Balancing flood control and ecological preservation/restoration of urban watersheds

摘要

Throughout recent history, urbanisation has altered the ecological structure of urban streams and rivers. They have been channelised, constricted, and ultimately covered to gain space for urban development and to accommodate increased flood flows. The Los Angeles River in California and the Kinnikinni River in Milwaukee represent the ultimate transformation of an urban stream into a concrete, high flow velocity channel with very little biological habitat. Concurrently, as a result of these modifications and diminished water quality, indigenous aquatic species have disappeared, resulting in a complete loss of sensitive species and the propagation of a few unwanted species tolerant to pollution and low quality habitat.