Fuzzy Rule-Based Assessment of Runoff for Abha, Saudi Arabia, Using the Watershed Modeling System (WMS) Software

The arid and semi-arid countries often experience floods due to torrential rainfall events. Appropriate strategy to collect and store rainwater and surface runoff can augment water resources in these countries. In Saudi Arabia, a total of 449 dams with capacity of 2017 million m ³ are available to control floods, recharge aquifers and to supply for domestic and agricultural applications. The southwestern region of the country experiences flash floods, indicating the scope of water resources augmentation through runoff collection. In this study, location of a new dam was identified in Abha, Saudi Arabia, using the watershed modeling system (WMS) software. The WMS software and HEC-HMS hydrologic model were used to delineate watershed and to quantify runoff. The fuzzy rule-based modeling approach was applied to incorporate uncertainty. This study demonstrates that the rainfall events of 25-, 50- and 100-year return periods can generate surface runoff of 10.18 (range 1.77–22.24), 13.08 (range 2.91–26.94) and 16.09 (range 4.25–31.62) million m ³, respectively. Use of runoff from these events can save US$ 0.94–35.4, 1.5–42.8 and 2.3–50.3 million, respectively, which can also reduce CO ₂ emission by 24.6–346.9, 40.5–420.3 and 59.1–493.3 million kg, respectively.