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Surface water and groundwater resources
Freshwater availability varies considerably across the archipelago. On the large volcanic islands, water resources with river systems are abundant due to the mountainous topography and weather conditions. The low coral atolls and islets have no perennial surface water resources and rely on rainwater and thin fresh groundwater lenses (ISF-UTS, 2011; SOPAC, 2007).
The longest river is Lunga river on Guadalcanal Island with a catchment area of 377 km▓ (Sullivan and Guglielmi, 2007). Aquifers on the islands are small and depend mainly on precipitation for recharge (ISF-UTS, 2011).
Total renewable surface water resources are estimated at 44 700 million m│/year. The renewable groundwater resources are estimated at about 11 920 million m│/year, which are considered to be drained entirely by the surface water network (overlap). The total annual renewable water resources in the country are thus estimated at 44 700 million m│ (Table 2).
Lakes and dams
Lake Tegano on Rennell island is the largest lake in the country, and consists of a mixture of brackish freshwater and salt water.
There are no important dams and there is limited hydropower development in Solomon Islands. There is only one single micro-hydropower plant (150kW) and about a dozen pico-hydropower installations in the rural areas which can sustain a small community. There is substantial potential for hydropower from water resources on at least seven islands but little effort has been made so far to evaluate the resource (SOPAC, 2007; Wairiu and Powell, 2006).