OPTIMIZATION OF CANAL LIFT A CASE STUDY

Abstract

Agriculture and industrial sectors are the major users of water. Water is drawn by gravity where the source of water is above, and pumping is resorted to when the water level of source is lower than the area to be benefited. Canal lift mainly indicates lift irrigation schemes from reservoir/stream or a lower level canal to higher areas. The canal lift schemes that are existing or are under construction are of limited discharges and serve small areas. National Perspective plan (NPP) proposals for India envisages interlinking rivers to divert surplus water from one river basin to another river basin deficit in water and involve high discharges. Pumping is also proposed at the source or enroute to the canal wherever necessary permitted by the topography. Planning and design of canal lift schemes require decisions on number of pumps, their capacity, dia of rising main, number of stages; number, size and type of sump and their position relative to the source of supply. The optimum size of various components are decided on techno- economic consideration which result in least annual cost of a unit of pumped water. The annual cost comprises the interest on total capital cost, depreciation cost, operation and maintenance and energy charges. The present study report includes an in depth study to arrive at guidelines to determine the number of pumps, their capacity, economic dia of rising main, number of stages; number, size and type of sump and their relative position to the source of supply. Hydraulic designs for civil components and empirical formulae as applicable for hydropower for electro- mechanical equipments have been assumed for the optimization study. A case study involving the proposed pumping stage at offftake point of Inchampalli (Godavari -R) - Nagajuna Sagar (Krishna -R) link canal of NPP proposal is taken to evolve the optimum size of various components of canal lift. Cost analysis has been carried out for alternatives of 3 types of sumps at 5 different locations within the link canal reach of 2 Km. The cost estimate has been framed based on hydraulic designs and the rates available for SriSailam Left Bank Canal (Lift component- 1997) near the vicinity. Annual cost of pumped water is worked out taking the interest rate, life of components and energy charges. The study reveals that the unitised sump at 1500 m with 22 nos of 28.0 Mw capacity having suction pipe of 5.0 m, and delivery main dia of 4.0 m is found to be the most economical one.