A river is flowing in a broad, alluvial valley and the river is silt- laden but also moves sand and a small amount of gravel. The government decides to build a dam across the valley for power and flood control. What will happen to the river, upstream of the dam? A) The river will not change. B) The river will start to deposit sand and gravel, frequently spilling out of its channel. C) The river will respond to the new temporary base level and cut laterally outside its valley, widening the valley. D) The river will downcut.

Question

Quizplus · Accepted Answer

Building a dam across a river causes the river to lose energy upstream of the dam, leading to deposition of the sediment it carries. Since the river in question carries sand and a small amount of gravel, these materials will start to deposit upstream of the dam, potentially causing the river to spill out of its channel as it fills with sediment.

A River Is Flowing in a Broad, Alluvial Valley and the River