Rivers

River levels have a direct influence on the activities and well-being of human beings. While low flowing rivers interfere with transport, trade, and navigation, high water threatens human life and property. Basically, floods are a result of a river's discharge behavior and the climate within which it is located. The most common cause of flooding is when it rains extremely hard or for an unusually long period of time. Additionally, areas that experience a great deal of snow in the wintertime are prone to springtime flooding when the snow and ice melt, especially if the thaw is relatively sudden. Furthermore, rainfall and snowmelt can sometimes combine to cause floods, such as when rain falls on an area covered with melting snow.

Under normal conditions, rivers move fairly slowly as they transport silt and other debris produced by rain and snow. During floods, however, this transport is achieved much more rapidly, sometimes with beneficial side effects and sometimes with disastrous ones. One example of beneficial flooding is where the high water transports new top soil to local crops. Furthermore, floods can provide local crops badly needed moisture. The negative aspects of flooding are fairly obvious; often people drown and their property is destroyed.

Rivers in more humid regions are less likely to experience significant flooding than those located in more arid climates. In fact, floods in humid areas occur an average of about one time per year. Although on rare occasions these rivers experience larger floods, the water is normally no more than twice the size of a normal flood. While rivers in arid regions experience small flooding on an annual basis as well, when they experience rare, large floods, it can be devastating.