PrintModule 5: Dam it All!
Introduction
In the preceding modules, we’ve discussed the uneven distribution of precipitation and water resources on Earth’s surface (Modules 1-2), and the dynamics of rivers and streams as the primary conduits for the return of water that falls over the continents to the oceans (Modules 3-4). One fundamental challenge to populations is that precipitation does not fall where we need it when we need it. This is amplified by the fact that many population centers are located in areas that are perennially dry, including those in the US Southwest.
How do we store water delivered by rivers to provide reliable and secure supply when we need it, where we need it, and tame the flow in abnormally wet conditions to mitigate flooding? The main solution is to dam rivers and fill the reservoirs behind them. This stores large volumes of water that ensure a stable supply, the reservoirs act as “capacitors” in the hydrologic system to absorb excess flow and thus prevent flooding downstream, and the dams simultaneously produce electric power as water is released in a steady, controlled discharge from the reservoir. However, dams and their reservoirs also profoundly impact the natural river system and can cause irreversible changes to the environment and to populations both near the dam and far up- and down-stream. In Module 5, we will explore the benefits and consequences of construction and removal of large dams, both in the US and globally, including a discussion of case studies along the Yangtze and Nile rivers.