| Description |
his research dissects and improves understanding of the implications of Utah's modified stormwater permit rule. By analyzing the 90th percentile (90th-P) storm depth calculation and modeling an urban watershed on the foothills of Salt Lake City, Utah; this project provides initial guidance to local governments and developers to plan and design bioretention facilities. The 90th-P storm depth calculation was analyzed through the manipulation of four variables: location, inclusion of snow, sample time period, and depression storage value. Analysis shows that the 90th-P storm depth was between 0.47 to 0.80 inches for eleven different stations across the state of Utah, between 0.54 to 0.69 inches for several 5-year sample time periods, and between 0.53 and 0.60 inches for varying depression storage values. These values are significantly different from the State of Utah Division of Environmental Quality, Division of Water Quality's (Division) suggested 90th-P storm depth of 0.6 to 0.7 inches. It is recommended that permit requirements are adjusted or expanded to accommodate these findings. The maximum storm depth recommended by the Division was modeled in a Storm Water Management Model (SWMM) to predict the size and cost of bioretention facilities needed to control the 90th-P storm depth. Bioretention facilities occupied anywhere from 0.16% to 1.09% of the subcatchment. It was found that the sizing is highly dependent on the runoff volume before bioretention implementation. This runoff volume is affected by many variables including impervious area, upstream characteristics, slope, and existing pervious areas. Additional research is need to fully understand this runoff volume. This research can guide developers to abide by these new permit restrictions. |
