Mohale Dam settles after spillage                                                                  <<..back

An important milestone was reached since completion of LHWP Phase 1B Construction Works, when Mohale Dam spilled on Monday 13, February 2006 at 9.00 p.m. for the first time since impoundment.  

As a result of the recent heavy rains, Mohale Reservoir experienced a rapid filling compared to previous seasons.   Eleven hours after the spillage, the monitoring team noticed that a kerb stone had popped out at the crest near the middle of the structure.  Upon close examination of the area, a slight dislocation and chipping of one of the slabs was observed on the upstream face of the dam, which was initially perceived to be a crack on the dam wall.

For a dam of this type, the rock fill is expected to settle due to its own weight as well as the water pressure over time.  These settlements normally commence during the construction of the dam and may continue for several years after impounding.

Further inspections revealed that indeed, a slight compressive displacement had been experienced by the dam structure due to increased loading.  This resulted in the horizontal displacement of the structure by a measured 7 cm shift downstream, generally considered normal for the dam type noting that the expected maximum movement is 100 cm.

Furthermore, dams of this type have water seeping through the rock fill from the reservoir; the amount of seepage experienced at Mohale Dam is for now within the expected range and significantly less than on other dams of this type elsewhere in the world.   LHDA can therefore report that the structure has been assessed to be intact and is behaving as expected. 

Since Mohale Dam’s  purpose is to store water that can be transferred into Katse Dam as needed, the said water is now being transferred as per the approved operating rules for the two reservoirs noting that whilst Mohale Dam reservoir is 100% full, Katse Dam reservoir is only 78% full.

Mohale Dam has a monitoring team stationed full time at the Dam since 2002.  Currently, an around the clock team is in place to monitor further developments at the dam.

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