Final answer:
Dams cause deposition of sediment upstream and channel downcutting downstream, additionally affecting river ecology and habitats by altering water flow and sediment transport.
Step-by-step explanation:
When a dam and reservoir are constructed on a graded river, there tends to be deposition upstream from the dam due to the slowing down of the river's flow, which allows sediments to settle out of the water. Conversely, downstream of the dam there can be increased erosion, also known as channel downcutting, because the flow of water is restricted and the water released can be faster and carry less sediment, leading to more erosion of the riverbed and banks. Additionally, dams interrupt the migration patterns of aquatic species and change the natural habitat by altering water temperature, chemistry, and flow characteristics.