Water Age in Stormwater Management Ponds and Stormwater Management Pond Treated Catchments

Increasing coverage of impervious surfaces in urban waterways result in 'flashy' hydrologic responses, elevated flood risk, and degraded water quality. Stormwater management ponds (SWMPs) are engineered into urban stream networks to mitigate this response. However, little is known about how SWMPs affect hydrological transit time at the catchment scale. This study aims to examine water age in SWMPs and catchments of varying SWMP control. Grab samples of ∂¹⁸O and ∂²H were collected bi-weekly from two SWMPs and five stream sites with varying land cover and stormwater control in their catchments. The damping ratio (DR), young water fraction (Fyw) and mean transit time (MTT) by sine-wave fitting were calculated for each sampled site. SWMP inlet water was consistently older than water arriving at SWMP outlets. MTT decreased as catchments SWMP control increased. Surficial geology was found to have the greatest influence on catchment MTT.