The weir

Fresh water must be used to separate sand because salty or brackish water would not enable the deposit to be rehabilitated successfully after mining. Rio Tinto QMM pumps the water it needs from a station on the winding river upstream from Lake Ambavarano. For this purpose, a weir was installed at the mouth of Lake Ambavarano to prevent salt water coming in from the ocean.

The weir was designed to maintain, upstream, fluctuations in the water level which correspond to current seasonal variations, without involving more flooding of the land. The final feasibility study favored the lock option, which makes it possible to keep canoes and tourist operators’ boats moving, in addition to the fish. Moreover, the weir will prevent salt water infiltrating into the lagoon network and reaching Fort-Dauphin’s water reserves. This improved water quality will help the city meet its future drinking water requirements.