TIDAL INCURSIONS AND WATER QUALITY IN A CSO-IMPACTED WETLAND CREEK: USE OF TEMPERATURE AND CONDUCTIVITY METHODS

Urban tidal wetlands often serve as discharge points for combined sewer overflows (CSO). Tidal dynamics in these systems cause water quality to varially temporally and spatially in response to rainfall events and tidal cycles. Since CSOs are intended to discharge only in wet weather, innovative methods are needed to monitor their impact on receiving waters over long time periods.

In a tidal creek downstream of a combined sewer overflow, multiple inexpensive temperature sensors and conductivity loggers were used to investigate how tides and CSO overflow events affect creek water quality in an urban wetland in New York City. Previous work indicated that this particular CSO outfall discharged sewage continuously, causing pathogen contamination downstream, however modifications to sewage infrastructure were carried out to mitigate this problem.

Temperature measurements revealed that high tides repeatedly cause water from the receiving embayment to move upstream almost to the location of the CSO. These data were used to estimate velocities of reverse flow up the creek and were confirmed by more recent conductivity measurements. Only at neap tides is the creek immediately downstream of the CSO not affected by these tidal incursions. Rain events combine with tidal cycles to reduce the time that the creek is impacted by tidal incursions. Monitoring temperature and conductivity is shown to be critical to placement of autosamplers to monitor water quality in such settings.