PROJECT NAME Wadi Dayqah Main & Saddle Dams

LOCATION Oman

CLIENT Ministry of Regional Municipalities, Environment & Water Resources

SCOPE Construction of the tallest Dam in Oman

DURATION 39 Months

DATE OF COMPLETION October 2009

Wadi Dayqah, Main & Saddle Dams

PROJECT DESCRIPTION

Wadi Dayqah Dam Project is the tallest in Oman and is located close to village Mazara, some 60 Km southeast of Muscat. This wadi (a local term for valley) is of the few in Oman that flow in its middle reaches most of the year. The flows to the point of dam construction are significant during the rains due to a catchment area spread over 1,688 Km². The water from wadi is used for irrigation by the local population of about 6,000 people settled in three downstream villages Al Mazara, Hayl Al Ghaf and Daghmar. Irrigation water in these areas is traditionally distributed through a network of small irrigation canals called “falaj”.

The site provided an opportunity to impound water, in excess of the downstream users’ irrigation needs, which could then be pumped for water supply to the nearby town of Quriyat and to Muscat. The impounding has been achieved by constructing the Wadi Dayqah Main and Saddle Dams. The water supply lines, water treatment and storage works, and pumping will be done through a separate project.

The 75 m high Main Dam is located on the line of Wadi Dayqah and is a Rolled Compacted Concrete (RCC) structure having an overall crest length of 400 m. The Saddle Dam is located at a higher elevation about 300 m away from Main Dam on the opposite side of a large rock outcrop that divides the wadi. It is 54 m in height with a crest length of 360 m, constructed in zoned rockfill having an impervious clay core n the centre.

MORE INFORMATION

A significant feature of the project is the extensive drilling and grouting of the relatively weak foundation rock to control potential seepage beneath the dam by providing a cutoff along the line connecting Main and Saddle dams and extending further at the extreme ends. To achieve this effectively and within the construction time frame, Lombardi’s GIN (Grout Intensity Number) method was used.

The largest flow into the wadi until the time of tender was recorded in the year 1982, which exceeded 5,000 m³/sec. During the initial construction period of the Project, Oman was struck by the infamous tropical cyclone Gonu with reported flows in the wadi reaching 13,500 m³/sec. The Consultant made revisions to the dam dimensions to ensure the safety of the dam. These changes were successfully integrated with the planning and construction, without any delays, to the satisfaction of the Client and the Consultant.