Assessment of flash flood hazard based on morphometric aspects and rainfall-runoff modeling in Wadi Nisah, central Saudi Arabia

Abstract

The lack of monitoring and observational data is hampering the assessment of flash flood hazard in arid environments. This study forecasts and investigates flash floods hazards in Wadi Nisah basin in the central region of Saudi Arabia. An integrated approach of Geographic Information System (GIS), Remote Sensing (RS), and Watershed Modeling System (WMS) is presented to determine the flash flood hazards based on morphometric analysis along with rainfall runoff modeling. RS datasets including Shuttle Radar Topography Mission (SRTM) data for digital elevation model (DEM), and SPOT-5 satellite images for land cover mapping, in addition to meteorological data (represented in historical rainfall logs) are used. The study area is divided into 14 sub-basins according to the 5th stream order. The morphometric parameter's analysis clearly show that 42.3%–62% of the total region of Wadi Nisah is highly prone to flooding. Furthermore, medium- and low-hazard areas make up 2.1%–36.4% and 16.5%–55.6% of the total area, respectively. Rainfall-runoff modeling shows that the peak discharge values of sub-basin 14, covers 39.6% of the Wadi Nisah total area, making it greater than that of other sub-basins for each return period, ranging from 12.3 m3/s for a 5-year return period to 294.5 m3/s for a 100-year return period. Accordingly, sub-basin 14 poses more flood risk than other Wadi Nisah sub-basins, as confirmed by the morphometric ranking method analysis.