Departemen Geografi FMIPA UI

Selamat H. Kuswantoro Marko., MSc.

Lulus S2 di King Abdulaziz University Jeddah

URBAN FLOOD HAZARDS MODELLING IN ARID ZONE (Case Study in Wadi Qows Jeddah)

 ABSTRACT: This thesis deals with the flood hazard that happened on November 25th, 2009. The extreme weather conditions and the unplanned housing developed by people in the low land areas of the wadi streams have contributed in the occurrence of such flash floods. The flood modeling is a useful tool to identify the inundation areas caused by the flood. In this study, an integration of the hydrologic and hydraulic modeling using WMS, HEC-HMS, HEC-RAS and supported by GIS software has been implemented. The results show that the measured rainfall from King Abdulaziz Airport station is 70mm, while the estimated from rainfall satellite images over Wadi Qows is 83mm. From frequency analysis the amount of 70mm corresponds to 10 year return period. The estimated peak discharge during the flood event on November 25, 2009 ranges between 34.8 m3/s and 116.2 m3/s, while the runoff volumes range between 0.98 to 2.93 million m3. The hydraulic modelling results were analyzed according to 1-D model using HEC-RAS and 2-D model using a coupled WMS and HEC-RAS software. For 1-D model results, the estimated average velocity ranges from 0.83 to 2.50 m/s, while the estimated average flood depth ranges from 0.96 to 1.95m. For 2-D model, the results are distinguished based on low resolution DEM (90m) and high resolution DEM (10m adjusted DEM). For the low resolution DEM, the estimated average flood depth ranges from 1.72 to 1.84 m. While for the high resolution DEM, the estimated average flood depth under normal condition at 10m resolution DEM is 1.9 m. The water level in this case is higher than the low resolution DEMresults which are without considering buildings within the DEM. Thus, high resolution DEM is essential to get more reliable results of flood inundation in urban area, particularly.