Estimation of potential runoff in Wadi Damad watershed, Jazan Province, southwestern Saudi Arabia

Abstract

This study aims to compute the potential runoff in the mountain Wadi Ḑamâd watershed located in the South Western of Saudi Arabia, using Soil Conservation Service-Curve Number (SCS-CN) method based on the maximum daily rainfall recorded during 47 years from 1970 to 2016 at the stations of Ḑamâd, Ayban, Wadi Ḑamâd and Jabal Fayfa, Malaki, and Al Aridhah. The SCS-CN method depends on land use, land cover, and soil complex characteristics of a watershed, and it is the hydrological model widely used for estimating runoff using curve number (CN). In the present study, SCS-CN method is used for estimating the potential runoff in the mountain drainage basin of Wadi Ḑamâd extends on area of 1084.0 km². The CN was obtained at every studied station using the sheet 78 of the land resources map 1:500,000, and it is 62 at Ḑamâd, 66 at Ayban and Jabal Fayfa, and 70 at Wadi Ḑamâd, Malaki, and Al Aridhah. The potential maximum retention corresponding to these CN was 141.2 mm, 117.2 mm, and 108.9 mm. Therefore, the initial abstraction corresponding to the potential maximum retention is respectively 28.2 mm, 23.4 mm, 21.8 mm, and 23.4 mm. The results of this study reveal that the average of yearly rainfall varies from 171.3 to 538.1 mm, and the maximum daily rainfall is ranged between 37.4 and 77.5 mm at Malaki and Ḑamâd respectively. In the opposite, the excess rainfall and the direct runoff vary systematically with the rainfall. The maximum excess rainfall is ranged between 60.6 mm at Jabal Fayfa and 103.2 mm at Wadi Ḑamâd. However, the direct maximum runoff rises respectively from 20.6 to 50.2 mm.