Design

Page 5 / 127

The scope of this present document is to provide a pre-design including specific data which

can be used by the Vietnamese partners for preparing the Final Engineering Design. The

development of this Final Engineering Design by the Vietnamese partners has to consider the

national standards, the actual local boundary conditions, the provision of materials, custom

duties, the domestic transport and the execution of the construction works. Both the Pre-

Design and the Final Engineering Design shall be comprehensively reviewed by the German

and the Vietnamese side in order to develop a collaborative project plan resp. plan of measures

considering all relevant influencing factors.

The basic concepts of the planned pilot implementation are explained in more detail in section 1.2.

The necessary measures are outlined in section 1.3 and specified in section 2. The bill of materials is

stated in section 3 and refers to the measures described within this pre-design. The preliminary time

schedule is shown in section 4.

1.2 Summary of the planned pilot system for hydro power driven water

pumping and distribution (Concept 1)

1.2.1 Motivation and objective

In the area of Dong Van Karst Plateau water supply is insufficient due to the regional topographic,

climatic, hydrological and geological conditions. Because of the karst underground in the mountainous

region and its high infiltration rate, most water bodies of the region are found only in complex cave

systems or deep valleys

typical concentration of rain over three to four months in summer, this leads to a glaring lack of water

in the region, especially in the dry months. The Dong Van Karst Plateau was declared Global Geopark

assisted by UNESCO in 2010. While the expected resulting increase in tourism in the region offers

opportunities for economic development, it will also increase the water demand and, thus, worsen the

already existing problem of water scarcity.

Especially in such climates with a distinctive dry season, small and micro hydropower plants without

seasonal reservoir often can only be operated in low partial load ranges with greatly reduced efficiency

grades due to low available discharges. As a consequence, power plants with low economic or

mechanical efficiency are temporarily shut down during dry periods. During these shutdown periods,

precious water for both power generation as well as for water supply remains unused. The scope of

the KaWaTech project is to develop a hydro power driven water pumping module to exploit the

remaining unused water quantities for pumping and supply (Concept 1).

It is planned to realize a pilot implementation of Concept 1 at the existing Seo Ho HPP, which is

situated at 705 meters above sea level (masl). By mechanically coupling reverse driven pumps, which

then function as turbines (Pump as Turbine, PAT), to high pressure water pumps, water can be

delivered from Seo Ho HPP via a high pressure supply pipe to a distribution tank in the village of Ma

U, situated on a mountain ridge at 1,250 masl. From there, the water will be distributed by an

innovative system of pipelines and storage tanks to the main town of the area, Dong Van City, the

villages surrounding Sang Ma Sao (supply area Sang Ma Sao) and the villages northeast of Dong Van

City (supply area North Slope). Due to the extreme topography and the associated high delivery heads

of up to approx. 550 m, requirements regarding machinery and supply pipes are high. Fig. 1 outlines

the situation. The hydro power driven water pumping module at Seo Ho HPP including the supply pipe

Pre-Design

Page 6 / 127

to Ma U is described in more detail in the next section 1.2.2. The planned system to distribute water

from Ma U to the supply areas Dong Van City, Sang Ma Sao and North Slope is described in the

subsequent sections 1.2.3 and 1.2.4.

Fig. 1: Map of Seo Ho HPP area Layout of the measures in the project area

1.2.2 Hydro power driven water pumping module at Seo Ho HPP for water conveying to Ma U

Fig. 2 illustrates schematically the infrastructure of the existing Seo Ho HPP as well as the main

components of the planned hydro power driven water pumping system. Fig. 3 shows the vertical

profiles of the existing penstock and the supply pipe to the distribution tank Ma U.

Fig. 2: Major components of the planned hydro power driven water pumping system (additional components to be

constructed are printed in blue; existing components to be restored/modified in red)

Pre-Design

Page 7 / 127

Fig. 3: Vertical profiles of the existing penstock and the supply pipe

The intake structure, which is situated on the weir crest, diverts water from Seo Ho River into the sand

trap. After passing the two sand trap basins, the water runs mostly underground through the headrace

channel into the intake pool. The lateral overflow of the intake pool is used to purge water in case the

available amount exceeds the amount required for machinery operation. From the intake pool, the

water runs into the penstock, where it is conducted to the existing turbines (see section 2.1 - 2.4).

As described in this present document, the penstock could be connected to new PAT-pump-modules

by a branch-off pipe (penstock bypass), which can be implemented according to the draft shown in

section 2.5. In order to secure these pumping modules, the existing powerhouse of Seo Ho HPP might

be extended (see section 2.6). Here, a pipe system feeds the two modules, each consisting of a PAT

and a pump.

The machines will be mechanically coupled, meaning that the energy generated by the PAT is

transmitted directly to the pump without the need of intermediate conversion to electrical energy (see

section 2.7). From the PATs, the water will be discharged into a tailwater pool and then flow back into

Seo Ho River through an open channel (see section 2.6). According to this concept, the water from the

pumps will run through a new high pressure supply pipe with approximate length of approx. 2,460 m to

a new distribution tank situated in the village Ma U, overcoming a total height difference of approx.

550 m referring to Seo Ho HPP (see section 2.8). Fig. 4 shows the flow system in the existing

powerhouse and the new extension building.

According to preliminary design approaches, the water supply machinery to be installed next to Seo

Ho HPP will consist of two identical modules, each using a KSB Multitec (multistage centrifugal pump)

with 5 stages as PAT (efficiency approx. max = 71 %) and a KSB Multitec with 16 stages as pump

(efficiency approx. max = 69 %). Each module has a total design flow (discharge PAT and pump) of

approx. Qtotal = 54 l/s including a design delivery rate of approx. Qpump = 11 l/s.

Pre-Design

Page 8 / 127

Compared to the PAT-driven modules Seo Ho HPP shows a lower maximum total efficiency of

max = 63 % (efficiency of turbines and generator). In low partial load operation (discharge below

100 l/s) the efficiency even decreases to 49 57 % (calculation by KIT based on on-site

measurements). To supply water with the electricity generated by Seo Ho HPP, an electric motor is

required which is also afflicted with energetic losses (maximum efficiency of a new electric motor

suitable for this application at 93 95 %) and further decreases the total efficiency. Thus, at

discharges below 100 l/s the PAT-driven modules can be operated more efficiently instead. Here,

besides the above mentioned efficiencies for PAT and feed pump no more energetic losses will occur

due to the direct coupling of both machines.

Fig. 4: Current draft of the flow schematics inside the power house and the extension building

Pre-Design

Page 9 / 127

In this regard the parallel setup of 2 modules is particularly advantageous since they can be operated

in single or in dual mode to cover a wide range of lowest discharges (see Fig. 5). Hereto, a throttling

device for both modules is included in the design to cover these low flow rates. Thus different

operational strategies are possible depending on the available water yield.

Fig. 5: PAT-pump-module and pump discharge diagram

Single module operation: The operation of 1 module requires a total minimum flow of approx. 42 l/s

(fully throttled down) to approx. 54 l/s (not throttled) delivering approx. 6 l/s (fully throttled down) to 11

l/s (not throttled). With the use of the throttling device, water pumping operation is ensured even in

times of extreme drought (which coincides with very high water demand of the local people).

Dual module operation: The operation of 2 modules requires a total minimum flow of approx. 83 l/s

(fully throttled down) to approx. 105 l/s (not throttled) and will net a delivery rate of approx. 11 l/s (fully

throttled down) to 20 l/s (not throttled). This operation mode is depending on a sufficient water yield

but shall be used in times of high water demand in the supply areas. According to data analyses and

measurements carried out by KIT in the last three years, the minimum runoff of Seo Ho River during

dry season amounted approx. to 100 - 120 l/s. This would be sufficient to operate both modules.

Parallel operation to Pelton turbine: Due to the low total flow required to operate a single module,

parallel operation of a module and a turbine (if requested) should be feasible throughout the whole

year. The minimum flow to operate one Pelton turbine is approx. 65 l/s. In addition to the necessary

discharge of 54 l/s for a PAT-pump-module (not throttled), the total required discharge of approx.

119 l/s corresponds to the average dry season runoff of 100 - 120 l/s (average value in the period the

last three years).

Pre-Design

Page 10 / 127

Within the stated discharge ranges the PAT-driven water supply plant can be operated highly flexible

regarding the prioritization of water supply and/or generation of electricity. Depending on the

respective demand the operating personnel can decide at any time if the works water shall be used for

water supply and/or generation of electricity.

In summary, the planned system has the following advantages:

High level of operating reliability even during extreme dry periods with minimal discharge

Redundancy concerning damage or malfunction of single machines and/or components

Interchangeability of (spare) parts

Low maintenance and training requirements

Low complexity of the control system

Parallel operation of PAT-pump-module and turbine possible throughout the whole year

Flexibility of control and regulation as well as towards future water demand increases

PAT efficiency

1.2.3 System to distribute water from Ma U to the supply area Dong Van City

Fig. 6: Overview project area with the supply system

To distribute the pumped water from the tank at Ma U to the supply areas technically robust solutions

were developed which basically do not require an -

Furthermore the solutions allow a planned limitation of the water quantities distributed. Thus, the

consumers are able to only realize withdrawals not higher than the water quantity allocated to the

consumers. This enables an equitable distribution of the available water resources. The distribution to

Dong Van City is described in the following.

Pre-Design

Page 11 / 127

The tank at Ma U has two functions. It has a certain storage capacity to buffer the variations between

inflow and outflow. In order to distribute certain proportions of the inflow to the supply areas, the tank

furthermore serves as a facility to divide the inflow proportionally into three defined outflows to the

supply areas Dong Van City, Sang Ma Sao and North Slope.

-chamber which collects the total inflow (water pumped from Seo

Ho HPP). The pre-chamber has three weirs. The weir overflows are collected in three chambers from

which the water is distributed through pipes to the supply areas. The allocation of the inflow to the

three chambers and, thus, the definition of the proportion of the inflow, each supply area is supplied

with, can be flexibly defined by choosing the width of the weirs (weir overflow/total inflow = weir

width/total weir width). The advantage of that solution is the fact that the varying inflow is proportionally

allocated to the supply areas without any daily operation.

Fig. 7: Unscaled scheme of the storage tank at Ma U

It is planned to distribute the water to the supply areas according to the prevailing water demand within

the supply areas. The main share will be distributed to Dong Van City via a supply pipe to a storage

tank above Dong Van City. The tank is connected to the distribution network of Dong Van City (close

to the existing pumping station). The elevation of the tank of 1,123 masl above Dong Van City allows a

supply of Dong Van City by gravity. The system input and pressure is controlled by a plunger located

at the connection point. The outflow pipe to the distribution network may be constantly open. The

installed house tanks with floating valves within the distribution network prevent wastage of water at

the consumer level. To limit the pipe pressure due to the elevation difference between the tank at Ma

U and the tank above Dong Van City a pressure breaker facility has to be installed. This facility

basically is a small tank.

Pre-Design

Page 12 / 127

Fig. 8: Unscaled scheme of a pressure breaker with floating valve

The pressure breaker and the tank Dong Van are equipped with floating valves to control the inflow

into the tanks. Whenever the water level within the tank Dong Van reaches its maximum the floating

valve stops the inflow and prevents tank overflow. The water level of the pressure breaker rises until

the according floating valve stops the inflow. Finally the water level within the according chamber of

the tank Ma U rises. Possibly it reaches the weir height and water level within the pre-chamber

respectively. In this case the water not used in Dong Van City is distributed to the other supply areas.

In case the existing elevation difference between the tank Ma U and Dong Van City shall be exploited

for hydro power generation someday in future the planned pipe infrastructure may be used. The

pressure breaker then simply has to be by-passed.

1.2.4 Systems to distribute water from Ma U to the supply areas Sang Ma Sao and North Slope

To supply the villages around Sang Ma Sao a new distribution tank is connected via a pipe to the

according chamber of the tank in Ma U (see section 1.2.3). The distribution tank consists of a pre-

chamber and two chambers. The functioning of the proportional allocation of the water works like the

tank in Ma U by weirs which is described in section 1.2.3. One chamber serves as storage for the

population and the school of Sang Ma Sao. The second chamber supplies the already existing three

village tanks.

To supply the 12 villages northeast of Dong Van City within the so called supply area North Slope a

pipe connects four distribution tanks to the according chamber of the Ma U tank. The design and the

operation of the distribution tanks are equal to the one in Sang Ma Sao. One chamber of each

distribution tank supplies village tanks and the second chamber the next distribution tank. In most

villages already existing village tanks and pipes can be integrated into the distribution system. The

village tanks have to be equipped with floating valves. These would close the inlet if the tank is full.

Thus, the water which is not needed in one village is available for other villages.

1.3 Overview of the measures described in the Pre-Design

In the following Fig. 9 an overview of the measures and its location is given. The specification of each

measure can be found in section 2.

Pre-Design

Page 13 / 127

Fig. 9: Overview of the measures and its location

Tab. 1: Overview of the measures in the project area (see Fig. 9)

Number Section of the measure

1 2.1 Weir and intake structure

2 2.2 Sand trap

3 2.3 Headrace channel

4 2.4 Intake pool

5 2.5 Penstock bypass to PAT-pump-modules

6 2.6 Extension of power house and tailwater pool

7 2.7 Machinery and equipment

8 2.8 Pressure supply pipe

9 2.9 Distribution Tank Ma U

10 2.10 Distribution from the tank Ma U to the tank Dong Van City

11 2.11 Storage tank Dong Van City

12 2.12 Distribution from the tank Dong Van City to the existing network of Dong Van City

13 2.13 Distribution to the supply area Sang Ma Sao, see annotation

14 2.14 Distribution to the supply area North Slope, see annotation

Annotation: The specification of the measures 13 and 14 are not part of this Pre-Design

document. These will be handed in later.

Pre-Design

Page 14 / 127

2 Specification of measures

Important note:

In this chapter the measures for the implementation of concept 1 are specified. For sections 2.2 and

2.4 it has to be noted that some measures are optional and have to be implemented only on

demand. The chronological dependencies between the construction measures, which are described in

detail in sections 2.5 to 0, have to be respected during the planning and implementation process. In

section 4 a time schedule is shown which summarizes all single implementation steps.

2.1 Weir and intake structure

2.1.1 Location and present state

The weir is the part of the hydro power plant which shows the most severe damages. It is located in a

steep part of the valley, shortly before the river overcomes a height difference of 200 m through

various cascades. The weir is a conventional overflow weir with a height of 5.8 m and a width of 17 m.

On the right side of the weir crest (in flow direction), there is an intake structure consisting of an inlet

channel, which directs water to the sand trap (see Fig. 10). The channel is covered by a metal grid

with a width of 0.5 m and a length of 5 m.

larger bed loads and other solid materials to enter the sand trap and the headrace channel,

respectively. According to the construction plans, the channel has a declination of 13.2 % and a depth

between 0.30 and 0.86 m.

Fig. 10: Weir and intake structure (5.12.2014, KIT)

The weir is subdivided in the middle in two parts with different geometry. The right part with the intake

channel has a length of 8.5 m and an inclination of 45. The other side also has a length of 8.5 m but

an inclination of 55 with a step at its end. The weir crest and the weir backs do not show a hydro-

Pre-Design

Page 15 / 127

dynamically optimized form. The structure does not consist completely of concrete, but shows a core

of raw and crude limestone stuck together, similar to prepacked concrete which is covered with a top

layer of concrete. A crosswise reinforcement of flat steel bars with a diameter of 8 mm in a distance of

100 mm was detected.

In the steeper part of the weir, an additional layer of concrete was apparently applied on the weir crest

at a later point of time, probably to restore the original crest height after strong erosion processes.

However, that layer is separated with an aquiferous crack over the whole length from the concrete

underground (see Fig. 11).

Fig. 11: Undermined weir part on the

right side of the weir (5.12.2014, KIT)

Fig. 12: Hydro abrasion on weir back (5.12.2014, KIT)

The whole weir shows severe damages due to hydro-abrasion and water undermining. Further, the

wall on the right side was recently damaged by a rock fall. The weir crest is heavily eroded, the

reinforcement partly not covered by concrete anymore.

The same can be stated for the weir back, where the concrete cover and even partly the reinforcement

are ground down on the whole width by hydro-abrasion. This is particularly apparent in the middle of

the weir where the concrete cover is completely gone and the rock core opened (see Fig. 12).

2.1.2 Description of measures

The intake structure is an integral part of the hydro power plant and is part of the weir. Therefore, as a

first step it is reasonable to secure the weir structure against any further damages which could result in

an impairment of the intake structure. This includes particularly the stabilization or reconstruction,

respectively, of the weir base on the right side to prevent a future slipping of the weir.

This measure could be realized similar to the construction of the present structure (compare Fig. 9)

with the usage of prepacked concrete. The omnipresent raw limestone aggregates are assembled at

the beginning without mortar to form the raw shape of the intended weir structure.

Pre-Design

Page 16 / 127

The aggregates generally should have a medium diameter between 80 and 150 mm. They can

originate from karst limestone quarries near to the site or can be even collected directly from the

surrounding of the site. These raw aggregates should be slightly fractionized and stuck together with

cement mortar to form the chosen structure, which should be subsequently covered with a layer of

crosswise reinforced concrete.

2.1.3 Materials and services

Tab. 2: List of materials and services for measures at the weir and intake structure

Position Materials / services and description Amount Unit

2.1 Transportation of materials to construction site 1 ls

2.2 Excavation of the weir base area on the right side (limestone can be partly used for reconstruction of the weir base)

10 m

2.3 Stabilization of the weir basis with prepacked concrete and reinforced concrete, respectively

20 m

2.2 Sand trap


From the intake structure on the weir crest, the water flows into the sand trap. The sand trap consists

of two long and narrow basins, measuring 17 and 14 m in length with a minimum width of 1.4 m. The

construction is separated in the middle with a cross-section constriction, which once kept a sluice gate,

but now is constantly open. The sand trap is bordered by a high and steep wall against the mountain

slope on the right side, on the left side by masonry with a width of 50 cm starting from the ground. This

results in a depth of the sand trap between 2.1 and 3.5 m. The masonry built out of raw limestone is

plastered with a cement mortar.

The first basin of the sand trap has a length of 14 m and a width of 1.4 m. Originally several

crossbeams made out of reinforced concrete were arranged 1 m below the wall crest to support the

right wall and probably to act as bearings for a channel ceiling. However, most of the beams were

destroyed by rock fall. The second basin has a length of 17 m and a starting width of 1.8 m, but

passes over at its end in a square basin with an edge length of 4 m. On the right side at the end of the

second basin, there is the intake opening to the headrace channel with a size of 60 70 cm (W x H).

Steel sluice gates are installed in both basins on the left side to allow emptying and sediment flushing.

The pools are overall seen in a sufficiently good structural condition and show, besides some

vegetation covering, no essential damages. An exception can be seen in the first basin, where both

the left and the right wall were damaged by a serious rock fall. Parts of the masonry were torn down

and a rock remained situated on the masonry (see Fig. 13). The mentioned cross-beams were

probably also destroyed due to this event. However the resulting debris in the sand trap was removed,

so that no further loss of its functionality currently exists. Other damages can be observed at the sluice

gate in the second basin, where the anchorage is broken out (see Fig. 15). The other sluice gate

shows no such damage, probably due to the larger width of the wall resulting in a bigger load

distribution area. Significant water losses (20 to 30 l/s measured during a field trip in February 2014)

can be observed at the sluice gates as the gates are not closing correctly, with remaining gaps on the

channel bed and on the lateral guidance of the gates.

Pre-Design

Page 17 / 127

Fig. 13: Sand trap, view from upstream (5.12.2013, KIT)

Fig. 14: Sluice gate of second pool (25.02.2014, KIT)

2.2.2 Description of measures to minimize water losses and to prevent flotsam entry into the

headrace channel

To minimize water losses and to improve the yield of the plant, especially during dry seasons,

leakages at the sluice gates have to be avoided. Therefore, the gate structures have to be examined

and restored to a proper functionality, sealing any gaps in the gate channel bed and the lateral

guidance. Additionally, concrete rehabilitation works are necessary at the gate anchorage structures.

Fig. 15: Broken sluice gate anchorage (13.12.2014, KIT)

Fig. 16: Water losses from gate (13.12.2014, KIT)

To prevent flotsam entering the headrace channel respectively the intake pool and penstock a trash

rack has to be installed between the outlet of the sand trap and the intake of the headrace channel.

Fig. 17 Fig. 18 a sketch with the

modification. The trash rack rods should have a round profile with a diameter of approx. 2 cm. The

Pre-Design

Page 18 / 127

spacing of the rods to each other should be approx. 6 to 8 cm. The trash rack itself should have a

leaning slope of 70 to 80 relative to the horizontal, should be side-mounted with hinges and lockable

e.g. with padlock. Thereby it can be opened for cleaning purpose and to access the headrace channel.

The trash rack should be embedded on a box of concrete or stonework and a metal plate (see Fig.

18). All metal parts of the trash rack should be rust-proof.

The trash rack should be installed on a concrete foundation made out of prepacked concrete. The

ground structure of limestone should be covered by a layer of reinforced concrete. The principal

construction method is explained in section 2.1.2.

Fig. 17: Current state of headrace channel intake

(25.02.2014, KIT)

Fig. 18: Intake of headrace channel intake after

modification with trash rack

2.2.3 Description of measures to improve the sediment deposition capacity

2.2.3.1 Background information sediment deposition capacity

Suspended loads are mineral or organic particles that are carried by water. Concentration and grain

size of suspended loads in works water of hydropower plants are significant parameters for the

durability of turbines and pumps. Medium to long-term exceedance of limiting values of those

parameters can cause hydro-abrasional damage to the machinery. To protect the intended PAT-

pump-modules (developed and delivered by KSB AG), it is necessary to comply with the following limit

values, which match with the common requirements for high-pressure hydro power plant applications:

- Maximum suspended load concentration: 20 mg/l

- Maximum grain size of suspended load: 0.25 mm

0.7 m

0.85 m

Pre-Design

Page 19 / 127

2.2.3.2 Evaluation of critical grain size

Sand trap and intake pool are located upstream to the intended PAT-pump-modules and have a

sediment deposition capacity which is depending on their geometric dimensions. Thereby those

structures can help to comply with the above stated limiting values. Hereto the critical grain size of

existing sand trap and intake pool was evaluated by KIT applying theoretical analysis approaches of

Vischer & Huber1 and Ortmanns

2. Generally, suspended grains, which are smaller than a certain

critical grain size, cannot be fully withheld inside a hydraulic structure; in the present case they would

partially enter the penstock. The mentioned approaches consider the settling path of a suspended

grain and the necessary sedimentation basin length (see schematic diagram in Fig. 19). Thereby the

approach of Vischer & Huber takes into account the reduction of the settling velocity caused by basic

turbulence which generally characterizes open channel flows. Ortmanns considers in addition the

turbulence impact in the inlet zone of a sedimentation basin.

Fig. 19: Simplified settling path of a suspended grain

With a discharge of Q = 400 l/s (max. hydraulic capacity of the headrace channel, calculated by KIT

based on on-site measurements including safety margins), an effective sand trap dimension of 15 x

1.4 x 0.8 m (L x W x H) and an effective intake pool dimension of 6.5 x 2.1 x 2.7 m (L x W x H), the

critical grain size can be determined with both approaches as shown in Tab. 3.The effective dimension

of the basin to their reduced sediment deposition capacity.

Tab. 3: Critical grain size of sand trap and intake pool (the inlet area is hereby not considered)

Approach Sand trap Intake Pool

Vischer & Huber ~ 0.5 mm ~ 0.3 mm

Ortmanns ~ 0.4 mm ~ 0.7 mm

1 Vischer und Huber, Wasserbau: Hydrologische Grundlagen, Elemente des Wasserbaus, Nutz- und

Schutzbauten an Binnengewssern. Publishing house Springer 2002 2 Ortmanns, Entsander von Wasserkraftanlagen. Publishing house Versuchsanstalt fr Wasserbau,

Hydrologie und Glaziologie ETH-Zentrum 2006

Pre-Design

Page 20 / 127

For these results it has to be considered that both approaches have been empirically developed and

entail uncertainties. However they lead to the conclusion that the limiting values for the maximum grain

size cannot be complied with the existing sand trap and intake pool of the Seo Ho HPP.

For further evaluations of the sediment deposition the KIT carried out in situ investigations of the

suspended loads and their concentration during field trips to Dong Van in July/August and November

2014. These investigations by the KIT-Institute for Water and River Basin Management (IWG,

KaWaTech-sub-project 1) were comprehensively supported by Institute for

Applied Geosciences, namely the Department of Hydrogeology (AGW, KaWaTech-sub-project 2) and

the Department of Aquatic Geochemistry (IMG, KaWaTech-sub-project 3). Fig. 20 exemplarily shows

a microscopic enlargement of suspended loads of works water from the Seo Ho HPP which was

extracted directly b . These investigations reassure that the limiting

values for the maximum grain size cannot be complied with the existing hydraulic infrastructure.

Fig. 20: Microscopic enlargement of suspended sediments of the works water of Seo HPP (16.01.2015, KIT)

2.2.3.3 Evaluation on suspension concentration

Additional in situ investigations of the suspended load concentration were carried out during field trips

to Dong Van in July/August and November 2014. In the November field trip an advanced method was

additionally applied to measure the suspended load concentration. Fig. 21 and Fig. 22 show the

results of these investigations complemented by discharge measurements. These results show that

the suspended load concentration complies with the limit value of 20 mg/l at most measurements.

Only in the period from 20th to 22

nd of July the limit was exceeded significantly (see Fig. 23). Further

investigations lead to the conclusion that in this period serious rainfall events in the Dong Van region

took place causing the exceedance of the limiting values. This context will be evaluated by further data

acquisition and analysis in the 1st term of 2015. Based on current insights it can be assumed that the

limiting value for the suspension load concentration is exceeded temporarily during the main rain

season triggered by serious rainfall events.

Pre-Design

Page 21 / 127

Fig. 21: Suspended load concentration and discharge July/August 2014

Fig. 22: Precipitation data of measurement stations in Lung Phin and Ta Phin

Pre-Design

Page 22 / 127

Fig. 23: Suspended load concentration and discharge November 2014

2.2.3.4 Summary of evaluation results and measures to improve sediment deposition capacity

The evaluation of the sediment deposition capacity

has shown that it cannot fully comply with the given limiting values for the tolerable suspended load

concentration and grain size.

To ensure high life expectancy of the machinery the sediment deposition capacity has to be improved.

The related technical and financial effort could be minimized by a successive approach. After

implementation of a first measure (test stage) at the intake pool (see section 2.4.2.2) and the

successive evaluation of the achieved improvements a decision is to be made if further improvements

are required.

If a further improvement is necessary the implementation of additional measures at the intake pool

(see section 2.4.2.3) has to be accomplished. If (against current expectations) even these measures

are not fully sufficient the implementation of optional measures at the sand trap (see section 2.2.3.5)

has to be considered. The successive approach is shown schematically in Fig. 24.

The suspended load concentration of the works water can be reduced significantly due to the in

sections 2.2.3.5, 2.4.2.1 and 2.4.2.2 described measures. However, with an appropriate effort it cannot

be supposed to achieve a sufficient retention of very high loads of suspended sediment caused by

extreme rainfall events. Therefore, the installation of a warning system is planned to temporarily shut

down the water supply system in case of extreme discharge events (see section 2.7). This warning

implemented by KIT.

Pre-Design

Page 23 / 127

Fig. 24: Successive approach to improve the sediment deposition capacity of Seo Ho HPP hydraulic system

2.2.3.5 Optional measures to improve the sediment deposition capacity of the sand trap

The measures described below are optional in case the settling efficiency of the intake pool

cannot be increased sufficiently (see sections 2.4.2.2 and 2.4.2.3). The implementation is hence

only on demand and could take place in the 1st

term of 2016. Therefore they have to be taken

into account in the budget, but not yet into the Final Engineering Design. These measures

contain the removal of the restriction between basin 1 and 2 and the enlargement of basin 2.

Fig. 25: Sketch of the sand trap with top view after optional modification to improve sediment deposition capacity (implementation only on demand)

Enlargement

of basin 2

Removal of

restriction

DRAFT

Pre-Design

Page 24 / 127

The restriction between basin 1 and 2 is a control cross section, which can be used to determine the

discharge at this point. However, the restriction decreases the sediment deposition capacity due to a

local increase of the flow velocity, which interrupts the process of deposition. A removal of the

restriction eliminates this local acceleration and thereby increases the sediment deposition capacity of

the sand trap. An enlargement of basin 2 elongates the possible sedimentation path and by that also

increases the sediment deposition capacity.

Fig. 25 shows a sketch of the sand trap after the described optional modification. In case of necessity

to carry out these optional measures a further Pre-design will be delivered from German side.


The list of materials below (Tab. 3) is mandatory to implement the required measures described

in section 2.2.2 and is within the responsibility of the Vietnamese partners.

Tab. 4: List of materials and services for measures to improve the sediment deposition capacity of the sand trap



4.2 Sealing of gaps in gate channel bed and lateral guidance of the sluice gates

Detailed localization and excavation of the existing gaps Roughening of the concrete surfaces Fitting and installation of steel parts Application of new concrete layer

2 ls

4.3 Steel parts for gate channel bed and lateral guidance of the sluice gates 2 ls

4.4 Rehabilitation of the anchorage of the sluice gate in basin 2 Excavation of the existing breaks-offs Roughening of the concrete surfaces Application of new reinforced concrete to restore the area Re-installation of sluice gate

1 ls

4.5 Trash rack 1 ls

4.6 Concrete foundation for the new trash rack 1 m

The list of materials below (Tab. 5) is within the responsibility of the Vietnamese partners and

is optional in case the sediment deposition capacity of the intake pool cannot be increased

sufficiently (see sections 2.4.2.2 and 2.4.2.3). Therefore they have to be taken into account in

the budget, but not yet into the Final Engineering Design.

Tab. 5: List of materials and services for optional measures at the sand trap


5.1 Removal of the restriction Concrete excavation works Concreting works to restore proper functionality

3 1

m m

5.2 Enlargement of the sand trap basin 2 Soil excavation works Concrete excavation works Concreting of basin bed with reinforced concrete Concreting of basin walls with reinforced concrete

16 - 32 4 5 12

m m m m

Pre-Design

Page 25 / 127

2.3 Headrace channel


Fig. 26: Map of Seo Ho HPP area - Headrace channel

The headrace channel connects the sand trap with the intake pool and is constructed as a U-shaped

concrete channel with dimensions of 0.6 x 0.7 m (W x H). The continuously concreted channel is

covered by concrete slabs. It runs mostly underground and is only visible at 2 spots (see Fig. 27),

which both are within the first third of the total length (starting from the sand trap). According to the

construction plans, it has an inclination of 2 With a levelling using the intake at the sand trap and

the above mentioned 2 visible spots as sampling points, the channel incline was validated by KIT. At

the beginning, the concrete slabs form the narrow path along the right side of the valley leading to the

intake pool (see Fig. 28). In the rear part however, the channel seems to be far deeper and is covered

completely with soil and rock to an unknown extent, so that the accessibility is not given anymore.

Although the construction materials stated in the construction plan, which are masonry plastered with

cement mortar and some concrete sections, could not be verified for the length, they

seem plausible taking into consideration the design of the sand trap. The distance between sand trap

and intake pool is 790 m, although the channel itself does not run directly into the intake pool. Instead,

a steel pipe of unknown length connects the intake pool with the headrace channel. The construction

plans of the hydropower plant state a channel length of 638 m. Due to the before mentioned facts, this

data could not be verified yet.

with the Darcy- -

shaped channel dimensions with 0.6 x 0.7 m (W x H) with a clearance of 0.1 m to the slab was

applied. Based on these boundaries a maximum discharge of approx. Qmax = 400 l/s was calculated

inclination). However, due to the unknown condition of some sections of the headrace channel this

value is afflicted with uncertainties.

Pre-Design

Page 26 / 127

Fig. 27: Open course of the headrace channel with

accessible concrete slab cover (5.12.2013, KIT)

Fig. 28: Underground, inaccessible (covered) course

(5.12.2013, KIT)

A partly channel inspection has revealed that the channel surfaces are in a quite good condition (see

Fig. 29). However, the concrete ceiling slabs show cavities due to edge fractures and unplastered

joints which give way to intruding roots (see Fig. 30). The incoming roots cause critical obstructions of

the channel at several spots, which result in a drastically reduced hydraulic capacity. Additionally, the

root obstructions can lead to flotsam jam, reducing the hydraulic capacity even further (see Fig. 31).

Fig. 29: Clean headrace channel section (25.02.2014, SPEKUL)

Pre-Design

Page 27 / 127

Fig. 30: Root obstruction (25.02.2014, SPEKUL)

Fig. 31: Root obstruction and flotsam (25.02.2014,

SPEKUL)


The described damages are to treat straightforward by removing the root obstructions and

subsequently renewing the joints of the affected concrete slabs. To being able to carry out these

measures, the channel has to be opened over its whole length in regular intervals of approx. 70 m.

Therefore it is necessary to get an access to the channel even in the areas with a high covering on top

which concerns especially the second half of the headrace channel. For example, it would be

conceivable to build vertical manholes by installing stacked concrete rings to a height depending on

the respective covering on top of the channel (see Fig. 32).

Fig. 32: Illustration of the vertical manhole

Pre-Design

Page 28 / 127

The quantities stated in Tab. 6 refer to the number of revision openings, not the amount of concrete

rings. The intruding roots and accumulated waste or flotsam jam have to be removed entirely.

Subsequently the corresponding concrete slabs have to be lifted and put back in place with a new

filling of their joints. However, the most important point in this regard is the establishment of a regular

inspection and maintenance management system to avoid such damages in the future. Through

removal of the root obstructions and the accomplishment of regular maintenance ensure a proper

discharge efficiency of the head race channel and therefore an output of the PAT-pump-modules and

existing Seo Ho HPP corresponding to the respective design.


Tab. 6: List of materials and services for measures at the headrace channel



6.2 Construction of inspection openings every 70 m Soil and rock excavation for approximately 10 openings (e.g.

manholes) Precast concrete rings (height 10 cm)

Unknown due to covering of the channel

6.3 Inspection & maintenance of the whole channel Removal of root obstructions and flotsam jams Lifting of concrete slabs and renewal of joints where

necessary (amount unknown)

700

m

2.4 Intake pool


The intake pool is a transitional structure from the headrace channel to the penstock. It serves multiple

purposes: For provision of sufficient water in case of sudden changes in turbine operation (surge tank

function), to purge surplus water over a lateral overflow and last but not least for the detention of

sediments.

The intake pool has a length of 10.5 m, a width of 2.1 m and a maximum depth of 3 m. It is built of

reinforced concrete with a wall thickness of 0.3 m. The area above the connection to the penstock

pipeline is overbuilt with a concrete pavilion. The area between the 4 columns of the pavilion amounts

to 2.5 4.5 m and has a height of 2.5 m. The columns have a square cross-section with an edge

length of 0.22 m. On the left side (flow direction) of the intake pool, there is a 4 m long weir acting as

lateral overflow. Its crest shows some slight damages (break-offs), through which further water is lost.

This overflowing water is used by the operating personnel at Seo Ho HPP to monitor the water level

visually. The more narrow part in front of the intake to the penstock pipeline is closed over the whole

height with a trash rack to withhold flotsam. However, the rack is heavily damaged for unknown

reasons. The irregular openings are closed with a mesh network (see Fig. 37). On the left side of the

trash rack, there is a sluice gate which is used for flushing sediments out of the pool. Currently, the

installed gate causes water losses due to leakages (see Fig. 39). During the field trip in February

2014, a total water loss of 10 l/s caused by leakages at the gate was observed. Behind the trash rack

there is another sluice gate, by which the penstock pipeline can be closed.

Pre-Design

Page 29 / 127

Fig. 33: Map of Seo Ho HPP area - Intake pool

Fig. 34 - Fig. 42 show the current dimensions and state of the intake pool.

Fig. 34: Intake pool (22.07.2011, KIT)

Pre-Design

Page 30 / 127

Fig. 35: Intake pool (empty, upstream view)

(22.02.2014, KIT)

Fig. 36: Intake pool (empty, downstream view)

(22.02.2014, KIT)

Fig. 37: Intake pool damaged trash rack (22.02.2014,

KIT)

Fig. 38: Intake pool flushing sluice gate (22.02.2014,

KIT)

Pre-Design

Page 31 / 127

Fig. 39: Water losses from sluice gate at intake pool

(9.12.2013, KIT)

Fig. 40: Lateral overflow with break-offs at intake pool

(9.12.2013, KIT)

Fig. 41: 3D model of the intake pool (before modification, present state)

Pre-Design

Page 32 / 127

Fig. 42: Lateral overflow at intake pool (see Fig. 40), break-off dimensions [mm]

Damages can be particularly seen at the roof of the intake pavilion. Two holes in the roof and one in

the bottom result most probably from rock fall. Also the columns and the girders are seriously

damaged. The holes in the roof are smaller than the bottom hole with a diameter of approx. 0.45 m. It

displays the remaining reinforcement, while the concrete in this spot completely vanished (see Fig.

43). Also the concrete of the columns feet is partly broken out up to the middle due to reinforcement

corrosion which results in a total demolition of the cross-section (see Fig. 44).

Fig. 43: Hole in the bottom (5.12.2013, KIT)

Fig. 44: Destroyed column foot (5.12.2013, KIT)

The roof in this part of the pavilion is partly broken. Particularly the corner girders are in poor condition

so their connection to the columns and their load bearing capacity is not ensured anymore (see Fig.

45 and Fig. 46). Besides the pavilion, the structure seems to be in quite good condition

although some sintered cracks can be observed and the lateral overflow shows two small break-offs.

Pre-Design

Page 33 / 127

Investigations with a reinforcement detector at the walls of the intake pool revealed a crosswise

arrangement of the reinforcement in a distance of 0.2 m with a strong fluctuating concrete cover

between 25 and 65 mm (see Fig. 47). The determination of the compressive strength with a rebound

hammer gave a mean value of 46 MPa.

Fig. 45: Pavilion roof (1) (5.12.2013, KIT)

Fig. 46: Pavilion roof (2) (5.12.2013,

KIT)

Fig. 47: Wall of the intake pool with reinforcement arrangement (5.12.2013, KIT)

Pre-Design

Page 34 / 127


The measures at the intake pool focus on two objectives: Restore the functionality and increase the

sediment deposition capacity.

2.4.2.1 Measure to restore functionality

To achieve this objective sustainably, the following measures are required: Restoring the lateral

overflow at the weir crest to ensure an even overflow height of the weir, examination and sealing of

gaps in the sluice gate channel bed and the lateral guidance, repairing or replacing of the trash rack to

prevent flotsam input into the penstock and complete demolition as well as reconstruction of the

pavilion as a protective construction against rock fall.

After the restoration of an even weir crest height of the lateral overflow, water discharge should be

avoided, since the full width will be overflowed. This concept interdicts the current method of visual

water level checking. It is therefore planned to install a water level monitoring device with radio

transmission to Seo Ho power house, where the water level will be shown on a digital display. This

system can also be used to display a warning signal in cases of impermissible low / high water level.

The necessary equipment for this system will be provided by the German project partners (see section

2.7). This monitoring method will be of great value both for water supply by the new facility as well as

for generating electricity applying the already existing Seo Ho HPP.

The new trash rack rods must have a rectangular profile with a thickness of 0.5 cm and a depth of at

least 3 cm. The spacing between the rods has to be 2 to 3 cm. The trash rack has to be bordered by a

metal frame and subdivided with horizontal metal beams in order to stabilize the construction. The

trash rack itself is to be mounted in the two vertical slots, which are embedded in the intake pool side

walls. The width of the trash rack has to be designed according to the distance between these two

slots. All used materials have to be rust-proof. Fig. 49 is showing a sketch of the new trash rack.

2.4.2.2 Measure to improve the intake pool sediment deposition capacity

In section 2.2.3.4 a successive approach is described to enhance the sediment deposition capacity of

The first measure of this approach focuses on the intake

pool. Suspended grains deposited underneath the height of the intake edge cannot enter the penstock

anymore (see Fig. 48 and Fig. 49). Therefore the height of this edge must be increased to improve the

sediment deposition capacity. A rounding of the intake zone as shown in Fig. 49 reduces locally

the vortex formation, homogenizes therefore the flow and by that improves the sediment deposition

capacity as well. While operating the Pelton turbines and PAT-pump-modules a water overlap of the

intake edge has to be at least 1.65 m (value according to state-of-the-art literature, including a safety

margin) to prevent the inclusion of air in the works water. This minimum water overlap was determined

with the approaches of Gordon3.

The adaption of the intake zone in front of the penstock could be realized also with a kind of

prepacked concrete as its only function (from a structural point of view) is to bear the vertical forces

3 Heinemann und Feldhaus, Wasserbau: Hydraulik fr Bauingenieure. Publishing house Teubner 2003

Pre-Design

Page 35 / 127

resulting of the hydrostatic pressure load. The proportions can be seen in Fig. 49. However, minor

adjustments of these geometric values to the conditions on site might be required. As construction

material also the omnipresent karst limestone may be used. The core of the intake zone can be

composed of thoroughly cleaned limestone and a cement mortar. To reduce the mortar consumption,

the limestone should have minimal porosity and a regular shape to avoid cavities when building the

intake zone. The outer appearance of the ground structure must show an equal but rough surface with

5 to 10 mm deep grooves to enable a strong bond with the top mortar layer to be applied in the next

work step.

Fig. 48: Cross-sectional downstream view of intake zone before modification

This mortar layer is applied on all surfaces of the intake zone with a layer thickness of 15 mm.

Subsequently, an appropriate reinforcement mesh is installed (e.g. with a layer of chicken wire) on

which a second mortar layer with a thickness of 10 mm is applied wet-on-wet before the hardening of

the first layer. This exterior plaster is intended to protect the core of the structure.

The measure described below regarding the installation of a baffle and 2 racks inside the

intake pool is financed and implemented by the German side. The measure will also be

optimized based on field investigations by the German side during the first term of 2015.

Therefore the baffle and 2 racks do not need to be included in the Final Engineering Design.

Due to the high flow velocity in combination with the high incline of the pool inflow

area, the water entrance through a pipe, which is connected to the headrace channel, has a large

turbulence impact into the intake pool. This turbulence impact causes a very high heterogeneous flow

situation and thus also a low sediment deposition capacity. To improve this state the German side will

install a vertical hanging baffle and 2 racks in the first term of 2015 (see Fig. 50). The baffle in

combination with the 2 racks will enable spatial concentrated energy dissipation, which will lead to a

more homogenous flow situation and therefore to a higher sediment deposition capacity.

Before modification

Pre-Design

Page 36 / 127

Fig. 49: Cross-sectional downstream view of intake zone after modification

Fig. 50: Cross section upstream view of the intake pool with installed baffle and 2 racks for reduction of the

turbulence impact

Water overlap of intake edge

Intake edge

Baffle

Racks

After modification

Pre-Design

Page 37 / 127

To prevent anthropogenic sediment and rubbish entry in the intake pool (e.g. due to playing children)

the entire inlet pool shall be surrounded by a fence including a gate (see Fig. 51). This measure is

within the responsibilities of the Vietnamese side.

Fig. 51: View on the intake pool after modification surrounded by an exemplary fence

The monitoring system mentioned in section 2.4.2.1 to keep the operating water level within a certain

range will be combined with a turbidity sensor. This sensor will be used to display an alert in case of

exceedance the limit for the suspension concentration caused e.g. by serious rainfall events. The

required measuring devices will be provided by the German project partners (see also section 2.7).

2.4.2.3 Optional measures to improve the sediment deposition capacity of the intake pool

The measures described in this section are optional in case the tasks explained in section

2.4.2.2 do not increase the sediment deposition capacity of the intake pool sufficiently.

Therefore they have to be taken into account in the budget, but not yet into the Final

Engineering Design. The implementation is only on demand and could be carried out in the 2nd

term of 2015.

Fig. 52 is showing a sketch of the optional measures to improve the sediment deposition capacity of

the intake pool. The measures contain the enlargement of the intake pool including an upstream

shifting of the baffle and racks, reducing the incline of the inlet zone, modification of the headrace

channel inlet pipe into an open channel structure and displacement (to upstream side) of the lateral

weir crest (overflow). All of these measures will lead to a more homogenous flow situation in the intake

pool and thereby to a higher sediment deposition capacity. In case of necessity to carry out these

optional measures further construction details will be additionally delivered from the German side to

the Vietnamese partners.

Gate

Pre-Design

Page 38 / 127

Fig. 52: View on the intake pool after implementation of optional measures (implementation only on demand)


The list of materials in Tab. 7 and Tab. 8 are within the responsibility of the Vietnamese

partners and are mandatory to implement the required measures of section 2.4.2.1 and 2.4.2.2.

The materials for the baffle and racks as well as the measuring devices (water level & turbidity

sensors) are within the responsibility of the German partners.

Tab. 7: List of materials and services for measures at the intake pool


7.1 Reinforced concrete 20 m

7.2 Various steel parts For gate channel bed and lateral guidance rehabilitation Possibly also rehabilitation of gate necessary

1 ls

7.3 Various steel parts for trash rack repairing / replacement 1 ls


7.5 Restoration of lateral overflow weir crest Excavation of the existing breaks-offs Roughening of the surfaces Application of new concrete layer and/or steel guidance parts

1 ls

7.6 Sealing of gaps in gate channel bed and lateral guidance Excavation of the existing gaps Roughening of the surfaces Application of new concrete layer Fitting and installation of steel parts

1 ls

7.7 Repairing or replacing of the trash rack 1 ls

7.8 Fence including gate 1 ls

7.9 Installation of the fence 1 ls

The list of materials below is within the responsibility of the Vietnamese partners and is

optional in case the sediment deposition capacity of the intake pool cannot be increased

sufficiently by implementing the tasks stated in section 2.4.2.2. Therefore they have to be taken

into account in the budget, but not yet into the Final Engineering Design.

Displacement of weir crest

Enlargement of intake pool Modification of the

headrace channel inlet

Upstream shifting of baffle

and racks

Pre-Design

Page 39 / 127

Tab. 8: List of materials and services for optional tasks to improve the intake pool sediment deposition capacity


8.1 Earth and rock excavation 100 m

8.2 Reinforced concrete 20 m

8.3 Steel or cast iron pipe, DN 500, PN 6 5 m

8.4 Breaking up of old concrete (existing pool) 15 m

8.5 Services for enlargement of the intake pool Earth and rock excavation of the enlargement area Concreting of the pool enlargement Earthworks for the restoration of the pathway

1 ls

8.6 Channel and pipe connection to headrace channel Excavation of the steel pipe at the beginning of the intake pool Cutting & welding of the pipeline according to conditions on site Installation of the new pipe according to the conditions on site Concreting of inlet channel Earthworks for the restoration of the pathway

1 ls

The list of materials below is within the responsibility of the German partners.

Tab. 9: List of materials and services for implementation of baffle and racks inside the intake pool


9.1 Various steel parts for installation of baffle and racks Construction of baffle and racks including guidance Installation of baffle and racks

1 ls

2.5 Penstock bypass to PAT-pump-modules


Fig. 53: Map of Seo Ho HPP area

Pre-Design

Page 40 / 127

The existing penstock is a 720 m long DN 500 steel pipe which is mainly installed above ground

connecting the intake pool with the turbines in the power house of Seo Ho HPP. The first and the last

section of the penstock run underground (see Fig. 53).


Fig. 54: Satellite view of Seo Ho HPP and a possible

routing of the bypass (Bing Maps 2014)

Fig. 55: Existing penstock of Seo Ho HPP and a possible routing of the bypass (5.12.2013, KIT)

To supply the PAT-pump-modules with water, a bypass from the existing penstock to the modules has

to be built. The bypass must be implemented as a DN 300 steel pipe, whereby its total length depends

on the final routing. Responsible for the implementation is the Vietnamese side, whereby the works

have to be accomplished in two construction stages.

2.5.2.1 Construction stages of the penstock bypass

1st

construction stage: Implementation of branch pipe and bypass laying

In a 1st construction stage the bypass connection to the existing penstock and the main part of the

bypass laying has to be done. Fig. 56 shows schematically where the bypass (red pipe) might end in

the 1st construction stage. The figure also shows the pressure supply pipe (blue), which is described in

more detail in section 0. Depending on the design of the power house of the water supply system it

would also be possible to end the 1st stage at the area behind the existing power house. As soon as

the decision about the power house design is made, the final routing of the bypass shall be clarified by

German and Vietnamese side. Based on this decision the Vietnamese side can then work out the

Final Engineering Design for this part of the plant. Independent from the final routing of the bypass its

final segment to the power house extension area (future location of the water supply facility)

has to build in a 2nd

construction stage. Thereby an easier and more precise connection of the

bypass to the PAT-pump-modules will be possible.

Penstock underground section

Extension area of power house

Bypass

Revision valve

Pre-Design

Page 41 / 127

Fig. 56: Schematic unscaled sketch of a potential routing of the bypass after 1

st construction stage

2nd

construction stage: Implementation of final bypass segment

In a 2nd

construction stage the final bypass segment to the power house extension area has to be

built. The last bypass abutment must be decoupled from the floor slab of the power house extension

(see section 2.6) to avoid an impact from any settling processes. The 2nd

construction stage must

be done in parallel to the implementation of the PAT-pump-modules. It has to be carried out by

the Vietnamese side in consultation with the German partners. The pipe laying in the 2nd

construction stage can be realized above or at the foot of the retaining wall. Fig. 57 shows

schematically where the bypass should end in the 2nd

construction stage. The final pipe segment

(black part in Fig. 57), which connects the bypass with the PAT-pump-modules, will be

provided and installed by the German side.

Fig. 57: Schematic unscaled sketch of a potential routing of the bypass after 2

nd construction stage

Final pipe segment

Retaining wall

Retaining wall

1st

construction stage

2nd

construction stage

Pre-Design

Page 42 / 127

2.5.2.2 Piping of the penstock bypass

The branch pipe shall be connected to the penstock with an angle of 90 before the penstock vanishes

underground (see Fig. 55). This angle will distinctly simplify the installation on site while causing only

minor hydraulic losses. As close as possible to the branch, a revision valve (PN 25, DN 300) is to be

installed in the bypass, which enables the decoupling of the entire water supply system from the

penstock e.g. for revision tasks. Fig. 54 and Fig. 55 show a possible bypass routing. However it would

also be possible to connect the branch with the target area on the powerhouse forecourt resp. the

extension area directly. In this case a partial removal of the mound would be required.

Independent from the final routing the components used for construction of the bypass have to be

defined as follows.

Straight pipe segments need to have a minimum wall thickness of 5.6 mm. The calculation is based

on a steel P235 (minimum strength 235 N/mm). Longitudinally welded or seamless pipes can be

used. For the welds a weld value of 0.8 was applied.

Pipe elbows have a lower pressure capability than straight pipe segments. Thus, greater wall

thicknesses are required. The strength test for the pipe elbows should be based on the standard DIN

EN 10253-2 type A (reduced utilization factor). For the pipe elbows a radius of 3 times diameter shall

be applied. Greater pipe elbow radii are permitted. If closer pipe elbow radii will be used, an increase

of the wall thickness is required.

Tab. 10 contains information about the recommended welding procedure as well as the specification

of the required materials.

Tab. 10: Specification of the welding procedure

Group of materials / no. according to CR ISO 15608 Base material Material no.

1 / 1.1 P235TR1 1.0254

Pipe dimensions 323.9 x 5.6

Welder qualification test corresponding to DIN EN ISO 9606-1

111 T BW FM1 B s5,6 D323,9 PH ss nb

Welding process Root run, filler bead, final run

Manual arc welding (111)

Welding filler corresponding to EN 12070 Bhler FOX EV 50 7018-1 E 42 5 B

Joint preparation DIN EN ISO 9692-1 Key figure Preparation of the welding edge

To produce by grinding or sawing

Weld heat treatment during welding Not required

Weld inspection According to DIN EN ISO 5817, assessment group C

Testing Visual inspection = 100 % Radiographic test scope of testing = 50 % Tightness vacuum = 100 %

Pre-Design

Page 43 / 127

To avoid any damages of the bypass caused by occurring loads during regular operation or in case of

water hammer (e.g. caused by pressure surge) and to ensure an economic construction process,

foundations combined with bearings have to be dimensioned with a systematic approach according to

the respective loading situation. In total 2 types of foundations and 3 types of bearings have to be

differentiated as follows. All components were dimensioned based on the loads given in Tab. 11,

which are calculated without safety margins.

Tab. 11: Forces occurring at the bypass both during regular operation and in case of water hammer do not include safety factors (see coordinate system Fig. 108 and Fig. 109)

Foundation type Fx Fy Fz Fx Water hammer*

Fixed point 61.5 kN 6 kN - 21 kN 23.1 kN

Slide and guide bearings

11.5 kN 6 kN - 17 kN -

* Additional axial load to the forces occurring during regular operation

All figures in the next sections which do show foundations and bearings shall be considered as

exemplary and schematic. Thus, the foundations and bearings have to be adjusted to the on-site

conditions (e.g. to the mountain slope).

2.5.2.3 Foundation types for the penstock bypass

To avoid future damages in the water distribution system and to ensure an economic construction

process, concrete foundations as support for the pipeline were pre-dimensioned with a systematic and

comprehensive approach according to the load situation of the separate bearing types (see Tab. 11).

According to the loads stated in Tab. 11 the permissible distance between bearing points was set to

10 m. In close proximity to kinks of the pipeline this distance has to be reduced (see attachment).

Fixed point foundations (15/201-ST-01-108-c):

The fixed points have to be dimensioned according to the respective forces which result from the

change of pipeline direction, from the pipes dead load as well as from wind load.

Fig. 58: Side view of the foundation for fixed points

WITH reinforcement

Fig. 59: Front view of the foundation for fixed points

WITH reinforcement

Pre-Design

Page 44 / 127

Under regular operating conditions the recommended dimensions of the concrete foundations can be

seen in Fig. 58 and Fig. 59. For fixed points the dimensions are length x width x height (L x W x H) =

2.0 x 1.5 x 0.75 m. They should be realized by a concrete of a characteristic strength of fck = C25/30.

The size of the foundations was calculated without partial safety factors. However, the concrete

properties were lowered by a factor of 0.85 and in addition a global safety factor for all concrete

foundations of 2.0 was assumed in this pre-design.

The installation of a minimum reinforcement to account for a ductile member failure is optional. The

permitted contact pressure was assumed to be 150 kN/m. However, it is recommended to verify this

assumption when checking the in-situ ground conditions before the beginning of the construction

works. Further, all proofs against sliding, tilting and ground failure must be verified according to the

respective national Vietnamese standards (especially in slope areas).

If it is decided to design the foundations to account also for the additional loads which may occur due

to a water hammer (see Tab. 11, right column), the foundations shall be fixed to the rock ground e.g.

with embedded reinforcement bars as illustrated in Fig. 60.

Fig. 60: Exemplary illustration of a concrete foundation fixed to the ground with embedded reinforcement bars

Slide and guide bearing foundations (15/201-ST-01-107):

Under regular operating conditions the recommended dimensions of the concrete foundations can be

seen in Fig. 64 and Fig. 65. For the slide and guide bearings the dimensions are L x W x H = 0.5 x 1.0

x 0.5 m. They should be realized with a concrete with a characteristic strength of fck = C25/30. The

installation of a minimum reinforcement to account for a ductile member failure is optional.

The permitted contact pressure was assumed to be 150 kN/m. However, it is recommended to verify

this assumption when checking the in-situ ground conditions before the beginning of the construction

works. Further, all proofs against sliding, tilting and ground failure must be verified according to the

respective national Vietnamese standards (especially in slope areas).

If it is decided to design the foundations to account also for the additional loads which may occur due

to a water hammer (see Tab. 11, right column), the foundations shall be fixed to the rock ground e.g.

with embedded reinforcement bars as illustrated in Fig. 60.

Pre-Design

Page 45 / 127

Fig. 61: Side view of the foundation for slide/guide

bearings WITH reinforcement

Fig. 62: Front view of the foundation for slide/guide

bearings WITH reinforcement

2.5.2.4 Bearing types for the penstock bypass

On top of each foundation a bearing has to be installed to guide the bypass and to transfer the

occurring forces to the respective foundation. In total 3 bearing types have to be differentiated as

follows. Note that the

of the foundation (i.e. with or without reinforcement).

Fixed point bearings (15/201-ST-01-108-c):

For the dimensioning of the fixed points the maximum design pressure is decisive. Fixed points have

to be arranged between all expansion bends, whereby a piping without fixed points is not permitted.

The bearings and their fixation on the foundations might be constructed as shown in Fig. 63 to Fig. 66.

Fig. 63: Side view fixed point bearing

Fig. 64: Front view fixed point

Pre-Design

Page 46 / 127

Fig. 65: Cross sectional views of the fixation

Fig. 66: Isometric view of the fixed point bearing

Sliding and guide bearings (15/201-ST-01-107):

Slide bearings in the area of expansion bends have to be constructed without guide rails (see

description for guide bearings below). All guide bearings should be equipped with guide rails (securing

the position of the pipe and absorption of wind loads). In Fig. 67 to Fig. 70 the recommended

construction of a slide bearing and of a guide bearing as well as of the fixations on the foundation are

shown. Guide bearings shall be applied in straight sections as shown in the routing attached to this

Pre-Design. In close proximity to the elbows slide bearings without the guide rail shall be applied. The

minimum distance between elbow and first bearing as stated in the attached routing has to be

respected. The bearings shall be constructed with steel/steel sliding surfaces (low-friction bearings

made of PTFE are not recommended.

Fig. 67: Side view slide and guide bearing

Fig. 68: Front view

kawatech pre design2015

Documents