Hydrological design aspects of small scale drainage project in Bangladesh

Abstract

The procedures and assumptions used for hydrological design for small scale project in Bangladesh by differenrt agencies have been reviewed. The design discharge calculation for a selected project have been studied by three different methods and compared with existing project situation. For the purpose of this study manuals and design reports were collected from Lhe organizations such as BWDB, LGEB and their Consultants. A particular subproject "Bannyar Khal" at Muktagacha Upazilla has been selected to apply Unit Hydrograph method, Soil Conservation Service(SCS) method and Richard's method for calculating inflow during premonsoon taking rainfall data used in original design. Again a unit hydrograph has been derived using. recent rainfall data. The unit hydrographs thus obained were compared with inflow used in original design. It is found that most of the organization used unit hydrograph method for calculation of inflow. The existing 2 vent regulator in the subproject area was found quite adequate compared Lo discharge calculated by the three methods. It is revealed that S.C.S and Richard's method require less time to calculate inflow hydrographh. provided rainfall frequency intensity and duration curves are available for the area concerned. On the other hand unit hydrograph method is scientific method but it needs long time to complete the calculation.