Drainage systems design in urbanized areas under land use changes scenarios: case study of Narok Town (Kenya)

Land use/land cover (LULC) changes due to urbanization have a strong influence on runoff process. In the case of Narok town, in Kenya, several flash floods have caused human losses and economic damages. Design hydrograph and its peak flow are the key elements to determine hydraulic geometrical properties in designing an adequate drainage system. In consideration of LULC changes and consequent hydrograph variability, in this study existing channel geometric properties were verified, using field measurements through a ground survey employing Real-Time Kinematic equipment at Kakia and Esamburmbur channels of Narok town. To improve the drainage system, the evaluated peak flows under assumed future LULC scenarios were used to design hydraulic properties for a sustainable urban drainage system. Three hydrological/hydraulic models (EBA4SUB, Manning's equation, and Civil 3D) were used under different LULC scenarios for computing channel geometry and correspondent water level. The change in channel geometry was found to obstruct free flow for different scenarios of peak discharge and flow volume. The presented results could be used to support the design of storm water drainage systems by local authorities, in order to mitigate flood hazards and consequently to reduce the hydraulic risk.