Problem: A dam is built on a river, forming a reservoir. Over time, this likely will cause: Need Assignment Help? Group of answer choices Rapid erosion of sand downstream of the dam, because the clean water coming out of the reservoir will be able to pick up the small sand grains. Reduced erosion of sand downstream of the dam, because the dam will stop floods, thus preventing the river from flowing fast enough to move the sand. Build-up of sediment downstream to bury the dam and smooth the river flow. Nothing to happen; dams don't matter to downstream conditions.