Hydrologic Evaluation of Low Impact Development Using a Continuous, Spatially-Distributed Model

Type of Document Master's Thesis
Author Bosley II, Eugene Kern
URN etd-07302008-220841
Title Hydrologic Evaluation of Low Impact Development Using a Continuous, Spatially-Distributed Model
Degree Master of Science
Department Civil Engineering
Advisory Committee
Advisor Name Title
David F. Kibler Committee Chair
G. V. Loganathan, in Memoriam Committee Member
Randel L. Dymond Committee Member
Vinod K. Lohani Committee Member
Keywords

* continuous simulation
* SWMM
* Low Impact Development
* hydrologic modeling
* urbanization

Date of Defense 2008-07-11
Availability unrestricted
Abstract

Low Impact Development (LID) is gaining popularity as a solution to erosion, flooding, and water quality problems that stormwater ponds partially address. LID analysis takes a spatially lumped approach, based on maintaining the predevelopment Curve Number and time of concentration, precluding consideration of the spatial distribution of impervious areas and Integrated Management Practices (IMP’s), runoff-runon processes, and the effects of land grading. Success is thus dependent on the accuracy of the assumption of watershed uniformity, applied to both land cover distribution and flow path length.

Considering the cost of long-term paired watershed monitoring, continuous, spatially-distributed hydrologic modeling was judged a better method to compare the response of LID, forest, and conventional development. Review of available models revealed EPA-SWMM 4.4H as the most applicable to the task. A 4.3-acre subwatershed of a local subdivision was adapted to LID using impervious surface disconnection, forest retention, and IMP’s. SWMM was applied to the LID development at a fine spatial scale, yielding an 80-element SWMM model. The LID model was modified to reflect conventional development, with gutters, storm sewer, and detention. A predevelopment forest model was also developed. Two parameter sets were used, representing a range of assumptions characterized as favorable or unfavorable toward a particular development form. Modeled scenarios included favorable and unfavorable versions of Forest, LID, uncontrolled Conventional Development, and Conventional Development with Stormwater Management. SWMM was run in continuous mode using local rainfall data, and event mode using NRCS design storms. Runoff volumes, peak flows, and flow duration curves were compared.

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