Hydrologic Calculations in Wadis Hada Al Sham and Usfan@@@حسابات مائية في وادي هدا الشام ووادي عسفان

Abstract

In this research, hydrologic calculations have been made for Wadis Hada Al Sham and Usfan including the runoff, the interception, the infiltration, and the sediment load. These calculations have depended on the meteor- ological, the morphological, and the geological characteristics of the wadis as well as the results of infiltration tests and sieve analyses of soil samples from the wadis. The calculations were repeated for storms of different return periods 2, 5, 10, 20, 50, and 100 years and variable storm duration of 0.5, 1.0, and 2.0 hours. The study results are presented in the form of runoff hydrographs and tables including water volumes and rates at the outlet of the wadis. A hydro- morphological model developed by MIT has been used in the calculations. It had been calibrated in Wadi Ghuran that extends on the northern boundary of the studied wadis and has runoff records. Results of study are presented only at the outlet of Hada Al Sham and Usfan at sections L2 and U1, respectively. Calculations at section U1 have shown that if the entire region is subject to a storm of one hundred-year and duration of half an hour (as an extreme case), the resulting runoff hydrograph has three peaks with a maximum discharge of 10100 m 3 /sec. The corresponding water volumes of interception, infiltration and runoff are 23.64, 79.47, and 163 millions cubic meters, respectively. The corresponding equivalent heights are 0.012, 0.043, and 0.0876 m over the en- tire area that is about 1861 km 2 . The sum of these equivalent heights is equal to the precipitation value (0.143 m) coming with the corresponding storm. It has been recommended to install gauging stations, for the runoff, at the outlet of the sub-basins of the studied wadis to provide continuous records that would help in any future calibration of the hydro-morphological model. Also, it has been advised to apply this methodology of study in other wadis of similar con- ditions.