Evaluation of Rainwater Harvesting Systems in the Western Desert of Iraq

Abstract

The Western Desert of Iraq is a large arid region that suffers from severe water shortage due to climatic conditions and lack of planning and management of water resources. Therefore, rainwater harvesting is the best method to conserve water resources. Wadi Horan is one of the largest valleys in the Western Desert located coordinates range from 32° 10′ 44″ to 34° 11′95 00″ N (latitude) and from 39° 20′ 00″ to 42° 30′ 00″ E (longitude), which suffers from a shortage of measurement stations and a lack of data available to forecast and calculate surface runoff. The present study aims to evaluate some small dams in Wadi Horan (Horan/2, Abila, Horan /3) dam. Using the SCS-CN method as integrated with the RS and GIS was efficient to estimate the surface runoff in Wadi Horan. The SCS method has proven its effectiveness as a better method as it consumes less time and the ability to deal with facility to handle extensive data set and large areas for estimating surface runoff. The Water Harvesting at Sub- Catchment level Model (WHCatch) used to evaluation thes dams. The (WHCatch) model proved the ability to deal with large and small catchment and knowledge of hydrological behaviors during the years of study, its ability to deal with large amounts of data, which abbreviated effort and time. The results of applying the water balance equation to the three dams under study were evaluated. The result showed that the Horan/2 Dam reached the designed capacity for a period of 8 years out of 30 years from1990 to 2019, with a rate of 67% of the years of surface runoff. The amount of the surface runoff entering the dam reservoir was 197.65 MCM. The amount of water outflow over the spillway was 151.85 MCM. The results indicated that the volume of the Horan/2 Dam reservoir is small compared to the predicted amount of water entering the reservoir. As for Abila Dam, the design capacity of 4 MCM was reached within only two years (2012, 2018) of the years of the occurrence of surface runoff, which constitutes of 16%. The amount of storage is small compared to the amount of evaporation and infiltration and thus the volume of the dam reservoir is large. The study of Horan /3 Dam indicated that the dam reached the design capacity for a period of 8 years, a surface runoff, which constitutes 67% of the total years of surface runoff is 222.74 MCM. The amount of water outflow over spillway was 173.78 MCM. As discussed herein, the volume of Horan / 3 Dam reservoir is relatively small compared to the predicted runoff.