Ch. 5 Hydrology and Water Assessment

65

Chapter – 5

Hydrology and Water Assessment

5.0 General

The proposed Ponnaiyar (Nedungal) - Palar link project envisages diversion of

86 Mm3 of flood waters of Ponnaiyar river occurring at Krishnagiri dam for recharging

ground water in Palar basin for stabilizing the existing ayacut being irrigated under open

wells/bore wells in Vaniyambadi taluka of Vellore district as well as feeding system tanks

(Eris) in enroute areas of Krishnagiri and Pochampalli talukas of Krishnagiri district and

Tirupattur taluka of Vellore district besides providing drinking water supply to about 1.52

lakh people enroute the link canal. The Ponnaiyar (Nedungal)-Palar link project area has

four distinct seasons viz., dry period from January to February, hot period from March to

May, south-west monsoon from June to September and north-east monsoon from October

to December. The climate is cold from December to February followed by hot season from

March to May. In general, the project area has a pleasant climate. The hydrology and water

availability studies of the project are based on the Rainfall-Runoff relationship developed at

Krishnagiri dam site. However, the divertable quantity is based on the average flood spills

during monsoon period from the existing Krishnagiri dam.

5.1 General Information about Regions

(a) Ponnaiyar Basin

The climate of the basin area is pleasant throughout the year, as per the

climatological data observed at Dharmapuri IMD station which is nearer to the project area.

The average annual rainfall of the basin is 977 mm. The basin receives about 76% of the

annual rainfall during monsoon period i.e. from June to December. The normal daily

maximum and minimum temperature found to be 37.1o C and 17.2o C in the months of April

and January respectively. The normal maximum and minimum relative humidity is found to

be 78% and 31% in the months of December and March respectively. The normal

maximum and minimum wind velocities are 10.30 km/hr in June and 4.60 km/hr in October.

The normal maximum cloud cover is 6.6 oktas during the month of July, where as the

normal minimum cloud cover is 1.50 oktas is found during the month of March.

66

(b) Palar Basin

The climate of the Palar basin area is pleasant throughout the year except

during summer. The average annual rainfall of the basin is 891 mm. The basin receives

most of the rainfall from the south-west and north-east monsoons as such June to

December is considered as monsoon period. As per the climatological data of IMD

observatory located at Vellore the basin receives about 80% of the annual rainfall during the

monsoon period. The normal daily maximum and minimum temperature is 38.9o C in May

and 18.1o C in January respectively. The normal relative humidity varies from 37% in the

month of March to 86% in the month of December. The normal maximum and minimum

wind speed is found 10.4 km/hr during June and 5.5 km/hr during October. The normal

maximum cloud cover is 6.9 oktas during July and minimum cloud cover 2.0 oktas in May.

5.1.1 Specific Information

5.1.1.1 Drainage Basin

(a) Ponnaiyar Basin

The Ponnaiyar is a major river amongst the streams between Palar and

Cauvery. The Ponnaiyar basin is part of the basin area covered by the streams between

Palar and Cauvery. The basin area covered by the streams between Palar and Cauvery

comprises four rivers viz., Ongur, Varahanadi, Ponnaiyar including Gadilam and Vellar with

each of the four rivers draining independently in to the Bay of Bengal. The Ponnaiyar river

originates near Nandidurg in Kolar district of Karnataka State at an elevation of about 900 m

above mean sea level. The total length of the river is about 351 km and its average bed

slope is 1 in 390. The river basin lies between latitudes 11o 45’ N and 13o 30’ N and

longitudes 77o 33’ E and 79o 47’ E. The total catchment area of Ponnaiyar including Gadilam

rivers is 15679 km2 of which 3545 km2 lies in Karnataka, 133 km2 in Andhra Pradesh, 11961

km2 in Tamil Nadu and 40 km2 in Union Territory of Puducherry. The entire basin area

covered by the streams between Palar and Cauvery has been divided in to three hydrological

zones viz., Zone-I: Varahanadi basin (4513 km2), Zone-II: Ponnaiyar basin including

Gadilum river (15679 km2) and Zone-III: Vellar basin (8086 km2). The river network in

Ponnaiyar and Palar basins showing the above three Zones is depicted in Fig 5.1.

The Ponnaiyar basin covers Kolar, Chikballapur, Bengaluru urban including Bengaluru

city and Bengaluru rural districts of Karnataka; Chittoor district of Andhra Pradesh;

Dharmapuri, Krishnagiri, Salem, Vellore Thiruvannamalai, Villupuram and Cuddalore districts

of Tamil Nadu; and Union Territory of Puducherry. The Ponnaiyar basin is bounded by

67

Arkavathi and Chinnar sub-basins of Cauvery basin on the west, Vellar sub-basin on the

south, Palar basin on the north and Bay of Bengal on the East. Markanda nadi, Vanniar,

Pambar, Kallar and Gadilam are the tributaries of Ponnaiyar river.

(b) Palar Basin

The Palar river originates in Kolar district of Karnataka state near Kaivara

village at an altitude of 900 m to the west of Ambojidurga and Rahamankhar peaks. The

river basin lies between the latitudes 12o 15’ N to 13o 37’ N and longitudes 77o 53’ E to

80o 10’ E. The total length of the river is 348 km. The total catchment area of the basin is

17871 km2 of which 2813 km2 lies in Karnataka, 5018 km2 in Andhra Pradesh and 10040 km2

lies in Tamil Nadu. The tributaries of Palar are Poini, Malattar, Kal Ar, Kaundinya Nadi and

Cheyyar. Poini joins Palar from the left side of the river near Ranipet and Cheyyar joins from

the right side near Gurumancheri.

The Palar basin covers Bengaluru Rural, Chikballapur and Kolar districts of

Karnataka state; Chittoor district of Andhra Pradesh; and Vellore, Thiruvannamalai,

Kancheepuram and Thiruvallur districts of Tamil Nadu. The basin is bounded by streams

between Palar and Cauvery in the west and south, Pennar basin in the north and

streams between Pennar and Palar in the east.

68

69

5.1.1.2 Command Area

The Ponnaiyar (Nedungal) - Palar link project envisages diversion of 86 Mm3

of flood waters of Ponnaiyar river from Nedungal Anicut to the water starved Vaniyambadi

Taluka of Palar basin along with enroute areas of Krishnagiri and Vellore districts for

recharging the Ground water for stabilizing the existing irrigated area to an extent of about

9850 ha annually which is now being irrigated through open wells and bore wells. Out of

9850 ha an area of 7950 ha will be benefitted in Vaniyambadi Taluka of Vellore district by

utilising about 57.926 Mm3 of water and 1900 ha in enroute areas of Krishnagiri and Vellore

districts by utilising about 17.215 Mm3 besides providing drinking water supply to 1.52 lakh

people by utilising 3.882 Mm3.

5.1.1.3 Floods and Drainage

(a) Ponnaiyar Basin

The gauge and discharge data is being observed by the Public Works

Department, Govt. of Tamil Nadu at Krishnagiri dam on Ponnaiyar river which is about

16 km upstream of the existing Nedungal Anicut. The daily inflow data is available for a

period of 52 years i.e., from 1958-59 to 2009-10. The maximum observed flood at

Krishnagiri dam was 3007 cumec on 11.11.1903. The design flood of Krishnagiri dam was

4234 cumec.

(b) Palar Basin

The gauge and discharge data is being recorded by Central Water

Commission at Arcot G&D site on Palar river and is available from the year 1972. The

maximum observed discharge at this G&D site was 528.2 cumec on 13.09.1981.

The Hydrometeorological, Hydrological stations and Isohyetals in Ponnaiyar

and Palar river systems are shown in Fig 5.2 and 5.3 respectively.

70

71

72

5.1.1.4 River Geometry

The schematic diagram of Ponnaiyar and Palar river systems is as in Fig. 5.4

gives an overview of the river geometry.

Fig .- 5.4 Schematic diagram of the Ponnaiyar – Palar river system with

Major structures and link canal

73

5.1.1.5 Groundwater Recharge

The proposed diversion through link canal recharges the ground water

enroute the link canal and in Palar basin, thereby raising ground water table as well as

improvement in the quality of water. As per the Central Ground Water Board studies the

long term water level fluctuation for the period from 1998 - 2007 indicates rise in water level

in Vellore district ranges from 0.0025 to 0.5264 m/year. The fall in water level ranges

between 0.568 to 2.3958 m/year.

5.1.1.6 Reservoir Area

The Ponnaiyar (Nedungal) - Palar link canal off-takes from the existing

Nedungal Anicut across Ponnaiyar river. The Anicut is situated in Krishnagiri Taluka of

Krishnagiri District near Nedungal Village at latitude 12o 22’ N and longitude 78o 16’ E. The

Anicut is located 16 km downstream of the existing Krishnagiri dam. The crest level of the

Anicut is 434.71 m. The Anicut is approachable by all weather roads nearby.

The flood water spills from existing Krishnagiri dam will be regulated to link

canal through existing Nedungal Anicut. The Krishnagiri dam is located in Krishnagiri District

of Tamil Nadu near Krishnagiri Town. The latitude and longitude of the Krishnagiri dam are

12o 28’ N and 78o 11’ E respectively. The catchment area of the Ponnaiyar river up to

Krishnagiri dam is 5428 km2. Height of the dam is 29.26 m and the length of earth dam and

masonry dam is 712.93 m and 277.67 m respectively. The spill way discharge capacity is

4061 cumec with 8 vents of 12.19 x 6.10 m size. The crest level of spillway is 477.01 m.

The submergence area of the reservoir at FRL 483.11 m is 10.723 km2 with gross storage

capacity of 47.184 Mm3.

5.1.1.7 Other Water Usage

The flood water spill down the existing Krishnagiri dam will be diverted into

link canal through Nedungal Anicut for stabilizing the existing area being irrigated through

open wells and bore wells by recharging the Ground water potential in Tirupattur and

Vaniyambadi talukas of Vellore District and Krishnagiri and Pochampalli talukas of Krishnagiri

District. In addition to irrigation use enroute villages will be supplied with domestic water to

the tune of 3.882 Mm3.

74

5.1.1.8 Navigation

The Ponnaiyar and Palar rivers are not presently used for any navigational

purpose. There is no proposal of navigation in the proposed Ponnaiyar (Nedungal) - Palar

link canal.

5.1.2 Data Availability

(a) Ponnaiyar Basin

5.1.2.1 Hydrological and Meteorological Investigations

Rainfall and Snowfall

There is no snowfall in Ponnaiyar basin. The precipitation in the basin is in

the form of rainfall and the intensity of rainfall varies fairly in time and space as observed

from the data. There are 67 raingauge stations in and around the Ponnaiyar basin, out of

which 18 stations are in the Ponnaiyar basin upto Krishnagiri dam site. The basin receives

almost 80% of the annual rainfall during monsoon period from June to December. The

average annual rainfall of the Ponnaiyar basin upto Krishnagiri dam site is 795 mm. The

period of availability of rainfall data and average annual rainfall (mm) of each raingauge

station of Ponnaiyar basin up to Krishnagiri dam site is given below in Table-5.1. The

location of the existing rain gauges in the Ponnaiyar basin is shown in Fig 5.2.

Table-5.1

Raingauge Stations in Ponnaiyar Basin up to Krishnagiri Dam Site and their Period of Availability

Sl. No. Name of the Rain gauge Station

Period of availability

Record length in

years

Average Annual Rainfall (mm)

From To

1. Rayakota 1901 2009 109 702

2. Krishnagiri 1901 2009 109 882

3. Hosur 1901 2009 109 757

4. Denkanikota 1901 2009 109 997

5. Anekal 1901 2009 109 915

6. Bengaluru 1901 2009 109 949

7. Hebbal 1901 2009 109 806

8. Devanahalli 1901 2009 109 777

9. Hoskote 1901 2009 109 780

10. Sol Devanahalli 1901 2009 109 711

11. Doddabalapur 1901 2009 109 810

12. Malur 1901 2009 109 725

13. Bangarpet 1901 2009 109 730

75

Sl. No. Name of the Rain gauge Station

Period of

availability

Record

length in

years

Average

Annual

Rainfall

(mm)

From To

14. Chikballapur 1901 2009 109 841

15. Siddalaghatta 1901 2009 109 757

16. Kolar 1901 2009 109 739

17. Chinthamani 1901 2009 109 655

18. Kuppam 1901 2009 109 779

Average 1901 2009 795

Sunshine, Cloud Cover and Visibility

The Dharmapuri Meteorological Station is located inside the Ponnaiyar basin

and nearer to the link project. As per this IMD observatory, based on the observations

during the period 1961-1990, the normal maximum cloud cover of 6.6 Oktas is observed in

the month of July and a normal minimum of 1.50 Oktas is observed in the month of March.

Wind Velocity

As per the IMD observatory of Dharmapuri, based on the observations during

the period 1961-1990, the normal maximum and minimum normal wind speed observed at

Dharmapuri IMD observatory is 10.3 kmph and 4.6 kmph during the months of June and

October respectively.

Relative Humidity


the period 1961-1990, the relative humidity is maximum during monsoon months and

minimum during winter and summer months. The monthly normal maximum and minimum

relative humidity observed at Dharmapuri IMD observatory is 78% in December and 31% in

March, respectively.

Temperature


the period 1961-1990, the normal daily maximum and minimum temperature recorded is

37.1OC in April and 17.2OC in January.

(b) Palar Basin

There are 60 rain gauge stations located in and adjacent of the Palar basin

including Poini and Cheyyar basins. There is no snowfall in Palar basin. The data at these

stations is available for varying periods from 1901-02 to 2009-10. The location of the

76

existing rain gauges in the basin is shown in Fig. 5.3. The basin receives almost 80% of

the annual rainfall during monsoon period from June to December.

5.1.2.2 Pan Evaporation

Though there is a Pan-evaporimeter installed at Krishnagiri dam site, the pan

evaporation data observed at this site is not used for calculating the evaporation losses of

the reservoir since the link project envisages transfer of flood waters spilling down the

existing Krishnagiri dam and as such no simulation study has been carried out.

5.1.2.3 Climatological Parameters like Temperature, Humidity

and Wind Speed

At Dharmapuri IMD observatory

The normal values (1961-1990) of various climatological parameters in the

vicinity of Krishnagiri dam (Dharmapuri IMD observatory) are as follows.

Max. Min.

Air temperature (oC) 37.1 (April) 17.2 (Jan.)

Humidity (Percentage) 78.0 (Dec.) 31.0 (March)

Wind speed (km/hr) 10.3(June) 4.6 (Oct.)

Cloud cover (oktas) 6.6 (July) 1.5 (March)

At Vellore IMD observatory

The normal values (1961 – 1990) of various climatological parameters for the

command area (IMD observatory at Vellore) of the link project are as follows.

Max. Min.

Air temperature (oC) 38.9 (May) 18.1(Jan.)

Humidity (Percentage) 86.0 (Dec.) 37.0 (Mar.)

Wind speed (km/hr) 10.4 (June) 5.5 (Oct.)

Cloud cover (oktas) 6.9 (July) 2.0 (March)

5.1.2.4 River Gauge and Discharge

Gauge and Discharge data is being observed by Public Works Department,

Govt. of Tamil Nadu at 5 G&D sites across Ponnaiyar river. The Central Water Commission

is also maintaining 3 G&D sites on Ponnaiyar river. The details of these G&D sites are given

in Table 5.2.

77

Table 5.2 Details of G&D Sites

Sl. No.

Name of Gauge & discharge site

Maintained by

River / Tributary

Catchment area

(Km2)

Year from which data is available

1. Krishnagiri Reservoir PWD Ponnaiyar 5428 1958

2. Nedungal Anicut PWD -do- 5694 1960

3. Sathanur Reservoir PWD -do- 10826 1960

4. Tirukkoilur Anicut PWD -do- 12318 1960

5. Ellis Choultry Anicut PWD -do- 12477 1960

6. Gummanur CWC -do- 4620 1978

7. Valavachchanur CWC -do- 10780 1978

8. Villupuram CWC -do- 12900 1973

Out of the above 8 G&D sites the G&D site at Krishnagiri reservoir located on

Ponnaiyar river for which the monthly inflow data is available for a period of 52 years from

1958-59 to 2009-10 has been used for correlating rainfall-runoff relationship by regression

analysis at Krishnagiri dam site.

5.1.2.5 Sediment (Suspended and Bed Load) Inflow

Sediment analysis is being carried out by Central Water Commission (CWC) at

Gummanur G&D site (C.A:4620 km2) and at Valavachchanur G&D site (C.A:10780 km2).

Since the existing Krishnagiri dam (C.A:5428 km2) is proposed as controlling structure to

divert the flood water of Ponnaiyar river the data on sediment inflow at Gummanur G&D

site which is located u/s of Krishnagiri dam for the period from 1982-83 to 2012-13 is

furnished in Table 5.3.

Table 5.3

Annual Sediment Load at Gummanur G&D Site on Ponnaiyar River

C.A: 4620 km2

Year Monsoon (M.T.)

Non-Monsoon (M.T.)

Annual Load (M.T.)

Annual Run-off (MCM)

1982-1983 33482 271 33753 64

1983-1984 43348 213 43561 83

1984-1985 138032 1152 139184 130

1985-1986 58559 19182 77741 62

78

Year Monsoon (M.T.)

Non-Monsoon (M.T.)

Annual Load (M.T.)

Annual Run-off (MCM)

1986-1987 123427 48 123475 198

1987-1988 285900 173 286073 220

1988-1989 194828 27 194855 243

1989-1990 89420 10965 100385 173

1990-1991 24680 83 24763 26

1991-1992 305967 3210 309177 532

1992-1993 29938 20 29958 70

1993-1994 12321 174 12495 170

1994-1995 3446 70 3516 78

1995-1996 13163 8 13171 141

1996-1997 18541 91 18632 234

1997-1998 118661 2153 120814 314

1998-1999 31774 176 31950 301

1999-2000 46108 132 46240 245

2000-2001 23572 21 23593 309

2001-2002 38780 90 38870 309

2002-2003 436 4 440 46

2003-2004 1597 80 1677 51

2004-2005 15692 1102 16794 197

2005-2006 207415 5653 213068 795

2006-2007 Sediment observation not done

2007-2008 Sediment observation not done

2008-2009 12834 1393 14227 311

2009-2010 7264 1391 8655 216

2010-2011 4497 2662 7159 205

2011-2012 6785 2079 8864 218

2012-2013 4491 1859 6350 99

Source: Office of the Executive Engineer, SR Division, CWC, Coimbatore, Tamil Nadu.

From the above data the average annual sediment inflow at Gummanur site

works out to 67222 M.T.

79

5.1.2.6 Water Quality

Public Works Department (PWD), Govt. of Tamil Nadu collected the Water

samples of Krishnagiri Dam during all the months from different points such as reservoir,

seepage water from drainage galleries, toe-drain of earthen section for analysis at Soil

Mechanics and Research Division, WRO, PWD, Chennai for both chemical and physio-

chemical analysis for ascertaining the water quality status. The latest data for the period

from 2009 to 2013 on laboratory test results of the water samples of Krishnagiri reservoir

has been collected. Details on results of the water samples are given in Chapter-4

‘Surveys & Investigations’ under para 4.6.7.

5.2 Surface Water Balance of Ponnaiyar Basin upto

Krishnagiri Dam Site

5.2.1 Hydrological Data Requirement

For development of rainfall-runoff relationship monthly rainfall and concurrent

stream flow data is required. The inflows to the reservoir are affected by water utilization in

the upstream. Hence the utilization data of the upstream projects is also required to

compute the reservoir inflows. The periodic water demands, releases from the reservoir and

evaporation rates in the reservoir area are also required.

5.2.2 Time Unit for Simulation Studies

The project envisages diversion of flood waters spilled down the existing

Krishnagiri dam as such no simulation studies are carried out. However, monthly monsoon

spill data at Krishnagiri reservoir for the period from 1958 to 2009 is considered to estimate

flood water spills down the Krishnagiri reservoir.

5.2.3 Compilation and Processing of Basic Hydrological Data

5.2.3.1 Hydrological Investigation

As indicated above, the observed monthly inflow data at Krishnagiri reservoir

is available for the period from 1958-59 to 2008-09 and the same is used for development

of rainfall-runoff relationship by regression analysis at Krishnagiri dam site. The catchment

area of Ponnaiyar basin upto Krishnagiri dam site is 5428 km2. The State-wise/District-wise

break up of catchment area upto Krishnagiri dam is furnished in Table 5.4.

80

Table 5.4

District wise break-up of catchment area up to Krishnagiri Dam Site

Sl. No.

State / District Catchment area in km2

Percentage to the total Catchment area

1. Karnataka

a) Kolar 1143 21.06

b) Chikballapur 498 9.18

c) Bengaluru urban

Incl. Bengaluru City

797

(241+556)

14.68

d) Bengaluru rural 1107 20.39

Sub-total: 3545 65.31

2. Andhra Pradesh

a) Chittoor 94 1.73

3. Tamil Nadu

a) Krishnagiri 1789 32.96

Total 5428 100.00

5.2.3.2 Data from other Sources

Most of the data used in this study was collected from other Central and

State Govt. Agencies. Rainfall data was collected from IMD and Department of Economics

and statistics, Govt. of Karnataka and Tamil Nadu. The inflows, spills and upstream project

utilizations were collected from Water Resources Department, Govt. of Tamil Nadu.

5.2.4 Processing of Data

The following hydrological variables were processed in this study: (i) rainfall

data (ii) reservoir inflow data (iii) upstream project utilisation data (iv) export from the

basin and import to the basin upto Krishnagiri dam site and (v) monthly spill discharges

from Krishnagiri reservoir.

5.2.4.1 Quality of Data

There are some missing records in daily rainfall data. The missing data have

been estimated using standard statistical methods. Further, analysis of the rainfall-runoff

correlation is carried out at Krishnagiri dam site. The intercepting catchment area between

the existing Krishnagiri dam and Nedungal Anicut is 266 km2 and the contribution of yield

from this area is computed on proportionate area basis using the yield series developed at

the Krishnagiri dam site.

81

5.2.4.2 Filling of Short Data Gaps

The rainfall data up to Krishnagiri dam site is mostly available for all the 18

stations from 1901-02 to 2009-10 and the same has been considered in this study. The gaps

in the rainfall data have been filled using standard procedure. The missing records in rainfall

data have been estimated using standard statistical methods. These gaps are filled by the

normal ratio formula as given below:

Px = Nx/m [ P1/N1+ P2/N2+ ……… Pm/Nm]

Where,

Px = estimated rainfall of a station

Nx = normal rainfall of a station

P1, P2…… Pm = observed rainfall values of neighbouring stations

N1 N2 …….Nm = normal rainfall values of neighbouring stations

5.2.4.3 Adjustment of Records

The observed inflow data of Krishnagiri reservoir is available for the period

from 1970-71 to 2009-10. To compute the monsoon virgin yield series at Krishnagiri

reservoir actual upstream utilizations under the existing projects and regeneration on import

from Bengaluru water supply schemes are considered based on the proportionate area of

Bengaluru city lying in Ponnaiyar basin from the date of stage-wise commissioning of the

water supply schemes. The gross monsoon virgin yield series at Krishnagiri reservoir are

arrived by adding the inflow at Krishnagiri dam to the net upstream utilizations by the

irrigation projects and subtracting regeneration from the Bengaluru water supply scheme

(import) for each year from 1970-71 to 2009-10.

5.3 Water Balance upto Krishnagiri Dam Site

The 75% and 50% dependable annual yields as well as estimated utilisations

for various uses by 2050 AD are computed as per various approved guidelines of TAC of

NWDA. The details of Water Availability analysis and projected utilisations are furnished as

Appendix 5.1. The water balance taking into account the availability, import, export,

regeneration and water needs for the basin area up to Krishnagiri dam site is given in

Table 5.5.

82

Table 5.5

Surface Water Balance of Ponnaiyar Basin up to Krishnagiri Dam Site

Unit : Mm3

Thus, the annual surface water balance of 156 Mm3 and 271 Mm3 at 75%

and 50% dependabilities respectively have been computed at Krishnagiri dam site.

1. Surface Water Availability

(a) Gross annual yield

i) At 75% dependability 200

ii) At 50% dependability 315

(b) Surface water import

(as regeneration from Cauvery basin)

293

(c) Surface water export Nil

(d) Overall availability



2. Surface Water Requirement

i) Irrigation 301

ii) Domestic 76

iii) Industrial use 113

iv) Hydropower needs Nil

490 490

3. Regeneration

i) Irrigation 2

ii) Domestic 61


153 153

4. Surface Water Balance



83

5.4 Water Balance upto Nedungal Anicut

Projected Domestic Water Needs of Basin Area up to Nedungal Anicut

Nature of Population

Estimated Population by

2050 AD (in ‘000)

Per capita Need (Litres)

Water Requirement by 2050 AD

(in Mm3)

Urban 1282 135 63

Rural 1267 70 32

Live stock 1257 50 23

Total: 118

The entire urban water requirement excluding Bengaluru city and 50% of

rural water requirement for human population are proposed to be met from surface water

resources. This works out to 79 Mm3. 80% of surface water to be utilized for domestic

purpose is considered to be available as return flow, which work out to 63 Mm3.

Industrial Water Requirement

In absence of relevant data, the industrial water needs by 2050 AD have

been assumed to be of the same order as that of domestic water requirement. Accordingly,

the industrial water requirement would be 118 Mm3. This requirement is proposed to be

met from surface water resources. 80% of this use is considered to be available as

regeneration, which works out to 94 Mm3.

The water balance taking into account the availability, import, export, regeneration

and water needs for the basin area upto Nedungal Anicut is given in Table 5.6.

Table 5.6

Surface Water Balance of Ponnaiyar Basin upto Nedungal Anicut

Unit : Mm3

1. Surface Water Availability

(a) Gross annual yield


ii) At 50% dependability

330

(b) Surface water import 293

(c) Surface water export Nil

(d) Overall availability



623

2. Surface Water Requirement

84

Thus, the annual surface water balance of 169 Mm3 and 289 Mm3 at 75%

and 50% dependabilities respectively have been computed at Nedungal Anicut.

In the assessment of overall availability of water at diversion point, the

requirement of downstream projects are also to be considered. There are 3 existing medium

projects viz., Inchampadi anicut, Tirukkoilur anicut and Sathanur anicut located on

Ponnaiyar river downstream of Krishnagiri dam. The utilizations and the availability of yields

at these projects are furnished below.

5.5 Downstream Projects

5.5.1 Computation of Yield at Inchampadi Anicut

The Inchampadi Anicut which is an existing medium project located at

downstream of confluence of Pulapatti Ar, a tributary of river Ponnaiyar. The catchment

area of this tributary is 908 km2 and the yield @ 75% dependability from this catchment

works out to 33 Mm3 (908/5428*200), on proportionate area basis of the yield computed at

Krishnagiri dam. The utilization under this project is 21 Mm3. Hence, the contribution from

this independent stream can cater to the needs of this project.

5.5.2 Computation of Yield at Tirukoilur Anicut

The intercepting catchment area between Krishnagiri dam and Tirukoilur

Anicut is 6890 km2 and this area lies in a rainfall zone of 800 - 1100 mm, where as the

catchment area above Krishnagiri dam site lies in a rainfall zone of less than 800 mm.

i) Irrigation 301

ii) Domestic 79


iv) Hydropower needs Nil

498 498

3. Regeneration

i) Irrigation

(Kalavarapalli : 2 Mm3)

(Krishnagiri : 5 Mm3)

7

ii) Domestic 63


164 164

4. Surface Water Balance



289

85

Hence, the yield computed at 75% dependability for the intercepting catchment area of

6890 km2 is on the conservative side which works out to 254 Mm3 on proportionate area

basis of yield worked out at Krishnagiri dam site by regression analysis. The yield available

at Tirukoilur Anicut at 75% dependability and its committed requirement for irrigation and

requirement for domestic and industrial needs and regeneration are furnished below.

Yield:-

Water balance available at Krishnagiri dam site at 75% dependability

156 Mm3

Yield at 75% dependability from the intercepting catchment below Krishnagiri dam site and upto Tirukkoilur Anicut including Pulapatti Ar tributary - (6890/5428*200 = 254)

254 Mm3

Total 410 Mm3

Requirement:-

1) Domestic (Mm3) 143

2) Industrial (Mm3) 273

416 (+) 416

3) Irrigation (Mm3)

i) Inchampadi Anicut 21

ii) Sathanur project 170

iii) Tirukkoilur project 122

313 (+) 313

Regeneration (Mm3)

1) Domestic and industrial use (-) 332

However, keeping in view the committed water utilizations from the existing

projects, it is proposed to divert the flood flows during monsoon period. The details are

given in para 5.7.

The 75% dependable yield available from the intercepting catchment area

between Krishnagiri dam and Tirukoilur Anicut and the surplus water balance at

Krishnagiri dam works out to 410 Mm3 against the committed irrigation requirement for

the projects downstream of Krishnagiri dam and domestic and industrial requirement of

313 Mm3, 416 Mm3 respectively. After considering regeneration of 332 Mm3 from the

domestic and industrial use, 397 Mm3 will be the net requirement. The contribution from

this intermittent catchment can cater the needs of this requirement.

The quantum of diversion (99 Mm3) proposed through Ponnaiyar (Sathanur) -

Palar (Cheyyar) link by Govt. of Tamil Nadu has not been considered in arriving the

86

availability of yield @ 75% dependability, since the proposal is framed for diversion of flood

flows of Ponnaiyar at Sathanur dam.

Ponnaiyar (Nedungal) – Palar Link Canal

Even though there is surplus water available at Krishnagiri dam and Nedungal

Anicut, only spills during flood season are proposed for diversion. Hence the hydrological

regime of the Ponnaiyar basin is not likely to be affected significantly. The diversion of water

is proposed during the months of October, November and December only.

5.6 Presentation of Hydrologic Inputs

5.6.1 Water Inflows

Water inflows observed at Krishnagiri G&D site on Ponnaiyar river were used

for Hydrological purpose. However, monthly spill data of Krishnagiri reservoir based on

regulated releases of flood/spills are used to assess the quantum of flood water for

proposed diversion.

5.6.2 Data Generation

The observed in-flow data at Krishnagiri reservoir is available for a continuous

period of about 52 years from 1958-59 to 2009-10. Therefore, the process of data

generation is not required.

5.6.3 Sedimentation Studies

5.6.3.1 Rate of Sedimentation

Sediment analysis was done by the Central Water Commission (CWC), at

Gummanur G&D site which is located upstream of Krishnagiri dam site. As per the sediment

data available at the site during the period from 1982-83 to 2012-13 the rate of average

annual sediment inflow to the reservoir works out to 67222 M.T, out of which 65343 M.T is

during the monsoon period.

5.6.3.2 Area Capacity Curves

The existing Krishnagiri dam on Ponnaiyar river with a catchment area of

5428 Km2 is proposed as a controlling structure for transfer of water through the link canal.

The Elevation - Area - Capacity curves of Krishnagiri reservoir are presented in Fig. 5.5.

87

01

23

45

67

89

10

11

46

7.3

47

0.3

47

0.9

47

1.5

47

2.1

47

2.7

47

3.4

47

4.0

47

4.6

47

5.2

47

5.8

47

6.4

47

7.0

47

7.6

47

8.2

47

8.8

47

9.5

48

0.1

48

0.7

48

1.3

48

1.9

48

2.5

48

3.1

05

10

15

20

25

30

35

40

45

50

46

7.3

47

0.3

47

0.9

47

1.5

47

2.1

47

2.7

47

3.4

47

4.0

47

4.6

47

5.2

47

5.8

47

6.4

47

7.0

47

7.6

47

8.2

47

8.8

47

9.5

48

0.1

48

0.7

48

1.3

48

1.9

48

2.5

48

3.1

CA

PA

CIT

Y

Mm

3

AR

EA

k

m2

RESERVOIR LEVEL in 'm'

CA

PA

CIT

Y

AR

EA

AR

EA

-C

AP

AC

ITY

CU

RV

E O

F K

RIS

HN

AG

IRI

RE

SE

RV

OIR

RESERVOIR LEVEL in 'm' Fig-5.5

88

5.6.4 Potential Evapotranspiration and Rainfall

Normal potential evapo-transpiration data of Vellore IMD observatory is used

for computation of crop water requirement in the command area. The command area

proposed for stabilisation through this link project is being irrigated by waters from local

tanks and bore wells. The link canal feeds the tanks and recharges the ground water.

5.6.5 Flood Inputs

Flood water available at the Krishnagiri dam is proposed for diversion through

Ponnaiyar (Nedungal) – Palar link project. The monthly spill discharges for all the months

based on the daily data of Krishnagiri reservoir are collected from the Project authorities for

the period from 1958-59 to 2009-10 and used to estimate the quantum of flood water

spilling down the existing Krishnagiri dam which can be available for diversion.

5.6.6 Inputs for Water Quality

Different chemical and physio-chemical parameters of water quality of

Ponnaiyar river at Krishnagiri dam are observed by PWD, WRD, Govt. of Tamil Nadu

regularly and are being tested at water quality testing laboratory of Soil Mechanics and

Research Division, PWD, WRD, Chennai. From the test results of the water samples of

Ponnaiyar river collected at Krishnagiri dam from reservoir water, seepage water from

Earthen dam toe-drain and Drainage galleries it is seen that in general the water is fit for

domestic, industrial and agricultural purposes.

5.6.7 Low Flow Inputs

The monthly inflow details of Krishnagiri reservoir were collected for the

period from 1958-59 to 2009-10. From the inflow data it is seen that the average flow

during non-monsoon (January to May) i.e., lean flow season is about 20 Mm3 only which

works out to about 6.5% of average annual inflow.

5.6.8 Surface to Ground Water Recharge

The Ground water Division, Public Works Department, WRO, Vellore, Govt. of

Tamil Nadu has studied the possible ground water recharge zones and identified the areas

having possibilities of ground water recharge enroute the link canal as well as on either side

of the rivers Kal Ar and Palar in Vaniyambadi and Tirupattur talukas of Vellore district. The

details are discussed in Chapter-8: Irrigation Planning and Command Area.

89

5.7 Study of Spill Waters from Krishnagiri Dam and Quantum of

diversion and Link Canal Capacity

The monthly spill discharges for all the months at Krishnagiri reservoir are

collected for the years from 1958-59 to 2009-10 from project authorities, from which the

quantum of average monsoon flood spills at Krishnagiri dam site has been assessed to be

157 Mm3. Out of 157 Mm3, 86 Mm3 is proposed for diversion through the link canal. Details

are furnished in Annexure-5.1. The summary of daily spill data for the months of October,

November and December for the period from 1979-80 to 2009-10 is furnished at

Annexures-5.2.1 to 5.2.3. The canal has been designed for 68 cumec capacity to flow for

a period of 18 days annually.

5.8 Design Flood and Diversion Flood

Since the diversion is proposed from the existing Nedungal Anicut, the

aspects of design flood and diversion flood etc. are not discussed in the present study.

5.9 Studies for Design of Drainage in the Command Area

No new command area is proposed to be brought under irrigation from the

project except stabilisation of existing command area through ground water recharge. As

such no studies are carried for design of drainage in the command area.

5.10 Determination of Levels for Locating Structures on Outlets

The crest level of the Nedungal anicut is 434.710 m. In order to divert

required water the pond level in the front of the proposed head regulator for link diversion is

considered as 435.01 m keeping in view the raise in water level during the floods. The sill

level of the Head Regulator is kept at 433.0 m with the FSL of the link canal at start as

434.450 m. The sill level of existing Barur channel sluice is 433.16 m, which is located just

60 m d/s of the proposed head regulator.

5.10.1 Location of Structures

The link project envisages construction of following components:

1. Canal Head Regulator at off-take point at Nedungal Anicut

2. A link canal of 54.15 km length with off-take at FSL 434.450 m from Nedungal

anicut.

3. Enroute Cross drainage and Cross masonry Structures.

90

5.10.2 Location of Outlets

There is no direct canal irrigation proposed enroute the link canal. However,

suitable outlets are proposed to be provided to feed the enroute existing system tanks. The

hydraulic particulars of these tanks are discussed in the Chapter – 6: Design Aspects.

5.11 Model Studies

Since the existing structures viz., Krishnagiri dam and Nedungal anicut are

proposed for regulation and diversion of flood flows, no model studies are required.

5.12 Minimum Flow for Environmental Consideration

Since, only flood water are proposed for diversion and also several small

streams are joining the Ponnaiyar river d/s of the diversion point viz., Nedungal anicut, no

adverse effect is anticipated on minimum flows in the river.

5.13 Effect of Project on Hydrologic Regime

During the flood period, the spillway operation of the Krishnagiri reservoir is

so controlled as to pass the design flood without adverse affects on the downstream side

due the floods. While the crest level of the spillway is at 477.01 m, the FRL and MWL are at

483.11 m and 484.63 m respectively. As per the flood rules of Krishnagiri Reservoir Project,

all the spillway gates shall be opened uniformly and the height of opening shall be increased

according to the intensity of flood. Whenever flood flows are received over 10000 cusecs

(280 cumec), the reservoir level will be gradually reduced to 482.50 m during the rising

floods. During the receding floods, the reservoir will be gradually filled upto FRL 483.11 m.

Since only the part of spills during the flood is contemplated for diversion through the link

canal, no adverse effect on d/s hydrologic regime is anticipated.

5.13.1 Effect on Low Flows

Since as already discussed, only flood flows during period of spill occurrence

are proposed for diversion during monsoon period, there will be no adverse effect on low

flows because of proposed diversion.

5.13.2 Effect on Peak Flood

It is expected that peak flood will be smoothened because of diversion of spill

flows during times of flood.

91

5.14 Water Allocation and Inter-state Aspects

Both Ponnaiyar and Palar basins are not covered under any tribunal awards.

Though the proposed project is an Intra-state link project of Govt. of Tamil Nadu, the

Ponnaiyar originates in Karnataka State. This aspect is already discussed in Chapter 3:

Interstate Aspects.

Documents

Ch. 5 Hydrology and Water Assessment