Establishing the Driving Forces and Modeling of flooding in the Lafa River Basin, Accra, Ghana.

Abstract

The Lafa River Basin (LRB) experiences increased frequency and magnitude of floods, causing increases in areal and depth of inundation. This translates into huge economic losses and loss of human lives. The effective management of flood disaster of the LRB is hinged on the identification of the factors responsible for the floods, modelling of the flood situations and a quantitative assessment of the hazard zones. Hydrologic Engineering Centre-Hydrologic Modeling System (HEC-HMS) and Hydrologic Engineering Centre-River Analysis System (HEC-RAS) models have been integrated with Geographical Information System (GIS) to identify the driving forces behind the floods, and assess the hazard zones of the Basin. Physiographical characteristics are responsible for the floods and analysis indicate that the LRB is a small urbanised elongated drainage basin of area 27.945 km2 with predominantly steep slopes, and impervious surface soils. The Peak flows produced by 2, 15, 25, 50, and 100 year return period storms have been found to inundate 233.88 ha, 292.92 ha, 298.36 ha, 305.00 ha, and 311.24 ha respectively. 1.68 %, 5.54 %, 5.91 %, 6.41 %, and 6.63 % respectively of total inundation areas were above inundated depth of 2 m and are located around culvert locations on the Lafa stream. Keywords-Basin, Flood plain, Hydrological analysis, Modelling, Peak flows