Reduction of soil fertility downstream due to impoundment

The problem of reduction of soil fertility downstream due to impoundment refers to the negative impact that the construction of dams or reservoirs has on the quality and productivity of soil in areas located downstream. When a river is impounded, the natural flow of water is disrupted, leading to the accumulation of sediment behind the dam. Over time, this sedimentation can result in the reduced availability of water downstream, affecting the soil's moisture levels and nutrient content. Additionally, the altered flow patterns impact the natural deposition of sediment, minerals, and organic matter, further compromising the fertility of the soil. This problem can have significant consequences for agricultural activities, as it impairs crop growth and decreases overall agricultural productivity in affected areas.

River Nile used to deposit 100 million tons of sediment a year on nearly one million hectares of land in the Nile Valley. After the building of the Aswan Dam, the Nile deposits only a few tons of sediment per year, most of that comes as a result of riverbed erosion, meaning the gradual loss of riverbed soils. To compensate the silt trapped behind the dam, Egypt must apply artificial fertilizers on an ever increasing scale.