The Influence of Karst Features on the Surface Runoff in Wadi Bir al- Ain of Al- Maa’za Limestone Plateau East of Sohag, Egypt

In general, studies of wadis (= dry valleys) in Al-Maa’za limestone plateaus in the Eastern Desert of Egypt have shown that water erosion is the main contributor to the formation of these wadis. However, spreading of karst features such as caves, sinkholes, collapsed underground streams, potholes, springs, gorges, karst pools, tufa and Terra Rosa soil in Wadi Bir al-Ain has led the present study to investigate the influence of the karst features on the water runoff in the trunk wadi and its tributaries.
The present study employs the systematic approach based on rain amount received by Wadi Bir al-Ain during the rainstorms; particularly occurred on 8 and 9 March 2014; the output was the net stream runoff stored in the lake on the front of the dam at the waid’s outlet. Difference between the input (rain volume) and the output (net runoff) was the result of the hydro-geomorphic processes carried out within the wadi during the water flow from the upstream to the downstream. These processes were infiltration, evaporation-transpiration and water swallow which form the total water losses. Amount of water swallow, which is the most important indicator for the underground discharge of the karst system, was estimated by calculating surface infiltration and evaporation-transpiration, as well as rain volume and net stream runoff yield. The study reaches to the following conclusion; that is 86.41% of the total rain which fell on Wadi Bir al-Ain on 8 and 9 March 2014 was swallowed by karst features through sinkholes, joints, and underground streams. Therefore, there is a great necessity to review and deepen our understanding about the nature of water runoff within the limestone’s areas. 
Keywords: Wadi Bir al-Ain, Al-Maa’za plateau, Eastern Desert, karst Features