Date of Award
Program or Major
Master of Science
This study examined the reduction of effective impervious cover (EIC) and watershed response by Low Impact Development (LID) and stream restoration efforts. The Berry Brook Watershed Renewal Project consisted of day lighting approximately 1,100 feet of stream and installation of 13 LID systems for a combined impervious area treatment of 20.7 acres on a 185 acre watershed. Watershed response was measured and modeled by hydrologic and water quality parameters.
Hydrologic daily flow analysis revealed that there was a significant decrease in average, maximum and minimum flows between preuo and postuo LID implementation and stream restoration improvements periods in the direction of a lesser developed watershed (p-value: <0.0001). Analysis of direct runoff unit hydrographs for mean, median, standard deviation, skew, kurtosis and peak at two locations indicated there was no statistically significant difference between preuo and postuo. This indicates that for the period of monitoring LID implementation and stream restoration improvements were not statistically detectable in direct runoff unit hydrograph parameters. A 46% decrease in median runoff volumes was observed at the watershed terminal postuo (p-value: 0.11). ICpre mapped impervious cover was calculated to be 30.1%. PreLID EIC was determined by three methods that had excellent agreement: direct calculation of runoff depth vs. rainfall (15.6%), Sutherland (16.5%) and USGS (16.5%). PostLID EIC values were determined by three methods and had modest agreement: runoff depth vs. rainfall (11.7%), EPA method (13.8%), EIC disconnection (8.2%) and a proposed method based on water quality volume treated (10.8%).
Water quality concentration improvements were observed for TSS, Zn and TP where storm event median values were reduced by (59%, 50% and 78%) (p-values: 0.018, 0.026, 0.002). At the watershed scale a comparison of pollutant loads between preup and post .LID time periods showed significant improvements in all analyzed parameters, median reductions of TSS by 95% (p-value: 0.033), TP by 97% (p-value: 0.010), and TN 80% (p-value: 0.130).
Three PCSWMM watershed models were built to examine the long-term response of restoration efforts. A Premodel represented the watershed prior to improvements. Two other models were constructed to simulate the watershed post-construction with LID and stream restoration improvements. One method simulated LID implementation at the system scale (LIDmodel). The other method also simulated the watershed post-construction of LID but at the watershed scale with the use of EIC (EICmodel). A 20-year rainfall runoff simulation of the LID model, . conditions showed reductions in runoff volume by 18% and pollutant load reductions of TSS by 28%, TN by 15%, and TP by 7%. LIDmodel runoff volumes and peaks were not statistically different from the Premodel at storm depths of 1 inch or greater. The ElCmodel and LIDmodel had excellent agreement over the 20 year simulation and were not significantly different in runoff volumes. This indicates that modeling LID implementation as EIC reduction may be an acceptable method for determining runoff volume.
Hlas, Viktor, "An examination of the reduction of effective impervious cover and ecosystem and watershed response" (2013). Master's Theses and Capstones. 834.