Wet retention ponds temporarily store and slowly release stormwater to mitigate peak flow rates and remove particulate-bound pollutants. However, with sandy underlying soils, wet retention ponds may provide additional benefits through infiltration, thereby recharging groundwater and supporting baseflow in streams. Current design guidance often requires lining wet ponds to prevent infiltration; however, modern stormwater management strategies recommend maximizing runoff volume reduction through infiltration. Two infiltrating wet retention ponds in Fayetteville, NC, USA, were monitored for one year to assess volume reduction, peak flow mitigation, and water quality. In some months, 100% of stormwater runoff infiltrated and evaporated, with cumulative annual volume reductions of 60 and 51% for the two ponds. For events up to 76 mm (equivalent to the local 1-yr, 24-hr storm), measured peak flow reductions were similar to those of typical (non-infiltrating) wet ponds (median 99% reduction). Dissolved nitrogen species, total and dissolved phosphorus, and total suspended solids (TSS) concentrations were significantly reduced in both ponds; mean percent reductions were greater than 30% for each of these pollutants. Effluent concentrations were on par with typical (non-infiltrating) wet ponds previously monitored in North Carolina. Due to the aforementioned runoff reduction, nutrient and TSS loads were reduced by (at minimum) 35 and 67%, respectively. Infiltrating wet ponds were able to meet both peak flow and volume mitigation goals, suggesting that they could be a common tool in regions with sandy soils.
A novel, hybrid, stormwater treatment practice, called infiltrating wet ponds was tested.
Two ponds signficantly and substantially reduced runoff volumes and peak flows over year-long monitoring periods.
Nutrient and TSS concentrations were generally reduced as well, with pollutant load reductions observed for all pollutants.
Design guidance is provided for those who wish to employ infiltrating wet ponds locally.