Rainfall-runoff simulation studies were conducted in conjunction with the Denver Regional Urban Runoff Program to: (1) Compare runoff characteristics from two different intensities of simulated rainfall on street-surface plots, (2) document a first flush of constituent washoff loads in runoff from 1,000-sq-ft street-surface plots, (3) compare runoff characteristics from the street surface plots with those from a 69-acre urban mixed land use subjected to natural rainfall, (4) perform statistical analysis of washoff loads, and (5) compare quantity and quality of runoff from 400-sq-ft plots of native pasture subjected to simulated rainfall and from a 405-acre basin of native pasture subjected to natural rainfall. Experiments on the street surface showed that higher intensity simulated rainfall produced a higher percentage of runoff than lower intensity rainfall, and a first flush of constituent loads occurred for most constituents. The event mean constituent concentrations in the street-surface runoff from simulated storms were generally much smaller than those in the runoff from an adjacent urban basin. Simulated rainfall in small native pasture plots produced runoff-to-rainfall ratios similar to runoff-to-rainfall ratios from a larger native pasture subject to natural rainfall. (USGS)
