RESTORING NATURAL WATERWAYS IN DENVER, USA AREA

摘要

The State of Colorado Legislature in 1969 established the Urban Drainage and Flood Control District (District), primarily in response to the disastrous 1965 flood on the South Platte River. Its main mission is to assist cities and counties in the Denver metropolitan area with drainage and flood control problems. The District covers an area of 4,116 km~2 and has approximately 2,600 km waterways that drain 350 ha, or more of tributary area. The present population of the District is approximately 2.3 million people. For over 30 years, the District has observed that the process of urbanisation profoundly changes the surface runoff hydrology in this semi-arid region of the United States. With an annual average precipitation of 360 mm, the number of observed surface runoff events increase from less than one to over 29 on an average annual basis. In addition, many streams that were ephemeral develop baseflows as a result of outdoor water uses by its residents. In response to these changes, the natural waterways erode downward and experience accelerated bank erosion as they geomorphically adjust to reduce their longitudinal slopes (see Figure 1).