ASSESSMENT OF THE RAINFALL STORM EVENTS OF JANUARY 2010 AND MARCH 2014 FOR THE CATCHMENT MODELING OF WADI EL ARISH AND WADI WARDAN BASINS, SINAI, EGYPT

The aim of this article is to analyze and assess two rainfall storms characteristics representing two different seasons i.e. winter (January 2010) and spring (March 2014) and the response of both Wadi El Arish (21787 km²) and Wadi Wardan (1385 km²) catchments in Sinai to such storms. Wadi El Arish, is debouching towards the Mediterranean Sea at north, and is dominated by carbonate rocks, while Wadi Wardan (1454 km²) is running towards the Gulf of Suez at west, and is dominated by clastic sediments. This study is based on the determination of the hydrologic parameters and variables of both basins as well as the analysis of rainfall data for the purpose of catchment modeling. The HEC-HMS model (version 4) is used to estimate the peak discharge and runoff volume occurred in each sub-basin (eight in Wadi El Arish and four in Wadi Wardan). The results show that the storms have not the same behavior neither spatially nor temporally, where they differ from sub-basin to another and from time to time. The results of storm simulation show that flash flood characteristics are highly variable from season to season in terms of storm amount and duration, runoff volume, runoff depth and runoff coefficient. Wadi El Arish received a considerable amount of runoff water during the storm of 2010 (107.68 *10⁶ m³), with a peak discharge equals to 1382.5 m³/s, while in the storm of 2014 the total runoff volume was only 16.1*10⁶ m³ and the peak discharge was 279.1 m³/s.  El Roak sub-basin (5988 km²), which represents the largest sub-basin in Wadi El Arish running from south to north, produced the maximum discharge (996.2 and 229.9 m³/s) and consequently the maximum runoff  volume (61.6*10⁶ and 13.3*10⁶ m³) for storms 2010 and 2014, respectively. The runoff coefficients in El Roak sub-basin are 27.65 and 15.88% for storms 2010 and 2014, respectively.  This means that more than 27% of the rainfall transform to runoff in this sub-basin. In Wadi Wardan, the peak discharges are 312 m³/s and 52.1 m³/s and the total runoff volume are 8.9*10⁶ m³ and 1.5*10⁶ m³ for storms 2010 and 2014, respectively. Somar sub-basin (441 km²), sub- basins in the upstream of Wadi Wardan and run in the east-west direction, have the maximum discharge (180.9 and 27.1 m³/s) and runoff volume (4.6*10⁶ and 0.76*10⁶ m³)for storms 2010 and 2014, respectively. The runoff coefficient is in Somar sub-basin are 36.55% and 13.04% for storms 2010 and 2014, respectively. From the catchment- storm modeling, one can recommend constructing two storage dams at the outlet of  El Roak and Somar sub-basins, where the runoff volume of these sub-basins represents about 55% of the total runoff volume, in order to protect the urban areas from the occasionally flash flood risk.