ABSTRACT
Dams and levees are two types of flood protection structures. Both consist primarily of earth or concrete masses intended to retain water. However, there are a number of important differences between the two, and these differences drive considerations about their reliability. As shown in Figure 12.1, dams are constructed perpendicular to a river, and are seldommore than 1 or 2 km long. They reduce flooding of downstream floodplains by retaining runoff from storms or snowmelt behind the dam and releasing it in a controlled manner over a period of time. The peak stage of the flood is reduced, but downstream stages will be higher than natural for some time afterward. Because dam sites are fairly localized, they can be chosen very deliberately, and a high level of geotechnical exploration, testing and analysis is usually done during design. Many dams are multiple-use structures, with one or more of the following beneficial uses: flood control, water supply, power supply, and recreation. These often provide substantial economic benefits, permitting substantial costs to be expended in design and construction. Finally, they are generally used on a daily basis, and have some operating staff that can provide some level of regular observation.
