Quantification of Surface Runoff Using Different Methods (Case Study: Waqf Infiltration Basin in the Gaza Strip)

Abstract

Background: The surface runoff created by rainfall is essential to recharge the Gaza coastal aquifer with fresh and clean water when adequately collected and infiltrated. Thus, accurate estimation of surface runoff can foretell the actual volume of incoming stormwater to the infiltration basin. Method: There are several methods for calculating rainfall-runoff only a few of them are accurate due to various restrictions and limitations. Rational formula was used to calculate the surface runoff entering Waqf infiltration basin located in Gaza city. Results: The daily surface runoff was estimated as 265,320 m3 using the Rational method while it was 324,000 m3 using the Soil Conservation Service (SCS) method at 67 mm rainfall depth for 5 year return period. Whereas, at 10 mm rainfall depth during the 2021-2022 wet season, a large difference was determined between the two methods. Thus, in-situ estimation was used as a third method, in which the water height in Waqf basin’s grit removal chamber was measured, thereby calculating the daily surface runoff as 360 m3 which was not far from the result obtained by the SCS method at 10 mm daily rainfall depth. Conclusion: It was concluded that using a reliable method was very important for the accurate estimation of surface runoff, which leads to a well-designed infiltration system in the Gaza strip.