catchment area

flow direction

Journal of Hydrology Regional Studies

Study region: The study area is the Iishana sub-basin located in north-central Namibia. The basin is characterised by low-lying interconnected ephemeral drainage networks locally known as Iishana. In the past decade, the basin has experienced frequent droughts and flooding events due to recent weather anomalies possibly enhanced by the sprawling urban development. Study focus: Although extensive studies have been conducted on water availability in the basin, no attempts have been made to update existing hydrological maps which provide limited information on the impacts of geo-hydrological dynamics in the area. The aim of this study was to test the effectiveness of the Advanced Land Observing Satellite Digital Elevation Model (ALOS DEM) for drainage network extraction. ArcHydro tools were used for drainage feature extraction. Validation of extracted networks was based on field observations and delineated networks from earth observation data and Normalized Difference Wetness Index (NDWI). The accuracy of extracted drainage networks was assessed through visual observation of data overlay and the coefficient of line correspondence (CLC). New hydrological insights: The resulting drainage networks will be used to update the current hydrographic map of the area which will aid in the development of flood and drought mitigating measures for environmental management. The CLC computed metric obtained a 0.91 match between extracted and delineated drainage networks. The results show that ALOS DEM is capable of extracting drainage networks within the Iishana sub-basin. Keywords: Semi-arid environments, Drainage networks, ArcHydro, Coefficient of line correspondence, Normalized Difference Wetness Index, Iishana sub-basin

The usefulness of alos-palsar dem data for drainage extraction in semi-arid environments in The Iishana sub-basin