Bathymetric and Tidal Discharge data for Wilderness Breach, Fire Island National Seashore, Long Island, NY, May 14, 2015

In 2012, Hurricane Sandy created an open breach in the barrier island system along the south shore of Long Island, N.Y. This breach formed at a location known as Old Inlet and migrated rapidly westward over the winter storm season following Hurricane Sandy. In response, the National Park Service sought assistance from the USGS New York Water Science Center to help evaluate the hydrodynamics and geomorphology of the breach. The evaluation is centered on measurement of water velocities and depths within the breach, and collection of water levels with the Great South Bay adjacent to the breach. This project is part of a larger ongoing study prepared in coordination with the National Park Service and the U.S. Army Corps of Engineers, titled Evaluation of a barrier-island breach created by Hurricane Sandy at Fire Island National Seashore, N.Y. The goals of this effort are to understand the formation and evolution of the breach and its impacts to the morphology of the adjacent barrier island, and to develop capabilities for predicting stability of future breaches that may occur on Fire Island or similar environments. In order to capture the morphology of the breach channel, depths, disharge, and velcoity data were collected at low and high tide. Periodic measurements of the breach (tidal discharge and bathymetry) taken since 2012 are available as GIS packages and can be found at https://ny.water.usgs.gov/projects/hurr_sandy_2012/. Data Collection On May 14, 2015, U.S. Geological Survey New York Water Science Center personnel collected data to evaluate channel geometry, water velocity, and discharge of an open breach in the Federal Wilderness area of Fire Island National Seashore. Data were collected using a Sontek M9 Acoustic Doppler Current Profiler with Real-Time Kinematic Global Positioning System. Depth soundings were collected during discharge measurements at locations along the approximate center line and adjacent to the shores of an open breach in the Federal Wilderness area of Fire Island National Seashore. The depth soundings were converted to sea floor elevations relative to the North American Vertical Datum of 1988 (NAVD 88). The mapped area includes data collected during discharge measurements of both incoming (flood) and outgoing (ebb) tide conditions at high and low tide respectively. An initial series of transects was collected starting about 4 hours before ocean low tide on May 14, 2015. Data were collected perpendicular to flow through the breach beginning at 0725 Eastern Standard Time (EST) and ending at 0811 EST. The first set of transects was taken near the bayward side of the breach, with subsequent sets collected progressively closer to the seaward side of the breach. Discharge ranged from 16,400 cfs (cubic feet per second) during the beginning set of transects to 17,400 cfs during the second set of transects. A second series of transects was collected starting about 4 hours before ocean high tide on May 14, 2015. Data collection began at 1335 EST and ended at 1445 EST. The first set of transects was taken perpendicular to the flood tidal channels bayward of the former Great South Bay shoreline; subsequent sets were collected progressively closer to the seaward side of the breach. Discharge ranged from 16,500 cfs during the beginning set of transects to 24,900 cfs during the final set of transects. Measured discharges are published and available at https://waterdata.usgs.gov/nwis/measurements/?site_no=01305207