Topographic Influences on Runoff and Torrent Pathways: A DEM-Based Study of Khartoum State, Sudan

Arid and semi-arid urban environments are increasingly threatened by catastrophic flash floods, where the physical geomorphology of the catchment serves as the primary driver of runoff intensity. This study evaluates the topographic attributes influencing torrential flow in the Omdurman and Sharg El-Neel localities of Khartoum State. Utilizing a high-resolution Digital Elevation Model (DEM) from ASTER (2011), the research extracts and models land surface configurations, specifically contour variations, slope gradients, and surface aspect. To contextualize these terrain-derived hazard indicators, the topographic results were cross-checked against historical annual precipitation records (1994–2018), confirming that the recurrence of high-intensity rainfall events coincides with the identified hydraulic hazard corridors. The results reveal that the seemingly flat landscape of Khartoum possesses critical topographic ripples and rocky outcrops that function as hydraulic accelerators. Elevation analysis shows Omdurman ranging from 300 m to 500 m across five contour classes, characterized by terrain features that create localized flow traps. In contrast, Sharg El-Neel exhibits a steeper elevation gradient ranging from 300 m to 600 m across seven contour classes, facilitating rapid, high-velocity drainage toward the Nile confluence. These geomorphological factors are found to be essential in the transition to destructive runoff events, dictating the spatial heterogeneity of water distribution and flow speed. The study concludes that sustainable hazard governance within Khartoum State must transition away from transient vegetative indicators toward a permanent, "Topography-First" spatial planning strategy, while recommending that future work incorporate field-observed flood and runoff measurements to further validate the modeled hazard corridors. Consequently, future infrastructure optimization, water harvesting networks, and flood mitigation efforts must be precisely aligned with the geomorphological path-mapping and hydraulic hazard corridors identified in this long-term topographic analysis.