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Does building a dam affect erosion? Does it have an equal effect on both sides of the dam?

- Maris (grade 8); Ladysmith, BC


This is a complex question and answer. The short version is yes - especially downstream. When the stream enters the lake behind the dam, its velocity drops suddenly, and therefore so does its energy, and any sediments that it is carrying (and moving water is always carrying something). This loss of sediment from the stream as it enters the lake gives the water renewed erosional power below the dam.

In addition, this same loss of sediment results in less sand and silt reaching the beach, and therefore greatly increased coastal erosion due to a process called longshore drift - a definite problem for all those expensive beachfront homes and properties.



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