Numerical Modelling of Flash Floods in Wadis from Rainfalls in an Arid Region

Abstract

ABSTRACT Flash floods worldwide are now more frequent with higher intensity than in the past due to global warming. Flash floods cause significant loss of life and damages properties, ecosystems, businesses and other facilities. In this paper initially flash flood risks from intense rainfall were assessed for a seafront development site. Then numerical modelling of wadi flood flow modelling was carried out using the REC-RAS model and the flash flood modelling was carried out using the MIKE21 Flow Model. Both 1 in 10 year and 1 in 100 year return periods were considered in the study for rainfall duration of 0.5, 1 and 9 hours. Flooding extent and maximum flood water depths were extracted from the model results from which flood water volumes were calculated. Model results were used to select an appropriate site for the development. Model results were also used to derive a flood mitigation option to prevent flood water entering the project site. The methodology described in this paper for numerical modelling of flash flood adopted by Royal HaskoningDHV (RHDHV) could also be applied to similar sites around the world.