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.
