Construction Division



A key project for Muna Noor Engineering & Contracting LLC has been the Wadi Thumaid Recharge Dam, constructed as part of the recharge scheme of agricultural development in the Dakhiliyah region.


Project Details

The Wadi Thumaid recharge dam has been constructed on the main Wadi Thumaid, in the south-west centre of Wilayat Bid Bid, 3 km from the Muscat–Nizwa dual carriageway. It is accessible by asphalt road.

The main purpose of the completed scheme is to enhance the groundwater resources along the Wadi Thumaid from Thumaid village to other villages, such as Hamin, Al Farfarah and Waghlah. The scheme will provide recharge benefits to the downstream areas in Wilayat Bid Bid by increasing groundwater in aflaj and wells.

The dam also provides some degree of flood protection to the farms and downstream properties, and is an attractive tourism spot, especially during the flood season.The dam has a total length of 107 m at the crest with a maximum height of 7.7 m. Optimum storage volumn up to the spillway crest is about 100,000 m³. A controlled release of the stored water to the downstream wadi channel enables flood water to infiltrate the wadi bed for recharge purposes. The dam consists of:

  • A reinforced concrete cut-off wall
    The dam has an upstream reinforced concrete cut-off wall constructed all the way along its front to prevent water seepage. A key trench sits 0.5 m below the surface with foundations and abutments to enhance the bound of the dam’s body.
  • A spillway
    The free overflow spillway section is constructed from stepped gabion boxes filled with boulders and has a total length of 50 m and a maximum height of 5 m. It was designed to discharge safely a flood of 550 m³/s. The crest of the spillway is covered with concrete to prevent erosion due to over-spilling.
  • Non-overflow sections
    The dam has two non-overflow sections, connected to either side of the wadi banks, that are also constructed from stepped gabion boxes filled with boulders. The right-hand-side non-overflow section is 37 m long, and the left-hand one is 20 m long. They cannot be over-spilled.
  • A stilling basin
    The spillway features a stilling basin constructed from gabion boxes filled with boulders. It is protected by riprap on the downstream side to reduce the velocity of water overflowing the dam and therefore prevent erosion.
  • An outlet and water release system
    To release water downstream, a galvanised iron pipe of 200 mm diameter, covered with concrete, is provided under the spillway of the dam. A penstock at the connection to the bottom outlet controls the discharge of water and is operated manually with a key on top of the spillway. It is accessed via a steel ladder from the right-hand-side non-overflow section of the dam.

Salient Parameters of the Project

1. Non Overtopping Sections

Total length 107 m = 37 m (RHS) + 20 m (LHS) + 50 M (spillway)
Maximum height 7.7 m
Crest width 1.4 m
Crest elevation 871 metres above sea level (m.a.s.l)
Crest wall elevation 871.7 (m.a.s.l)
Construction Material Upstream reinforced concrete cut-off wall, downstream of stepped gabion boxes filled with boulders, additional filter layers and geotextile.

2. Spillway

Type Free overflow stepped gabion spillway
Length 50 m
Height over wadi ground 5 m
Crest elevation 869.6 m.a.s.l
Maximum flood 550 m³/s

3. Bottom Outlet

Conduit type Galvanised iron pipe covered with concrete
Total number 1
Length 7.4 m
Diameter of the conduit 200 mm

4. Hydrology

Catchment area 8 km2
Reservoir storage capacity 100,000 m³


More images of this project may be seen in the gallery - click here to view



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