Estuarine Physical Response to Storms—Jamaica Bay Active

Problem

Coastal communities are susceptible to damage from coastal storms and associated storm surge, and although tidal wetlands provide a buffer against shoreline erosion and aid in shoreline stabilization, they too are vulnerable to the action of storms. Tidal wetland dynamics need to be better understood, as they are also intrinsically valuable as nursery, feeding, and refuge areas for many commercial and recreational fisheries, and significantly contribute to the base of the marine food web. Wetlands trap sediments, reduce turbidity, and absorb nutrients and pollutants thereby improving water quality, and they provide many recreational opportunities. Tidal wetland stability needs to be assessed using a sediment budget under both storm and non-storm conditions. Jamaica Bay National Wildlife Refuge lies within the metropolis of New York City and contains extensive wetlands that are vulnerable to storm impacts, and is the focus of this investigation.

The U.S. Geological Survey (USGS) Woods Hole Coastal and Marine Science Center (WHCMSC) was awarded DOI Hurricane Sandy Supplemental funding (Estuarine Physical Response to Storms) to assess the estuarine and adjacent wetland responses of three Atlantic lagoonal estuaries to major storm events such as Hurricane Sandy. The estuarine systems include the Barnegat Bay-Little Egg Harbor Estuary (New Jersey), Chincoteague Bay (Maryland-Virginia), and Jamaica Bay (New York).  In the Jamaica Bay project, net sediment fluxes to the wetland complex and estuary will be measured and compared with modeled sediment fluxes. In addition, high-resolution models of hydrodynamics and sediment transport in vegetated marshes will be tested in order to evaluate depositional patterns as well as vulnerability of marsh shorelines to wave attack.

A critical data need for model validation is continuous measurement of sediment flux at the mouth of the estuary—in Rockaway Inlet (labelled “Flux” in fig. 1)—for at least one year. To achieve this, the WHCMSC is collaborating with the USGS New York Water Science Center (NYWSC), and has provided funding for the establishment of a sediment-flux monitoring system in Rockaway Inlet. The system has recently begun to monitor for tidal water elevation, salinity, velocity, and turbidity within Rockaway Inlet; the WHCMSC and NYWSC are now working to continue operating this system and collect sufficient samples of suspended-sediment concentration (SSC) to reliably compute sediment flux for one year.

Objective

Continue operating the sediment-flux monitoring system and collect SSC samples sufficient to reliably compute sediment flux into and out of Jamaica Bay during a 1-year period.

Approach

The sediment-flux monitoring system will be operated for a 1-year period during calendar year 2015 (and beyond pending available funding). The system consists of a water-quality monitor that provides water temperature, specific conductance (used to compute salinity), and turbidity readings collected near mid-water depth; and an acoustic Doppler velocity meter (ADVM) that provides velocity readings collected at the same depth. Data are being collected at the existing NYWSC tide gage on Rockaway Inlet near Floyd Bennett Field, NY. The data are recorded at 6-minute intervals, stored onsite, and then transmitted to USGS offices every hour during non-storm conditions; transmission times for select parameters are more frequent during coastal flooding events. Data from this site are relayed to USGS offices via satellite and telephone and are available for viewing within minutes of arrival at the USGS website for Coastal Conditions in Southeastern New York.

The tidal flow of water through the estuary mouth will be measured discretely using a boat-mounted acoustic Doppler current profiler (ADCP) that is traversed across Rockaway Inlet throughout the tidal cycle for both spring and neap phases of the tide (see fig. 2 for spring tide examples). Results will be used in combination with a profile of the seabed across the Inlet, and continuous (6-minute) measurements of tidal water elevation and velocity, to compute continuous tidal discharge through the estuary mouth in real time.

The variability of SSC across the estuary mouth will be measured discretely with a boat-operated D-96 sampler that is used to collect a depth-integrated sample of suspended sediment at the middle (or centroid) of five intervals of equal discharge across the Inlet. This cross-sectional variability in SSC will be defined for peak ebb and flood conditions during both spring and ebb phases of the tide. In-situ samples of SSC will be collected using a point-sampler lowered to near mid-water depth adjacent to the turbidity sensor at select times of continuous (6-minute) measurement. These samples that define the in-situ relation between turbidity and SSC will be collected throughout the tidal cycle for both selected spring and neap conditions.

Samples of SSC will be analyzed by the USGS Kentucky Water Science Center Sediment Lab for the sand-fine break (includes concentration) at low concentrations. Results defining the in-situ and cross-sectional relations in SSC will be used in combination with continuous discharge to compute continuous sediment flux through the estuary mouth in real time. Time series of continuous discharge and sediment flux will also be tidally filtered to assess the daily net discharge and flux into and out of the estuary during the 1-year period.

Products

 Continuous-record data on tidal water elevation, temperature, specific conductance, salinity, turbidity, velocity, discharge, SSC, and sediment flux will be publically disseminated online via the National Water Information System (NWIS), as they become available. Daily statistics (for example, maximum, minimum, and mean values) for these parameters will be published online annually. A summary of the methodology used to collect, analyze, and process SSC samples and compute sediment-flux data will be documented in the NYWSC Site Information Management System (SIMS).

Project
Location by County

Nassau County, NY