Die Trinkwassertalsperre Wadi Dayqah im Oman - Erfahrungen aus Planung, Bau und Betrieb

The Sultanate of Oman is a semi-arid country with few permanent surface-water resources. Wadi Dayqah is unique in Oman with the perennial flow around 1,5 m³/s. Severe storms result in flush floods. The catchment area extends 1 700 km² with an average rainfall of 150 mm/year. Studies identified a potential site across a gorge above Mazara village, some 100 km southwest of the capital Muscat. A RCC dam 75 m high and an adjacent secondary saddle dam provide 100 million m³ of storage, sufficient for a yield of 35 million m³ per annum of portable water delivered by a pipe line to the capital of Muscat. The site of the main is exposed limestone that of the saddle dam comprises inter-bedded soft fine sandstones and claystones. Cyclone Gonou caused a flush flow with 10 000 m³/s which exceeded the assessed 1:10 000 year flood on which the design of the spillway had been based. The design revision comprised an increase of spillway length by 6 m and provision of a parapet wall on the upstream edge of the dam road crest comprising counterbalanced precast concrete units. During the first impoundment strong seepage below the foundation of the rockfill dam took place. Additional sealing works like grouting and cut-off by piles were necessary.