COMPUTER AIDED DESIGN OF UNFLUMED GLACIS CANAL FALL

Abstract

A canal fall is an irrigation structure constructed across a. canal to lower its water level and destroy the surplus energy liberated, from the falling water which may otherwise scour the bed and banks of the canal. Its necessity arises whenever natural slope of the country is steeper than the longitudinal slope provided in the irrigation canal. The falls have been classified into vertical and glacis type falls. These have been further divided into meter and non-meter flumed and unflumed types. Unflumed glacis type fall utilises the principle of standing wave for dissipation of energy. Water flowing on an inclined floor has vertical component of flow which generate dangerous potentialities in eroding the bed and sides of the earthen channel downstream of falls. Energy of the fall due to this reason, is not completely destroyed in hydraulic jump. The downstream portion of the canal fall where the energy dissipation is deliberately allowed to occur so that the out going stream can safely be conducted to the channel below is known as stilling basin. The most suitable hydraulic jump type basin designs for Froude number less than 4.5 are (1) 1SSB I ,(2) USER baSin IV, (3) SAF basin and for greater than 4.5 are (1) ISSB 11 , (2) USER basin III , (3) SAF basin. Stilling basin without any appurtenances or unaided stilling basin for both cases can also be provided.