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Forney council hears drainage design for Wayfair site; engineer says detention basins add about 6 acre-feet of storage
Summary
City engineering staff and the project presenter described two detention basins and use of an existing drainage easement to route runoff from the Wayfair site, and said further storm-event analyses are still pending before approval.
Forney City Council received a presentation on the proposed drainage design for the Wayfair development, which uses two detention basins and an existing 25-foot drainage easement to limit downstream impacts.
The presentation said the project’s drainage design is “primarily governed by 2 principles,” including state drainage rules that developments must not cause adverse impacts to adjacent properties and a required downstream assessment under the region’s iSWIM guidance. The presenter, Mr. Casey, told the council the project will construct an east basin and a smaller west basin to attenuate peak flows.
Mr. Casey said, “The larger east basin currently shows an approximate storage volume of approximately 5 acre feet. The west basin, which is the smaller 1, has a storage volume of approximately 1 acre feet.” He added the basins together represent “a net total of around 6 acre feet of storage, which is significant.” According to the presentation, much of the site discharge will be redirected using a 25-foot easement established through the adjoining Holt Lunceford project and will discharge to a tributary of Big Brushy Creek identified as Tributary 14 in the Las Lomas flood study (Cardinal Strategies, 2020).
City engineering staff told the council they had modeled revised 100-year flows in Tributary 14 and “found them to have a negligible impact,” but said additional analyses for the 2-, 10- and 25-year storms are required before final approval. Mr. Casey said the plans have not been approved and remain in the city’s review queue. He described public improvements that will be dedicated to the City of Forney and said once those improvements are accepted the developer may file a plat and pursue building certificates of occupancy.
Council members asked questions about whether the plan would improve conditions for downstream neighborhoods such as Emerald Ranch Estates. The presenter said the Holt Lunceford project previously modeled a net positive effect on Tributary 14 by reducing peak flows and water-surface elevations, and that in his opinion the Wayfair design appears likely to perform better than the predeveloped condition, though he described that as his opinion rather than a final finding.
Next steps: staff will complete the outstanding downstream storm-event evaluations and continue plan review. No formal action or vote was taken on the Wayfair design at the meeting; the presentation was informational.
