Introduction
The Tungabhadra Dam near Mallapuram village along with Right and Left banks was begun during 1944 by the erstwhile States of Madras and Hyderabad Governments respectively to impound 133 TMC of water in the reservoir. The 1.739 km long dam, with its two saddles on the left side impounded the monsoon flow up to 491.62 m (1613 ft) level in the year 1953. Water was let into the canals on both the banks on 01 July 1953. However, erection of spillway gates, bridge, road on top of dam etc. were completed in June 1958. As the reservoir submerged, the Valvapur and Hosakote Anicuts constructed by the erstwhile Rayas, a sluice was provided on the right side of the dam with a lead channel to connect the old Raya and Basavanna canals to provide irrigation for 11 months in a year. Similarly, the old Koregal Anicut (Left flank of Valvapur Anicut) and its channel got submerged in the reservoir. So, a channel was connected to the first distributary of left bank main canal to serve the old Ayacut. The project comprised construction of a masonry dam near Mallapuram of length of 1040 m across the Tungabhadra River including spillway of 701 m, composite dam of 546.8 m and earthen dam of 152.40 m totaling 1739.20 m. The Tungabhadra dam has five canals taking off from sluices located in it, namely:
- Right Bank High Level Canal (RBHLC);
- Power canal on right side which is named as Right Bank Low Level Canal (RBLLC) beyond 21.09 km;
- Raya Basava Canal (RBC on right side);
- Left Bank Main Canal (LBMC) also called as Tungabhadra Left bank canal (TLBC), and
- Left Bank High Level Canal (LBHLC).
The TLBC system has a command area of 244,000 ha. Irrigation water is supplied from the Tungabhadra dam via a 227 km long main canal. Construction commenced in the 1960s envisaged to supplement erratic rainfall during the kharif season. Tungabhadra LBMC with a total length of 226 km was originally designed with a head discharge of 7,000 Cusecs up to Right Outfall Sluice (ROFS) located at Ch 0+430 m beyond which the canal carries 4100 cusecs. The Tungabhadra Right Bank High Level Canal (TRBHLC) system has a command area of 73,117 ha. supplied from the Tungabhadra dam via a 105.47 km long main canal. TRBHLC with total length of 105.47 Km was originally designed with a head discharge of 3,800 cusecs. The TRBHLC consists of 16 distributaries having a total length of 227 km and with the total length of 441 km laterals.
TBP Feasibility Study
As part of the KISWRMIP, a feasibility study is to be prepared by PSC for TLBC. The demarcation of areas as per ADB Financing Framework criteria for the TBP sub project has been posing a challenge. After considering TLBC for some time, and then shifting to TRBC, the focus is now back on TLBC. The TRBC work is being taken up by the government with its own funds.
Currently, details are being looked into within the DPR of the CWC approved TLBC to identify areas that satisfy the ADB Financing Framework criteria namely: (a) the investment should be preferred in under-performing areas, (b) the area should be contiguous, and (c) the area should not be less than 2000 ha.