ANTHROPOGENIC ALTERATIONS TO AN ALLUVIAL FLOODPLAIN WITHIN THE YAKIMA RIVER BASIN, WASHINGTON

摘要

Human impacts to riverine ecosystems have severed the physical connectivity of the river to the riverine environment. During the past 120 years, an extensive and complex assemblage of anthropogenic features, the degree of which increases in a down-stream direction, has been integrated into the disturbance regime template of all floodplains directly associated with the Yakima River. Dams and storage reservoirs regulate and supplement in-stream flow for irrigated agriculture. Railroad and highway beds, which often act as levees, dissect the riverine landscape. Wetlands and riparian forests are cleared for utilization by agriculture, industry, recreation, and rural development, and a system of dikes that protects and maintains these land use activities has emerged. To assist in identifying how these cultural features alter the structure and function of riverine ecosystems, an in-depth study focused on mapping their emergence across five alluvial floodplains within the Yakima basin was recently undertaken. A final analysis shows more than a 60 percent reduction in riverine habitat once inundated by small, frequent flood events within just one of these floodplains. The real contribution of the study is the creation of an ecological baseline that will help managers implement changes directed at preserving and promoting riverine ecosystem health.