Flood modeling along Nalukolongo channel using ArcGIS, HECHMS and HECRAS softwares

Abstract

ABSTRACT Floods are among the most catastrophic natural disasters around the globe impacting human lives and infrastructure. The changing climate and land use have raised challenges associated with increased runoff and flood management. The effect is significant in urban catchments due to inadequate drainage systems, poor disposal of wastes and flood plain development leading to material losses and loss of lives. This study aimed at producing flood inundation maps for 10,25,50 and 100 year return periods through development of hydrologic and hydraulic models to simulate the hydrology and hydraulics of Nalukolongo drainage system catchment located in Rubaga division, Kampala city. Topographic datasets i.e. the Digital Elevation Model (DEM), soil types, climatic datasets i.e. precipitation from Intensity Duration Frequency curves of Kampala, channel geometric properties like slope and human factors i.e. land use were integrated using ARC-GIS, HEC-HMS and HEC-RAS software’s. ARC-GIS extensions HEC-GeoRAS and HEC-GeoHMS were also used for the spatial analysis of the catchment. Hydrologic model simulations gave peak discharges of 8.34, 10.06, 12.15 and 12.8 m3/s for 10, 25, 50 and 100 year return periods respectively. Depths of 2.1m and 4.7m resulted from flood maps of 10 and 100-year flood events with corresponding velocities of 2.5 and 3.6 m/s respectively from the velocity maps. The maps showed that the upstream side of the channel is more susceptible to higher flooding depths (> 1.5m) than downstream. This signifies the need to construct the channel with at least a 2m depth both upstream and downstream. In contrary, due to the steeper channel slope downstream, flood waters move with higher velocities than upstream. Therefore, more water resistant materials should be used during construction of the channel at points where the velocities are high to prevent erodibility of the materials.

Keywords:Hydrologic Model, HEC-HMS, HEC-GeoHMS, Hydraulic model, HEC-RAS, HEC- GeoHMS