A North Carolina Piedmont Application ofProtocols for Studying Wet Weather Impacts and Urbanization Patterns

摘要

Eight watersheds spanning a gradient of urbanization were used to identify linkagesbetween indicators of aquatic ecosystem health and hydrologic and geomorphicmetrics derived from a 20-year continuous stream flow record. The geomorphicmetric used to evaluate linkages is erosion potential calculated using excess shearstress, which describes the energy exerted on the stream channel that is capable ofcausing bed scour and bank erosion. The hydrologic metric used to evaluate linkagesis the duration of time that in-stream flows are above the 0.5-year return interval peakdischarge rage, which is a measure of stream flashiness. The 20-year continuousstream flow records for each watershed were generated using EPA Storm WaterManagement (SWMM5) Models calibrated to 18 months of measured flow data. Abenthic index of biotic integrity was used as one indicator of aquatic ecosystemhealth, and was calculated from aquatic macroinvertebrate sampling data collected bythe United States Geological Survey in the eight watersheds, ranging from three toeight square miles in size.Various land use and stormwater management practices were modeled in one of theeight gradient watersheds to determine the effect of these practices on the hydrologicand geomorphic metrics. The influence of development density (percentimperviousness) and of land use patterns, such as the proximity of dense urbandevelopment to stream corridors and headwater development versus downstreamdevelopment, on hydrologic and geomorphic metrics was examined. Additionally, theeffects of stormwater management practices such as traditional stormwater detention,water quality control and low impact development on hydrologic and geomorphicmetrics were also examined. Hydrologic and geomorphic metric values generated bythe various practices were compared to those generated along the urbanizationgradient to identify the management practices that best generated conditions favorableto meet ecologic targets.