Allendale duck pond: staff outline short‑term drainage fixes and longer‑term stormwater options after major drawdown

Parks and Watershed Protection staff told the Environmental Commission on Feb. 4 that the Beverly Sheffield (Allendale) duck pond experienced an unusual drop in water level after pool‑renovation work, the repair of a leaking pool service line, and a dry period reduced customary supplemental inflows. Lindsey Mokimer (Division Manager, Park Development) and Lee Sherman (Supervising Engineer, Watershed Protection) described three historical sources that fed the man‑made pond: stormwater runoff from roughly 25 acres, pool filter backwash historically routed to the pond, and a groundwater pump near the pool. During pool renovations the backwash discharge was routed to a grassy infiltration area and a leaking water service feeding the pool was repaired; combined with a dry spell, staff said the pond dropped more than two feet before October rains partially refilled it.

Short‑term actions already under way include clearing sediment from channels, regrading to restore positive flow paths from parking areas and low points that currently trap runoff, and removing or adjusting small berms that redirect runoff away from the pond. Watershed staff began surveying the site in November and plan to complete basic design work this summer with potential construction by fall; staff said some maintenance tasks could be performed by Parks maintenance crews while other channel work would likely use Watershed crews trained for open‑channel maintenance.

Sherman presented two longer‑term options that are unfunded and require feasibility and hydrologic study: (1) divert a limited portion of flow from a 72‑inch storm drain that currently carries runoff from a roughly 106‑acre watershed (including Burnet Road commercial areas) into an expanded detention/water‑quality pond footprint, which would also provide stormwater treatment benefits to Shoal Creek; or (2) excavate accumulated sediment, install a liner to reduce infiltration and manage pond water as a Watershed asset without diverting additional storm drain flow. Staff emphasized that each option requires modeling (to ensure flood detention capacity is not diminished), geotechnical and ecological study (to assess tree roots and substrate), permitting, and community engagement.

Neighborhood speakers urged caution. Caroline Reynolds (licensed professional engineer) provided a hydrogeology report and cautioned that underlying Eagle Ford shale and weathered carbonate/clay soils may limit the effectiveness of bentonite liners; Mary Farrow (Allendale resident) urged that the pond remain a child‑friendly, wildlife habitat and warned that digging near cypress roots could damage trees; and Gordon Thompson reported pond level monitoring and suggested low‑cost channel fixes while more study proceeds. Commissioners asked staff for water‑balance modeling (to separate infiltration from evapotranspiration), actual design elevations and maximum desirable pond depth (staff cited an original center depth of about 5.5 feet), estimates of incremental runoff gains from short‑term channel fixes, and public outreach. Staff said they are open to additional community briefings, will incorporate resident reports and technical materials, and will return with modeling and recommended next steps once survey and preliminary design work are complete.