A Study of Detention in Urban Stormwater Management

摘要

The concept of stormwater detention was analyzed for effectiveness in controlling urban flooding and stream-channel enlargement in North Carolina. Model studies, statistical analyses and theoretical analyses were conducted using gaged watersheds in Charlotte, North Carolina. Existing conventionally developed watersheds were found to have effective stormwater detention unintentionaly incorporated behind culverts and bridges. Statistical analysis of long-term historical streamflows suggests that flood peaks diminished with urbanization until about 1950, when peaks began to rise again. Although detention can be shown to be present and effectively by simulation and statistical analysis, stream channel enlargement and consequent high sediment loads are observable in the streams of the study area. Impulse analysis of channels subjected to discharges from hydrographs with and without detention suggess that detention can worsen streambank degradation by intensifying the impulse intensity at the channel sides near the bottom to cause more severe slumping. Stormwater detention is recommended for control of nuisance flooding immediately downstream of radical changes in land use. It should be incorporated in a comprehensive watershed management program wherein the drainage system is treated as a public utility so that economies of scale can be gained and facilities can be located strategically.