Due to uncontrolled urban expansion and increased rainfall events in the desert regions of Saudi Arabia, effects of frequent flash flooding have become greater on infrastructures and human life in recent years. With the availability of high resolution datasets, detailed Terrain information resulting from frequent on going aerial survey, it is promising for modeling and analyzing flash flood in urban areas more accurately using such higher precision data derived from LIDAR. The purpose of this Master's Project was to evaluate and compared low and high resolution elevation in use for assess effects on identification of flooding risk potential areas in Saudi Arabia using Um Qaser Areas in Riyadh as study area. The paper presents literature review carried, methodology, results achieved and there comparison, discussion, limitations and future research areas. The processing successfully resulted in identifying an increase of about50% in water accumulation points of 59 quantity using LIDAR terrain data in comparison to processed Satellite ASTER 30m Elevation data of 26 quantity. Processing LIDAR based terrain data also resulted in generation of hyrdro network information in better detail then satellite DEM. More future work needs to be carried out to integrate cadastral information to the DTM processing of LIDAR for higher accurate water flow network generation leading to better modelling.