Layer: Mean Higher High Water (MHHW) (ID: 4)

Name: Mean Higher High Water (MHHW)

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Description: 2010 saw the beginning of The Northeast Multiphase LiDAR Project. Across the region, the same problems were being addressed – the almost total lack of contiguous, consistent, high-resolution elevation data. Coordinated by the USGS with representatives from each of the participating states, this work sought to collect seamless LiDAR data for all of the coastal counties between New York and Maine. With accuracies 25 – 100 times better than what is currently available for much of Rhode Island, a contiguous and consistent elevation dataset derived from this new data collection initiative will facilitate a number of statewide applications including transportation planning, floodplain mapping, and hazard mitigation. As part of this project, the contractor delivered to the State of Rhode Island raw and classified LiDAR points along with a hydro-flattened 1m digital elevation model (DEM).In 2012, the RI Department of Transportation funded the project "Open Access to High Resolution Elevation Data for Transportation Planning in RI". The three primary goals of this work were to: 1) make the USGS Northeast LiDAR data and derivative products readily accessible to RIDOT and RIGIS users; 2) to develop a statewide ArcGIS terrain dataset as the primary container for storing/accessing the state's elevation data; and 3) develop refined engineering quality elevation products for RIDOT project planning. As part of this work, the 2011 USGS-delivered LAS data was subset to extract just the bare earth elevation points. These were reprojected to the RI State plane coordinate system, and horizontal/vertical units were converted to feet. These points were put into an ArcGIS Terrain dataset and combined with bathymetry values for interpolation and conversion into a seamless, state-wide, topobathy DEM.Bathymetry data was obtained from 2 sources: the NGDC Bathymetry Data Viewer (http://maps.ngdc.noaa.gov/viewers/bathymetry/), and the Army Corps of Engineers 2010 coastal LiDAR survey. The ACOE data focused specifically on the south coast of RI, out to a distance of approximately 1km; NOS soundings and multibeam data were used everywhere else. All NOS surveys for RI coastal waters were used from 1980 thru 2009. Pre-1980 surveys were only used when needed to fill in large data gaps offshore.Using this LiDAR-derived DEM as the starting point, multiple, single-source flood levels were calculated to highlight potential problem areas for each scenario.

Copyright Text: USGS, RIDOT, NOS, NGDC, USACOE

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