ankanda geology report

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Ankanda Mini Hydro Power Project

Engineering Geological Report

March 2010


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1.0 Introduction

As per request made by Mr. P.S.P.S.De Saram Managing Director, Munex (Pvt) Ltd, a

preliminary engineering geological study was carried out at site of proposed AnkandaMini Hydro Power Project located in Ankanda GS division in Matale AGA division to

evaluate geotechnical conditions of the project.

The main objective of this assignment is to study prevailing engineering geologicalconditions of weir, powerhouse area and upstream inundation area once pond is

impounded. The above study comprises a one day site inspection, field observation,

evaluation of basic information and submission of a report. A site inspection was carried

out on 25th

January 2010 at proposed Ankanda Mini Hydro Power Project site in orderto achieve the above objectives:

2.0 Location

Ankanda proposed mini-hydropower project is located in the valley of Sudu Ganagaabout 4km distance from Matale-Dambulla highway turning towards right at

Kawudupalla junction which is between 38th and 39th kilometer posts.

The proposed site is in Ankanda Gramsewaka Division in Matale district lying on 185-190 E and 260-265 N grid of 1:50 000 scale topographic map sheet. Location is shown in

fig.1.

3.0 Project Features

The proposed Ankanda mini hydro power project is a low head hydro power project on

Sudu-Ganga which is planning to generate 4.5MW electric power for the national grid. It

is proposed to raise existing concrete weir from 1m to make the weir of total 2m high and

60m long. The power house is located about 800 m downstream of the proposed weir onthe left bank .

4.0 General Geology

Sri Lanka is sub divided into three major Geological units as Highland, Wanni and

Vijayan compleses. Owala mini-Hydrpower site area belongs to Highland complex androck types, charnockitic gneisses, biotite gneisses, quartzites and marbles are

characteristic in this zone. The rocks of Highland Complex are folded in to a system

name taprobain fold system .The general direction of these folds are N-S to NW-SE.


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5.0 Topography of Proposed Weir Site and Powerhouse Site

The proposed weir axis is located on the existing anicut across Sudu-Ganga. At weir axis

river gauge is about 60m wide. The slope on left bank rises gradually while left bank

follows flat morphology forlong distance

Upstream of proposed weir along the river, The left bank rises gradually while the rightbank covered by paddy fields maintains flat terrain.

The power house is proposed on left abutment about 400m downstream of proposed weir

on paddy field. This location is about about 30m offset from left bank.

6.0 Engineering Geology of Main Structures Sites

6.1 WeirExposed bed rock of Garnet biotite gneiss can be seen on river bed and existing anicut

foundation is sitting on bed rock. General strike and dip of foliation of bed rock isN100W and 55E. Foliation joints in 0.5-1m intervals can be observed on exposed bed

rock just downstream of existing anicut. Another joint set N 800W IN 2-3m intervals are

pre-dominant at this area. Exposed bed rock can be observed on left bank and right bank

is covered by alluvium clay. (See photo-2)

6.2 Channel Trace

Propose channel route is lying on alluvium clay area.

6.3 Power House

Powerhouse is located on paddy field and the area covered by alluvium clay.

6.3 Periphery of the Pond-

The right bank of reservoir Periphery is mainly covered by alluvium deposits of silty clay

while left bank is mainly covered by exposed bed rock about 70m upstream of proposed

weir and no land slides prone areas could be observed.

7.0 Geotechnical Findings and Observations

Geotechnical findings and observation at main structures sites, water tightness ofproposed weir and stability of slopes along reservoir periphery are discussed below.

7.1Weir Site

7.1.1 Foundation Rock

The existing anicut is exactly positioning on the fresh bed rock of Garnet biotite gneiss.

This anicut is concrete weir founded on rock barrier and can be raised the existing weir


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on the same rock barrier. It is necessary to install some dowels to firmely found the weir

foundation

The right abutment covered by alluvium material of silty sand and existing weir is

abutting on to a rubble wall parallel to the river. The left abutment can be placed on

exposed bed rock.

7.1.2 Water Tightness Of Weir Foundation

The exposed bed rock on weir axis is fresh rock of Garnet botite gneiss and permeable

zones could not be identified. Also existing weir does not any water leaking and

foundation rock is water tight for proposed low height weir.

7.2 Power House AreaPower house location is covered by alluvium clay material and placing the foundation at

this location is not feasible.

7.3

Stability Along Reservoir Periphery

The right abutment of the reservoir is controlled by existing river bund and left abutment

manly covered by bed rock and. Also no major land slide could be observed on left bank

and stable geological condition against landslides.

8.0 Conclusions and Recommendation

8.1 Weir

Bed rock is exposed on river bed and weir foundation can be placed on exposed rock.

Right abutments is a constructed wall and existing height of this wall about 3-4m and can

be abut onto the wall. Left abutment can be placed on exposed bed rock.

8.2 Power House

Power house is located in a paddy field and not feasible to place a foundation.

8.3 Channel Trace

Channel route runs along the area covered by alluvium clay and detailed study has to be

carried out after finalizing the layout.

8.3 Periphery of the Pond

No major landslide could be observed along the periphery and very small scale localized

slope failures could be noticed.


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Fig 1. Location of Proposed Ankanda Mini-Hydropower Site (Not to Scale)

Location of Proposed Weir


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Exposed bedrock

Existin Weir

Photo 1. Exposed bed rock on river bed and location of existing weir

Right Abutment


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Photo 3. Topography of left bank upstream of Proposed weir axis

Left Bank

Photo 4. Proposed Powerhouse location

Power house location

ankanda geology report

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