Working Table of Tungabhadra Reservoir


At the time of preparation of working table, i.e., in the beginning of the water year, inputs like quantity of inflows and its temporal distribution, schedule of opening of canals, pattern of drawals by the states etc., cannot be assessed realistically and have to be adopted based on statistics of the previous years. Modifications in pattern of drawals depending upon the rainfall supplementation etc. cannot be avoided. As such, depending on the changing hydro-meterologic, agro-climatic and other conditions, changes are bound to be made in the working table from time to time. In view of the above it is neither practicable nor desirable to have a rigid approach towards the working table in the Khariff season. As experienced in the past years there are cases of excess or short drawals by the states than provided for in the working tables in the Khariff season. Thus a Working Table during Khariff season can at best serve as a guide.

On the other hand working table for the Rabi season can be more realistic. The demand pattern is not likely to change significantly during the season as no rainfall supplementation is expected. However, a little uncertainty in the operation of reservoir still remains due to stochastic nature of anticipated inflows during Rabi season. Despite this uncertainty, it is necessary that the Working Table shall be strictly followed for the day to day operation of the reservoir. Marginal modifications in the working table can be made by reviewing the water availability position at close intervals with the specific approval of the Board.

As per the practice in vogue any direct requisitions received from Superintending Engineers for the discharge lesser than provided for in the approved working table are being honoured immediately. 0nly in case the requisition is for discharges over and above the working table provisions, endorsement from respective Chief Engineer is being insisted in Khariff season. In Rabi season releases for higher discharges over and above the provision of Working Table, are made after endorsement from respective Members keeping in view the carrying capacity of the canals.

Whenever the actual reservoir level and storage goes abnormally below the anticipated, as compared to the draft working table, releases to both the States is proportionately reduced so that the anticipated reservoir level is maintained. This is followed scrupulously in Rabi season.

The ten-day water accounts are prepared based on the actual drawals which are generally within the provision of working table and submitted to the 0fficers concerned with the water regulation in both the States.

Separate sheet enclosed

Anticipated Inflows.

In order to assess the availability of water for the water year 1998-99 the inflows are worked out as follows.

Annual Yield.

The 75% dependable Annual Yield based on the data of 46 years are arrived at 291.341 TMCft. Out of this total yield, anticipated inflows to the end of November 1998 amounts to 278.007 TMCft. In the Rabi season (i.e.) from 1-12-98 to 31-5-99 the anticipated inflows are 13.333 TMCft, which are normally expected in the months of December, April and May. January, February and March do not contribute any significant inflows to the annual yield.

Monthly yield.

Based on the monthly inflow data available for the past 46 years the 75% month wise dependable inflows add up to only 227.776 TMCft for Khariff season. For Rabi season i.e., December to May the net 75% monthwise dependable inflows add upto a net (-) 1.412 TMCft. The net total inflows for the year 1998-99, as per monthly 75% dependability this year works out to (227.776 – 1.412) = 226.364 TMCft.

Negative Inflows.

For the period from 1-1-99 to 30-4-99, keeping in view the performance of the Reservoir during the above period in the past, a provision of (-) 13.9 TMCft is made in Working Table tentatively towards inflows. In rabi season, the availability of water will be reassessed from time to time in the review meetings at S.E’s level and the provision towards inflows for the remainder period suitably reassessed based on the current trend of inflows.

Debit for Lift Irrigation Schemes.

In order to quantify drawals from the reservoir direct by lift irrigation schemes, during rabi season, while approving the working table for the water year 1988-89, the Board in its 133rd meeting held on 11-1-1989 resolved to debit 1.25 TMC from 15-10-1988 to 31-12-1988 and 0.75 TMC from 1-1-1989 to 15-2-1989 to Karnataka share provisionally, duly accounting this 1.25 + 0.75 = 2 TMC as inflow into the reservoir for working out the inflows. Pending final decision of the Board, debit as well as accounting of inflows of this 2 TMC in the manner aforesaid is continued.


The Reservoir evaporation losses for the water year 1998-99 are assumed at 11.813 TMCft against an average of 11.115 TMCft for the past eleven years. A statement showing the Reservoir evaporation losses recorded in the past eleven years is given below.

All fig. are in TMC ft.

Month 87-88 88-89 89-90 90-91 91-92 92-93 93-94 94-95 95-96 96-97 97-98 Total Avg. Proposed for
1 June. 0.183 0.199 0.231 0.398 0.884 0.397 0.337 0.294 0.088 0.360 0.176 3.547 0.322 0.199
2 July 0.802 0.395 0.687 1.207 1.267 1.408 0.620 0.911 0.341 0.795 1.073 9.506 0.864 1.014
3 Aug. 0.829 1.568 1.491 1.218 1.266 1.879 1.043 1.299 1.120 1.036 1.246 13.995 1.272 1.300
4 Sep. 1.187 1.316 1.557 2.022 1.639 1.812 1.220 1.696 1.335 1.180 1.574 16.538 1.503 1.600
5 Oct. 1.076 2.065  2.088 1.443 1.711 1.873 1.062 1.137 1.183 1.188 1.303 16.129 1.466 1.500
6 Nov. 0.927 1.600 1.538 1.207 1.143 1.211 1.118 1.081 1.220 1.147 0.919 13.111 1.192 1.300
7 Dec. 0.942  1.230  1.168  1.266  1.527  1.266  0.893  1.148  1.261 0.931 0.975 12.607 1.146 1.200
8 Jan. 0.988 1.121 1.229 1.207 1.277 1.326 1.023 0.827 1.087 0.978 1.036 12.099 1.100 1.200
9 Feb. 0.896 0.860 1.003 1.050 1.005 1.156 0.900 0.833 0.818 0.957 0.934 10.412 0.947 1.000
10 March 0.734 0.441 0.883 0.774 0.779 1.034 0.843 0.761 0.452 0.845 0.898 8.444 0.768 0.800
11 April 0.254 0.136 0.357 0.304 0.355 0.561 0.398 0.209 0.153 0.384 0.371 3.482 0.317 0.400
12 May 0.188 0.114 0.233 0.422 0.252 0.268 0.243 0.134 0.174 0.186 0.183 2.397 0.218 0.300
Total   9.066 11.045 12.465 12.518 13.105 14.191 9.700 10.330 9.232 9.987 10.688 122.267 11.115 11.813


On account of unauthorised drawals and uncontrolled leakages along the RBLLC & RBHLC at various structure point’s substantial amount of water is lost. This lost water is termed as system loss. Due to occurrence of pipings/ breaches escapes are operated to enable to take up restoration works. A substantial amount of water may therefore be lost to the river. Quantum of water released through escapes is also considered as system losses. In order to deliver the requisitioned discharges at lower down reaches, it was found necessary to release extra water duly making provision towards system loss not exceeding 120 cusecs for RBLLC as per the decisions of the Board taken in its 130th meeting. In previous years system losses accounted were as follows.

Year Accounted
1987-88 1.074
1988-89 2.127
1989-90 2.845
1990-91 3.000
1991-92 2.038
1992-93 3.716
1993-94 4.093
1994-95 4.260
1995-96 3.428
1996-97 2.830
1997-98 4.171
Average 3.053

In the 165th meeting of TB Board it was decided to make similar provision of system losses in RBHLC with effect from current water year 1998-99. A provision of 4.418 TMCft towards system losses is made in the Draft working table for the water year 1998-99. Out of 4.418 TMCft, the provision made under RB LLC and RB HLC is 2.982 TMCft and 1.436 TMCft respectively.


The T B Board in its 135th meeting decided to consider transmission losses in RB LLC at 4 cusecs per Million square feet of wetted area. Accordingly, provision towards transmission losses in RB LLC is made in the Draft Working table. In case of RB HLC the maximum provision towards transmission losses are kept at 200 cusecs as per the decision taken by the Board in its 81st meeting.


During the flood season inevitable releases over spillway are to be made. Before the commencement of the spillway surplus and during the spillway surplus, maximum releases are made through Power houses, on both the banks, for generation of extra power. Extra power generation is started, when the reservoir level is around 1631 ft and if there is forecast of further inflows leading to possible spilling of the reservoir without jeopardising the Irrigation interests. As per the assumed inflow pattern and drawals for irrigation, 22.356 TMCft is expected to be used for Extra power generation during the water year. Anticipated releases over spillway during surplussing period amounts to 35.861 TMCft during the period from 1-8-98 to 31-8-98 and 21-9-98 to 30-9-98. The drawals for extra power generation commenced from 3-8-98. Spillway surplussing is expected from 6-8-98.


Based on the availability of water for the year, the State Governments through their Superintending Engineers submit a pattern of drawals in various canals. Keeping in view the constraints like carrying capacity of the canals, the drawal patterns are incorporated in the draft working table. The drawals in different canals for irrigation as provided in the draft working table are in accordance with the proposals received from the States with slight modifications for reasons explained above.

Opening and closing of canals

As proposed by the states the opening and closing of canals during the current water year is proposed as follows:

Name of the canal system Date from which
drawals of water proposed.

Date up to which
drawal of water


Intermittent closure period.

PC + LLC (R/s)
18-6-1998 20-3-1999
2 HLC (R/s) 12-7-1998 15-12-1998 24-8-98 to
25-10-98 to
3 Raya Basavanna channels 1-6-1998 31-5-1998 11-12-98 to
4 River Releases (VNC+RDS) 1-6-1998 20-3-1999 11-12-98 to
5 LBMC 10-7-1998 10-5-1999 21-4-1999 to
6 HLC (L/s) 10-7-1998 15-3-1999 – –
1-7-1998 20-3-1999 – –
2 RB HLC 15-7-1998 15-12-1998 – –
3 a. River Assistance (RDS) 21-7-1998 1-3-1999 21-8-1998 to
21-9-1998 to
  b. -do- KCC 21-7-1998 1-3-1999 1-10-1998 to

Reserve Stock.

The prorata entitlement for Karnataka State out of 170 TMCft of proposed drawals for the current water year is 111.454 TMCft. Out of this only 110.973 TMCft is distributed as per the pattern of drawals received. The balance quantum of 0.481 TMCft is kept as reserve stock for Karnataka State for future adjustments. Similarly for Andhra Pradesh a quantum of 57.408 TMCft alone is distributed out of the prorata entitlement of 58.546 TMCft for the year 1998-99. The balance quantum of 1.140 TMCft is kept as reserve stock for future adjustments.

 Closing balance.

After proposing a drawal of 170 TMCft for Irrigation based on the pattern of inflows assessed, 9.372 TMCft is arrived as closing balance at the end of the water year 1998-99. Since this Draft Working Table is proposed to be reviewed after fully meeting the requirements of kharif season, the closing balance will also get revised after kharif season, when the working table is modified for Rabi season .