For a strategy to be 'sustainable' it must meet the needs of today without compromising the needs of the future and causing environmental degradation. Therefore, it is important to assess the social, economic and environmental viability of different management strategies. Dams are large infrastructures which intercept river flow and cause the build up of water behind the dam, resulting in a reservoir. Reservoirs provide a constant supply of clean water for the use of the community all year round, even if the location experiences seasonal precipitation. The construction of the dam would also provide local jobs. However, since dams are large infrastructures their construction is very expensive and often requires maintenance to allow continued efficiency. Also, their size means often settlements are lost and people are displaced. Dams can also negatively impact the environment since they stop river and sediment flow, locations downstream will be impacted. For example, flora and fauna are unable to adapt to the lack of water as well as habitat loss due to the erosion of banks from a reduction of sediment flow ,leading to species decline.