Scale model study on head discharge relationship for regulator with flap gate

Abstract

There are about twenty drainage regulators having 2 to 21 vents exist III Khulna-Jessore Drainage Rehabilitation Project. These were constructed mainly using the developed head discharge relation obtained from desk study. In this regard, drainage discharge may differ from the actual discharge because of using different values of contraction coefficient. For better operation and performance of these drainage regulators, accurate head-discharge relationship is necessary. Therefore an attempt was made to perform the physical model study for developing the exact head-discharge relation. A scale model 0 f 'Sholmari regulator' having 10-vents with gravity flap was developed using the selected len[:1h scale ratio of I : 10. A total of three twenty five experimental tests were conducted in a laboratory large tilting flume through the regulator for different opening angle of flap, different discharges, and different upstream and downstream waterlevels. All instruments were calibrated before their use. Headloss-discharge relation for different opening angle of flap was developed. This model study result was significantly different from the result obtained from theoretical desk study. Based on model 3tudy necessary changes were introduced in determining different coefficienls. But for without :.lap i.e., 90 degree flap angle, the plot fits well with the theory: q = f(~h). In this case computed discharge obtained from desk study is appeared to be higher (up to 20%) than the measlL-ed discharge. For submerged condition, drainage discharge depends on headlosses, upstream water level and the flap angles. The discharge coefficient did not remain constant because flap opening angle is directly related to the contraction coefficients. Thus model study identified 20 to 70% variation in discharge estimated by the equations based on desk study.