When a natural area—that is, an area undisturbed by humans—is inundated with heavy precipitation, the plant-protected soil absorbs much of the excess water. What the soil cannot absorb runs off into the river, which may then spill over its banks onto the flood plain. Because rivers meander, the flow is slowed, and the swollen waters rarely cause significant damage to the surrounding area. (See Figure 6-12 on page 140 for a diagram of a typical river, including its flood plain.)
When an area is devloped for human use, much of the water-absorbing plant cover is removed. Buildings and paved roads don't absorb water, so runoff, usually in the form of storm sewer runoff, is significantly greater in developed areas (Figure 10-5). People who build homes or businesses on the flood plain of a river will most likely experience flooding at some point (Figure 10-6).
The main goal of water management is to provide a sustainable supply of high-quality water. Sustainable water use means humans use water resources carefully, so water is available for future generations.
Water supplies are obtained by building dams, diverting water, or removing salt from seawater or salty groundwater. Conservation, which includes reusing water, recycling water, and improving water-use efficiency, augments water supply and is an important aspect of sustainable water use. Economic policies are also important in managing water sustainably: When...