36

CHAPTER 3: DESCRIPTION OF THE STUDY AREA AND PRESENT OPERATING CONDITION

3.1 THE PONNAIYAR RIVER BASIN

3.1.1 Physiography

The Ponnaiyar river originates on the south eastern slopes of Chennakesava Hills, North

west of Nandidurg of Kolar district in Karnataka State at an altitude of 1000 m above

Mean Sea Level (MSL). The river is called Dakshina Pinakine in Karnataka state. After

flowing through Karnataka, the river enters Tamilnadu near Bagalur village of Hosur

taluk and takes the name of Ponnaiyar. Ponnaiyar river basin is sandwiched between

Cauvery river basin at its west and south and Palar and Varahanadhi basins at its east and

north. The basin is located within the geographical co-ordinates North Latitude 10° 45’

and 13° 14’ and East Longitude 77° 45’ and 79° 45’. The total area of the basin is 11441

km2 including the area under Union Territory of Pondicherry (90 km2).

The main tributaries of Ponnaiyar river are Chinnar I, Chinnar II, Markandanadhi,

Kambainallur, Pambar, Vaniyar, Kottapatti, Kallar, Vayalar Odai, Ramakal, Pambanar,

Aliyar, Mushkundanadhi and Thurinjilar.

The major reservoirs are Nedungal reservoir, Kumarapatti reservoir, Ichambadi reservoir,

Sathanur reservoir, Tirukoilur reservoir, Ellis Choultry reservoir and Sornavur reservoir.

The Sathanur reservoir is the largest among the reservoirs. In addition to this, 152 minor

barrages and about 66 open offtake channels are also available in this basin. The total

length of Ponnaiyar River is 432 km of which 85 km lies in Karnataka state, 187 km in

Dharmapuri, Krishnagiri and Salem districts, 54 km in Thiruvannamalai and Vellore

districts and 106 km in Cuddalore and Villupuram districts of Tamilnadu.

37

Normally there is no flow in the river except during monsoon seasons. The maximum

discharge of the river so far measured is 8100 m3/s. Total actual dependable run off is

1215 million m3 per year.

3.1.2 Topography

The Ponnaiyar river basin area from Tamilnadu State boundary to Krishnagiri reservoir

site has an undulating and hilly terrain. This terrain slopes from an altitude of about 880

m in a distance of about 50 km. Average topographical gradient is 8 metres per kilometre.

The basin area from Krishnagiri Reservoir to Sathanur Reservoir has an undulating

terrain with many hills and valleys along the eastern and western boundaries. An average

topographical gradient is 2.27 metres per km. The Ponnaiyar river basin drainage map is

shown in figure 3.1.

The basin area from Sathanur Reservoir to Tirukoilur barrage has a plain terrain

moderately sloping from an altitude of about 222 m at Sathanur reservoir to 81.25 m at

Tirukoilur barrage. The average topographical gradient is 2.5 metres per km.

The basin area from Tirukoilur barrage to sea is a plain terrain and slopes gently from an

altitude of about 81.25 m at Tirukoilur to the mean sea level at the eastern and joins at

Bay of Bengal. Average topographical gradient is 0.70 meters per km.

3.2 SATHANUR RESERVOIR

The Sathanur reservoir is located across the Ponnaiyar river near Sathanur village, about

32 km from Thiruvannamalai town in Thiruvannamalai District, Tamilnadu. The river

rises on the south eastern slopes of the Chennakesava hills in Karnataka, flows for 85 km

in that State before entering Tamilnadu near Bagalur village, Hosur; passes through

erstwhile North and South Arcot Districts and outfalls in to the Bay of Bengal near

38

Cuddalore Town. The total catchment above the dam is 10835 km2 of which about 90%

is in Tamilnadu and the balance in Karnataka.

A number of diversion weirs viz., Tirukoilur barrage, Ellis Choultry barrage and

Sornavur barrage and flood channels were located along the downstream of the Sathanur

reservoir before independence. They were constructed before Sathanur reservoir. These

three barrages together irrigate about 33,000 ha, mostly under tanks supplemented by

Ponnaiyar river and they are known as the “old command area”. The Sathanur command

area map is shown in figure 3.2.

The major sub commands are served by the Tirukoilur (8910 ha) and Ellis Choultry

(5065 ha) barrages, with the last Sornavur barrage commanding areas not only in

Tamilnadu but also in the Union Territory of Pondicherry. To safeguard the riparian

rights of the old command area, the inflow into the Sathanur reservoir is shared between

the Sathanur command area and old command area based on certain limit flow conditions

as detailed in the next section. Under present operating rules, these downstream areas

have priority rights for stream flows totaling about 170 million m3 in an average year. In

addition upto 34 million m3 of stored water from Sathanur reservoir is to be provided for

a second paddy crop under Tirukoilur barrage.

Sathanur reservoir was constructed in 1958 with 116 million m3 live storage, a pick up

weir 7.2 km downstream of the reservoir and a Left Bank Canal (LBC) system fully

localized for 9771 ha of paddy, of which 1130 ha are under 41 tanks. During the mid-

1960s, Sathanur reservoir was raised, increasing gross storage to 229 million m3 and live

storage to 215 million m3. Right now the present live storage of the reservoir is 207

39

million m3. This improved security of supply to the LBC command, allowed support for a

second paddy crop on 2025 ha under Tirukoilur barrage.

3.2.1 Development of Sathanur reservoir after 1971

There were surplus flows in 11 out of 14 years (1958 – 1971) in this reservoir.

Subsequently, the third, and to date final-stage of expansion was completed in 1982,

comprising a Right Bank Canal (RBC) system taking off from the existing pickup weir

serving a total command of 8449 ha of which 1890 ha are indirect command (wet

command) under 49 established tanks between 1st October and 15th February. The

remaining command area (6559 ha) belongs to direct command and is localized for ID

crop (groundnut). Apart from the tank commands and a small (37 ha) area served by

direct sluices, RBC was designed with a capacity of 7.1 m3/s However, the storage

potential of the reservoir has not been very encouraging since the RBC came into

existence. After the advent of the Sathanur reservoir, many diversion schemes have been

developed across the Ponnaiyar river and its tributaries in the upstream side of the

Sathanur reservoir in the early 1980’s. Inflow into the Sathanur reservoir is reduced by

the upstream reservoir construction. The unfavourable monsoons and impounding of the

available flows by the upstream barrage systems subsequently reduced the inflow into the

Sathanur reservoir.

3.2.2 Soil classification

A soil survey of LBC has been carried out in 1977. Two types of soil series were

observed in the command, namely Edathanur series and Mudiyanur series. As per the soil

survey conducted, the following observations are drawn.

i) The soils available in the command area are free from saline or alkaline problems.

40

ii) While the Mudiyanur series are heavy soils, the Edathanur series are light soils.

The cultivation pattern also is in accordance with the soil availability.

3.2.3 Surface water resources

Monthly and annual flows to the Sathanur reservoir were worked out for the period from

November 1985 to October 2007. The mean annual flow was computed as 314.08 million

m3 with a range of 5.53 million m3 (2001 – 02) to 605.14 million m3 (1985 - 86).

3.3 SATHANUR RESERVOIR SYSTEM BEFORE REHABILITATION (1987)

3.3.1 Development of Sathanur irrigation system

The Sathanur reservoir system was commissioned for irrigation in November 1957, with

a storage capacity of 129.5 million m3 through LBC, starting at the pick up weir, 7.2 km

downstream of the Sathanur reservoir. During the first stage of development, the LBC

was constructed with a capacity of 11.32 m3/s to serve 8854 ha (inclusive of 1130 ha of

land under 41 tanks) fully localized for paddy between 15th December and 30th April,

every year. With the improved storage capacity of the Sathanur reservoir from 129.5

million m3 to 229 million m3 in the early 1960’s, the system facilitated to feed an

additional command area of 917 ha - totaling to 9771 ha, under LBC and a command

area of 2025 ha for second crop paddy under the downstream Tirukoilur barrage. The

designed duty of the LBC main canal is 1.16 l/s/ha to serve 9771 ha. The assumed

overall efficiency is 60% implying an average delivery at the plant of about 6 mm/day

when the main canal is at full discharge. The duty for canals off taking from the main

canal is in most cases 1.40 l/s/ha although a few small direct outlets and the two tail

distributories have a higher duty (1.6-1.91 l/s/ha). Duty at outlet is 1.00 l/s/ha). The sum

of all at outlets is 13.2 m3/s. The total water allotted to the LBC command during the

41

1990-1991 period was 128 million m3 equivalent to 1320 mm over the whole command

or 790 mm at the plant assuming a 60% overall efficiency.

3.3.2 Left Bank Canal system

The LBC is a contour canal 35.2 km long with a full supply depth of 1.7 m. There are 42

gated outlets, of which three feed large distributor canals command more than 1600 ha

each, 11 feed small distributories, 26 feed direct outlets and 2 feed directly into tanks.

The secondary and tertiary canals are generally aligned down the slope, requiring the

installation of numerous drop structures, most of which are unregulated. Flow-dividing

structures have been placed in some of the larger distributories. Outlets from both

distributories and minors are normally gated and wherever possible are located upstream

of drop structures. Variable flows in the system are in principle, regulated through

operation of these gates. The total length of the distributories is 70 km. A few tanks are

served directly from the main or distributory canals. Others are served through the tail

end of minors. The LBC command area map is shown in figure 3.3. The salient features

of LBC are presented in the Appendix, A-1. No field channels were initially constructed.

Farmers have constructed their own field channels.

3.3.3 Right Bank Canal system

The RBC system is designed for a discharge of 7.1 m3/s to serve a command area of 8449

ha at a duty of 0.84 l/s/ha over the whole command, equivalent to 5.7 mm/day at a design

efficiency of 60%. The RBC is lined for the first 28.64 km and after that an unlined

section of about 6 km, delivers water to two canals (Branches 2 and 3) each about 10 km

in length. 25 gated offtakes depart from the main canal before this bifurcation. Of which

2 are classified as branch outlets, 6 as distributory outlets and 17 as direct outlets, having

42

small commands up to 70 ha. There are a number of siphons in the main canal, which

passes through some fairly rugged country, and one cross regulator at downstream of the

first branch outlet. Measuring devices are installed at the head of the main canal and of

the branches.

As on the LBC system, secondary and tertiary canals are generally aligned down the

slope, and are provided with drops, most of which are unregulated. All tanks are at the

end of canals and are provided with direct feeder channels. Below the tanks traditional

field to field irrigation is practised as in the LBC system. Off takes from the main canal

are designed to serve ID crops on the direct command and paddy under tanks

simultaneously, at duties of 0.58 l/s/ha and 1.16 l/s/ha respectively. The salient features

of RBC are presented in the Appendix, A-2.

3.4 PHYSICAL DESCRIPTION

3.4.1 Sathanur reservoir

• Location : Across Ponnaiyar river

• Catchment Area : 10835 km2

• Length = Masonry Dam : 418 m

Earth Dam : 362 m

• Height of Masonry Dam : 45 m above foundations

• Capacity of Reservoir : 229 million m3

• Present live storage capacity : 207 million m3

• Spillway : 9 Vents of 12.2 m x 6.1 m

•

• Maximum Spillway Capacity : 3285 m3/s

• Saddle Spillway length : 161.5 m

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• Saddle Spillway capacity : 2234 m3/s

• Average inflow (1987-2007) : 314.08 million m3 per year

• Length of the river : 7.2 km upto pickup weir

• Period of wet season : September – January

• Period of dry season : December – March

• Command area under wet : 3020 ha season paddy

• Command area under dry : 15200 ha season ID crop

• Total Registered command : 18220 ha

3.4.2 Sathanur pick-up weir

• Location : 7.2 km below the reservoir

• Length : 122 m

• Maximum Flood Discharge : 7951 m3/s

3.4.3 Left bank canal

• Location : Takes off from the pick-up weir

• Total length : 35.20 km

• Period of wet season : September – January

• Period of dry season : December – March

• Command area under wet : 1130 ha season-paddy (ie.,-under tanks)

• Command area under Dry : 8641 ha season – ID crop

• Total registered command area : 9771 ha

• Tank feeders : 41 Nos.

• Gauging bridges : 9 Nos.

44

• Location of cross regulator : 2 Nos. (at 27.141 km & 35.46 km)

• Proportional Distributors : In the command of all Distributories

• Duck-bill weir cum regulator : 5 Nos. (at L.S. 9.5 km, 13.45 km, 15.3 km, 22.02 km and 25.77 km)

• Carrying capacities of : 11.32 m3/s Main canal at head

• Major Distributories (above 100 ha) : 11 Nos.

• No. of Tanks : 41

• No. of Zones : 3 Nos. Zone I = (0 – 15.30 km) Zone II = (15.30 km - 27.1 km) Zone III = Below 27.14 km.

3.4.4 Right bank canal

• Location : Takes off from the pick-up weir

• Total length : 34.00 km

• Period of wet season : Same as for LBC

• Period of dry season : Same as for LBC

• Command area under wet season : 1890 ha (ie.,-under tanks) – Paddy

• Command area under Dry : 6559 ha. season – ID crops

• Total registered command : 8449 ha Area

• Tank feeders : 37 Nos.

• Location of cross regulator : 3 Nos. (at 8.870 km, with gates 16.83 km & 25.56 km)

• Proportional Distributors : In the command of BC3

• Duck-bill weir cum regulator : 4 Nos. (at L.S. 7.17 km, 10.68 km, 14.00 km &

45

20.92 km)

• Carrying capacities of : 7.08 m3/s main canal at head

• Major Distributories (above 100 ha) : 10 Nos.

• No. of Tanks : 49 Nos.

• No. of Zones : 3 Zones

Zone I = (0 -16.83 km) Zone II = (16.83 km - 25.50 km)

Zone III= (25.50 km- 34.00 km)

3.5 LOSSES IN CANALS

The total losses in the canal and branches of LBC and RBC are taken based on the length

of channel, lined or unlined, wetted perimeter etc. (PWD, 1993).

1. Main Canal 2%

2. Distributory/Branch 2%

3. Minor 5%

4. Field channel 5%

5. Field application 20%

6. Total losses 34%

7. Overall conveyance

Efficiency 66%

Accordingly duties at various nodes of the distribution system for both Left Bank Canal

and Right Bank Canal have been arrived at as follows:

LBC RBC

Irrigation requirement

in l/ s/ ha

1. Delivery to main Canal 1.09 1.09

2. Delivery to Distributory/Branch 1.07 1.07

3. Delivery to minor 1.05 1.05

4. Delivery to field channel 1.00 1.00

5. Field out let head 0.95 0.95

6. Field level 0.76 0.76

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3.6 OLD OPERATIONAL RULES AND THEIR REPERCUSSION

3.6.1 Operational plan - Physical system

The Sathanur reservoir is located in Thiruvannamalai town in Thiruvannamalai District

of Tamilnadu where the mean annual rainfall is about 1000 mm. Improvements to the

physical infrastructure were carried out under National Water Management Policy

(NWMP) to facilitate better system operations. An area of 3020 ha of paddy during

September-January for supplementation and 15200 ha of ID crop during December-

March benefits from this scheme apart from establishing 2025 ha of second crop under

the next barrage, the Tirukoilur barrage of Ponnaiyar river.

The old operational rules and regulation for Sathanur reservoir and LBC came into effect

in July 1976 and that for RBC in January 1983. The salient features of these rules are as

follows.

(i) To maintain the riparian rights of the downstream users, the inflow into the

Sathanur reservoir is shared between Sathanur command and the old

command based on the following limit flow conditions.

Table 3.3 Limit inflow conditions for old command area

Sl. No. Period Discharge in m3/s

1. 1st January – 15th April 56.7

2. 16th April – 15th June Nil

3. 16th June – 30th September 56.7

4. 1st October – 31st October 42.1

5. 1st November – 30th November Nil

6. 1st December – 31st December 42.1

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The rules stipulate that the inflows in excess of the quantities specified in the table 3.3

above alone can be impounded for use in LBC and RBC of Sathanur command.

(ii) RBC is opened for irrigation between 1st October and 15th February to

command ID crop up to a total of 41.1 million m3 and to command wet crop

under tanks up to a limit of 18.4 million m3.

(iii) LBC is opened from 15th December to 30th April to release continuous supply

of water for paddy crop to the tune of 128 million m3.

3.6.2 Problems caused by the old operational rules

(i) The upstream irrigation development has reduced the inflow into the reservoir,

while the demands on the Sathanur reservoir have increased due to the

construction of RBC. This impact is high during the poor rainfall years.

(ii) The crop development in the commands of LBC and RBC was not as planned.

At the beginning the LBC was fully localized for paddy. Later on groundnut

crop was cultivated. Groundnut crop became the predominant crop in the

command except in the low lying areas in which paddy crop is cultivated.

The cultivation of paddy crop in the LBC command declined after the

commissioning of RBC.

(iii) The early operation of the RBC in October had three important effects. First,

the early release in October coincided with the monsoon rains and encouraged

the cultivation of paddy. Secondly, the farmers who had sown groundnut in

December/January in RBC had to face severe stress in the late season, that is,

after the closure of the canal in February. Thirdly, capacity of the RBC,

designed for an ID crop, was not enough to meet the demands of the paddy

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crop and hence the RBC was operated for a longer period than planned. This

in turn reduced the water availability for LBC command, which is opened in

December.

While in principle, the LBC receives priority over the RBC, the early release into the

RBC reversed the priority in practice. Also, in principle, the LBC is to be operated

for a paddy crop and the RBC for an ID crop. But, in practice, this is also reversed.

This has often resulted in conflicts between the commands of the LBC and the RBC.

3.7 SATHANUR IRRIGATION SYSTEM AFTER REHABILITATION UNDER NWMP

This section elaborates the developments in the Sathanur irrigation system under the

National Water Management Project, a rehabilitation project. It also speaks of the

new operational plan and present issues in the Sathanur irrigation system.

3.7.1 National Water Management Project (NWMP)

National Water Management Project, a World Bank funded project aims at improving

the existing irrigation systems with rehabilitation of the physical system and the

managerial components, especially in the southern states of India like Andhra

Pradesh, Karnataka and Tamilnadu. Sathanur irrigation system has been chosen as a

pilot project under the NWMP in 1987. The main objective of this water

management project is to increase agricultural productivity and farm income in the

existing irrigation commands by providing the farmers with a reliable, predictable and

equitable irrigation service. The essential feature of this project is the preparation of

an operational plan to improve the water distribution and management in the system.

The necessary physical system improvements required for better management of the

system were provided under this project.

49

3.7.2 National water management project at Sathanur – New operation rules

To overcome the differences between the LBC and RBC, a new operational plan was

developed under the NWMP (SAR, 1987). The salient features of this new operation

rules and regulations, which came into existence from 1991, are given below:

i) Operation of the LBC and RBC simultaneously during the post monsoon

season, that is, from middle of December to March.

ii) Provision of irrigation for an ID crop in the direct command on intermittent

basis / rotational basis and supplemental releases to the tanks for irrigating

paddy in both the commands.

iii) Resorting to zonal operation for irrigation during the years of poor storage by

dividing each main canal into three viable zones of equal size. The zones of

the LBC and RBC are given equal priorities for operation depending on the

storage in the reservoir, in rotation over years.

iv) Minimization of human intervention in water distribution by introducing the

micro network system (like Proportional Distributors (PD), Adjustable

Proportional module (APM) and Open Flumes (OF) in the distribution system

and Duck Bill Weirs (DBW) in the main canal) to maintain the level control.

Physical improvements like cross regulators, tank feeders, lining of the canals

and measuring devices are provided to facilitate better water management in

the system.

v) Introduction of Monitoring and Evaluation practices at the scheme level.

Preparation of regular reports on the outcome of the seasonal performance,

that is, Water deliveries, Irrigation deficiencies, Cropped areas, Farmer’s

50

satisfaction and modification of the operational plan for the coming season

based on the successes and failures of the previous seasons.

vi) Formation of a Scheme Level Irrigation Committee (SLIC) representing both

the officials of Public Works Department (PWD), Agriculture Engineering

Department (AED), Agriculture Department (AD) and farmers to meet and

discuss the plan before the season; define rules for its implementation and

meet and discuss the performance after each season.

3.7.3 Problems with the new operational rules

The new operational plan provides equal priority to the LBC and RBC commands by

simultaneously operating both the canals in the post-monsoon period. The new

operational rules have been followed from 1991, since most of the rehabilitation

works have been completed. Experience in the past few decades (more than last two

decades) has shown that there are a few problems with the new operational policy

too.

i. The main canals are not able to be operated on an intermittent basis as

envisaged in the new plan. The farmers benefiting from the continuous

supply have not agreed to the intermittent supply. Instead, the main canals are

operated continuously and rotations are practised among the distributaries.

ii. Farmers make use of the residual moisture to sow groundnut crop. Mostly,

they prefer to have the canal opening in January and subsequently shifting the

closure of canal to April so as to raise an additional crop, sesame.

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iii. Deliveries to the tanks are not made either in September or in December as

mentioned in the Rules. Instead, deliveries are made in spells in January,

February and March.

iv. Storage in the reservoir during the period 1991-92 has been encouraging

enough to operate both the LBC and RBC commands, giving equal priority.

The potential impact of this priority has to be verified in the years of poor

storage.

3.7.4 Sathanur irrigation system – Organisation and coordination

The Sathanur irrigation system has been in operation since 1957. It is managed by the

following four departments at different levels of coordination.

i) Public Works Department (PWD)

ii) Agricultural Engineering Department (AED)

iii) Agricultural Department (AD) and

iv) Revenue Department (RD)

The PWD is responsible for the Operation and Maintenance (O&M) of the system. It is

in charge of the system from the reservoir upto the heads of the minors. The AED is

responsible for On-Farm-Development (OFD) works, promotion of Rotational Water

Supply (RWS) within the 10 ha blocks and establishment of Block Committees. The AD

takes care of the agricultural extension services and the RD collects the water taxes along

with other taxes. Coordination at the State Level is looked after by the State Level

Coordination Committee consisting of the Chief Secretary to the Government of

Tamilnadu, the Secretary (PWD), the Chief Engineer (O&M), the Chief Engineer (AED)

and the Director of Evaluation and Applied Research Unit.

52

The Project Coordination Committee coordinates the various departments at project level

in Thiruvannamalai. The members of the committee include the Executive Engineer of

O&M, the Executive Engineer of NWMP, the Assistant Executive Engineer of Project

Preparation Cell (PP Cell), the Joint Director of Agriculture, the Superintendent Engineer

of AED and the Collectors of Thiruvannamalai and Villupuram Districts.

3.7.4.1 Organisation for Operation and Maintenance (O&M)

Various officials at all levels are responsible for the O&M of the Sathanur system. At the

scheme level, the EE (O&M) placed at Thiruvannamalai is in charge of the operation and

maintenance of the system. The Assistant Executive Engineer (AEE) at Sathanur sub

division takes care of the Sathanur reservoir and the water distribution in the system on

an overall basis. There are four Section Offices, each being under the jurisdiction of an

Assistant Engineer (AE). The AE at Sathanur reservoir is in charge of the operation and

maintenance of the Sathanur reservoir. The AE at Thenmudiyanur Section is in charge of

O&M activities upto 15.4 km of the LBC and 21 km of the RBC. He has about 4968 ha

(2695 ha of LBC and 2273 ha of RBC) of the direct command and 456 ha of indirect

command under tanks under his jurisdiction. The AE at Vanapuram West Section is in

charge of the rest of the LBC, covering about 5946 ha of the direct command and 1108 ha

of the indirect command. The AE at the Vanapuram East Section is in charge of the rest

of the Right Bank Canal. He has about 4286 ha of the direct command and 1456 ha of

the indirect command under his jurisdiction. There is a Work Inspector (WI) and one or

two Lascars (Irrigation Assistants) under each Assistant Engineer to look after the

operation and maintenance activities at the lower level. Each Lascar has about 1000 ha

53

under his jurisdiction. The organizational flow chart mentioning hierarchical order

involved in the O&M of Sathanur irrigation system is shown in figure 3.4.

3.7.4.2 Organisation for design and execution of rehabilitation works

NWMP Unit placed at Thiruvannamalai carried out the rehabilitation work and the PP

Cell takes care of the project planning. Currently, it is carrying out the Monitoring and

Evaluation (M&E) procedures in this system on a sample basis.

3.8 PRESENT OPERATING CONDITION

3.8.1 Design operation schedules for irrigation water releases

The design operation schedules for both reservoir and canal operations followed after

taking into consideration the seasonal water availability and the infrastructural facilities

of the system and the operation rules.

3.8.2 Operation rules

a. Non irrigation demand

Water supply to colonies receives the first priority. Thereafter Sathanur command

gets priority for the first 128 million m3 of end November live storage and

Thirukoilur barrage scheme for the next 34 million m3. The usage of the residual

water belongs to Sathanur command. The details of requirement of non-irrigation

demand and irrigation demand is given in table 3.4.

b. Irrigation demand

Normal date of opening the reservoir shall be 1st December for ID crops under

direct irrigation. Special supplies to tanks for raising wet crops shall be given

from 1st September to 10th September, if storage of 30 million m3 is available in

the reservoir on 1st September.

54

The Executive Engineer, PWD, Thiruvannamalai shall review the storage position

on 20th November, 1st December and 10th December to ascertain the extent of

command area that could be irrigated as below:

(i) If the total storage is 30 million m3 below, the storage is wholly allocated

for water supply to colony.

(ii) If the storage is between 30 to 70 million m3, issues shall be made to all

tanks in LBC & RBC.

(iii) If the total storage is above 70 million m3, issues shall be made to one

zone in LBC & one zone in RBC.

(iv) If the total storage is 100 million m3, issues shall be made to two zones

consisting of area both in LBC & RBC.

(v) If the total storage is above 140 million m3, issues shall be made to the

entire Sathanur command.

(vi) If the storage is above 140 million m3, issues of 34 million m3 shall be

made to the second crop for 2025 ha under Thirukoilur barrage.

Table 3.4 Various water demands in Sathanur irrigation system

Sl. No. Type of demand Priority

Quantity required

per period (in million

m3)

Season

No. of Periods of

demand per year

01

Drinking water demand

1

1

Throughout the year

36 periods

9.50 I period of September 13.61 III period of

December 4.28 II period of January

2.57 III period of January

6 periods

55

3.40 II period of February 02 Tank demand 2 3.43 III period of February

03 Crop demand - Groundnut

Based on the crop scenario of the research

04 Crop demand - Paddy

Based on the crop scenario of the research

05

Down stream side Thirukoilur barrage demand for stabilizing the second paddy crop

5

5.67

Required in the post monsoon season

6 periods - as and when required in that command

3.8.3 Direct command

i) When the reservoir is opened for irrigation (10thDecember), both the canals will

be running at their full capacities for a week for providing irrigation service for

the entire command for pre-sowing operations.

ii) Provision has been made for 2 days for water to reach the tail end.

iii) Reservoir will normally be opened for irrigation on 10th December.

3.8.4 Indirect command (Tank command)

i) Tank will be provided with supplementation from the reservoir in 6 spells as

mentioned in the table 3.4.

ii) Nurseries are normally raised with monsoon rainfall supplemented by the storage

in tanks.

iii) No supply will be made for direct command when there is a supply for tanks in a

spell.

In responding to rainfall the releases from the reservoir will either be reduced or

increased or cut off temporarily for a few days depending upon the volume of

effective rainfall.

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3.8.5 Rotational water deliveries (farming practice)

The Sathanur system is designated for cultivating ID crops in the post monsoon period in

the direct command and supplementation for wet crop. The pattern of operation plan

namely the pattern of irrigation delivery schedule, was prepared in consultation with the

farmers to suit the local condition of the command and the system. The pattern is given

below.

Water in main canal will flow continuously at half supply mode while in the

distributories except two numbers in LBC and one number in RBC it will be rotated with

7 days ‘ON’ and 7 days ‘OFF’ at full supply mode and the system has been divided into

two groups of more or less of equal areas, for the above purpose. The three distributories

4R, 5R and 11R (A&B) of LBC and two distributories BC2 and BC3 of RBC will be run

at continuous full supply mode with internal turn of 7 days ‘ON’ and 7 days ‘OFF’. This

is recommended to suit the local condition of command and system (PWD, 1993).

3.8.6 Operational procedures followed in both LBC and RBC

a. The reservoir release is to be stepped up gradually starting from 25% of full

supply and then increasing by 25% every two hours till the level reaches the

desired level of supply.

b. The same procedure is adopted either for reduction in reservoir releases or for

cutting off supplies completely.

c. The water in the main canal is allowed to travel to the tail end and the flow

condition at all regulator points is observed continuously.

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d. As soon as the water level in the tail end reaches three fourth of full supply level,

the off take gates are opened one by one commencing from the tail end and

proceed upstream upto the regulator at 15.30 km.

e. Simultaneously, as and when the discharge at 15.30 km of main canal reaches half

supply discharge, the off take gates are opened one by one from 15.30 km

upstream to the canal head.

f. The water supply is to be increased gradually into the branches and distributories

upto full supply discharge and allow the water upto the tail end. Since

proportional distributors are available at all the distributories, the flow is to be

monitored to ensure that the water reaches the tail end of distributories.

g. After cutting off release from the reservoir, the gates of all off-takes are to be

closed on the main canal one after another.

h. The gates of off takes near the cross regulators are to be operated in such a way as

to maintain maximum water level upstream of the structures to reduce the main

canal filling up time during the next release of water from the reservoir.

3.8.7 Monitoring plan

Both upstream and downstream water levels in the main canal will be recorded at all the

regulator points once a day between 7.00 a.m. and 8.00 a.m. The data for all structures

will be compiled and sent directly to the Superintending Engineer’s office with a copy to

the Divisional office. Similarly the flow in each off take point will be monitored upto tail

end once a day between 7.00 a.m. and 9.00 a.m. The off take canals selected for

monitoring in LBC is presented in Appendix, A-3 and that for the RBC is presented in

Appendix, A-4.

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Figure 3.1 Ponnaiyar river basin – Drainage map

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Figure 3.2 Sathanur reservoir - Command area map

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Figure 3.3 Command area map of LBC

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PWD (REGULAR) O & M PP CELL M & ENWMP UNIT CONSTRUCTION

EXECUTIVE ENGINEER THIRUVANNAMALAI

ASST. EXECUTIVE ENGINEER SATHANUR RESERVOIR

ASST. ENGINEER THENMUDIYANUR

ASST. ENGINEER VANAPURAM EAST

WORK INSPECTOR

LASCAR-I

LASCAR-I LASCAR-II

ASST. ENGINEER VANAPURAM WEST

LASCAR-II

LASCAR-I LASCAR-II

WORK INSPECTOR WORK INSPECTOR WORK INSPECTOR

ASST. ENGINEER SATHANUR RESERVOIR

LASCAR-I LASCAR-II

Figure 3.4 Organisational flow chart showing the O&M of Sathanur irrigation system