Effectiveness of Site Design and Low-impact Development on Stormwater Runoff Patterns at Partridgeberry Place LID Subdivision
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Fitsik, R., "Effectiveness of Site Design and Low-impact Development on Stormwater Runoff Patterns at Partridgeberry Place LID Subdivision, " Proceedings of the International Low Impact Development Conference, American Society of Civil Engineers, San Francisco, California, April 11-14, 2.

Partridgeberry Place Subdivision (LID Subdivision) located in Ipswich, Massachusetts incorporates an environmentally sensitive site design by using a variety of Low-Impact Development (LID) storm water management techniques and Open Space Residential Design (ORSD). The LID Subdivision is a compact site design, clustering 20 single family homes on residential lots less than 0.20-acres in size, preserving 74% (28-acres) of the 38-acre site as undeveloped open space. LID techniques used in the subdivision include dry wells, vegetated swales, bioretention, and reduced impervious area. Using an ORSD approach, the amount of open space was maximized and the amount of impervious area was reduced. The study compared the hydrology of the LID Subdivision, as built, and developed three theoretical model alternatives: 1) a subdivision that is clustered but that contains no additional LID storm water features (Cluster Only), 2) a conventionally developed subdivision (Conventional Subdivision), and 3) the pre-development (forested) condition (Pre-development Watershed). To understand the storm water runoff dynamics at the LID Subdivision, storm water runoff volumes from the developed portion of the site were monitored. During this time, forty-four (44) storm events (ranging from 0.01 to 2.45 inches) were collected, totaling approximately twenty (20) inches of precipitation. The monitoring data were used to calibrate storm water models to predict the hydrologic responses of both the LID Subdivision and the Pre-Development Watershed for a range of design storms. The LID, Cluster Only, Conventional, and Pre-development Watershed models were used to predict and compare storm water runoff dynamics over the entire 38-acre parcel for a variety of design storm events (2-year, 10-year, 25-year, 50-year, and 100-year, 24-hour). Based on the model results, the LID Subdivision generates the smallest volume of storm water runoff among the three development scenarios. For the 2-year design storm, the Cluster Only Subdivision reduced runoff volume relative to the Conventional scenario by 35 percent. The LID Subdivision reduced runoff volume relative to the Conventional scenario by an additional 3 percent, for a total 38 percent reduction. A comparison of the of three development scenarios to the Pre-development Watershed showed that runoff volumes from the LID Subdivision most closely resembled those of the pre-development condition. For the 2-year design storm, the LID Subdivision generated 11 percent more runoff volume than the Pre-development Watershed, while the Cluster Only generated 16 percent more, and the Conventional Subdivision generated 45 percent more. Historically, studies have produced little data and few benchmarks related to pre-development storm water runoff. Thus, predicting pre-development storm water runoff remains a great challenge. This study is among few in the nation that use actual field measurements from two land-use types in the same watershed to compare pre-development and post-development storm water conditions. Results reveal that pre-development hydrology is hard to fully replicate even with the incorporation of LID storm water management features and the preservation of open space. Implementing LID features in conjunction with an Open Space Residential Design approach, however, allows us to significantly minimize storm water runoff and more closely approximate the pre-development conditions.

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