Clovelly Dam construction nearing completion

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Clovelly Dam construction nearing completion


The Clovelly Dam is nearing completion, after a construction period of 5 months. The dam, situated on the Bhobhobho River east of Underberg, is expected to be completed in mid-October 2021. This marks a major milestone for the project, which MBB has been involved with since its inception in 2009.

At 14,3 m high with a storage of 650 000 m³, the dam has been classified as a Category 2 dam with a significant safety risk, requiring the involvement of an Approved Professional Person in the design of the embankment.

This project highlights MBB’s skills and experience in managing a project through its full life cycle. In addition to the design and the construction supervision of the works, MBB processed and submitted the Water Use Licence Applications, facilitated the necessary environmental studies and approvals, and obtained the required permits from the Dam Safety Office.

The dam consists of a zoned earth embankment dam with an upstream and downstream earth shell, a clay core and a core cut off trench. A 60 m wide by-wash spillway with 2,8m of freeboard is located on the right flank of the dam. The spillway is reinforced with concrete sills, and will be grassed after completion. In addition to the spillway, a trickle flow system has been designed to cater for the perennial flows and reduce the frequency of small flows through the spillway.

Notable features of the dam design include:
  1. The design of an innovative upstream closure plate on the inlet to the outlet pipe. The upstream closure plate is installed for rare situations when all downstream flow control valves have failed or need to be removed. The design of the stainless-steel closure plate allows the plate to be closed and re-opened without a diver ever needing to enter the outlet box or removing the trash grating, which would be a very dangerous exercise.
  2. The central portion of the embankment clay core is founded at shallow depth on hard shale, which is susceptible to rapid weathering. This required the foundation surface to be cleaned, prepared and covered with clay immediately to prevent slaking of the shales, and to ensure a good contact between the clay and the parent rock. As the core moves away from the shallow central rock section, it transitions from a shallow wide base to a traditional deeper core trench rising along the flanks of the valley.
  3. The downstream drainage blanket has been installed in segmented drainage panels, separated by clay fingers between the panels. Each panel is drained by a single finger drain linked to the toe drain at the base of the dam embankment. This toe drain exits at the outlet headwall of the dam where the rate of seepage can be easily measured. Should seepage water ever increase markedly, it will be possible to trace the increased seepage back to a specific panel, thus narrowing down the location of a potential leak or problem.
MBB are proud of its contribution to this project and the benefits and growth that this dam will bring to the owners dairy farming operations.

Please visit our webpage at the link below for more information on the services MBB can provide with regards to Water Use Licence Applications, Dam Safety Evaluations and Dam design and construction.

Click here to visit our webpage
Click here to download the Water Use Licensing factsheet
Click here to download the Dams and Water factsheet
Click here to download the Dam Safety Evaluation factsheet
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