Investigation of

7/29/2019 Investigation of

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DRAFT July, 2009

STANDARDS / MANUALS / GUIDELINES

FOR SMALL HYDRO DEVELOPMENT

SPONSOR:

MI NI STRY OF NEW AND RENEW ABLE

ENERGY

GOVERNMENT OF I NDI A

INVESTIGATION OF SMALL HYDRO

PROJECTS


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AHEC/MNRE/SHP Standards/Investigation of Small Hydro Projects/July 2009 1

INVESTIGATION OF SMALL HYDRO PROJECTS

SMALL HYDRO

The hydro power installations are normally classified by the output of hydropowerstation. The main category are Major hydropower schemes, medium hydropowerschemes & small hydropower schemes. In India, hydropower schemes up to 25 Mw

capacities are termed as small hydropower schemes. Central electricity authority has

further sub-classified the small hydro in three subcategories.

(i) Micro: Those having output upto 100kw.

(ii) Mini: Those having output from 101kw to 2000kw with unit size 1000kw.(iii) Small: Those having output from 2001kw to 25000kw with unit size 5000kw.

Small hydro may further be grouped under:

(i) Type-1: Run of the river schemes.

(ii) Type-2: Schemes on canal falls.

(iii) Type-3: Schemes utilizing the existing dam/barrage for water supply.

For type 2 & type 3 schemes, the availability of water is well defined. The schemes can

therefore be formulated on the basis of water available or water to be released from dam /barrage for the irrigation or for any other purpose for which the dam / barrage was

originally constructed. However the field investigations for layout of penstocks, power

channel, power house, switchyard, tailrace channel and other appurtenant works will be

required, similar to type 1 schemes i.e. run of the river schemes.

1.00 Run of the river schemes: The following field investigations would beessential.

(1) Topographical survey.(2) Geological mapping and exploration.(3) Hydrological and silt data collection.(4) Investigation and identification of construction material sites.(5) Power utilization/ evacuation facility.(6) Access to different components of the scheme.

Object of detailed investigations are:

(i) To access the general suitability of site for small hydropower project.(ii) To enable adequate & economical design to be prepared.(iii) To foresee and provide solution against difficulties that may arise due to

ground and other local conditions.

Selection of a proper site for project is the first important task which can be done with

the help of Survey of India topo sheets and reconnaissance survey of project area. The


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reconnaissance should involve visiting all possible locations which are available forconsideration and gathering information relative to each site as is possible without

detailed field explorations. The best map available should be obtained in many locations.

Preliminary layout of different components of projects should be laid out and the mostfeasible layout may be selected.

Next, detailed field surveys are to be carried out. The run of the schemes are mostlylocated in hilly terrain at Small River or large nalas. The stability of side slopes are most

important considerations for siting different structures. Unstable slopes are to be ignored

and sites which are away from slip zones, easily accessible site for men & materials

should be given more weightage.

1.1.0 TOPOGRAPHICAL SURVEYS:

After selection of suitable site, detailed surveys are required to be carried out. A survey

of India bench marks should be located and based on this survey of India bench mark a

project bench mark should be installed in the project area. This is very-very important forthe successful completion of project as well as to the life of project. Surveys for different

components of project as detailed below are to be carried out.

TABLE-1.1: Topographical Surveys for run of the river schemes

S.No. Feature Survey Requirement Scale Contour

Interval

Additional Requirement

1. L-section

along the

Stream

Bed level of the stream

along its center line from

5 km upstream of

diversion structure to 2

km downstream ofconfluence of tailrace.

1:10000 _ (i) Date of survey

(ii) Water levels on date

of survey along the stream

2. General

layout

(1) Contour plan to

cover all

components of the

project extending

from 2 km upstream

of diversion

Structure to 1 km

downstream of

confluence of

tailrace with the

river.

1:10000 5m

_

(2) River cross sections

at 200 m interval to

cover both banks

well above the

highest flood marks

and include water

conductor for the

1:500 _ The following information to

be included:

(i) Date of survey

(ii)Water level on date of

survey

(iii)Max. observed HFL on the

basis of flood marks.


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reach where it is

close to the river.

(3) Access road. 1:10000 5m _

3. Diversion

Structure

(1) Contour plan to

cover reach 50 m

upstream to 50 mdown stream of the

proposed structure

and extend at least

10 m above

anticipated highest

Flood level.

1:200 2m _

(2) 3 cross section,1

along the axis and 2

on either side

i.e.Upstream and

downstream of the

axis.

1:200 _ The following to be include

(i) Date of survey

(ii) Water level on the date of

survey

(iii) Max. Observed HFL on

the basis of flood marks.

4. Water

conductor

system

(1) Contour plan along

water conductor

alignment extending

20 m towards the hill

side and 10m

towards the valley

side.

1:500 5m _

(2) L section along the

alignment of water

conductor.

1:500 _ _

(3) Cross section along

the water conductor

at 100 m intervals

and at locations

where nalas are

intercepted as also at

locations where

topography change

abruptly.

1:500 _ _

(4) Three cross section

of the nalas one on

the alignment andone each on either

side of the

alignment.

1:500 _ _

(5) L section along

nalas 100 m on

either side of water

conductor.

_ _ The following information to

be include :

(i) Date of survey(ii) Water level on date of


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survey

(iii) HFL based on floodmarks to be indicated.

(6) Contour plan to

cover sufficient area

of the nalas and its

bank .

1:200 _ _

5. Forebay (1) Contour plan to

cover entire area of

forebay including its

vicinity.

1:500 2m _

(2) Longitudinal section

and 2-3 cross

section.

1:500 _ _

6. Penstock (1)Contour plan

extending 20 m either

side of the alignment.

1:500 2m _

(2)L sections alongpenstock alignment.

1:500 2m _

(3) Cross-section at

100m intervals along

alignment and at

anchor block

locations.

1:500 2m _

7. Powerhouse (1) Contour plan to

cover sufficient area

to include differentalternative layouts of

powerhouse and

switchyard and

tailrace channel up

to its confluence

with the river.

1:200 2m _

(2) L sections along the

powerhouse and

tailrace channel upto

its confluence with

the river.

1:200 - The following information to

be included:

(i) Date of survey.(ii) Water level at the point of

confluence of the tailrace

with the river on the dataof survey.

(iii) Max. observed HFL onthe basis of flood marks.

(3) Access road to

powerhouse.

1:200 2m -


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1.1.2 For schemes on canal falls detailed field surveys are to be carried out after aninitial reconnaissance survey when information needs to be collected about the

topographical features and constraints for locating the bypass channel and powerhouseadjacent to the fall structure. After a study of these particulars the alignment should be

identified in the first instance. Detailed field survey is to be carried out for the identified

alignment and location, covering sufficient area to examine all possible shifts in locationsto arrive at an optimum alignment and positioning of structures. The scale and particularsof the survey are included in table 1.1.2 below.

TABLE-1.1.2 Topographical Surveys for schemes on canal falls


Interval

Additional

Requirement

1. General

layout

(1) Contour plan(2) Longitudinal section 1:10001:1000 2m Approach roadrouting to

intake andpowerhouseswitchyard

locations to be

included.

2. Intake of the

canal

(1) Contour plan(2) Longitudinal section and 2

cross-section

1:200

1:200

2m Longitudinal

section toinclude canal

and inlet area.

3 Widenedcanal bypass

canal

(1) Contour plan(2) Longitudinal section and

cross-sections.

1:2001:200

2m -

4 Powerhouse

and

switchyard

(1) contour Plan(2) Longitudinal section and 2

cross-sections.

1:200

1:200

2m -

5 Tailrace (1) Contour plan

(2) Longitudinal section and cross-Sections.

1:200

1:200

2m Longitudinal

section toinclude outfall

area

(connecting tothe canal)

6 Outfall into

canal

(1)Contour Plan(2)Longitudinal section and 2

cross-sections.

1:200

1:200

2m Longitudinal

section toinclude canal

and outletarea.

1.1.3 For Powerhouse located downstream of an existing Dam/Barrage detailed fieldsurvey will be carried out after initial reconnaissance survey when the alignment of the

water conductor system and the location of the powerhouse, tailrace and switchyard are


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identified taking into account topographical constraints. Detailed topographical surveyshall be carried out for the identified alignment and locations. The survey shall cover

sufficient area to enable examination of all possible shifts in alignment and locations to

arrive at an optimum alignment and positioning of structures. Accurate drawings ofexisting structures which are linked with the planned small hydroelectric scheme should

be obtained and used for necessary co-ordination. The scale and particulars of the surveyare indicated in table 1.1.3 below

TABLE-1.1.3 Topographical Surveys for Powerhouse located downstream

of an existing Dam/Barrage


Interval

Additional

Requirement

1. General

layout

(1) Contour plan.(2) Longitudinal section.

1:1000

1:1000

2m Approach

road routingto intake and

powerhouse

andswitchyard to

be included.

2. Intake area (1) Contour plan.(2) Longitudinal section and

cross-section.

1:200

1:1000

2m -

3 Water

conductor

(1) Contour plan(2) Longitudinal section and

cross-section.

1:200

1:200

2m(2m in

flatterrain or

5m in

hilly

terrain)

-

4 Powerhouse

andswitchyard

(1) Contour plan.(2) Longitudinal section and

cross-section.

1:200

1:200

2m -

5 Tailrace (1) Contour plan.(2) Longitudinal section and

cross-section.

1:2001:200

2m -

6 Outfall fromtailrace (1)

Contour plan.(2) Longitudinal section andcross-section.

1:2001:200 2m -

2.0 GEOLOGICAL INVESTIGATIONS:


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Small hydro electric schemes involve comparatively small size structure as comparedto major hydroelectric schemes. Exploration by trial pits or trenches for various features

is sufficient to meet the requirement, for small dams and tunnels. A judicious & careful

geological assessment with limited geological exploration is essential for electingappropriate alignment and siting the various structures of the scheme. A reconnaissance

survey of the alignment shall be carried out for obtaining a general idea of the regional &localized geology to identify the problem areas to firm up the layout. The problem areasshould be studied from geotechnical aspects and layout firmed up with necessary

modifications.

2.1 DIVERSION STRUCTURE:

Geological explorations to be conducted with trial pits as close to deepest bed level as

possible & two trial pits on each bank. One of three locations should be at proposedintake structure. Geological assessment of abutment conditions and the hill slopes of the

abutment with a geological section indicating the dip & strike direction shall be made.

This will be helpful in assessing the stability of the hill slopes of excavated abutment.

2.2 WATER CONDUCTOR SYSTEM:

A few trial pits along the alignment at every 500m, which should include vulnerablereaches should be taken for the geological assessment of the foundation strata as also

permeability & other subsidence characteristics. Slope stability of excavated hill slopes

for laying water conductor system is very impartment. For this a geological sectionsshould be developed by surface observations at 200m. Interval including at vulnerable /

critical locations. If water conductor system comprises of tunnel reach, in addition to ageological section along the alignment, more detailed information on the nature of &

classification of rock mass, joint patterns encountered along the alignment, the strike &

dip pattern needs to be collected with identification of reaches of shear zone and rockclassification. The inlet & outlet portal of tunnel needs to be investigated for stability of

excavated slope .

2.3 FOREBAY:

A trial pit at the location of forebay shall be taken to assess the foundation strata. The

hill slope behind & below forebay may be assessed for stability. The foundation stratashall be assessed for permeability characteristics.

2.4 PENSTOCKS:

Penstock slope shall be investigated for slope stability by developing a geological

section on the basis of reconnaissance survey on the alignment. Foundation strata atanchor block and saddle locations shall be assessed by trial pits at representative

locations.


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2.5 POWERHOUSE:

Foundations strata at powerhouse shall be assessed by trial pits. Powerhouseexcavation slopes shall be assessed for slope stability by developing geological sections

on the basis of reconnaissance survey by the geologist.

2.5.1 Type 2: Schemes on canal falls.The stability of excavated slopes for intake channel and tailrace channel/bypass

channel and powerhouse needs to be investigated by developing geological section and/orstudy of soil characteristics and ground water conditions. The foundation strata of the

powerhouse, inlet and outlet structures shall be investigated by trial pits.

2.5.2 Type 3 : Powerhouse located downstream of an existing dam/barrage.

The stability of water conductor system shall be ascertained by geological sections as

in case of type 1. In case water conductor system comprises a tunnel a geological section

along the tunnel alignment is to be developed as suggested for the tunnel reach of type 1.The assessment has also to be based on borehole logging data at the inlet portal, exit

portal and reaches of low rock cover. Powerhouse foundation needs to be investigated by

either trial pits or by bore holes where warranted. Geological assessment for approachchannel and tail race needs to be made.

Requirement of Geological Field Investigations

It is desirable that a geological assessment of the geological features at the various

locations of the scheme is made through a site visit by a well experienced geologist inconsultation with the design engineers regarding technical aspects. The requirement of

geological field investigations are as below.

Table 2.1: Geological Field Investigation (Type-1)

S.No. Structure No. of trial

pits/borehole

Location of trial

pits

Depth of

trial pits

Additional

requirement

1 Diversion structure

(i) conventionalweir/trench

weir

(ii) Low dam

Trial pits 3nos.

Borehole 3

nos.

One trial pit atmiddle and two

trial pits, one

each on eitherabutment end.

One borehole at

middle and oneborehole at intake

location.

1.5 -2 m

Up to

foundationlevel of

dam

Geological assessmentof stability of rock

slope on either

abutment

----

2 Water Conductor

(i) Surface Trial pits 3-5 Trial pits at every 1.5-2 m Geological assessment


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(ii) Tunnel

nos.

Borehole 3nos.

500m. c/c and at

critical locations.

Intake portal 1

no.Outlet portal 1

no.

Low cover reach 1 no.

Up totunnel

grade

of stability of rock

slopes along the

alignment reach-wise.(1)Delineation of

shear zone

(2)Geologicalassessment along

alignment

(3)Geophysicalassessment

3 Forebay Trial pits 2nos.

One trial pit inforebay area and

another trial pit at

penstock intakelocation.

1.5 2 m Geological assessmentof rock slope on hill

side of forebay.

4 Penstock Trial pits 2

nos.

Along the

alignment ofpenstock

preferably at

another block

locations.

1.5 2 m Geological assessment

of penstock slope.

5 Powerhouse Trial pits 1

no.

Powerhouse area 1.5 2 m Geological assessment

of excavation slope.

6 Tailrace Trial pits 1no.

Along thealignment

1.5 2 m Geological assessmentof excavation slope.

Table 2.2 : Geological Field Investigation (Type-2)

S.No. Structure No. of

trial pits

Location of trial pits Depth

of trial

pits

Additional

requirement

1 WaterConductor

4 (1) At inlet 1 no.(2) Upstream of

powerhouse - 1 no.

(3) Downstream of

powerhouse 1 no.

(4) At outlet 1 no.

1.5 -2 m Geological assessmentof stability of

excavation slopes.

2 Powerhouse 1 Powerhouse area. 1.5-2 m Geological assessmentof excavation slopes

and powerhouse

foundation grade.


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Table 2.3: Geological field investigation (Type-3)

S.No. Structure No. of trial

pits

Location of trial pits Depth of trial

pits

Additional

requirement

1 Intake Borehole-1no.

Intake area Uptofoundation

level ofstructure

Geologicalassessment of

stability ofexcavation slopes.

2 Approachchannel

1no. Approach channellocation.

1.5m to 2m Geologicalassessment of the

area.

3 Water

conductor

(a) Open

(b) Tunnel

Trial Pits-2-3no.

Borehole-3no.

Along alignment

(1)Intake portal-1no.(2)Outlet portal-1no.(3)Low cover reach-

1no.

1.5m to 2m

Delineation ofshear zones

upto tunnel

grade


stability ofexcavation slopes

Geologicalassessment along

alignment.

4 Power

house

Trial Pit-

1no.

Powerhouse area 1.5 to 2m Geological

assessment of

stability ofexcavation slopes

and powerhouse

foundation grade.5 Tailrace

(a) Open

(b) Tunnel

Trial Pit-1.3no.

Borehole-3no.

Along alignment

At portal, alongalignment and at low

cover reach.

1.5 to 2m

Upto tunnelgrade


excavation slopes.

(1)Geologicalassessment

along

alignment.

(2)Delineation ofshear zones.

Subsurface Explorations are also required if tunneling is involved.Generally for major

and medium hydroelectric projects this aspect is important but for small hydro the need is

rare.For small hydro projects drilling and drifting gives a fare idea of subsurface geology.

3.0 HYDROLOGICAL INVESTIGATIONS:


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Acquiring a set of reliable hydrological data for a reasonable length of time forassessing the pattern of stream flow at different times in representative years, good as

well bad ,is the most essential requirement for a dependable formulation of a

hydroelectric project, be a big or small. Besides the pattern of stream flows, otherHydrologic inputs required for the design of project components are design flood, water

quality and sediment transportation. The hydrological data cannot be acquired by justvisiting the site for carrying out discharge measurements for a short while. It is necessaryto acquire the long duration data.

It is necessary first to collect the minimum essential hydrological data and secondly,

make analysis to establish a reliable flow quantity and other hydrological inputs.

3.1 DATA REQUIREMENT

The following data are required for a project.

(a) Rainfall and snowfall(b) Climatological parameters like temperature, humidity, wind and cloudiness.(c) River gauges and discharges.(d) Past flood discharges.(e)

Sediment load.(f) Water quality.

The rainfall, snowfall and other climatological data are available with the India

Meteorological Department (IMD). Most of the major rivers and their tributaries are

being continuously gauged by the state governments and central water commission. Suchgauging includes water levels, discharges, flood discharges and sediment samples.

However such data is normally not available in respect of small hydro projects located on

small streams.The streams across which small hydroelectric schemes are proposed, lack in most

cases any measured stream flow data. The entire catchment may not have even a singlerain gauge station. In such situation, there is need for establishing a gauging station near

about the proposed project site. The discharge measurements should preferably cover a

minimum period of two lean seasons and one flood season. A period of two years is tooshort for assessing a long term flow series but, the small hydro electric schemes are

meant to be taken up for quickly deriving benefits without waiting for long period and

without investing much capital so as to prove most economical project in limited capital.

Discharge measureing techniques: For discharge measurement the followingtechniques are employed. Bureau of Indian Standards(BIS) are available for detailed

guidance.

(i) Notches, weirs and flumes. BIS no. 1193-1959(ii) Velocity area method. BIS no. 1192-1959

(iii) Slope area method. BIS NO. 2912-1964

(iv) Stream gauging CWPRS manual for stream gauging.Discharge measuring instruments: The measuring instruments comprises ofrectangular or a v- notch, flumes, gauges, floats, current meters, stop watches etc. While

using current meters, care should be taken that the current meter is properly calibratedfrom a reliable institution. Current meters are calibrated by CWPRS Pune, IRI Roorkee

and in some Engineering institutions. The accuracy of measurement is totally based on

the calibration chart of a particular current meter. Simultaneous with river gauging, the

rain gauge (s) should be installed, if there is no rain gauge in the project catchment.


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Along with river discharges, the samples of silt in river during monsoon flows should becollected.

3.2 WATER AVAILABILITY

The water availability is the basic hydrological input for assessing power potential and

energy generation. A great care is needed to assess river flows as accurately as possible.Depending on the type and length of data, technique of water assessment would beapplied to get best possible and most dependable water availability.

The spillway of diversion structure is designed to pass safely a predetermined flood

discharge

3.3 DESIGN FLOOD LEVEL

Design flood level are computed for the intake and power house site for providing

necessary protection works if necessary.

3.4 SEDIMENTATION

The generation unit may suffer heavily due to damage of underwater components onaccount of highly erosive action of silt water. Besides damaging runners and guide vanes,

the erosive action of silt causes operation and maintenance problems.

The small diversion structure without storage, divert silt laden water into the water

conductor. Some of the silt would get removed through trash racks and desiltingarrangement provided before the fore bay. A desilting chamber is generally constructed

to minimize the silt load

4.0 CONSTRUCTION MATERIAL SURVEY:

Availability of required quantity & quality construction material like aggregate,boulders, sand for construction works and its location shall be surveyed in project area or

nearby area. Material testing laboratory shall be required for testing the quality ofmaterial which may have to be established or samples may be sent for testing to some

nearby reliable laboratory.

5.0 SURVEY FOR EVACUATING POWER:

The following survey shall be carried out:

(iv) Present position of power supply in the region, system loads, loadfactor, unit generated per kw installed capacity.

(v) Detailes of major loads to be served, energy demand etc.(vi) A plan showing the proposal for evacuation of power.(vii) Study of near by grid substation where power is likely to be fed.

6.0 ENVIRONMENTAL CONSIDERATION:

A careful evaluation of impact of proposed scheme on the environment shall be

carried out and necessary measures to be planned well in advance to mitigate the adverseeffect. Major hydroelectric projects are being considered as potential threat to the

environment. Tehri , Sardar Sarover and other so many projects are the glaring example.


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Projects are being throttled either by delaying environmental clearance or by imposingunreasonable conditions in terms of environmental cost. Environment specialists however

seem somewhat inclined towards small hydro perhaps with a feeling that impacts of small

hydro projects are going to be smaller which can be mitigated easily. Small hydro isfavorable due to the following.

(i) Lesser submergence.(ii) Lesser requirement of land including forest land.(iii) Least impact on flora and fauna (both aquatic and terrestrial)

(iv) Less possibility of community displacement.(v) No environment pollution.

Following surveys would be required.(i) Area to be used for project construction, staff colony and resettlement of local

population.

(ii) Area of submergence.(iii) Details of families likely to be displaced, numbers. of SC/ST families, their

trade and scheme of their rehabilitation.

(iv)

Social/ cultural/religious compensation.(v) If any important mineral resources to be lost, if so its magnitude andestimated loss.

(vi) If any monument/site of cultural, historical, religious or archaeologicalimportance fall in project area if so, plan of relocation.

(vii) Any rare endangered species of flora and fauna in the project area andmeasures to salvage/rehabilitate them.

(viii) Wild life if affected.(ix) Potential loss to aquatic life such as fish, impact to their migratory behavior.(x) Expected loss to trees and to make up the loss, identification of land for

plantation.

(xi) Arrangement to meet fuel requirement of labour force during constructionand afterwards.

(xii) Arrangement for restoration of land in construction area.

7.0 SOCIO-ECONOMIC SURVEY

The following information will be collected.

(i) Area of land required for physical components of project.(ii) Type of land i.e. agricultural, residential, details of crop, vegetation

etc.

(iii) Ownership of land i.e. government, private, traditional population,encumbrances details etc.

(iv) Current land use in proposed area and surroundings.

(v) Possible land use change expected after project implimentation.(vi) Possible strategy for procurement of land i.e. government lease, direct

purchase, negotiated settlement or compulsory acquisition etc.,

Detailed description of area falling under each category(vii) Name of the people and families affected( details as necessary)


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(a) Including those loosing home and livelihood.(b) Those deriving benefits (employment, electricity etc) from the

project.

(c) Those adversely affected by imposition of an external population onlocal cultures (i.e. women, tribals)

(viii) Assessment of positive and negative impact.(ix) Assessment of cultural impact on population due to land acquisitionfor project.

(x) Assessment of need for rehabilitation and resettlement implementation.

(xi) Study of national and state legal frame work existing, the relevant

provisions and applicability for the specific case as identified above.(xii) Entitlement calculations for payment of compensation for various

losses or replacement values.

(xiii) Existing and proposed mechanisms/ efforts for public consultationsand disclosures of information/ statutory requirement, if any for

above.

(ix) Expected public participation during the project implementation.(xv)Grievances redressal mechanism legally available as well as socially

acceptable.

(xvi) Remedies available through Lok Adalats, Village Pachayats,NGOsetc.

(xvii) Manpower locally available.8.0 ACCESS TO THE DIFFERENT COMPONENT OF SCHEME

On the topographic plan, layout of existing roads shall be marked. The requirement ofthe new approach roads, bridges, culverts, shall be assessed for smooth construction work

& later on maintenance of works.

_________________________

Documents

Investigation of