a report on fewa watershed siltation dams problems and

A REPORT ON FEWA WATERSHED SILTATION DAMS PROBLEMS AND MITIGATION MEASURES 2020

A REPORT ON FEWA WATERSHED SILTATION DAMS PROBLEMS

AND MITIGATION MEASURES

(KHAHARE DAM, HARPAN DAM, BETINI DAM AND LAURUK DAM)

Study Team Signature

Coordinator Dr. Bishnu Raj Baral, Member, Policy and Planning Commission, Gandaki Province

Member Dr. Anup Gurung, Chief Executive Officer, Lake Conservation and Development Authority, Gandaki Province

Member Er. Sharada Mohan Kafle, Chief Engineer, Pokhara Metropolitan City

Member (Expert)

Er. Mani Raj Dahal, MSc. Hydraulics & River Basin Development (Expert River Hydraulics/Hydropower Components Design); Chief Engineer, Clean Energy Consultants, Kathmandu

Member (Expert)

Mr. Ghan Bdr. Shrestha, MSc. Eng. Geology (Expert Geologist/Watershed Sediment); Geologist, Clean Energy Consultants, Kathmandu

Member Secretary

Mr. Krishna Ghimire; Chief, Soil Conservation and Watershed Management Office, Tanahu, Gandaki Province

Submitted to:

Province Government

Ministry of Industry, Tourism, Forest and Environment Gandaki Province, Pokhara, Nepal

October 2020


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कामयकायी सायाॊश

पेवातार ऩोखया भहानगयऩालरकाको दक्षऺण-ऩक्षिभी ऺेत्रभा अवक्षथथत नेऩारकै दोस्रो ठूरो तार हो। पेवाताररे जराधाय ऺेत्रवाट आउने ऩानी शदु्धीकयण, ऩनुबययण तथा बण्डायण गनय, काफयन य ववववध ऩौविक ऩदाथयहरूको प्रशोधन गनय, तार ऺेत्रभा यहेका फोटलफरुवा य जनावयहरूराई वासथथान/ऩौविक ऩदाथय उऩरब्ध गयाउने जथता ऩमायवयणीम सेवाहरु प्रदान गनय भहत्त्वऩूणय बलूभका खेरेको हदुा मस ऺेत्रराई अन्तयाविम भहत्वको याभसय ऺेत्र घोषणा गरयएको छ।पेवाताररे लसॊचाई, जरववद्यतु ्य ऩमयटन ववकासभा ऩलन मोगदान ऩरु् माएको छ। ववक्रभ सॊवत २०2९ सारभा तारको दक्षऺण-ऩूवॉ बागभा लनभायण गरयएको फाॉधरे ३२० हेक्टय जलभनभा लसॊचाई गनय य ५०० वकरोवाट ववद्यतु उत्ऩादन गनय भद्दत गयेको छ। त्मथतै, पेवाताररे राखौ आन्तरयक य अन्तयायविम ऩमयटकहरू आकवषयत गयी आम य योजगायीका अवसयहरू लसजयना गनय तथा सभग्रभा ऩोखयाराई नेऩारकै एक गलतशीर य जीवन्त ऩमयटकीम शहयको रुऩभा नेऩार य ववश्व बरय थथावऩत गयाउन उल्रेखनीम बलूभका खेरेको छ।

थथानीम अथयतन्त्रभा ठूरो मोगदान ऩमुायउदै आएको पेवातार ऺेत्रभा ववगत केही दशकदेक्षख बने तारको ददगो व्मवथथाऩनका सन्दबयभा ववलबन्न सभथमाहरु देखा ऩयेका छन।्जथतै, शहयी ऺेत्रफाट ववना प्रशोधन तारभा ऩगु्ने ढरको ऩानी तथा पोहोय तथा वषायतभा भूर सडक हदैु तारभा ऩगु्न ेऩानीरे तार प्रदषुण फढाएको छ।त्मथतै, जराधाय ऺेत्रभा अव्मवक्षथथत रुऩभा गरयने खेलत प्रणारी य सडक लनभायणका कायण बूऺ म हनुे तथा ऩवहयो जाने य ठुरो भात्राभा गेग्रान तथा वारवुा उत्ऩादन बई पेवातार ऩरुयएय तार ऺेत्र ववथतायै खकु्षचचदै गईयहेको छ। नेऩार सयकायरे सन ् २००२ भा वपलनश इन्टयनेशनर डेवरऩभेन्ट एजेन्सी (FINIDA) को सहकामयभा गयेको अध्ममनरे वावषयक १,४२,००० भेविक टन भाटो तारभा ऩगु्ने गयेको जनाएको छ। पेवातारको प्रभखु खोरा हऩयन य सहामक खोराहरु जथतै: खहये, फेलतनी य रौरुक भध्मे खहये खोरारे सफैबन्दा फढी गेग्रान तथा वारवुा ल्माउन ेगदयछ बन ेत्मसऩलछ हऩयन, रौरुक, फेलतनी खोरारे ल्माउन ेगदयछन।् हऩयन खोरारे वगाएय ल्माएको गेग्रान तथा वारवुा/भाटो तारको भखुभा थपु्रन ेय हऩयन खोरारे धाय ऩरयवतयन गने लनमलभत रुऩभा हनुे गदयछ। खोरारे धाय ऩरयवतयन गयेको सभम य तारको फाॉध नवनेको वेराभा तार ऺेत्र उल्रेख्म अलतक्रलभत बएको ऩाईन्छ।ववक्रभ सॊवत २०१३ भा २२,००० योऩनी ऺेत्रपरभा पैलरएको तार ऺेत्र ववक्रभ सॊवत २०64 भा आईऩगु्दा ८,२५६ योऩनीभा खचुचेको ववगतका प्रलतवेदनहरुरे उल्रेख गयेका छन।्मवह गलतभा तार ऺेत्र ऩरुयदै जान े तथा जग्गा अलतक्रभण फढ्दै जान ेहो बने १०० फषयभा तार ऩूणयरुऩभै रोऩ हनु ्सक्न ेववगतका अध्ममनहरुरे उल्रेख गयेका छन।् तसथय, नेऩार सयकाय, प्रदेश सयकाय य ऩोखया भहानगयऩालरकारे पेवातार ऺेत्रको ददगो ववकास य सॊयऺण गने कामयराई उच्च प्राथलभकता ददएका छन।्


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पेवातार सॊयऺण सचवक्षन्ध सवोच्च अदारतको ववक्रभ सचवत २०७६ को पैसराराई भध्मनजय गदै तारभा आउन े गेग्रान तथा वारवुा/भाटोराई तारभा आउन ु ऩूवय नै जचभा गरय तार ऩरुयनवाट जोगाउन ेउद्देश्मरे आलथयक वषय २०७६/०७७ भा ऩोखया भहानगयऩालरका य प्रदेश सयकायको सॊमकु्त रगानीभा चायवटा लसल्टेसन ् फाॉधहरू (खहये, हऩयन, रौरुक य फेलतनी) को लनभायण कामय सचऩन्न बएको लथमो। मद्यवऩ, २०७७ को फषायतको सभमभा खहये य हऩयन खोराभा लनलभयत फाॉधभा उल्रेख्म ऺलत ऩगु्मो य फाॉध वरयऩरयको ऺेत्रभा वाढी ऩथमो। जसरे गदाय, फाॉधको क्षथथयता य ददगोऩन सचफन्धभा प्रश्नहरु उठे। मस अध्ममनको भखु्म उद्देश्म फाॉधभा देक्षखएका सभथमाराई ऩवहचान गने, सचफद्ध जोक्षखभहरूराई कभ गनयका रालग ववकल्ऩ खोज गने य रागत तथा आचदानी आकरन गरय सयकायराई भागयलनदेशन गनुय यहेको छ। मो अध्ममन प्रलतवेदन थथरगत अवरोकन य उऩरब्ध बएका सूचना तथा तथमाॊकहरुको ववश्लषेणको आधायभा तमाय गरयएको छ। प्रलतवेदनभा फाॉधको सॊचारनभा आउन सक्ने जोक्षखभहरु न्मूनीकयण गनय सहमोगी हनुे सॊयचनाहरुको प्रायक्षचबक लडजाईन य रागत अनभुान सभेवटएको छ। त्मथतै, थवुप्रएका गेग्रान तथा वारवुाको आमतन आकरन गरय त्मसभापय त हनु सक्न ेआचदानी य भनुापा सवहतको प्रायक्षचबक आलथयक ववश्लषेण सभेत सभेवटएको छ। मस अध्ममनको भखु्म लनष्कषय तथा सझुाफहरु लनचन अनसुायका छन:्

1= खहये य हऩयन खोराभा ढुॊगाको ऩखायर (Stone Masonry) फाट लनभायण गरयएका फाॉधका सॊयचनाहरु उच्च जोक्षखभभा यहेको य आउन ेवषायतभा थऩ बत्कन सक्ने जोक्षखभ यहेको हदुा वषायत शरुु हनु ुऩवुय नै भभयतसचबाय तथा ऩनु्थथाऩना य सदुृढीकयण गनुयऩने देक्षखन्छ।

2= फेलतनी य रौरुक खोराभा लनलभयत वाधभा २०७७ को वषायतको लसजनभा खासै सभथमा नदेक्षखएको हदुा अवथथा हेरयकन आगाभी वषयहरुभा भभयत सचबाय तथा ऩनु्थथाऩना य सदुृढीकयण गनय सवकन्छ। मद्यवऩ, फेलतनी य रौरुक दवैु वाधको वकनायभा वाढी लनमन्त्रण गनयका लनक्षचत लनलभयत ऩखायरहरुको उचाई मसै वषय फढाउन ुऩने देक्षखन्छ।

3= खहये य हऩयन खोरा फाॉध बक्षत्कन ेसक्न ेजोक्षखभ न्मूनीकयण गनय फाॉधको दवैु लतयको थरोऩभा कॊ वक्रट ज्माकेवटङ्, थरोऩको अन्त्म लतयको बागभा कॊ वक्रटको ऩखायर (कट आप वार), ४.५ लभटयको उचाईवाट खसेको ऩानीको फहाफराई लनथतेज ऩानय फाॉधको तल्रो कट अप वारऩलछ कॊ वक्रटको ऩोखयी (क्षथटलरॊग वेलसन) लनभायण गनुयऩने देक्षखन्छ। त्मथतै, खहये वाधको दवैु वकनायभा लनभायण गरयएको फाढी लनमन्त्रण गने ऩखायरको उचाई फढाउन ुऩने देक्षखन्छ बन ेहऩयन खोरा फाॉधको दामा वकनायभा लनलभयत फाढी लनमन्त्रण गने ऩखायरको उचाई फढाउन ु ऩने देक्षखन्छ।


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4= आकक्षथभक रुऩभा आउन सक्न ेफाढीराई लनमलभत रुऩभा फाॉधको तल्रो बबूागभा प्रवाह गनय तथा गेग्रन लनकाल्न ेसभमभा फाॉधभा जभेको ऩानीराई तकायएय गेग्रान तथा वारवुा लनकाल्न सक्षजरो फनाउन फाॉधको कुनै एक खण्डभा थरइुस गेट लनभायण गनुयऩने देक्षखन्छ।

5= खोरारे ल्माउन े गेग्रान तथा वारवुाको तरुनाभा लथग्राउन े बाग न्मून यहेको छ। मसथय, वषायतको सभमभा गेग्रान तथा वारवुाको लनमलभत उत्खनन नगयेको खण्डभा एक फाढीभा आउन ेगेग्रान तथा वारवुारे ऩलन फाॉधको भालथल्रो बाग ऩयैु बयाउन ेय फाॉधको दईु वकनायावाट ऩानी वावहय प्रवाह बई नोक्सान गयाउने जोक्षखभ देक्षखन्छ। मसथय, फाढी य वेड रेवेर अनगुभन गरय गेग्रान तथा वारवुा उत्खननको कामय लनमलभत गनुयऩने देक्षखन्छ।

6= चायवटै फाॉधका सॊयचनाहरुको भभयत सचबाय तथा ऩनु्थथाऩना य सदुृढीकयणको प्रायक्षचबक रागत सऩुरयवेऺण रागत सवहत करयफ ३६ कयोड ८४ राख अनभुान गरयएको छ। सो भध्मे खहये फाॉधका रालग करयफ १७ कयोड ८८ राख, हऩयन फाॉधका रालग करयफ ८ कयोड ३५ राख, रौरुक फाॉधका रालग करयफ ३ कयोड ६७ राख य फेलतनी फाॉधका रालग करयफ ३ कयोड ५६ राख राग्न ेआकरन गरयएको छ। मस वहसाफरे मसै वषय भभयत सचबाय तथा ऩनु्थथाऩना, य सदुृढीकयण गनय सझुाईएका खहये य हऩयन फाॉधको रालग करयफ २६ कयोड २३ राख राग्न ेअनभुान गरयएको छ।

7= एक ऩटक चाय वटै फाॉध ऺेत्र बरयएको खण्डभा करयफ २ राख ६५ हजाय घन लभटय लगटी, फारवुा तथा अरु रयफय फेड साभग्री थवुप्रने प्रायक्षचबक आकरन गरयएको छ। लफवक्र हनु सक्न ेलगटी य फारवुा भापय त करयफ २० कयोड ७१ राख आचदानी हनुे देक्षखन्छ। कुर आचदानी भध्मे ५० प्रलतशत गेग्रान तथा वारवुा उत्खनन, प्रशोधन तथा भभयत सचबायभा खचय राग्न सक्न ेआकरनको आधायभा करयफ १० कयोड ३३ राख खदु भनुापा हनुे देक्षखन्छ।

8= फाॉधको भभयत सचबाय तथा ऩनु्थथाऩना य सदुृढीकयणको रालग अनभुान गरयएको रागत य ढुॊगा लगट्टी वारवुा भापय त प्राप्त हनुे आचदानी सभेतराई भध्मनजय गरय ववश्लषेण गदाय आलथयक तथा ववक्षिम ऩरयसूचक याम्रो (Project IRR = 16%; Project B/C Ratio = 1.35; Simple Payback= 4.94 Years; Return on Investment = 23%; Investors B/C Ratio = 2.80) देक्षखन्छ। मसथय, मस आमोजनाभा फैंकको रगानी ऩलन आकषयण हनु सक्न ेसाथै थव-रगानी (Equity Investment) ऩलन चाडै उठ्ने देक्षखन्छ।

9= फाॉधको भभयत सचबाय तथा ऩनु्थथाऩना य सदुृढीकयण तथा ढुॊगा, लगट्टी य वारवुा व्मवथथाऩनको रालग ऩवहरो ववकल्ऩको रुऩभा ऩोखया भहानगयऩालरका य प्रदेश सयकायरे सॊमकु्त रुऩभा रगानी गयेको खण्डभा तारको सॊयऺण य ववकासको रालग आवश्मक ऩने उल्रेख्म स्रोत त्मवहफाट


6

जटुाउन सवकन े देक्षखन्छ।दोस्रो ववकल्ऩको रुऩभा लनक्षज ऺेत्रराई फाॉधको भभयत सचबाय तथा ऩनु्थथाऩना, ऩनु:लनभायण य सदुृढीकयणका साथ् साथै ढुॊगा, लगट्टी य वारवुा व्मवथथाऩनको ऩलन क्षजचभा ददन ेगरय अगालड फढ्न सवकन्छ।

10= मस प्रायक्षचबक अध्ममनभा प्रथताव गरयएको सॊयचना, रागत य आचदानी ववना ववथततृ टोऩोग्रावपक सवे, साभान्म थथरगत अवरोकन य उऩरब्ध सूचना तथा तथमाॊकको आधायभा गरयएको हदुा फाॉधको भभयत सचबाय तथा ऩनु्थथाऩना, ऩनु:लनभायण य सदुृढीकयणको कामय शरुु गनुय ऩूवय ववथततृ सवे गरय प्रथताववत सॊयचनाहरुको वपल्डभा रेआउट गरय प्रभाणीकयण गने तथा लडजाईन, रागत तथा आचदानी ऩनुयारोकन गनुयऩने हनु्छ। त्मथतै, लनभायण अवलधबय ववऻ तथा राब ग्रावह टोलर भापय त लनमलभत सऩुरयवेऺण गरय गणुथतय लनमभन गनुयऩने देक्षखन्छ।

11= लनभायण गरयएका फाॉधरे ढुॊगा, लगट्टी तथा वारवुा लथग्राउन भद्दत गदयछ बने अलधकाॊश लसल्ट तथा भाटो फगेय हऩयन खोरा हदैु पेवातार गएय लथलग्रन्छ। मसथय, तारभा ऩगु्न ेलसल्ट तथा भाटोको आमतन ववथततृभा आकरन गरय त्मसको व्मवथथाऩनभा ध्मान ददनऩुने आवश्मकता यहेको देक्षखन्छ।


7

Executive Summary

Fewa Lake located in the south-western part of the Pokhara Metropolitan City is the second largest

lake of Nepal. The lake has been declared as a Ramsar area of international importance as the lake

area has played an important role in purifying, recharging and storing water; processing carbon and

various nutrients; providing habitat/nutrients to the plants and animals, and providing ecosystem

services as a whole. Fewa Lake has also contributed to irrigation, hydropower, and tourism sector.

The dam, built in the south-eastern part of the lake in Bikram Samvat 2029 BS, has helped to irrigate

320 hectares of land and generate 500 kilowatts of electricity. Similarly, Fewa Lake has played a

significant role in attracting millions of domestic and international tourists, to create income and

employment opportunities, and to establish Pokhara as a dynamic and vibrant touristic city in Nepal

and around the world.

Over the past few decades, the Fewa Lake region, which has been a major contributor to the local

economy, has faced various problems in terms of sustainable management of the lake. The

unorganized farming system and road construction in its catchment have led to erosion and

landslides and production of a significant amount of sediment. The shrinkage of the lake area is

often attributed to the heavy sedimentation production in the catchment. A study conducted by the

Government of Nepal in 2002, in collaboration with the Finnish International Development Agency

(FINIDA), stated that 142,000 metric tons of sediment reaches the lake annually. Among the major

tributaries of Fewa Lake (Khahare, Harpan, Betini, and Lauruk), Khahare brings the highest amount

of sediment which is then followed by Harpan, Lauruk, and Betini. Sediment brought by the Harpan

accumulates at the mouth of the lake and the Harpan River changes its course regularly. In the past,

the lake area encroached significantly when the river changed its course and before the construction

of Fewa dam. Past studies have shown shrinkage of lake area from 22,000 ropani in Bikram Samvat

2013 to 8,256 ropani by Bikram Samvat 2064. The past studies have also pointed out that the lake

could disappear completely in 100 years if this trend continues. The Government of Nepal, the

Province Government, and the Pokhara Metropolitan City have, therefore, given high priority to the

sustainable development and conservation of the Fewa Lake area.

Considering the Supreme Court's decision of Bikram Samvat 2076 regarding the conservation of

Fewa Lake, Pokhara Metropolitan City and the Province government jointly constructed four siltation

dams (Khare, Harpan, Lauruk, and Betini) in 2076/077 in order to help reduce lake sedimentation.

However, during the rainy season of 2077, the dam on the Khahare and Harpan were severely


8

damaged and the areas around the dam were flooded. As a result, questions were raised about the

stability and sustainability of the dam. The main objective of this study was to identify the problems

in dams, to suggest alternatives measures that help to reduce the associated risks, to determine

preliminary design and estimate for the suggested measures, and to provide suggestions to the

government. This study report has been prepared based on field observation and analysis of

available information and data. The report includes preliminary design and cost estimates of

structures that will help to minimize the risks involved in the operation of the dam. Similarly, a

preliminary economic/financial analysis has been carried out by approximating the volume of sand

and gravel and the possible income and profit through it. The main conclusion and suggestions of

this study are as follows.

1. The stone masonry dam structures of Harpan Khola and Khahare Khola are at high risks and

may collapse during the next rainy seasons, so maintenance, rehabilitation, and

reinforcement should be done before the onset of the monsoons.

2. The dams built on the Betini and Lauruk have not seen much of a problem in the 2077 rainy

season, so maintenance, rehabilitation, and reinforcement of those dams can be executed

in the following years. However, the walls along both Betini and Lauruk dams should be

heightened to prevent flood overtopping.

3. In order to reduce the risk of breakage of Khahare and Harpan dams, concrete jacketing on

slopes in both sides of the dam, construction of the concrete wall (cut off the wall) at the

end of the slope and, provisioning of stilling basins to dissipate energy of overflowing water

from 4.5 m height dam are highly recommended. Similarly, the height of the flood control

wall constructed on both sides of Khahare dam should be increased while the flood control

wall height on the right bank of Harpan dam should be increased.

4. Sluice gates should be constructed in one sections of the dam to facilitate draining of water

during sediment mining works and to release floods during emergency.

5. The siltation area is very small as compared to the volume of sand and gravel that the

stream brings. Therefore, if regular excavation of sediment is not done during the rainy

season, there is a risk of the complete filling even during one flood period and flood

overtopping from flood control walls. It is therefore necessary to regularly monitor flood

and bed levels, and carry mining works.

6. The initial investment for the maintenance, rehabilitation and strengthening along with

primary supervision of the structures of all the four dams is estimated at around NRs. 368.4


9

million. Out of this, it is estimated that it will cost around NRs 178.8 million for Khahare

Dam, Rs 83.5 million for Harpan Dam, Rs 36.7 million for Lauruk Dam, and Rs 35.60 million

for Betini Dam. For the Khahare and Harpan dams alone, NRs. 262.3 million will be required

for the maintenance, rehabilitation and strengthening.

7. Once the four dams are filled, about 265,000 cubic meters of gravel, sand, and other river

bed material will accumulate. It is approximated that the deposited material could generate

around NRs. 207.1 million of gross revenue through the sale of the deposited gravel and

sand. The net benefit that could be obtained through the sale of deposited material (while

assuming 50 percent of the gross income be spent on the excavation of material, processing

them, and maintenance) is estimated to be around 103.3 million.

8. The economic and financial analysis considering the estimated cost for maintenance,

rehabilitation and strengthening of the dam and the potential revenue generation through

the sale of deposited material indicators reveals very good economic and financial

indicators (Project IRR = 16%; Project B/C Ratio = 1.35; Simple Payback= 4.94 Years; Return

on Investment = 23%; Investors B/C Ratio = 2.80). These economic and financial indicators

clearly imply that investment of bank could also be attracted and quick return on equity

investment is also possible.

9. If the Pokhara Metropolitan City and the province government jointly invest in the

maintenance, rehabilitation, strengthening of dams and management of deposited

material, significant resources required for the conservation and development of the Fewa

Lake could be generated from it. As a second alternative, the private sector can be

entrusted with the maintenance and rehabilitation, and strengthening of the dam as well as

the management of deposited material.

10. The proposed mitigation measures, cost and profit from this study are based on site

observation without any detail topographic survey and, available primary and secondary

reports and data. Therefore, before the construction, it should follow the detailed survey,

layout of proposed structures on the field, and updating of construction cost, income and

profit. Similarly, the quality construction work should be monitored closely through regular

supervision of experts and beneficiary stakeholders during the construction period.

11. The siltation dams help to retain gravel-sand categories sediment while still allowing silt

and mud to flow into Fewa Lake through Harpan Khola. It is therefore strongly

recommended to assess the volume of silt and mud reaching the lake in detail and pay

attention to its long-term management.


10

Table of Contents

कामयकायी सायाॊश ............................................................................................................................ 3

Executive Summary ...................................................................................................................... 7

List of Tables .............................................................................................................................. 12

List of Figures ............................................................................................................................. 13

Chapter 1: Introduction .............................................................................................................. 15

1.1 Background ........................................................................................................................... 15

1.2 Objectives and Scope of Work .............................................................................................. 16

1.3 Methodology ......................................................................................................................... 17

1.4 Structure of the Report ......................................................................................................... 18

Chapter 2: Status Review and Mitigation Measures .................................................................... 19

2.1 Introduction .......................................................................................................................... 19

2.2 Geology of Fewa Lake Watershed ........................................................................................ 20

2.3 Mass movements and erosions ............................................................................................ 21

2.4 River Geomorphology ........................................................................................................... 22

Braided Channel ............................................................................................................ 22 2.4.1

Meandering Channels ................................................................................................... 23 2.4.2

Mouth/Delta formation ................................................................................................ 23 2.4.3

2.5 Khahare Khola Siltation Dam ................................................................................................ 24

Salient Feature .............................................................................................................. 24 2.5.1

Problem and Mitigation Measures ............................................................................... 26 2.5.2

Properties of Deposited Material ................................................................................. 32 2.5.3

2.6 Harpan Khola Siltation Dam .................................................................................................. 33

Salient Features ............................................................................................................. 33 2.6.1

Problem and Mitigation Measures ............................................................................... 34 2.6.2



11

2.7 Lauruk Khola Siltation Dam ................................................................................................... 42


Problems and Mitigation Measures .............................................................................. 42 2.7.2


2.8 Betini Siltation Dam .............................................................................................................. 46


Problems and Mitigation Measures .............................................................................. 46 2.8.2


Chapter 3: Typical Design and Estimate of Risk Mitigation Facilities ............................................. 51

3.1 Design Parameters ................................................................................................................ 51

3.2 Retrofitting Option for Khahare Siltation Dam ..................................................................... 51

3.3 Retrofitting Option for Harpan Khola Dam ........................................................................... 55

3.4 Lauruk Dam ........................................................................................................................... 57

3.5 Betini Dam ............................................................................................................................. 59

3.6 Summary Cost for Retrofitting Option .................................................................................. 61

Chapter 4: Management, Operation and Maintenance Plan ........................................................ 63

4.1 Revenue potential from construction material .................................................................... 63

4.2 Sample financial analysis ...................................................................................................... 64

4.3 Finding and Remarks ............................................................................................................. 67

Chapter 5: Conclusion and Recommendations ............................................................................ 69

5.1 Conclusion ............................................................................................................................. 69

5.2 Recommendations ................................................................................................................ 70

Annexes..................................................................................................................................... 71


12

List of Tables

Table 2-1: Catchment Area, 100 Years Flood, Siltation dam width, specific discharge and sediment

load at the siltation dam. ..................................................................................................................... 19

Table 2-2: Technical problem with the planning, design, construction and operation of Khahare

Siltation Dam (Khahare dam). ............................................................................................................. 26

Table 2-3: Lithology and usefulness of deposited material in Khahare siltation dam....................... 32

Table 2-4: Technical concerns on planning, design, construction, operational issues and mitigation

measures (Harpan dam) ....................................................................................................................... 34

Table 2-5: Lithology and usefulness of deposited material in Harpan siltation dam. ....................... 41


measures (Lauruk dam)........................................................................................................................ 43

Table 2-7: Lithology and usefulness of deposited material in Lauruk siltation dam. ........................ 45


measures (Betini dam). ........................................................................................................................ 46

Table 2-9: Lithology and usefulness of deposited material in Lauruk siltation dam. ........................ 49

Table 3-1: Technical design parameters for the assessment of dam planning and design ............... 51

Table 3-2: Different components of retrofitting option for Khahare siltation dam. ......................... 53

Table 3-3: Different components of retrofitting option for Khahare siltation dam. ......................... 56

Table 3-4: Different components of retrofitting option for Lauruk siltation dam. ............................ 58

Table 3-5: Different components of retrofitting option for Betini siltation dam. ............................. 60

Table 3-6: Summary cost estimate of the suggested retrofitting option for four siltation dam. ...... 61

Table 4-1: Sediment load in Khahare, Harpan, Lauruk and Betini (GoN/UNDP report based data). 63

Table 4-2: Deposited approximate volume of sediment load in 2020 monsoon season. ................. 63

Table 4-3: Revenue generation from deposited sediment during 2020 monsoon season. ............... 64

Table 4-4: Financial parameter for analysis ........................................................................................ 65

Table 4-5: Projected Cash Flow Analysis for Economic model ........................................................... 65

Table 4-6: Investor CASH FLOWS Statement for Financial Model ...................................................... 66

Table 4-7: Financial analysis results..................................................................................................... 67


13

List of Figures

Figure 2-1: Location of 4 dams U/S of Fewa Lake in its catchments for sedimentation control. ...... 19

Figure 2-2: Engineering geological map of Pokhara Area. .................................................................. 20

Figure 2-3: Active landslides distributions Khahare Khola sub-watershed ........................................ 21

Figure 2-4: Brained channels at the lower reaches ............................................................................. 22

Figure 2-5: Meandering channels of the Harpan khola ...................................................................... 23

Figure 2-6: Mouth or Delta of the Fewa lake ...................................................................................... 24

Figure 2-7: Location of Khahare Dam and river training works. ......................................................... 25

Figure 2-8: A typical section of existing Khahare siltation dam. ........................................................ 25

Figure 2-9: Khahare Siltation Dam on August 2020 ............................................................................ 30

Figure 2-10: Khahare Siltation Dam on September 18, 2020.............................................................. 30

Figure 2-11: Breech of right embankment after filling the dam and changed river course .............. 31

Figure 2-12: The most suitable location for construction of siltation dam (1 km upstream of present

dam location). ...................................................................................................................................... 31

Figure 2-13: A typical section of existing Harpan siltation dam. ........................................................ 33

Figure 2-14: Harpan Dam on Aug 2020 ................................................................................................ 37

Figure 2-15: Harpan dam having proximity to good access road at pre-inspection visit Aug 2020 .. 37

Figure 2-16: Overtopping from left side flood wall near dam due to skewed planform. .................. 38

Figure 2-17: Damaging pattern on the D/S glacis and even some part is taken away at middle...... 38

Figure 2-18: Bank cutting beyond left flood wall by overtopping the wall ........................................ 39

Figure 2-19: Site visit team for assessment of siltation dams on Harpan Dam left bank .................. 39

Figure 2-20: Scouring of toe of dam. ................................................................................................... 40

Figure 2-21: Scouring of toe of flood wall and channel degradation downstream. .......................... 40

Figure 2-22: Lauruk Khola Siltation dam which relatively in better condition as compared to the

Khahare and Harpan dam. ................................................................................................................... 44

Figure 2-23: Catchment and location of Lauruk dam. ......................................................................... 44

Figure 2-24: Relatively better condition of the dam but the river gradient is still high .................... 47

Figure 2-25: The chance of overtopping from just u/s of the dam (View from Upstream) ............... 48

Figure 2-26: Fully deposited dam and overtopping from left bank (View from D/S) ........................ 48

Figure 2-27: U/s reach of the dam showing flood control gabion walls on both bank and road,

houses at the left bank. ....................................................................................................................... 49


14

Figure 3-1: Khahare Dam layout and its components/Facilities ......................................................... 52

Figure 3-2: Typical section of Khahare dam (existing situation-top) and (suggested retrofitting

option-bottom) ..................................................................................................................................... 53

Figure 3-3: Under sluice plan and section proposed at the dam edge for water level control. ........ 54

Figure 3-4: Harpan Dam layout and its components/Facilities (retrofitting option) ......................... 55

Figure 3-5: Typical section of Harpan dam (suggested retrofitting option). ...................................... 56

Figure 3-6: Lauruk Dam layout and its components/Facilities (retrofitting option) .......................... 57

Figure 3-7: Typical section of Lauruk dam (suggested retrofitting option). ....................................... 58

Figure 3-8: Betini Dam layout and its components/Facilities (retrofitting option) ........................... 59

Figure 3-9: Typical section of Betini dam (suggested retrofitting option). ........................................ 60


15

1. Chapter 1: Introduction

1.1 Background

The Fewa Lake, second largest Lake of Nepal, is located in the south-western region of Pokhara

Metropolitan City in Gandaki province. The lake has been declared as Ramsar site -- as its wetlands

help in water purification, water storage, processing of carbon and other nutrients, support

hundreds of plants and animals, and provide ecosystem services as a whole. It has contributed in

irrigation, hydropower and tourism development. The dam constructed in the south eastern part of

the lake in 2029 BS has helped to irrigate 320 hectares of land and to produce 500 kilowatts of

electricity. The lake has also helped to establish Pokhara as one of the most vibrant tourism cities of

Nepal by attracting thousands of domestic and international tourists and, thereby, creating income

and employment opportunities.

While the Fewa Lake has significantly contributed to the local economy, some management and

conservation issues has also arisen since the last few decades. Direct feeding of municipal sewerage

and storm water into the lake has degraded the lake water quality. The soil erosion and landslides

caused by the haphazard construction of roads together with the imprudent land use in its

catchment has accelerated lake sedimentation and loss of lake water surface area. A study

conducted by Nepal Government in collaboration with the Finnish International Development

Agency (FINNIDA) in 1992 has estimated 142,000 metric tons of sediment deposition every year. The

major tributaries of the Fewa Lake are Harphan Khola, Khahare Khola, Betini Khola and Lauruk Khola.

The Khahare Khola is the main tributary carrying highest sediment which is then followed by Harpan,

Lauruk, Betini. The Harpan Khola reaches just after the Harpan-Betini confluence has a typical

meandering morphology (cut off generation and shifting of its channel regularly). In this reach, the

Harpan Khola flows in single meander channel and piles sediment at the mouth of the lake delta. The

cut off generation process in meandering channel and the deposition process at the delta play a

major role in shifting the Harpan Khola and formation of the dry abandoned aggraded area near the

lake delta. In the past, some of the abounded channel area has been encroached and registered by

the public leading to significant loss of the Fewa Lake area. Noticeably, the 22,000 ropani of the lake

area in 2013 BS has gradually shrunk to 8,256 ropani in 2064 BS. It has been projected that if the

trend of lake sedimentation and land encroachment continues, the lake may be completely

disappeared in the next 100 years (Study Report on investigation of encroached land on Fewa Lake,

2069 BS).


16

In the fiscal year 2076/077, the Pokhara Metropolitan City and the Province government jointly

constructed four stone masonry siltation dams (Khahare Khola, Harpan Khola, Lauruk Khola, and

Bitini Khola) to retain sediment and help reduction of lake sedimentation. During the 2077 monsoon,

however, the downstream slope of the stone masonry wall on Khahare and Harpan Khola were

severely damaged, raising question about the stability of the dam and its long-term functioning. The

Minister for Industry, Tourism, Forest and Environment and the Mayor of the Pokhara Metropolitan

City, therefore, jointly formed a study team composed of six members in 2077/05/21 BS to identify

problems and suggest the mitigation measures to reduce the associated risks. The composition of

the study team was as follows:

Composition of Study Team

Coordinator Dr. Bishnu Raj Baral, Member, Policy and Planning Commission, Gandaki Province

Member Dr. Anup Gurung, Chief Executive Officer, Lake Conservation and Development Authority, Gandaki Province

Member Er. Sharada Mohan Kafle, Chief Engineer, Pokhara Metropolitan City Office

Member

(Expert)

Er. Mani Raj Dahal, MSc. Hydraulics & River Basin Development (Expert River Hydraulics/Hydropower Components Design); Chief Engineer, Clean Energy Consultants, Kathmandu

Member

(Expert)

Mr. Ghan Bdr. Shrestha, MSc. Eng. Geology (Expert Geologist/Watershed Sediment); Geologist, Clean Energy Consultants, Kathmandu

Member Secretary Mr. Krishna Ghimire Chief, Soil Conservation and Watershed Management Office, Tanahu, Gandaki Province

1.2 Objectives and Scope of Work

The main objective of the study was to identify problems of siltation dams and suggest alternative

solutions in the prevention of further damages. The specific objectives of the study were:

1. To review design and identify technical and managerial problems associated with the

siltation dams.

2. To suggest alternative solution to minimize further damaging of siltation dams and suggest

effective operation strategies.

3. To carry preliminary design and prepare drawing and cost estimate for the suggested

mitigation measures.


17

In order to achieve the main and specific objectives, the scopes of work for the study were as follow:

Review previous study reports and construction details of the siltation dam.

Carry field visit of four siltation dams and identify their status.

Identify technical problems in design and construction of dams.

Find the management problems associated with the siltation dam.

Suggest mitigation measures and classify short-term, mid-term and long-term plan to reduce

lake sedimentation.

Design, prepare drawing, and estimate cost for the mitigation measures.

Prepare a report and present the main content of the report to related stakeholders.

Prepare the final report incorporating suggestions from stakeholders.

1.3 Methodology

The following works were carried out to produce the study report:

The problems in the siltation dam and methodology for this study were discussed among the

team members.

Historical studies and available documents were reviewed.

Site visit of four siltation dam was carried out by the study team together with the minister

for Industry, Tourism, Forest and Environment.

Preliminary findings of field observation were presented to stakeholders (Chief Minister,

Minister, Mayor and Government Officials).

The root cause of the problem was identified and previous design was reviewed.

Technical problems associated to design of the siltation dams and their operations were

identified.

Necessary repair and corrective measures for effective and safe operation of siltation dam

were identified.

Alternative solutions to manage sediment trapped by the dams were discussed.

Hydraulic and structural design of the suggested alternative solution was carried out.

Typical drawing was prepared for the suggested design.

Quantity calculation and cost estimate was carried out based on the current district rate.

Economic and financial analysis of the sediment management project was carried out by

approximating market value of sediment and the cost of the suggested retrofitting

measures.


18

Report writing was carried by incorporating all above works to produce the final report.

1.4 Structure of the Report

The content of the study report has been structured in six chapters as follow:

Chapter 1: Introduction

Chapter 2: Status Review and Mitigation Measures

Chapter 3: Typical Design and Estimate of Risk Mitigation Facilities

Chapter 4: Management, Operation and Maintenance Plan

Chapter 5: Conclusion and Recommendations


19

2. Chapter 2: Status Review and Mitigation Measures

2.1 Introduction

The major tributaries of feeding discharge and sediment into the Fewa Lake are Harphan Khola,

Khahare Khola, Betini Khola and Lauruk Khola. The catchment areas at Harpan, Khahare, Betini and

Lauruk siltation dam are 35.7 sq km, 25.3 sq km, 7.1 sq km, and 4.5 sq km, respectively (Figure 2-1).

Figure 2-1: Location of 4 dams U/S of Fewa Lake in its catchments for sedimentation control.

The 100 years flood at the Khahare, Harphan, Lauruk and Betini dam have been estimated at 66

m3/s, 87 m3/s, 17 m3/s and 24 m3/s, respectively. The Khahare Khola brings highest volume of

sediment which is then followed by Harpan Khola, Betini and Lauruk (Table 2-1).

Table 2-1: Catchment Area, 100 Years Flood, Siltation dam width, specific discharge and sediment

load at the siltation dam.

SN Dam

Catchment Area

(Sq. Km)

Flood

Q100 yr

(m3/s)

Dam

Width

(m)

Discharge per meter

(m2/s)

Sediment Estimated *

(Metric Ton)

1 Khahare 25.3 66 100 0.66 238000

2 Harpan 35.7 87 90 0.97 143000

3 Lauruk 4.5 17 40 0.43 Small

4 Betini 7.1 24 40 0.60 Negligible

Note: * the sediment data presented here are based on rough approximation. No detail analysis has been carried out.


20

2.2 Geology of Fewa Lake Watershed

The Pokhara has Quaternary deposits around the valley (Yamanaka, et. al., 1982). The area

comprises of Kuncha Formation and Fogfog Quartzite of the Lesser Himalayan Rock Sequences and

over lined by the Quaternary deposits of Residual Soils, Colluvial Soils, and Alluvial Fan Deposits

(Engineering and Environmental Geological map of Pokhara, scale 1:50 000, DMG, GON, 1998).

Figure 2-2: Engineering geological map of Pokhara Area.

The followings are formation around Pokhara Valley and at the catchment of Fewa Lake

Residual soils (srs): The residual soils (Loamy to sandy gravel) are distributed on the hill slopes of

Fewa Lake watershed. The thickness of the soils varies between 1 to 5 m deep on average.

Colluvial soils (sco): The colluvial inhomogeneous deposits (silt and sand with boulders on top) are

found at the lower reaches of the watersheds at foot slopes. The thickness of the soil is greater than

1 m.


21

Nonactive (nf) alluvial fan: These types of the deposits are poorly sorted gravels, sandy, gravel, sand

and silt, fine material towards margin and the thickness generally increases towards centre of the

fan.

Fogfog Quartzite: It consists of fine-grained, massive, quartzite, but bedded in upper part,

intercalated of green phyllite and basic rocks at places. Mostly the sub-watershed of the Harpan

Khola covered with white, massive, bedded, quartzite, as results the 90% of boulders observed at

Ghatichina area are Quartzites.

Kuncha Formation: The formations composed of gritty phyllites, and quartzite, interbed and are very

soft rock mass as well as moderately to deeply weathered and thick colluvium deposits. Mostly the

sub-watersheds of the Khahare, Betini and Lauruk cover with sort rock mass and forming deep soil

profiles.

2.3 Mass movements and erosions

The slope of the Fewa Lake watershed is unstable. There are numbers of old slides and intensive,

gully erosions problems. Some old landsides are still active and some are dormant types. Few slides

are very large in size. The mechanisms of the failures are translations, spreads/creeps, complex, and

channelized flow. The wetness of the failed material is moist to very wet and the rate of the

movements is slow to rapid.

Figure 2-3: Active landslides distributions Khahare Khola sub-watershed


22

There are 32 active landslides in Khahare sub-watershed. The largest active landslide in Khahare sub-

watershed is about 0.12 km2 areas. These slope instabilities, landslides, gully erosions, and channel

flows contributes to production of huge amount of the sediments.

2.4 River Geomorphology

The upper reaches of the watersheds have dendric and sub parallel drainage patterns. The stream

channel continuously shape and reform their channels through erosion of the channel boundary:

bed and banks and reworking of sediments.

Braided Channel 2.4.1

After the sloped hill, the Harpan Khola, Khahare, Betini and Lauruk enter into the gentle wider plain

where the river channels become braided (see at Ghatchhina, Bhadure, Bhidabari up to Pame area

for braided reach). The braided reach are capable of transporting sediment across wide range of

flows which leading to high rate of bed turnover and production of temporally diverse mosaic of bars

and channels. The braided reach has ready source of easily available aggregate that is economically

prized.

Figure 2-4: Brained channels at the lower reaches


23

Meandering Channels 2.4.2

After the braided reach, the Harpan Khola morphology resembles meandering morphology (see the

reach downstream of Pame area). Meandering streams develop in relatively flat areas, such as a

floodplain, and where sediment consists primarily of fine sands, silts, and clay.

Figure 2-5: Meandering channels of the Harpan khola

Mouth/Delta formation 2.4.3

At the lake mouth/delta, the Harpan Khola Plunge into the lake. Fine sand and silts are deposited at

the mouth whereas the suspended sediments are deposited into the lake.


24

Figure 2-6: Mouth or Delta of the Fewa lake

2.5 Khahare Khola Siltation Dam

Salient Feature 2.5.1

The Khahare khola reach near the dam area has 2 % longitudinal slope. The width of Khahare Khola

varies from 80 m to 316 m. The overall morphology of the reach resembles with the braided

morphology (Multichannel River). The salient features of the dam and flood protection structure on

the Khahare Khola are as follows:

• Planform: U shape

• Flow length : 100 m

• Left flood wall length : 100 m

• Right wing wall length: 100 m

• Top width of dam : 0.5 m

• Bottom width of dam: 7 m

• Height of dam : 4-4.5 m

• Downstream gabion apron width : 10 m (to protect d/s erosion)


25

• Upstream right embankment: 300 m (starting the dam section to upstream)

The location of Khahare siltation dam and other structure has been shown in Figure 2-7.

Figure 2-7: Location of Khahare Dam and river training works.

A typical longitudinal section of the siltation dam constructed on the Khahare Khola has been shown

in Figure 2-8. The dam composed of a simple stone masonry trapezoidal wall together with a gabion

launching apron at the downstream. The height of the dam at the right corner is 4 m which gradually

increases to 4.5 m at the left corner.

Figure 2-8: A typical section of existing Khahare siltation dam.

Siltation Dam

Right flood wall

Right flood Wall

Left flood Wall

Stone Masonry Wall

Gabion Launching Apron

u/s

d/s


26

Problem and Mitigation Measures 2.5.2

The problems associated to the Khahare siltation dam were overtopping of right embankment and

river course change, scouring of dam toe, scouring of downstream slope of the dam, complete filling

of the dam/no sediment mining. Overtopping of the right embankment can be attributed to the

inappropriate location of the siltation dam, unfavorable geological and topographic condition and

excessive sediment retention/river bed aggradation. Scouring of dam toe can be attributed to

inappropriate design of dam structure without the provision of cut off and energy dissipation

structure that are requisite in dam construction (cf. most of the dam constructed in run river

hydropower projects consider low height (1-2 m) weir structure with provision of cut off and energy

dissipation structure). The scouring of the downstream slope of the dam can be attributed to the

excessive slope of the dam and uneven dam height (4 m at the right side and 4.5 m at the left side).

Due to the uneven dam height, most of flood discharges were concentrated to the right corner of

the dam. The high slope of the downstream face, without having hard stone/concrete lining, could

not resist the force of high current leading to stability problems and erosion. The dam was filled by

2-3 floods of the season but sediment mining was not carried out which led to excessive bed level

aggradation and overtopping.

The issues wise analysis of problems and their mitigation measures has been summarized in the

Table 2-2. The pictures taken during different site visit have been shown in the Figure 2-9, 2-10,2-11

and 2-12 to provide insights about the site condition.

Table 2-2: Technical problem with the planning, design, construction and operation of Khahare Siltation Dam (Khahare dam).

Technical

Concern

Provided Feature/

Present Situation

Operational /Safety

Issues

Precautions/Mitigation

Measures

1. Location

of

siltation

dam

The siltation dam was

constructed at the

left side of the flood

plain restricting the

river into narrow

width.

The flood level

analysis considering

the construction of

the siltation dam and

other river training

embankment were

There is possibility of

river course change

as the river can

overflow and scour

right embankment

due to rapid bed

aggradation

upstream.

The geological and

topographic

condition around the

dam is such that the

Construct higher and

stronger embankment

on right bank of the

dam with cutoff

If possible relocate the

dam on better location

i.e 1 km upstream of

current location having

rocky right bank and

favourable geological

and topographic

condition


27

Technical

Concern

Provided Feature/

Present Situation

Operational /Safety

Issues


Measures

not carried out. flood has tendency to

directly hit the right

embankment

2. Retention

of

sediment

without

removal

plan

No road access for

gravel mining and

transporting vehicle

into the dam

Upstream deposit

area.

No provision of

emergency flood

regulating gates.

No provision for

draining water from

dam which may be

required while

mining the deposit.

No plan for

monitoring of flood,

sediment and bed

level.

Without the event

based sediment

removal plan the

siltation dam could

not function

properly.

If sediment is not

removed regularly,

there is always

tendency of sudden

deposition,

overtopping and

flooding the

surrounding lands.

Construct a ramp to

U/S of the dam to

facilitate mining from

inside and transport.

Construct a sluice gate

at the dam edge to

regulate flood in the

case of emergency and

to drain the water

while mining gravel.

3. Retention

volume

There are numbers of

active slides in the

catchment and can

deliver more than

expected sediment

episodically.

The dam could be

filled even by a flood

event leading to

overflow from the

embankment and

flooding in the

surrounding land.

Construct series of

check dams just

upstream of the dam

to retain most of the

course gravel and use

the dam for retaining

finer material.

4. Design of

main dam

The dam consists of

stone masonry wall

having high slope

(1.2:1) at d/s as well

as u/s glacis.

The dam height is

uneven (4 m at the

right side and 4.5

meter at the left

side).

Uneven dam height

hinders uniform

distribution of flow

over weir

concentrating

discharge on the

right corner of the

dam.

High downstream

slope of the dam

produces high

current on the wall

Flatten D/S slope of

the dam as much as

possible and install

energy dissipating

structure.


28

Technical

Concern

Provided Feature/

Present Situation

Operational /Safety

Issues


Measures

which the stone

masonry could not

resist.

Downstream slope

erosion and tow

erosion not avoidable

at the current

situation due to high

current.

5. Dam body

material

selection

and safety

The dam was

constructed using

stone masonry and

plum concrete

Erosion of

downstream face of

the dam is

unavoidable at the

current situation as

the stone masonry

wall is not enough to

resist the eroding

force of water

flowing through the

high slope

Concrete jacketing

could improve stability

and hard and dressed

stone Lining could help

controlling of surface

erosion

6. Absence

of U/S

and D/S

Cutoff

The 4-4.5 m height

stone masonry dam

has been built

without any cut-offs

Due to the absence

cut-offs there is

possibility of piping

and increase seepage

from base

Extend the concrete

jacket deeper to U/S

and D/S cutoff.

7. Energy

dissipatio

n

structure

missing at

the d/s

Most of the gabion

blocks laid at the

base were damaged

There was no energy

dissipation structure

at the d/s

The gabion laid at the

D/S bottom is not

competent to resist

scouring and to

dissipate energy

Construct a stilling

basin with depressed

flood and plunge in the

pool for energy

dissipation for dam

overflow discharge.

8. Flood wall

(embank

ment

wall) on

right bank

Earthen, stone

masonry and gabion

structure is reported

at the right

embankment

The coverage length

and type of structure

is not suitable for

protection

Construct

concrete/stone

masonry wall having

cut off at the bottom

considering 100 years

flood and 2 m free

board.


29

Technical

Concern

Provided Feature/

Present Situation

Operational /Safety

Issues


Measures

9. Flood

Regulatio

n

There is no any

provision of

emergency sluice

gate for the case of

emergency flood

regulation and

draining of water

while mining

There will be

problem on mining

material having high

water level for

control during

removal of material

One side can have

sluice gate which will

reduce water level u/s

making the channel

water level down so

that the mining shall

be possible; the sluice

gate could also be

used to regulate

emergency flood.

10. Additional

boulder/

debris

retention

check

dam

No any check dams

just upstream of the

dam that could have

retained sediment

The present dam

area may not be

sufficient enough to

trap the sediment

load

Construction of series

of temporary check

dams just upstream of

the dam can help

retaining sediment

load before entering

into the dam (course

gravel could be

retained by the check

dam and the main dam

could be used for fine-

course gravel

trapping).


30

Figure 2-9: Khahare Siltation Dam on August 2020

Figure 2-10: Khahare Siltation Dam on September 18, 2020

Concentration of discharge on the right corner of the dam due to uneven construction of the dam height

Overtopping location

Damaged downstream slope of the siltation dam

(middle of dam to right corner)


31

Figure 2-11: Breech of right embankment after filling the dam and changed river course

Figure 2-12: The most suitable location for construction of siltation dam (1 km upstream of present

dam location).

Upstream of the dam completely filled with sediment

Changed River Course


32

Properties of Deposited Material 2.5.3

The field observations suggest that the material deposited in Khahare siltation dam are very good to

use as constructions aggregates. The lithology and usefulness of deposited material in Khahare

siltation dam has been summarized in the Table 2-3.

Table 2-3: Lithology and usefulness of deposited material in Khahare siltation dam

Locations/sites Lithologies Usefulness

Khahare Khola 60 to 70% of gravels, pebbles, cobbles are glassy, smooth, and, rough, flat and platy, composed of Phyllites, Schists, and Meta-Sandstone

30 to 40% of mostly gravels and pebble and cobbles are of equidimensional, elongate, glassy, smooth, and rough, subangular to sub rounded, white, light green, F-C-G, are composed of Quartzite

60 to 70% of sands and gravels

20 to 30% of clay to silt

<10% of boulders

30% to 40% volume of the materials are Good to Excellent for crashing stones, and useful for constructions aggregates, and remaining are useful for filling only


33

2.6 Harpan Khola Siltation Dam

Salient Features 2.6.1

The Harpan Khola reach near the dam area has 2.3 % longitudinal slope. The width of Harpan Khola

varies from 35 m to 110 m. The overall morphology of the reach resembles with the single thread

channel morphology having point bar. The salient features of the dam and flood protection structure

on the Harpan Khola are as follows:

• Planform: U shape

• Flow length: 100 m

• Left wing wall length: 100 m

• Right wing wall length: 100 m

• Top width of dam: 0.5 m

• Bottom width of dam: 9 m

• Height of dam: 4 m

• Downstream gabion apron width: 10 m (to protect d/s erosion)

• Left embankment: 100 m

A typical longitudinal section of the siltation dam constructed on the Harpan Khola has been shown

in Figure 2-13. The dam composed of a simple stone masonry trapezoidal wall together with a

gabion launching apron at the downstream. The height of the dam is 4 m.

Figure 2-13: A typical section of existing Harpan siltation dam.


34

Problem and Mitigation Measures 2.6.2

The major problems associated to the Harpan siltation dam were overtopping of the left flood wall,

scouring of dam toe, scouring of downstream slope of the dam, scouring at the bottom of flood wall

and no sediment removal. Overtopping at the left embankment can be attributed to the curved

nature of the flood wall near the dam axis/wrong orientation of flood wall in comparison to the dam

axis. Scouring of dam toe can be attributed to inappropriate design of dam structure without the

provision of cut off and energy dissipation structure that are requisite in dam construction (cf. most

of the dam constructed in run river hydropower projects consider low height (1-2 m) weir structure

with provision of cut off and energy dissipation structure). The scouring of the downstream slope of

the dam can be attributed to the excessive slope of the dam. The high slope of the downstream face,

without having hard stone/concrete lining, could not resist the force of high current leading to

stability problems and erosion. The dam was completely filled during one monsoon but sediment

mining was not carried out which led to excessive bed level aggradation and overtopping from the

left flood wall.

The issues wise analysis of problems and their mitigation measures has been summarized in the

Table 2-4. The pictures taken during different site visit have been shown in the Figure 2-14 to 2-21 to

provide insights about the site condition.

Table 2-4: Technical concerns on planning, design, construction, operational issues and mitigation measures (Harpan dam)

Technical

Concern

Provided Feature/

Present Situation

Operational/Safety Issues Precautions/Mitigation

Measures

1. Plan

shape of

the flood

wall

The flood wall has not

been positioned at 90-

degree angle with dam

axis especially at the

end of left bank, wall is

rotated.

The height of the left

flood wall is not enough

to control high flood

discharge.

The curved wing wall

(oblique with the dam

axis) have tendency to

push water to left

corner and erode.

River is overtopping

the embankment wall

due to less freeboard

problem and curved

geometry of the wall.

Needs to remove

ome part and need

to make Straight for

the curve part of

the left flood wall

and increase height

of the left flood wall

+1m considering

100 years flood

along with enough

free board.

Or regularly

monitor flood level

and maintain

minimum 1 meter


35

Technical

Concern

Provided Feature/

Present Situation


Measures

free board.

2. Retention

of

sediment

without

removal

plan

No access of gravel

mining and transporting

vehicle into the dam.

No provision of

emergency flood

regulating gates.

No provision for

draining water from

dam which may be

required while mining

the gravel.

No plan for monitoring

of flood, sediment and

bed level.

Without the event-

based or continuous

sediment removal

plan the siltation dam

could not function

properly.

If sediment is not

removed regularly,

there is always

tendency of sudden

deposition,

overtopping and

flooding the

surrounding lands.

Construct a ramp to

U/S of the dam to

facilitate mining

and transport.

Construct a sluice

gate at the dam to

regulate flood in

the case of

emergency and to

drain the water

while mining

deposited material.

3. Design of

main

dam

The dam consists of

stone masonry wall

having high slope (1.2:1)

at d/s as well as u/s

glacis.

High downstream

slope of the dam

produces high current

on the wall which the

stone masonry could

not resist.

Downstream slope

erosion and tow

erosion not avoidable

at the current

situation due to high

current.

Flatten D/S slope of

the dam.

4. Flood

Wall

The bottom of the left

flood wall just

downstream of the dam

axis has experienced

scouring.

Flood has overtopped at

left flood wall

Due to absence of cut

off at the bottom of

flood wall there is

tendency of failure of

wall (left and right

wall downstream of

the dam) at any time.

At the present

situation, there is

possibility of

overtopping of left

flood wall.

Correct alignment

and Provide cut off

at the bottom of

flood wall especially

at the flood wall d/s

of the dam

Heighten the flood

wall or maintain at

least 1 meter of

free board.


36

Technical

Concern

Provided Feature/

Present Situation


Measures

5. Dam

body

material

selection

and

safety

The dam was

constructed using stone

masonry

Erosion of

downstream face of

the dam is

unavoidable at the

current situation as

the stone masonry

wall is not enough to

resist the eroding

force of water flowing

through the high

provided slope

Concrete jacketing

could improve

stability and hard

stone pitching could

help controlling its

surface erosion

6. Absence

of U/S

and D/S

Cutoff

The 4 m height stone

masonry dam has been

built without any cut-

offs at the bottom

Due to the absence of

cut-offs there is

possibility of piping

and seepage from the

base

Extend the concrete

jacket deeper to

U/S and D/S cut-off.

7. Energy

dissipatio

n

structure

missing

at the d/s

There was no energy

dissipation structure at

the d/s

Due to lack of energy

dissipating structure

and absence of

sediment flow, the

channel downstream of

the dam seems to be

degrading.

The gabion laid at the

d/s floor is not

competent to resist

scouring and to

dissipate energy

Construct a stilling

basin with

depressed flood

and plunge in the

pool for energy

dissipation.

8. Flood

Regulatio

n

There is no any

provision of emergency

gate for the case of

emergency flood

regulation and draining

of water while mining

There will be problem

on mining material

and water level

control during

material removal time

One side can have

sluice gate which

will reduce water

level u/s making the

channel water level

down so that the

mining shall be

possible; the sluice

gate could also be

used to regulate

emergency flood.


37

Figure 2-14: Harpan Dam on Aug 2020

Figure 2-15: Harpan dam having proximity to good access road at pre-inspection visit Aug 2020


38

Figure 2-16: Overtopping from left side flood wall near dam due to skewed planform.

Figure 2-17: Damaging pattern on the D/S glacis and even some part is taken away at middle


39

Figure 2-18: Bank cutting beyond left flood wall by overtopping the wall

Figure 2-19: Site visit team for assessment of siltation dams on Harpan Dam left bank


40

Figure 2-20: Scouring of toe of dam.

Figure 2-21: Scouring of toe of flood wall and channel degradation downstream.


41


The field observations suggest that the material deposited in Harpan siltation dam are excellent to

use as construction material. The lithology and usefulness of deposited material in Harpan siltation

dam has been summarized in the Table 2-5.

Table 2-5: Lithology and usefulness of deposited material in Harpan siltation dam.


Harpan Khola 70 to 80% of mostly boulders and gravels, pebbles and cobbles of equidimensional, glassy, smooth, and rough, sub-angular to sub-rounded, White, Light Green, F-C-G, are composed of Quartzite

20 to 30% of gravels, pebbles and cobbles are glassy, smooth, and, rough, flat and platy, composed of Phyllites, Schists, Meta-Sandstone

Boulder dominates with and cobble, (>70%) gravel and very few portions of silt and sand

80% to 90% volume of the materials are Good to Excellent for crashing stones, and useful for constructions aggregates


42

2.7 Lauruk Khola Siltation Dam


The Lauruk khola reach near the dam area has 7.7 % longitudinal slope. The width of Lauruk Khola


morphology. The salient features of the dam and flood protection structure on the Lauruk Khola are

as follows:

• Shape of Dam: U shaped

• Flow Length : 40 m, Total Height: 3 m ie 0.5m Bottom, Transition : 2m, Top : 0.5m

• Left wing length :66m

• Right wing Length: 66m

• Top width :0.5m

• Bottom Width: 6.7m on Flow Path, Left and Right wing width : 7m

Low discharge per meter dam length

Upstream settling zone partially occupied

Relative clean water flow

Less siltation/less severe flood

No any scouring detected on lunching apron

Source of material from soft rock so less erosion on dam d/s face

Problems and Mitigation Measures 2.7.2

The Lauruk siltation dam has not serious problems as compared to Khahare and Harpan Dam. The

major problems and their mitigation measures in Lauruk dam have been summarized in Table 2-6.


43

The pictures taken during site visit have been shown in the Figure 2-22 and 2-23 to provide insights

about the site condition.


measures (Lauruk dam).

Particular Concern

Provided Feature/ Present Situation

Operational/Safety Issues

Precautions/ Mitigation Measures

1. Approaching River section is in High gradient or Slope

The River slope is high at the location of dam surrounding by Paddy Field and small height of flood wall

There can be overtopping also from the sides during high flash flood by excessive bed load

There is requirement increasing height of the left flood wall

2. D/S Face of erosion of Stone Masonry dam

The Dam is created by Stone Masonry wall with high down side slope

Face Erosion shall be high making dam in danger

Concrete jacketing with D/S cut-off be helpful

3. D/S Apron Stability

There is gabion Crates filled and paced at the toe of the dam for energy dissipation

The gabion life is very short, and can erode easily from toe of the dam having common material

There can be precast Concrete slab or additional slab at the base

4. Removal Facility

There is no access ramp to go vehicle U/S of dam for removing the deposit

There will be difficult to remove material trapped u/s of dam

There can be Access Road as Ramp down into the storage area

5. Further D/S Glacis of the dam erosion and slope stability

There is free flowing channel d/s with high gradient which can cause more erosion due to storage of sediment u/s of dam

The aggradation of immediate Downstream of the dam can cause dam instability

D/S can have another Check Dam or Cut off together with boulder lining


44

Figure 2-22: Lauruk Khola Siltation dam which relatively in better condition as compared to the

Khahare and Harpan dam.

Figure 2-23: Catchment and location of Lauruk dam.


45


The field observations suggest that the material deposited in Lauruk siltation dam are not good for

construction purpose. Instead, the material can be used for filling purpose. The lithology and

usefulness of deposited material in Khahare siltation dam has been summarized in the Table 2-7.

Table 2-7: Lithology and usefulness of deposited material in Lauruk siltation dam.


Lauruk Khola 80 to 90% of gravels, pebbles, cobbles are glassy, smooth, and, rough, flat and platy, composed of Phyllites and Schists

5 to 10% of mostly gravels and pebble and cobbles are of equidimensional, elongate, glassy, smooth, and rough, subangular to sub rounded, are composed of Quartzite

Bulk volume of the materials is very poor to poor quality, so that the materials are useful for filling only.


46

2.8 Betini Siltation Dam


The Betini khola reach near the dam area has 5.35 % longitudinal slope. The width of Betini Khola


morphology. The salient features of the dam and flood protection structure on the Betini Khola are

as follows:

• Shape of Dam: U shaped

• Flow Length : 40m, Total Height: 3m ie 0.5m Bottom, Transition : 2m, Top : 0.5m

• Left wing length :66m

• Right wing Length: 66m

• Top width :0.5m

• Bottom Width: 6.7m on Flow Path, Left and Right wing width : 7m

• Downstream gabion stilling basin width 6m: Height 0.6 m

• Low flood discharge per meter of dam as compared to others

• No any structural damage yet on apron

• Absence of any scouring as well as damage on apron

Problems and Mitigation Measures 2.8.2

The Betini siltation dam has not serious problems as compared to Khahare and Harpan Dam. The

major problems and their mitigation measures in Betini dam have been summarized in Table 2-8.

The pictures taken during site visit have been shown in Figure 2-24 to 2-27 to provide insights about

the site condition.

Table 2-8: Technical concerns on planning, design, construction, operational issues and mitigation measures (Betini dam).

Particular Concern


Operational/Safety Issues Precautions/Mitigation Measures

1. River is in high gradient

The river slope is high at the location of dam, one side is valley other side is housing area

There can be overtopping also from left side during high flash flood if bed load is not removed on regular basis

There is requirement of D/s Protection and also increasing height of the flood wall U/S of the dam on left side

2. D/S Face of dam erosion

The dam is created by stone masonry wall on high slope like

There can be d/s face damage similar to others in the coming

Planning of concrete jacketing and heightening of


47

Particular Concern


Operational/Safety Issues Precautions/Mitigation Measures

others dam

years the left flood wall considering the instantaneous flood is recommended

3. D/S Apron Stability

There is gabion boxes filled at the toe of the dam for energy dissipation p/ protection

There is tendency of removal of gabion boxes in few leading to downstream toe erosion and dam safety

There can be precast concrete slab or additional slab at the base

4. Removal Facility

There is no access into the U/S are of dam

There will be difficult to remove material trapped u/s taking vehicle down inside he deposited area

There can be Access Road and Ramp going down to the dam

5. D/S river slope stability

There is free flowing channel d/s and can cause more erosion due to storage of sediment u/s of dam

The aggradation of immediate Downstream of the dam can cause dam instability

D/S can have more cutoff followed by boulder lining

Figure 2-24: Relatively better condition of the dam but the river gradient is still high


48

Figure 2-25: The chance of overtopping from just u/s of the dam (View from Upstream)

Figure 2-26: Fully deposited dam and overtopping from left bank (View from D/S)


49

Figure 2-27: U/s reach of the dam showing flood control gabion walls on both bank and road, houses at the left bank.


The field observations suggest that the material deposited in Betini siltation dam are not good for

construction purpose. Instead, the material can be used for filling purpose. The lithology and

usefulness of deposited material in Betini siltation dam has been discussed in Table 2-9.

Table 2-9: Lithology and usefulness of deposited material in Lauruk siltation dam.


Betini Khola 70 to 80% of gravels, pebbles, cobbles, boulders are glassy, smooth, and, rough, flat and platy, composed of Phyllites and Schists

20% to 30% of mostly gravels and pebble and cobbles are of equidimensional, elongate, glassy, smooth, and rough, subangular to sub rounded, are composed of Quartzite

About 20 to 25% of the material can use for crasher stone after sieving, and remaining usable for the filling only


50


51

3. Chapter 3: Typical Design and Estimate of Risk

Mitigation Facilities

3.1 Design Parameters

Previous study considered simple regression technique to calculate design discharge over the dam

for design of the spillway length. In this study, the Hydest 2004 method was used to calculate 100-

year return period flood and instantaneous flood. As there is trend of concentrated rainfall and

severe flash floods, the instantaneous flood is recommended for design of the dam facilities. The

100-year return period flood, instantaneous flood, width of the dam, head over crest on the dam,

specific discharge per m length of dam have been listed in Table 3-1 for design reference.

Table 3-1: Technical design parameters for the assessment of dam planning and design

SN

Siltation Dam

Catchment

Area

(km2)

Q100yr

Return period flood (m3/s)

Instantaneous flood (m3/s)

Width

(m)

Head over crest (m)

Flood wall

(m)

Specific Discharge (m2/s)

Estimated Sediment Load (m3/yr)

1 Khahare 25.3 66 212 100 1.26 2.3 2.12 238000

2 Harpan 35.7 91 281 90 0.77 1.8 1.01 100000

3 Lauruk 4.5 17 61 40 0.43 1.4 0.43 42332

4 Betini 7.1 24 85 40 0.54 1.5 0.60 66791

3.2 Retrofitting Option for Khahare Siltation Dam

There will be concrete jacketing over the current stone masonry dam surface to retrofit main body

of the dam. Additionally, there will be stone lining panel, on both u/s and d/s slope supported by

holding keys. The concrete jacket will be extended to u/s and d/s cut off. There will be concrete

stilling basin downstream of the dam in order to dissipate spilling energy and to avoid downstream

bed degradation. The stilling basin will have stone lining (or Concrete Precast Blocks) for extra safety.

There is a challenge of construction of cutoff maintaining the profile extending the jacket and to

safeguard machinery while digging below foundation. Hence, excavation of cutoff need to be in

offset and support wall is needed inside part which can act as formwork. Also, for the purpose of

reducing water level during removing of deposited sediment out of dam, a small sluice gate will also

be provided. The gate can be used to lower water level during sediment removal time and

emergency flood. A ramp like structure should is also provided to provide access of


52

instrument/vehicle to the dam during maintenance and sediment mining time. The planform and a

typical longitudinal section of the retrofitting design have been shown in Figure 3-1, 3-2, and 3-3

respectively. The detail of the retrofitting option has been summarized in Table 3-2.

.

Figure 3-1: Khahare Dam layout and its components/Facilities


53

Figure 3-2: Typical section of Khahare dam (existing situation-top) and (suggested retrofitting

option-bottom)

Table 3-2: Different components of retrofitting option for Khahare siltation dam.

SN Retrofitting Component Details about the components Remarks

1 Concrete Jacketing 60 cm on top and 90 cm in bottom d/s face in total

30 cm on top and 60 cm in bottom Concrete d/s face

2 Hard Stone Lining 30 cm stone lining on all surface with 40cm key concrete and panels width 2m each

3 U/S and D/S cutoff 2m deep cutoff 30 to 60cm thick

4 D/S Stilling Basin 10 m width 0.7 to 1.2m deep sloping bottom type stilling basin

5 D/s Cutoff of Stilling basin

After Basin further 1.75m deep cutoff

6 Boulder Riprap D/s for extra safety 1.2m dia boulder riprap

7 U/S Geotextile Blanket U/s face Boulder Lining with Geotextile base and Red Clay filled carpeting for seepage/piping control

8 Sluice Gate on Left bank 3x2m size 1 sluice gate for level regulation

9 Divider and Parapet of sluice blocks

Lifting mechanism of Gate and access platform

10 Access Road and Ramp Track inside basin for Truck access to remove deposit

There will be requirement of access Road and Sloping ramp at least 4 m wide at 10% Slope to take truck down to the basin for removal of the debris.

11. Flood Wall and river Training works right bank

There is massive River Training Works including Scour Protection cutoff and Stone Masonry Base and back side support dike


54

Figure 3-3: Under sluice plan and section proposed at the dam edge for water level control.


55

3.3 Retrofitting Option for Harpan Khola Dam

Most of the problems in Harpan Khola siltation dam are similar to problems in Khahare dam. The

suggested component for retrofitting are construction of concrete jacketing, cut off, stilling basin

and heightening of the left flood wall. There is also requirement of re-alignment of left side flood

wall just after dam and extension of the flood protection d/s further till river has bend. There is also

requirement of heightening of the side flood channel especially on left bank of the river u/s of the

dam. The planform and a typical longitudinal section of retrofitting design have been shown in

Figure 3-4 and 3-5, respectively. The detail of the retrofitting option has been summarized in Table

3-3.

Figure 3-4: Harpan Dam layout and its components/Facilities (retrofitting option)


56

Figure 3-5: Typical section of Harpan dam (suggested retrofitting option).

Table 3-3: Different components of retrofitting option for Khahare siltation dam.

SN Retrofitting Component Details about the components Rem





4 D/S Stilling Basin 10 m width 0.7 to 1.2m deep sloping bottom type stilling basin

5 D/s Cutoff of Stilling basin

After Basin further 1.75m deep cutoff



8 Sluice Gate on Left bank

3x2m size 1 sluice gate for level regulation


Lifting mechanism of Gate and acces plateform

10 Acces Road and Ramp Track inside basin for Truck acces to remove

There will be requirement of access Road and Sloping Ramp at least 4m wide at 10% Slope to take truck down


57

SN Retrofitting Component Details about the components Rem

depoit to the basin from Highway side on right bank.

11 Flood Wall Heightening The left bank u/s flood wall needs heightening for the safety on the flooding left bank settlement and paddy field.

12 Relocation of D/S flood wall

The Flood wall constructed in oblique to the dam axis needs to be relocated, straight on the alignment of the river

13 Extension of Flood wall D/S on left bank

There is requirement of extending the Flood wall on the left bank further downstream up to the river bend position.

3.4 Lauruk Dam

The field observation suggests that the Lauruk dam is operating well and there are not serious

issues. However, the stone masonry dam and downstream protection structures are not enough for

longevity of the dam. The heightening of left flood wall is therefore strongly suggested in order to

avoid overtopping. The planform and a typical longitudinal section of the retrofitting design have

been shown in Figure 3-6 and 3-7 respectively. The detail of the retrofitting option has been

summarized in Table 3-4.

Figure 3-6: Lauruk Dam layout and its components/Facilities (retrofitting option)


58

Figure 3-7: Typical section of Lauruk dam (suggested retrofitting option).

Table 3-4: Different components of retrofitting option for Lauruk siltation dam.

SN Project Component Details Proposed for development Rem





4 D/S Apron 6 m width 0.6 deep Apron with Stone Lining

5 D/s Cutoff of Apron After Basin further 1.75m deep cutoff



8 Sluice Gate on Left bank 1.2x1.2m size 1 sluice gate for level regulation


Lifting mechanism of Gate and acces plateform

10 Acces Road and Ramp Track inside basin for Truck acces to remove depoit

There will be requirement of access Road and Sloping Ramp at least 4m wide at 10% Slope to take truck down to the basin from left bank.


59

SN Project Component Details Proposed for development Rem

11 Flood Wall Heightening The left bank as well as right flood wall needs heightening for the safety on the flooding paddy field both side in the area.

3.5 Betini Dam

The field observation suggests that the Betini dam is operating well and there are not serious issues.

However, the stone masonry dam and downstream protection structures are not enough for

longevity of the dam. The heightening of flood wall is suggested in order to avoid overtopping. The

planform and a typical longitudinal section of the retrofitting design have been shown in Figure 3-8

and 3-9 respectively. The detail of the retrofitting option has been summarized in Table 3-5.

Figure 3-8: Betini Dam layout and its components/Facilities (retrofitting option)


60

Figure 3-9: Typical section of Betini dam (suggested retrofitting option).

Table 3-5: Different components of retrofitting option for Betini siltation dam.

SN Project Component Details Proposed for development Remarks





4 D/S Apron 6 m width 0.6 deep Apron with Stone Lining

5 D/s Cutoff of Apron After Basin further 1.75m deep cutoff


7 U/S Geotextile Blanket

U/s face Boulder Lining with Geotextile base and Red Clay filled carpeting for seepage/piping control

8 Sluice Gate on Left bank

1.2x1.2m size 1 sluice gate for level regulation


Lifting mechanism of Gate and access platform

10 Access Road and Ramp Track inside basin for Truck access to remove deposit

There will be requirement of access Road and Sloping Ramp at least 4m wide at 10% Slope to take truck down to the basin from left bank.


61

SN Project Component Details Proposed for development Remarks

11 Flood Wall Heightening

The left bank flood wall needs heightening for the safety on the flooding area on that side already overtopping.

3.6 Summary Cost for Retrofitting Option

The bill of quantify was calculated using typical section and profile of the suggested retrofitting

option. The district rate provided by the Pokhara Metropolitan City office was used for item cost

estimation. The summary of cost for the suggested retrofitting option has been presented in Table 3-

6. The detail Bill of Quantify (BoQ) and Rate Analysis has been presented in Annex 02 and 03

respectively. The grand total cost for retrofitting Khahare, Harpan, Lauruk and Betini siltation dam is

calculated at NRs 368,484,000. The cost for each dam has been shown in Table 3-6.

Table 3-6: Summary cost estimate of the suggested retrofitting option for four siltation dam.

S.N.

Descriptions Amount

(NRs)

Misc and

Contingency 10%

Base Cost (NRs)

VAT 13%

Total Cost With

VAT(NRs)

A Engineering, Supervision, Management of Retrofitting works

LS @ 10% of the Cost

27,108

2,711

29,819

3,877

33,696

Sub-Total of A

27,108

2,711

29,819

3,877

33,696

B BETINI Siltation Dam

B1

General Items (Insurance, Mobilization, Camping, Power etc.)

2,045

-

2,045

266

2,311

B2

Betini Dam Strengthening/Retrofitting

19,370

1,937

21,307

2,770

24,077

B3

Betini Undersluice

7,458

746

8,204

1,066

9,270

Sub-Total of B

28,873

2,683

31,556

4,102

35,658

C Harpan Siltation Dam

C 1


4,792

-

4,792

623

5,415

C 2

Harpan Dam Repair/Retrofitting

52,700

5,270

57,970

7,536

65,506

C 3

Harpan Undersluice and Approach

10,168

1,017

11,185

1,454

12,639

Sub-Total of C

67,660

6,287

73,946

9,613

83,559


62

S.N.

Descriptions Amount

(NRs)

Misc and

Contingency 10%

Base Cost (NRs)

VAT 13%

Total Cost With

VAT(NRs)

D Lauruk Siltation Dam

D 1


2,109

-

2,109

274

2,383

D 2

Lauruk Dam Strengthening/Retrofitting

20,895

2,089

22,984

2,988

25,972

D 3

Lauruk Undersluice

6,768

677

7,445

968

8,413

Sub-Total of D

29,771

2,766

32,538

4,230

36,768

E KHAHARE Siltation Dam

E 1


10,254

-

10,254

1,333

11,587

E 2

Khahare Dam and River Training works

126,041

12,604

138,645

18,024

156,669

E 3

Khahare Undersluice

8,485

848

9,333

1,213

10,547

Sub-Total of E

144,780

13,453

158,233

20,570

178,803

Grand Total Cost

298,193

27,899

326,092

42,392

368,484

Note: The cost presented here was based on the Google map based information and field observations. Indeed, no detail topographic survey was carried out. It is therefore suggested to take this cost as preliminary which needs further verification while preparing detail project report. During detail study, it is strongly recommended to carry detail topographic survey, to update design as per the topography, to carry field verification by laying out every in the field and estimate final cost.


63

4. Chapter 4: Management, Operation and Maintenance

Plan

4.1 Revenue potential from construction material

The study report "Development of Ecosystem based Sediment Control Techniques & Design of

Siltation Dam to Protect Fewa Lake" by GoN/UNDP, 2015 estimated the sediment load in Khahare,

Harpan, Lauruk and Betini by using Mayer-Peter and Muller Formula (Table 4-1).

Table 4-1: Sediment load in Khahare, Harpan, Lauruk and Betini (GoN/UNDP report based data).

SN

Dam

Location

Catchment

Area (km2)

Q100yr

Flood (m3/s)

Instantaneous

flood (m3/s)

Sediment

Load (m3/yr)

Remarks

1 Khahare 25.3 66 212 149,145

2 Harpan 35.7 91 281 86,522

3 Lauruk 4.5 17 61 26,528

4 Betini 7.1 24 85 41,855

GD. Total

304,050

Field observation suggested that the sediment deposited in Khahare and Harpan dam are of

commercial quality for production of aggregate, chips and sand. However, sediment deposited in

Lauruk and Betini dam is from different geological settings so that they can only be used as filler,

sub-base coarse or low grade concrete. All dams have been filled completely. The volume of

sediment filled at the dam in one season has been approximated in the Table 4-2.

Table 4-2: Deposited approximate volume of sediment load in 2020 monsoon season.

SN Dam Observation Filling

Dimension u/s of dam

Remarks

Location By Filled Volume (m3)

1 Khahare 135000 100*300*4.5

2 Harpan 90,000 100*200*4.5

3 Lauruk 24000 60*100*4

4 Betini 16,000 40*100*4

Grand Total 265,000


64

The value of sediment deposited in the dam was calculated by considering current district rate

(Table 4.3). Once four dams are filled, about 265,000 m3 sediment could be accumulated. However,

deposited material on Harpan and Khahare dam can only be used as construction material which

estimates to be 225,000 m3. The material from Lauruk and Betini has to be dumped safe on some

area or road pavements/embankments. The saleable volume of gravel and sand from Khahare and

Harpan could generate NRs. 207,187,500 gross revenue. The net revenue after deducting processing

cost (50 % of gross revenue for processing) could be approximated at NRs. 103,593,750.

Table 4-3: Revenue generation from deposited sediment during 2020 monsoon season.

Dam

Dam U/S deposit sediment

(m3)

Sand recove

ry %

Sand Volume

(m3)

Sand

Rate (NRs/

m3)

Aggregate recovery

% Aggrade (m3)

Rate (NRs/m)

Total Gross sales (NRs)

Rem

Khahare 135000 15% 20250 2100 35% 47250 1850 129937500

50% Recover

Harpan 90,000 10% 9000 2100 30% 27000 1850 68850000

40% Recover

Lauruk 24000 10% 2400 2100 30% 7200

No sell 5040000

Dumping

Betini 16,000 10% 1600 2100 30% 4800

No sell 3360000

Dumping

Total 265,000

33250 sales 86250

207187500

Gross income deducting processing cost @ 50%

103379400

Note: the sales volume calculation is done with assumed recovery rates of the deposited material.

This is consideration with one time fill only and processing/screening material removal after summer,

more revenue is also possible if more extraction I needed.

4.2 Sample financial analysis

The cost of the Repair/Protection works is estimated about 368 million whereas gross revenue is

estimated about NRs. 103 Million. The cost of construction is financed 70% from Bank @ 12%, and

construction major in first year with 60% draw down, 30% 2nd year and 10% third year for

maintenance and miscellaneous cost (Table 4-4).


65

Table 4-4: Financial parameter for analysis

Base Cost 2020 price level 368484 NRs, 000

Scenario what happens after FINANCING WITH BANK Before Banking

After Banking

Total Cost 368484 100%

Total Cost 427617 100.0%

Pure Cash Loan 240183 65.18%

Total Loan 299311 70.0%

Equity 128301 33.18%

Equity 128307 30.0%

Interest Rate 12.0%

Interest Calculation

Time (year) Interest Tot Interest

First year drawdown 60% 2.5 43233 43233

Second year drawdown 30% 1.5 12970 56203

Third year drawdown

10% 0.5 1441 57644

Total Interest 57644 57644

Loan Arrangement Fee 0.50%(Theki) 1489 0.50%

Total Interest to be capitalized 59133 NRs 16%

Cost including IDC 427617 ie Gross Revenue each year

103594 NRs

A Simple financial model based on Simple cash flow is prepared to evaluate the internal rate of

return and Return on Investment of the project based on cost/benefit projection.

Table 4-5: Projected Cash Flow Analysis for Economic model

Year Revenue O/M Royalty Profit before Tax Tax Cash flows

1

(256,570)

2 (128,285)

3 (42,762)

Cash Flow

1 103,594 10,359 5,179.69 73,801 14,760 73,295

2 106,702 10,670 5,335.08 54,989 10,998 79,698

3 109,809 10,990 5,490.47 57,919 11,584 81,745

4 112,917 11,320 5,645.86 60,757 12,151 83,800

5 116,025 11,660 5,801.25 63,528 12,706 85,859

6 119,133 12,009 5,956.64 66,247 13,249 87,917

7 122,241 12,370 6,112.03 68,925 13,785 89,974

8 125,348 12,741 6,267.42 71,571 14,314 92,026

9 125,348 13,123 6,267.42 71,239 14,248 91,710

10 125,348 13,517 6,267.42 70,883 14,177 91,388

11 125,348 13,922 6,267.42 70,508 14,102 91,057

12 125,348 14,340 6,267.42 70,114 14,023 90,718

13 125,348 14,770 6,267.42 69,704 13,941 90,370

14 125,348 15,213 6,267.42 69,277 13,855 90,013

15 125,348 15,669 6,267.42 68,835 13,767 89,645

16 125,348 16,140 6,267.42 68,377 13,675 89,266

17 125,348 16,624 6,267.42 67,902 13,580 88,877

18 125,348 17,122 6,267.42 67,413 13,483 88,476


66

Year Revenue O/M Royalty Profit before Tax Tax Cash flows

19 125,348 17,636 6,267.42 66,907 13,381 88,063

20 125,348 18,165 6,267.42 66,385 13,277 87,639

21 125,348 18,710 6,267.42 65,846 13,169 87,202

22 125,348 19,271 6,267.42 65,291 13,058 86,751

23 125,348 19,850 6,267.42 64,718 12,944 86,288

24 125,348 20,445 6,267.42 64,127 12,825 85,810

25 125,348 21,058 6,267.42 63,519 12,704 85,319

26 125,348 21,690 6,267.42 62,891 12,578 84,813

27 125,348 22,341 6,267.42 62,244 12,449 84,291

28 125,348 23,011 6,267.42 61,578 12,316 83,754

29 125,348 23,702 6,267.42 60,891 12,178 83,201

30 125,348 24,413 6,267.42 60,183 12,037 82,632

The cash Flow Statement for calculation of Rate of Return is also presented paying back loan and

interest of the bank (Table 4-6).

Table 4-6: Investor CASH FLOWS Statement for Financial Model

Year

Depreciation

Unpaid Loan Interest

Principle

Before Tax Tax

Cash flows After Tax

Gross Return

1 188832 to Bank (76,984)

2 273851 (38,492)

3 299311

(12,831)

Cash Flow

1 14,254 299,311 35,917

12,402

48,320

37,884 7,577 32158

2 14,254 286,908 34,429

13,891

48,320

42,013 8,403 33974

3 14,254 273,017 32,762

15,558

48,320

46,313 9,263 35746

4 14,254 257,460 30,895

17,425

48,320

50,802 10,160 37471

5 14,254 240,035 28,804

19,516

48,320

55,506 11,101 39143

6 14,254 220,520 26,462

21,857

48,320

60,451 12,090 40757

7 14,254 198,662 23,839

24,480

48,320

65,666 13,133 42306

8 14,254 174,182 20,902

27,418

48,320

71,185 14,237 43784

9 14,254 146,764 17,612

30,708

48,320

74,092 14,818 42820

10 14,254 116,056 13,927

34,393

48,320

77,384 15,477 41768

11 14,254 81,663 9,800

38,520

48,320

81,105 16,221 40618

12 14,254 43,143 5,177

43,143

48,320

85,310 17,062 39359

13 14,254 0 90,057 18,011 86300

14 14,254 89,614 17,923 85945


67

Year

Depreciation

Unpaid Loan Interest

Principle

Before Tax Tax

Cash flows After Tax

Gross Return

15 14,254 89,158 17,832 85580

16 14,254 88,688 17,738 85204

17 14,254 88,203 17,641 84817

18 14,254 87,705 17,541 84418

19 14,254 87,191 17,438 84007

20 14,254 86,662 17,332 83583

21 14,254 86,117 17,223 83147

22 14,254 85,556 17,111 82698

23 14,254 84,977 16,995 82236

24 14,254 84,382 16,876 81759

25 14,254 83,769 16,754 81269

26 14,254 83,137 16,627 80763

27 14,254 82,486 16,497 80243

28 14,254 81,816 16,363 79707

29 14,254 81,126 16,225 79154

30 14,254 80,415 16,083 78586

4.3 Finding and Remarks

The financial analysis revealed IRR of more than 16%, BC Ratio of 1.35 times and Return on

Investment of 23% from this venture (Table 4-7).

Table 4-7: Financial analysis results

Results

NPV 127487 NRs

Project IRR 16%

Project B/C Ratio 1.35

Simple Payback 4.93 Years

Equity Holders NPV 170278

Return on Investment 23%

Investors B/C Ratio 2.80

The following conclusion could be drawn from the preliminary financial analysis:


68

1. The cost and benefit analysis shows that the Dam Repair project seems to be a bankable

project based on nominal revenue from the sales of construction material.

2. The rate of return is remarkable and private sector can also be attracted on this project.

3. The investment is possible on 70: debt 30% Equity ratio and loan from commercial bank is

also possible.

4. The loan can be paid with interest and principal within 12 years.

5. The return on investment shall be more than 20%.

6. The repair works can be implemented immediately making suitable policy framework for the

repair and collection of revenue from the sales of retained volume.


69

5. Chapter 5: Conclusion and Recommendations

5.1 Conclusion

Watersheds of Harpan Khola consist of the hard and good rock quality whereas the other

sub watersheds have soft rock mass.

Active landslides, soil erosion, channel flows and new haphazardly constructed rural roads

are main geohazard of the Fewa Lake watersheds contributing to sediment production and

lake sedimentation.

The Khahare and Harpan dam have severe stability problem because of D/S face erosion of

the dam and they can fail completely at any time. The Lauruk and Betini dams have not

severe stability problem for now but they are also susceptible to failure in the long-term.

The simple stone masonry dam without having concrete jacket, cut off both upstream and

downstream toe of dam, and stilling basin is not enough to resist the sediment and

discharge load. It is therefore, recommended to retrofit these dams sequentially.

In the first phase, it is recommended retrofitting Khahare and Harpan dam. For both dam, it

is imperative to provide concrete jacket with stone lining, cut off, and stilling basin. It is also

recommended heightening flood walls considering the instantaneous flash flood.

It is recommended to observe functioning of Lauruk and Betini dam in the coming flood

season and carry necessary retrofitting. However, heightening of left flood wall in Lauruk

and Betini is immediately necessary as the stream is overtopping the flood wall already.

Once four dams are filled, about 265,000 m3 sediment could be accumulated. However,

deposited material on Harpan and Khahare dam can only be used as construction material

which estimates to be 225,000 m3; rest (material from Lauruk and Betini) has to be dumped

safe on some area or road pavements/embankments.

There is no use of the dam if the removal/withdrawal of the material is not done regularly

by monitoring flood and bed level. No more investment is suggested without having proper

sediment removal mechanism. There is requirement of truck access to dam u/s, ramp, and

side sluice gate to facilitate sediment removal works.

The preliminary cost of repair/rehabilitation, retrofitting and strengthening the dam and

river training works is estimated at NRs 368 million including supervision cost.


70

The net revenue from the sales of aggregate and sand from the dam deposit could be in the

order of 103 million (One time filling of dam). The Khahare dam could be filled more than

one time in a year generating more aggregate and revenue.

Preliminary financial analysis based on the retrofitting cost and the market values of the

deposited material suggest that the project is bankable and attractive (IRR = 16%, BC Ratio =

1.35 and Return on Equity =23%).

5.2 Recommendations

Before implementing the dam retrofitting option suggested in this study, it is strongly

recommended to carry detail study. The main activities during the detail study could be:

detail topographic survey, updating of retrofitting option suggested in this study based on

the topographic map, field verification, and final quantity and cost estimation.

It is recommended to estimate of revenue from the deposited material before bidding the

sediment mining project. In order to determine the revenue more accurately, it is

recommended to carry sediment sampling/sieve analysis, development of gradation curve,

quantification of saleable and non-saleable material and determine their market value.

As a first option, it recommended running the sediment mining project by province

government and the Pokhara Metropolitan city. The revenue generated from the sediment

mining project could be used for conservation and development of Fewa Lake and its

catchment. As the project is bankable and attractive, private sector could also be invited to

do this business through BOOT model.

The siltation dam is not the final solution to get rid of lake sedimentation. The siltation dam

is applicable to retail most of the coarse-gravel sediment and small proportion of sand-silt-

clay. Most of the supply based materials (sand-clay) are still transported to the lake. It

therefore recommended determining effectiveness of the siltation dam reducing lake

sedimentation by carrying detail catchment scale analysis.

The scope of catchment scale study could be: watershed landslides hazard mapping,

quantification of sediment production, analysis of human intervention such as cropping

pattern, construction activities and their contribution to sediment production.


71

Annexes


72

Annex 01: Quantity Calculation and BoQ Estimate of the Repair works

FEWA WATERSHED SILTATION DAM Total Repair/Retrofitting Cost

in '000

Annex: 01

S.No

. Descriptions

Amount (NRs)

Misc and

Contingency 10%

Base Cost (NRs)

VAT 13%

Total Cost With VAT

(NRs)

Remarks

A Engineering, Supervision, Management of Retrofitting works

LS @ 10% of the Cost

27,108

2,711

29,819

3,877

33,696

Sub-Total of A

27,108

2,711

29,819

3,877

33,696

B Betini Siltation Dam

B1 General Items (Insurance, Mobilization, Camping, Power etc.)

2,045

-

2,045

266

2,311

B2 Betini Dam Strengthening/Retrofitting

19,370

1,937

21,307

2,770

24,077

B3 Betini Undersluice

7,458

746

8,204

1,066

9,270

Sub-Total of B

28,873

2,683

31,556

4,102

35,658

C Harpan Siltation Dam

C 1


4,792

-

4,792

623

5,415

C 2

Harpan Dam Repair/Retrofitting

52,700

5,270

57,970

7,536

65,506

C 3

Harpan Undersluice and Approach

10,168

1,017

11,185

1,454

12,639

Sub-Total of C

67,660

6,287

73,946

9,613

83,559

D Lauruk Siltation Dam

D 1


2,109

-

2,109

274

2,383

D 2

Lauruk Dam Strengthening/Retrofitting

20,895

2,089

22,984

2,988

25,972

D 3

Lauruk Undersluice

6,768

677

7,445

968

8,413


73

Sub-Total of D

29,771

2,766

32,538

4,230

36,768

E Khahare Siltation Dam

E 1 General Items (Insurance, Mobilization, Camping, Power etc.)

10,254

-

10,254

1,333

11,587

E 2 Khahare Dam and River Training works

126,041

12,604

138,645

18,024

156,669

E 3 Khahare Undersluice

8,485

848

9,333

1,213

10,547

Sub-Total of E

144,780

13,453

158,233

20,570

178,803

Grand Total Cost 298,193

27,899

326,092

42,392

368,484


74

Annex: 02

FEWA LAKE WATERSHED SILTATION DAM

Bill of Quantity of Repair/Retrofitting works

S.N. Description of Items Unit Quantity Unit Rate (NRs.) Amount (NRs) Rem

A: GENERAL ITEMS

1

Insurance of Contractor's Resources (Personnel, labours, Equipment's Third Party etc.) all as per Contract Conditions except Contractor's All Risk (CAR)

LS 1.0 5,000,000.00 5000000.00

2 Mobilization and Demobilization

LS 1.0 700,000.00 700000.00

3 Contractor, Site Facilities including Labour Camp

LS 1.0 3,000,000.00 3000000.00

4 Provision for Standby Power Supply

LS 1.0 3,000,000.00 3000000.00

5

Established the material testing lab, Lab test in or off sore the project

LS 1.0 1,000,000.00 1000000.00

6 River Diversion and Dewatering

LS 1.0 5,000,000.00 5000000.00

7 Construction Power and Lighting for Works

LS 1.0 1,000,000.00 1000000.00

8

Progress Report, Construction Drawings and As Built Drawings

LS 1.0 500,000.00 500000.00

- Total 19,200,000.00 For all

B. Betini Siltation Dam B1. Dam Repair/Retrofitting

1 Site Clearance m2 0.00 83.00 -

2

Excavation of Earth soil (Including Boulder <3.0m

3

Volume) by equipment

m3 2417.63 116.00 280,445.52

3

Earth Work in excavation in boulder mix soil including disposal up to 10m lead and

m3 284.43 142.00 40,388.71


75


1.5m lift

4

Earth Work in excavation in hard rock without blasting including disposal up to 10m lead and 1.5m lift

m3 142.21 1,290.00 183,455.74

5

E/W in Backfilling by Ordinary Soil in 15cm thick layer and compaction with sprinkling of water, haulage distance 10m.

m3 284.43 120.00 34,131.30

6 Dry Stone Soling m3 26.33 1,988.28 52,349.76

7

Laying 30cm thick Filter material inclusive haulage up to 10 m and lift up to 1.5m

m2 1363.80 1,360.95 1,856,060.20

8 Boulder Riprap (upto 1.0m Dia. Boulder)

m3 891.00 1,650.00 1,470,150.00


m3 567.36 2,210.00 1,253,865.60

10 30 cm thick. Hard Stone Lining with M25/20 Concrete

m2 99.05 4,354.70 431,335.74

11

Providing and Placing M10/40 Cement Concrete machines mixed for the foundation, footing etc., including upto 30m lead.

m3 13.16 12,070.00 158,896.72

12


m3 71.57 12,704.29 909,259.25

13

Providing and Placing M25/20 Cement Concrete machine mixed for Super Structure, including up to 30m

m3 306.61 17,101.67 5,243,619.50


76


lead.

14

Providing and Placing M35/20 Cement Concrete machine mixed for Super Structure, including up to 30m lead.

m3 58.79 19,271.82 1,132,996.31

15

Providing, fixing and removing formworks for Concreting Works.

m2 1232.51 887.09 1,093,345.39

16 Reinforcement works for RCC Concrete.

MT 26.22 117,702.20 3,085,981.15

17

Random Rubble Masonry in 1:4 Cement and sand mortar

m3 139.62 10,368.88 1,447,702.33

18 300mm PCV Water Stop

m 191.45 1,673.65 320,420.29

19 25mm thick Expansion Joint Board

m2 95.73 2,525.05 241,710.41

20 Joint Sealant m2 95.73 1,403.05 134,306.96

Sub Total

19,370,420.87

B 2. Undersluice

1 Dry Stone Solling m3 8.24 1,988.28 16,382.51


m2 8.59 4,354.70 37,398.57

3


m3 4.12 12,070.00 49,725.68

4

Providing and Placing M15/40 Cement Concrete machines mixed for the foundation, footing etc., including up to 30m lead.

m3 31.11 12,704.29 395,287.62


77


5

Providing and Placing M20/40 Cement Concrete machines mixed for the wall, column, beam etc., including up to 30m lead.

m3 11.31 16,070.85 181,833.65

6


m3 184.91 17,101.67 3,162,219.05

7


m2 326.30 887.09 289,456.13


MT 13.64 117,702.20 1,605,477.23

9 Stone Masonry Work in 1:4 Cement mortar

m3 4.86 10,368.88 50,423.84

10 300mm PVC Water Stop

m 15.00 1,673.65 25,104.75


m2 7.50 2,525.05 18,937.88

12 Joint Sealant m2 7.50 1,403.05 10,522.88

13 Sluice Gate MT 7.00 145,000.00 1,015,000.00

14 Gate Lifting Mechanism

LS 2.00 300,000.00 600,000.00

Sub Total 7,457,769.78

Total 26,828,190.65

C. Harpan Siltation Dam C1. Dam Repair/Retrofitting


2


3


m3 6578.81 116.00 763,142.43

3

Earth Work in excavation in boulder mix soil including disposal up to 10m lead and 1.5m lift

m3 773.98 142.00 109,904.89


78


4


m3 386.99 1,290.00 499,215.89

5


m3 773.98 120.00 92,877.38


7


m2 3025.90 1,360.95 4,118,091.04


m3 1955.80 1,650.00 3,227,070.00


m3 1284.12 2,210.00 2,837,905.20


m2 504.85 4,354.70 2,198,464.17

11


m3 34.44 12,070.00 415,731.84

12


m3 235.57 12,704.29 2,992,803.06

13


m3 997.80 17,101.67 17,064,128.08


79


14


m3 131.42 19,271.82 2,532,628.43

15


m2 2067.91 887.09 1,834,425.04


MT 81.89 117,702.20 9,638,364.21

17


m3 291.46 10,368.88 3,022,078.61


m 334.25 1,673.65 559,417.51


m2 167.13 2,525.05 421,998.98

20 Joint Sealant m2 167.13 1,403.05 234,484.73

Sub Total

52,699,697.56

C 2. Undersluice



m2 14.56 4,354.70 63,414.66

3


m3 5.01 12,070.00 60,529.54

4


m3 43.16 12,704.29 548,375.82

5

Providing and Placing M20/40 Cement Concrete machines mixed for

m3 13.76 16,070.85 221,207.24


80


the wall, column, beam etc., including up to 30m lead.

6

Providing and Placing M25/20 Cement Concrete machine mixed for Super Structure, including upto 30m lead.

m3 262.14 17,101.67 4,483,038.02

7


m2 409.22 887.09 363,013.03


MT 19.14 117,702.20 2,253,311.03


m3 4.86 10,368.88 50,423.84


m 15.00 1,673.65 25,104.75


m2 7.50 2,525.05 18,937.88

12 Joint Sealant m2 7.50 1,403.05 10,522.88

13 Sluice Gates MT 10.00 145,000.00 1,450,000.00


LS 2.00 300,000.00 600,000.00

Sub Total

10,167,820.60

Total

62,867,518.16

D. Lauruk Siltation Dam D1. Dam Repair/Retrofitting


2


3


m3 2601.38 116.00 301,760.17

3


m3 306.04 142.00 43,458.36

4

Earth Work in excavation in hard rock without blasting including

m3 153.02 1,290.00 197,398.90


81


disposal up to 10m lead and 1.5m lift

5

E/W in Backfilling by Ordinary Soil in 15 cm thick layer and compaction with sprinkling of water, haulage distance 10m.

m3 306.04 120.00 36,725.38


7


m2 1436.78 1,360.95 1,955,384.33

8 Boulder Riprap (up to 1.0m Dia. Boulder)

m3 848.78 1,650.00 1,400,489.64

9 Boulder Riprap (up to 1.2m Dia. Boulder)

m3 705.60 2,210.00 1,559,376.00


m2 144.77 4,354.70 630,427.23

11

Providing and Placing M10/40 Cement Concrete machines mixed for the foundation, footing etc., including up to 30m lead.

m3 10.04 12,070.00 121,192.15

12


m3 67.61 12,704.29 858,936.58

13


m3 390.98 17,101.67 6,686,348.31

14

Providing and Placing M35/20 Cement Concrete machine mixed for

m3 50.85 19,271.82 980,051.75


82


Super Structure, including up to 30m lead.

15


m2 816.56 887.09 724,359.75


MT 30.57 117,702.20 3,597,735.88

17


m3 125.66 10,368.88 1,302,932.09


m 126.00 1,673.65 210,879.90


m2 63.00 2,525.05 159,078.15

20 Joint Sealant m2 63.00 1,403.05 88,392.15

Sub Total

20,894,854.41

D 2. Undersluice



m2 6.57 4,354.70 28,598.60

3


m3 3.74 12,070.00 45,165.03

4


m3 28.87 12,704.29 366,806.56

5

Providing and Placing M20/40 Cement Concrete machines mixed for the wall, column, and beam etc., including up to 30 m lead.

m3 12.11 16,070.85 194,690.33


83


6

Providing and Placing M25/20 Cement Concrete machine mixed for Super Structure, including upto 30m lead.

m3 160.00 17,101.67 2,736,283.19

7


m2 272.94 887.09 242,120.36


MT 12.06 117,702.20 1,419,404.55


m3 4.86 10,368.88 50,423.84


m 15.00 1,673.65 25,104.75


m2 7.50 2,525.05 18,937.88

12 Joint Sealant m2 7.50 1,403.05 10,522.88

13 Sluice Gate MT 7.00 145,000.00 1,015,000.00


LS 2.00 300,000.00 600,000.00

Sub Total 6,767,937.93

Total

27,662,792.34

E. Khahare Siltation Dam E 1. Dam Repair/Retrofitting


2


3


m3 10036.80 116.00 1,164,269.22

3


m3 1180.80 142.00 167,673.66

4


m3 590.40 1,290.00 761,616.27


84


5


m3 1180.80 120.00 141,696.05


7


m2 5150.00 1,360.95 7,008,879.63


m3 2500.00 1,650.00 4,125,000.00


m3 3180.00 2,210.00 7,027,800.00


m2 215.10 4,354.70 936,695.22

11

Providing and Placing M10/40 Cement Concrete machine mixed for the foundation, footing etc., including upto 30m lead.

m3 64.52 12,070.00 778,761.83

12


m3 1071.25 12,704.29 13,609,468.25

13


m3 2140.99 17,101.67 36,614,483.87

14


m3 174.22 19,271.82 3,357,575.72


85


15


m2 4680.96 887.09 4,152,435.50


MT 203.19 117,702.20 23,915,634.59

17


m3 2012.06 10,368.88 20,862,797.08


m 318.75 1,673.65 533,475.94


m2 159.38 2,525.05 402,429.84

20 Joint Sealant m2 159.38 1,403.05 223,611.09

Sub Total 126,040,872.89

E 2. Undersluice



m2 11.16 4,354.70 48,594.49

3


m3 2.46 12,070.00 29,719.36

4


m3 20.93 12,704.29 265,962.46

5

Providing and Placing M20/40 Cement Concrete machines mixed for the wall, column, beam etc., including up to 30m lead.

m3 12.56 16,070.85 201,922.21

6

Providing and Placing M25/20 Cement Concrete machine mixed for Super Structure,

m3 216.12 17,101.67 3,695,959.55


86


including upto 30m lead.

7


m2 350.97 887.09 311,340.45


MT 14.98 117,702.20 1,762,822.97


m3 5.23 10,368.88 54,265.51


m 15.00 1,673.65 25,104.75


m2 7.50 2,525.05 18,937.88

12 Joint Sealant m2 7.50 1,403.05 10,522.88

13 Sluice Gate MT 10.00 145,000.00 1,450,000.00


LS 2.00 300,000.00 600,000.00

Sub Total 8,484,943.78

Total 134,525,816.67

Note: The cost in this table is without considering miscellaneous cost and VAT.


87

Annex:03

FEWA WATERSHED SILTATION DAM Items Rate Summary

Item No. Description of Items Unit Rate (NRs) Remarks

1 Site Clearance/Earthwork

1.1 Site Clearance m2 83.00

1.2

Earthwork Excavation in common materials (Including Boulder <1.5m3

Volume) by equipment m

3 116.00

1.4


m3 142.00

1.4A

Earth Work in excavation in boulder mix soil including disposal up to 30m lead and 1.5m lift manually

m3 210.00

1.5


m3 1,290.00

1.8


m3 120.00

1.9

E/W in Backfilling by River Gravel with compaction with sprinkling of water, haulage distance 10m.

m3 240.00

1.10 Impervious Clay (Red Soil) Material Filling m3 1,349.85

2 Soling/filter/Lining Works

2.1 Dry Stone Soling m3 1,988.28

2.2

Laying 30cm thick Graded Filter material inclusive haulage up to 10 m and lift up to 1.5m

m2 1,360.95

2.3

Laying 50cm thick Inverted Filter material inclusive haulage up to 10 m and lift up to 1.5m

m2 1,595.11

2.4 Boulder Riprap (up to 1.2m Dia. Boulder) m3 1,650.00

2.5 Boulder Riprap (up to 1.5m Dia. Boulder) m3 2,210.00

2.6 River Gravel Packing m3 2,581.82

2.7 30 cm thick. Hard Stone Lining M25/20 Cement Concrete m2 4,354.70

2.8

Laying of 50mm thick layer of slate of size 300mm x 300mm and pointing the joints by 1:3 c/m

m2 1,280.00

3 Concrete/Formworks/Reinforcement Works

3.1

Providing and Placing M10/40 Cement Concrete machine mixed for the foundation, footing etc., including up to 30m lead.

m3 12,070.00

3.2

Providing and Placing M15/40 Cement Concrete machine mixed for the foundation, footing etc., including up to 30m lead.

m3 12,704.29

3.3

Providing and Placing M20/40 Cement Concrete machine mixed for the wall etc., including up to 30m lead.

m3 16,070.85

3.4

Providing and Placing M20/20 Cement Concrete machine mixed for the wall, column, beam etc., including up to 30m lead.

m3 16,268.73

3.5


m3 17,101.67

35A


m3 17,743.22


88


35B


m3 19,271.82

3.6

Providing and Placing Plum M15/40 Cement Concrete machine mixed for the foundation, footing etc., including up to 30m lead.

m3 10,921.13

3.7

25mm Cement Concrete Flooring in M20/20 cement sand mortar with 20mm gauge stone

m2 522.19

3.8 Providing, fixing and removing formworks for Concreting Works. m2 887.09

3.9 Providing, fixing and removing formworks for Column, height up to 9m

m2 1,328.03

3.10 Reinforcement works for RCC Concrete. MT 117,702.20

4 Masonry Works

4.1 Dry Stone Masonry Work up to 0-5m ht. m3 4,339.23

4.2

Providing and Laying Random Rubble Masonry in mud mortar, lead 30m masoned height 0-5m

m3 4,428.99

4.3

Providing and Laying Random Rubble Masonry in 1:4 Cement and sand mortar

m3 10,368.88

4.4 Providing and Laying Random Rubble Masonry in 1:6 Cement and sand mortar

m3 9,615.38

4.5 Gabion Works m3 4,059.79

4.6 Brick Work in foundation in 1:4 cement and sand mortar m3 16,551.70

4.7 Block Masonry Work in Superstructure in 1:4 cement and sand mortar m3 19,808.25

5 Plastering/Pointing Works

5.1 12mm thick Cement Plaster in 1:4 cement and sand mortar m2 390.45

5.2 20mm thick Cement Plaster in 1:4 cement and sand mortar m2 624.71

5.3 Cement Pointing Work in 1:3 Cement mortar in Stone Masonry Wall m2 290.93

5.4 3mm thick neat cement punning m2 34.73

6 Wood/Glass Works

6.1 Wood works in Chaukhat of Door/Window. m3 254,267.28

6.2 1.5" thick Saalwood Door Shutter. m2 11,745.44

6.3 Glass Shutter for Windows. m2 7,854.45

6.4 False Ceiling with 3 mm plywood m2 4,622.63

7 Painting Works

7.1 Two Coat Water Proof Cement Painting on plastered surface. m2 123.76

7.2

One Coat Enamel Painting over One Coat Priming on Door and Windows.

m2 177.57

8 Roofing Work

8.1 CGI Sheet Roofing works with supply of Materials complete. m2 1,214.58

8.2 Making CGI Sheet ridge including supply of material, fixation etc. m2 880.28

8.3 Steel pipe truss for CGI sheet roofing Kg 246.63

9 Road Works

9.1 Subgrade Construction and preparation of Formation in cutting (Excluding Rock Excavation) including disposal of material upto 10m

m3 122.93

9.2

Subgrade Construction and preparation of Formation in Rock cutting with regulation course of natural materials

m3 1,411.53

9.3

Providing, Laying, Spreading, watering, levelling and Compaction of crusher run material as sub-base course grading SB1 lead upto 10m

m3 2,281.27


89


9.4

Providing, Laying, Spreading, watering, levelling and Compaction of crusher run material as base course lead upto 10m

m3 2,649.83

9.5

Providing and Placing of 1.60m dia. RCC Pipes with or without collars, jointed with cement mortar in the proportion of 1:2 lead upto 100m

rm 28,712.68

9.6


rm 10,766.79

9.7


rm 9,310.98

9.8


rm 8,188.39

9.9

Providing, jointing and laying 110mm dia. HDP Pipes with or without collar etc. complete in place for Weep Hole and Sub Surface

rm 735.94

9.10 Providing, jointing and laying 160mm dia. HDP Pipes with or without collar etc. complete in place for Sub Surface

rm 1,648.34

10 Miscellaneous Items

10.1 300 mm PVC Water Stopper rm 1,673.65

10.2 25mm thick Expansion Joint Board (Saltax Board) m2 2,525.05

10.3 Joint Sealant m 1,403.05

10.4 Barbed Wire Fencing with Wooden Post m 1,629.29

10.5 Barbed Wire Fencing with Angle Iron Post m 1,187.67

10.6 Providing and Laying and fixing of Geo-textile (Filter Fabrics), lead 30m m2 148.62

10.7 Flat iron grill in windows with red oxide paint Kg 143.00

10.8 Glazed tile in kitchen and bathroom in 1:4 Cement Sand m2 2,759.34


90

Annex 04: Sample Design Drawings for Repair/Retrofitting

a report on fewa watershed siltation dams problems and

Documents