M/s WAPCOS, New Delhi has entrusted the work of finding the canal conveyance Efficiencies of Narayanapura Left Bank Canal and its distributaries to M/s Design Group Project Consultants Private Ltd., Bangalore.

    The Narayanapura Left Bank Canal is having Five distributaries, viz.,

  • Hunasigi Branch Canal
  • Shahapur Branch Canal
  • Mudbal Branch Canal
  • Jeevargi Branch Canal
  • Indi Branch Canal.

    Discharge Measurements at  regular length intervals has been found out by Current Metre Gauging(CMG) and also using 2G Accostic Current Meter Gauging(2G ACM).  In the regular Current Metre, the number revolutions and the time taken is noted down and the velocity is calculated.  Wherever as in the 2G  ACM, the instrument gives directly records the velocity, temperature of water, wave action in the water etc.,  For measurement of discharge, the velocity is taken directly from the ACM.

    Conveyance Efficiency is the ratio of total water delivered at the outlet to the block fields and the water released at the project head works. It is expressed in percentage.

    The conveyance efficiency of main canal/ branch canal/ distributaries have been calculated after field measurements of the discharge and adopting inflow-outflow method as suggested by Bureau of Indian Standards for field measurement of conveyance efficiency. A brief description about the inflow-outflow method, which has been adopted for measurement of conveyance efficiency, is given below.

    The inflow-outflow method consists in measuring the water that flows into and out of the section of canal being studied. The difference of water quantities flowing into and out of the canal reach is attributed to seepage. Evaporation from the canal water surface and precipitation is also taken into consideration.

  • Selection of test site

    The selection of the site has been done by the assessing availability of the measuring service at the site of inflow and outflow and accuracy of the measuring devices. Current meters have been preferred for measurement of discharges.

    The length of the reach has been adopted such that the losses from the reach, measured by this method, are of a higher order compared to the accuracy of the measuring devices at inflow and outflow. The current meter gauging sites have been selected such that the canal has well defined section in a straight reach.

  • Preliminary arrangement and experimental procedure adopted

    Having selected the site for tests following preliminary arrangements were made:

  • As far as possible all outlets from the canal were kept closed. In case it was unavoidable, some of the outlets remained open. The outlets decided to be kept closed during the test period were kept closed and locked.
  • The measuring devices were checked for their dimensions and efficiency in giving accurate discharges.

    Known discharge from the parent canal or reservoir is let into the canal. The discharge was kept constant during the period of tests.

    All diversions and losses from and inflow into the test reach including the discharges through the open outlets were measured accurately.

    Further Analysis of the results have been carried out.