An-Najah Staff

Storm water drainage is as important in arid and semiarid regions as in humid regions because it is not only a drainage problem but also water resources management and planning problem. In the West Bank, storm water drainage has not been given enough care and no intensive studies have been done. This paper studies the rainfall runoff process in the West Bank as a case study towards understanding storm water drainage in arid and semiarid regions, where the process has different characteristics as being rarely heavy but significant in terms of pollution, annual runoff and/or in improving the sustainability of the water resources. The runoff to rainfall ratio in the West Bank proved to be considerably variable with no clear relation controlling the process. The arid and semiarid watersheds seem mostly to behave as variable sources and as partial contributing areas. In the Soreq and Rujeeb watersheds, studied as example watersheds, no runoff was recorded for daily rainfalls of less than 30mm. Rainfalls of more than 50mm having intensities of 10mm/hr or more proved to produce considerable runoff events. These are still characterized as partial contributing. Subsurface flow in the Soreq watershed is dominated, which indicates that the traditional unit hydrograph approach might not be applicable. Keywords: Storm Water Drainage; Arid and Semiarid Regions; Rainfall Runoff Process; Unit Hydrograph; Partial Contributing Areas.