Uganda Manafwa River early flood warning system development hydrologic watershed modeling using HEC-HMS, HEC-RAS, ArcGIS

Abstract

The Manafwa River basin spans several districts in Eastern Uganda. Over the years, frequent floods have constantly posed a great threat to the local communities in these districts. The Uganda Red Cross Society (URCS) intends to design a precipitation based flood forecasting system for the Manafwa River Basin. Towards this end, the URCS initiated collaboration with MIT's Department of Civil and Environmental Engineering in January 2013, in an attempt to establish a hydrologic modeling system that relates upstream precipitation with downstream stream discharge using ArcGIS, HEC-HMS and HEC-RAS. This work is dedicated to present the progress in the modeling endeavor, provide technical guidance to the extent possible, and facilitate hydrologic modeling efforts of similar nature. The main focus is on the loss methods used in HEC-HMS: the Curve Number loss method and the Initial and Constant loss method It is found out that the neither the Curve Number nor Initial and Constant loss method is perfectly suitable to modeling both short-term and long term simulations. The Curve Number method is able to better model the precipitation-runoff processes in short term simulations. The Initial and Constant loss method tends to underestimate water volume runoff in short term simulations from what is observed The Curve Number loss method produced results that are on average closer to observed values in short term simulations; however, the resulting curve number values from calibration are considerably lower than the estimated values.