Planned Residential Development Design
Challenge & Solution
The Owner of a 50-acre residential development envisioned the community as a Planned Residential Development (PRD). A certain percentage of usable open space is required to meet PRD specifications. Because of space constraints, a cost/benefit analysis was performed to compare the use of an underground stormwater detention system beneath an open space area with the construction of an above-ground stormwater detention pond that would eliminate a portion of the residential lot footprint. Rhea, as a subcontractor, completed the design work and assisted in the costing for this analysis.
Project Description & Highlights
The development is a 60-lot subdivision with approximately seven acres of open space and walking trails within the development site. Rhea’s scope for this project included erosion and stormwater control design. Erosion controls designed for the site included stone construction entrance roads, filter fence, diversion and collection channels, energy dissipators, and a temporary sedimentation pond.
The elements of the stormwater management systems designed by Rhea included street and yard inlets and collection piping, stormwater detention pond(s), and an underground stormwater detention system that included corrugated steel pipe discharging through a 12-inch diameter orifice. The goal for stormwater control at the site outlet was post-development flow less than or equal to pre-development flow.
With the flow detention systems designed, this goal was met for the required design storms. Narratives that described the design basis along with the design calculations were submitted to the Westmoreland County Conservation District and the Unity and Hempfield Township engineers for their review and approval. Both the Erosion and Sedimentation Control Plan and Stormwater Management Plan were approved after minor revisions.
Approval of the residential development was complicated because of its location in two townships– Hempfield and Unity Townships, PA. Because our client, who was the engineer for the development, was unavailable to attend the Planning and Zoning hearings, Rhea assisted the Owner with preparation and also attended the meetings, where final approvals were granted in each case.