Feasibility of Sediment Budgeting in an Urban Catchment with the Incorporation of an HEC-HMS Erosion Model: A Case Study from Sri Lanka

This study aimed at studying the feasibility of using a sediment model built in HEC - HMS incorporating Modified Universal Soil Loss Equation (MUSLE) in aiding the separation of sediment contribution as point and non-point, an important aspect in sediment pollution control. The model was developed and verified using a representative sub-catchment and a canal reach of a tropical climate. The field observations and model developed had a good agreement and indicated about 16% and 35% of total sediments in the canal may be from nonpoint sources for the dry and wet seasons, respectively. Results suggested that a major fraction of eroded sediment ended up in the main canal through the dense drainage network across the catchment. This meant sediment trapping should focus tributary drainage ditches or at point source inputs to canal rather than the main canal banks. The study recognized that HEC - HMS is also capable of simulating sediment generation with acceptable errors. Being a free software package, HEC - HMS would be an effective sediment modelling tool for jurisdictions where sediment analysis has been constrained by cost.