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Terrace Floodplain or divides. Like floodplains, watersheds are formed over time by various climatic, hy- drological and geological processes. But a watershed is much bigger than a floodplain and can therefore be more difficult to manage, since large land areas are usually cov- ered by a number of separate municipalities with different governments and land-use strategies. It is important to understand, however, that upstream uses ofland and water within a river's watershed are likely to have adverse impacts downstream including the potential for increased flooding. Natural Resources and Ecosystems - Both the hydrological and the geological char- acteristics of the landscape play an extremely important role in determining what veg- etation will inhabit the area. Many of the plant species that grow in floodplains are adapted to thrive in the specific conditions created by the soil types and water flow cycles that characterize river corridors. In turn, this vegetation plays an important role in determining how water flows across the land, and is a major factor in controlling erosion and sediment deposits that can change the face of the landscape. In a mutually supportive cycle, the living and nonliving parts of natural floodplains interact with each other to create dynamic systems in which each component helps to maintain the characteristics of the environment that supports it. These systems of inter- acting parts of the physical and biological worlds are called ecosystems. Together, these parts of the floodplain ecosystem function to store and convey floodwaters, pro- tect water quality, prevent erosion, and maintain rich habitats for fish and wildlife. In recognizing the relationships between the hydrological, geological and biological fea- tures of these systems, we can begin to understand how changes to one feature can alter the entire system in significant ways. This was dramatically demonstrated during the Great Midwest Flood of 1993 when the Mississippi River reclaimed much of its flood- plain. The flood reconnected the river to traditional spawning areas, resulting in a significant increase in fish populations. Natural Communities - Throughout a floodplain and its adjacent landfonns there may be a number of different ecological communities, groups of plant and animal species ... Figure 4 - Major ph.vsio[.?raphic elements of a typical floodplain. Figure 5 - Coastal floodplains are geologically dynamic areas where moving sand~', ~hifting inlets, and erosion are common. Coastal sait mnrshes are among the most productive ecosystems on earth and are a vital link in both commercial and recreational fishing.