We build levees to keep flood flows within the channel. The overall result of our control efforts is a tremendous reduction in diversity and populations. Many trees evolved to set seed in spring when the river stage was slowly declining. If we drop the level fast, the roots of the seedlings cannot grow fast enough to keep up with falling groundwater in the highly permeable gravel bars. If we raise the level after the seeds sprout, they are drowned.
Many aquatic insects have a very short adult phase in their life cycle.
They have to synchronize emergence to be successful at finding mates. Constant temperature water from deep-release reservoirs provides no cues for synchronized emergence. We have reduced lateral migration of meanders without changing the rate of succession in riparian habitats. Early stages convert to later stages which are often converted to agriculture. It seems there are two basic alternatives to dealing with rivers.