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

摘要

This contribution presents part of the work that had been done to develop the water resourcesnin Wadi Naman east of Makkah City to form a strategic water reserve for the city of Makkah andnthe nearby holy shrines. The aim of the strategic water reserve is to be used as water supplynin emergencies when the desalination plant or the pipelines from the desalination plant to thencity have to be out of the service for a considerable amount of time due to planned or unplannednshutdowns. The development plan calls for a constructing of a subsurface dam across the Wadinat a prescribed location. The proposed subsurface dam will extend from 3m below the naturalnground surface to a depth of 2–3 metres inside solid bedrock. The suggested dam may benconstructed using plain plastic concrete and utilizing the diaphragm wall technique fornconstruction. The crest of the subsurface dam can serve as a buried spillway to convey accessnwater downstream and the overflow freeboard will provide a room for utilities that passesnthrough the wadi to serve cities and villages upstream. The alluvium thickness upstream of thenproposed dam location is ranging from 20–70m and the total volume of the alluvium behind thendam that can store water is 218 ￡ 106m3. Pumping test revealed that the transmissivity isn1,376m2/day and the yield storage coefficient is 0.15. The safe water yield that can be storednin the alluvium behind the dam due to natural recharge of 6.53 ￡ 106m3/year and interception ofnthe groundwater flow by the dam can reach an amount of 32.7 million cubic metres of waternin a period of about 5 years from the date of completion of the dam. This amount of water cannserve the city and the nearby holy shrines for a period of up to four months with a good demandnmanagement program. However, to maintain the desired levels of water quality and quantitynin the reservoir and to minimize the adverse effect of the dam on the downstream area a verynstrict management program of the basin has to be followed. This management program can benused to control the urban and rural development in the area upstream of the dam and enhancingnartificial and natural recharge in the upstream and downstream sides of the dam.