Development of strategic water reserve for the Holy City of Makkah, Saudi Arabia

This contribution presents part of the work that had been done to develop the water resources in Wadi Naman east of Makkah City to form a strategic water reserve for the city of Makkah and the nearby holy shrines. The aim of the strategic water reserve is to be used as water supply in emergencies when the desalination plant or the pipelines from the desalination plant to the city have to be out of the service for a considerable amount of time due to planned or unplanned shutdowns. The development plan calls for a constructing of a subsurface dam across the Wadi at a prescribed location. The proposed subsurface dam will extend from 3 m below the natural ground surface to a depth of 2–3 metres inside solid bedrock. The suggested dam may be constructed using plain plastic concrete and utilizing the diaphragm wall technique for construction. The crest of the subsurface dam can serve as a buried spillway to convey access water downstream and the overflow freeboard will provide a room for utilities that passes through the wadi to serve cities and villages upstream. The alluvium thickness upstream of the proposed dam location is ranging from 20–70 m and the total volume of the alluvium behind the dam that can store water is 218 × 10⁶ m³. Pumping test revealed that the transmissivity is 1,376 m²/day and the yield storage coefficient is 0.15. The safe water yield that can be stored in the alluvium behind the dam due to natural recharge of 6.53 × 10⁶ m³/year and interception of the groundwater flow by the dam can reach an amount of 32.7 million cubic metres of water in a period of about 5 years from the date of completion of the dam. This amount of water can serve the city and the nearby holy shrines for a period of up to four months with a good demand management program. However, to maintain the desired levels of water quality and quantity in the reservoir and to minimize the adverse effect of the dam on the downstream area a very strict management program of the basin has to be followed. This management program can be used to control the urban and rural development in the area upstream of the dam and enhancing artificial and natural recharge in the upstream and downstream sides of the dam.