Mohale Dam is the second-largest dam in the Lesotho Highlands Development Project. Built as a backup reserve to the Katse Dam project, the two dams are connected by a tunnel that ensures there’s enough water to meet South Africa’s ever-increasing demand. At 145 m, Mohale is the highest concrete-faced rock-filled dam in Africa. An entire mountain was crushed and moved to build the rock wall. Driving in from Maseru, once again marvel at the beauty of the three mountain passes before arriving at the dam. The drive from Mohale to Katse via Thaba-Tseka is one of the finest Lesotho has to offer. Admire the reflections of the clouds as one drives around the lake on 4×4 roads. Enjoy the visitors centre’ and Mohale Village where there is a dam wall tour several times a day.
Mohale Dam is constructed at the confluence of the Senqunyane and Likalaneng Rivers and forms part of Phase IB of the LHWP. At 145 m high, the dam is the highest concrete-faced rock fill dam in Africa.
In contrast to Katse’s complicated structure, the construction of Mohale Dam worked on a simple principle: a mass rock compacted across a valley to form a reservoir, sealed by a concrete slab.
A large basalt hill inside the dam basin was crushed to provide the material required for this engineering feat.
The Mohale Tunnel was constructed as part of Phase IB of the Lesotho Highlands Water Project (LHWP). A 32km long segmentally lined tunnel, transfers water from the Mohale Reservoir and thereby augments the yield of the LHWP by a further 9 m³. It was constructed entirely through the Lesotho basalt formation using double shielded tunnel boring machines on two headings.
The tunnel connects the Mohale reservoir to the Katse reservoir. It is designed to allow water to flow in either direction. The flow of water will generally be in the direction of Katse as its level is drawn down by water delivery to South Africa. In this manner the hydrostatic balance is each reservoir is maintained automatically and their total combined storage is optimized.
MATSOKU WEIR AND TUNNEL
Phase IB also included the construction of a 15-metre high weir and its 5.7 kilometre long tunnel, designed to divert flood flows in the Matsoku river into the Katse reservoir by gravity. This component of the project is located at Matsoku, in the Katse area.
Principal Statistics of the Mohale Dam
|Dam Type||Concrete-Faced Rockfill Dam|
|Maximum height above foundation||145 metres high|
|Base thickness||600 metres|
|Crest length||620 metres|
|Rock Volume||7,8 million m³|
|Volume of reservoir||950 million m³|
|Length of Spillway||48 metres|
|Maximum Spill Capacity||2,426 m³|