Stream Channelization and Changing Vegetation Patterns in the U. S. Coastal Plain

The southeastern U.S. Coastal Plain contains high-density stream networks and the largest area of alluvial wetlands in North America. Among the most common flood-control methods in this region is stream channelization. Its purpose is to increase channel capacity and flow velocity so that water moves more efficiently downstream and thereby reduces flooding. Channelization typically includes deepening and widening the stream channel and shortening it by cutting off meanders. Landowners and those who cultivate in the adjacent floodplains are the primary beneficiaries. In addition to closely involved government agencies, such as the U.S. Army Corps of Engineers and the U.S. Soil Conservation Service, local landowners have been the strongest advocates for channelization. Awareness of the physical and biological problems caused by channelization is growing. Environmental degradation of alluvial habitats has been given serious attention in channelization project planning in recent years. Less destructive channel modifications have been implemented, and some attempts have been made to restore riparian habitats affected by channelization. For example, the Kissimmee River in south Florida, which was channelized in the 1960s, is being restored by reintroducing river flow into remnant channels (Loftin, Toth, and Obeysekera 1990; Shen, Tabios, and Harder 1994). The primary justification is the reestablishment of natural hydrologic conditions and the consequent enhancement of the river's biological resources. A similar restoration project is in the early planning stages for the Obion-Forked Deer River system in western Tennessee, also channelized in the 1960s. The destructive effects of channelization on water quality and aquatic ecosystems are well documented in Brookes's review of 1988. But until recently, little attention has been paid to the effects of channelization on bottomland terrestrial ecosystems. Flood frequency and related physical conditions (including the depth of surface water and the water table, as well as the accumulation of sediment and organic matter) are among the most important factors controlling the presence and distribution of bottomland terrestrial species and are the basis for most classifications of floodplain plant communities (Penfound 1952; Huffman and Forsythe 1981; Wharton and others 1982). Stream channelization significantly alters these conditions in the adjacent bottomlands. But few attempts have been made to link changes in floodplain hydrogeomorphic conditions following stream channelization directly to plant-community composition. Western Tennessee and northwestern Mississippi is an area of the Gulf Coastal Plain in which almost all of the major streams and many of their large and small tributaries have been channelized [ILLUSTRATION FOR FIGURE 1 OMITTED]. These river systems have been studied extensively, and much is known about channel behavior, floodplain hydrology, and bottomland vegetation (Schumm, Harvey, and Watson 1984; Hupp 1987; Simon and Hupp 1987; Simon 1989, 1994; Shankman and Drake 1990; Shankman and Pugh 1992). But the response of forest communities to changing physical conditions is by no means clear. Most floodplain tree species in this region live for decades or centuries, which greatly exceeds the amount of time that has elapsed since extensive channelization began. As a result, short-term observations of bottomland forest are, in all but a few cases, unlikely to reveal forthcoming changes. In this article I examine the potential effects of channelization on bottomland terrestrial habitats in the southeastern United States. Probable changes induced by channelization in forest communities are assessed based on geomorphic processes and life-history characteristics of common bottomland species. In addition, changes in flooding, sedimentation, and restricted-channel migration that follow channelization are evaluated. Changes in natural hydrogeomorphic conditions are directly linked to floodplain habitats and to regeneration of bottomland species

Channelized · Coastal plain · Geography · Geotechnical engineering · Hydrology (agriculture · Telecommunications · Vegetation (pathology · Botany, Ecology, and Taxonomy Studies · Engineering · Environmental Science · Geology · Hydrology and Sediment Transport Processes · Soil erosion and sediment transport

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