Flood generation in South Dhofar: hydrodynamic modelling and identifying management challenges

There is a lack of studies on flooding in dryland regions, despite these systems covering 41.5 % of the Earth’s land surface and being home to 44% of the world’s human population. Here I examined flood management and flood datasets in Dhofar governate, Oman, finding major problems with hydrometeorological infrastructure, communication and the existing flood risk maps. These issues hamper flood preparedness. Hydrological and hydraulic models were developed for Sahalnout, Darbat, and Hamran catchments in the study region, modelling three previous significant flood events (2002, 2018, and 2020). The model validation used a range of data sources including conversations with experts, citizen surveys, and remote sensing. The area-weighted discharge contribution was calculated for the main tributaries in the three catchments. For example, Raithout tributary in Sahalnout contributed the greatest discharge in the 2020 event (325 mm) and the 2002 event (201 mm) compared to the other tributaries in the same catchment, most likely due to the greater drainage density of these tributaries. For the three catchments, several major tributaries peaked at almost the same time as the peak in the main channel suggesting that they could be good candidates for upstream management to attenuate and slow the peak. A set of scenarios was tested using modelling. When small dams were installed in stream channels, the flood velocity and peak discharge were reduced but the depth and flooded urban area increased. Larger rainfall intensities/volumes of 1.15 and 1.30 times that of a baseline storm led to a non-linear increase in peak discharge and inundated area. When upland areas were well vegetated the downstream flood impact was reduced, while overgrazing had the opposite effect, particularly in downstream sub-catchments. The findings support consideration of new spatial approaches to mitigate impacts of flooding in populated arid zones.