2 | STUDY AREA

Wadi Al-Lusub is a watershed located in the western part of Saudi Arabia (Figure 1a). It is the upper part of the alluvial fan of Wadi Usfan, which is called Hadat Ash-Sham area. This area was well known in the past with its agricultural activities. At present, relatively larger areas are being cultivated at Hadat Ash-Sham, the agricultural experimental station of the Faculty of Environmental Sciences, King Abdulaziz University (KAU). The geographical coordinates of the station are 39o 43’ 15”– 39o 43’ 57” and 21o 47’ 36”– 21o 54’ 15” with total area 789.68 m2. The station has a total of 14 wells distributed over the farm. However, only 11 wells are working and used for pumping and monitoring. The 11 wells are monitored at static conditions and are shown in Figure 1b. Wadi Al-Lusub flows into Wadi Usfan that runs in East-West direction, having its outlet towards the Red Sea in the west. Wadi Al-Lusub area has an arid climate with an annual average rainfall rate is 113 mm/year verified at Madrakah village (El-Hames, 2005). This area has a temperature range between 130 C – 400 C.
Geologically, the Hadat Ash-Sham experimental station lies on Precambrian – Cambrian complex with Cretaceous-Tertiary sedimentary formation sequences, and Tertiary – Quaternary – Recent alluvial deposit (El-Hames, 2005).
A geomorphological study is performed using ArcGIS software to analyze the hydrological and morphological features in the Al-Lusub Basin (Figure 1c). The watershed has a total area of 803.53 km2, with catchment perimeter is 275.46 km, and the catchment mainstream length is 77282.76 m. The catchment elevation ranges between 224–1295 m above sea level. The stream is flowing from North East to the South West (Figure 1c and 1d). The topographic map (Figure 1d) shows two-stream branches: one is flowing to the north of the farm, and the other is flowing to the south of the farm. Topographically, the stream in the south is relatively at a higher elevation than the stream in the north. Flash floods often attract the farm from the stream in the north.