Elevation of marsh units in Hudson Valley and New York City salt marsh complex, New York
This data release contains coastal wetland synthesis products for the geographic region of Hudson Valley and New York City, New York. Metrics for resiliency, including unvegetated to vegetated ratio (UVVR), marsh elevation, and mean tidal range, are calculated for smaller units delineated from a Digital Elevation Model, providing the spatial variability of physical factors that influence wetland health. Through scientific efforts initiated with the Hurricane Sandy Science Plan, the U.S. Geological Survey has been expanding national assessment of coastal change hazards and forecast products to coastal wetlands with the intent of providing Federal, State, and local managers with tools to estimate the vulnerability and ecosystem service potential of these wetlands. For this purpose, the response and resilience of coastal wetlands to physical factors need to be assessed in terms of the ensuing change to their vulnerability and ecosystem services.
Welk, Robert, Defne, Zafer, and Ganju, Neil, 20200721, Elevation of marsh units in Hudson Valley and New York City salt marsh complex, New York: data release DOI:10.5066/P9XV0JMJ, U.S. Geological Survey, Coastal and Marine Hazards and Resources Program, Woods Hole Coastal and Marine Science Center, Woods Hole, MA.
Planar coordinates are encoded using coordinate pair
Abscissae (x-coordinates) are specified to the nearest 0.6096
Ordinates (y-coordinates) are specified to the nearest 0.6096
Planar coordinates are specified in Meter
The horizontal datum used is D_WGS_1984.
The ellipsoid used is WGS_1984.
The semi-major axis of the ellipsoid used is 6378137.0.
The flattening of the ellipsoid used is 1/298.257223563.
Altitude_Datum_Name:North American Vertical Datum of 1988 Altitude_Resolution:0.001 Altitude_Distance_Units:meters Altitude_Encoding_Method:Attribute values
Attribute information associated with the mean elevation of the conceptual marsh units of the Hudson Valley and New York City salt marsh complex.
(Source: U.S. Geological Survey)
Internal feature number.
Unique whole numbers that are automatically generated.
Coordinates defining the features.
Unique whole numbers used to identify each conceptual marsh unit.
Range of values
Surface area of vegetated part of a marsh unit in square meters.
Range of values
Total surface area of a marsh unit in square meters
Range of values
Mean elevation of the vegetated area in a marsh unit in meters. Value is set to -9999 if there is no vegetated area in the marsh unit.
Range of values
Mean elevation of a marsh unit in meters.
Range of values
LOW3RD is the percent of elevation values that fall within the lowest third of the elevation range within the vegetated part of a marsh unit. Values of -9999 indicate no vegetated area within the marsh unit.
Range of values
SKWNSS is the measure of skewness of the elevation distribution in the vegetated part of a marsh unit. Positive skewness values, i.e. right-skewed distribution, indicate clustering of elevation distribution towards lower elevations. Negative numbers indicate a left-skewed distribution and clustering towards higher elevations. Values of -9999 indicate no vegetated area within the marsh unit.
Range of values
Marsh unit flag indicating anomalous marsh units based on elevation, surface area, and absence of vegetation. FLG values indicate: (-1) no vegetated area in the marsh unit; (-10) marsh unit elevation higher than the 99.8 percentile; (-100) marsh unit elevation less than 0.2 percentile; (-1000) marsh unit surface area less than 900 m^2; (-10000) mean tidal range of marsh unit is extrapolated; and (0) no flag. Combination of negative values indicate combination of flags. For example, -1001 indicates no vegetated area and area less than 900 m^2.
Range of values
In this dataset, mean elevation for each conceptual salt marsh unit in the Hudson Valley and New York City salt marsh complex has been calculated based on the 1-meter resolution raster source dataset. Decimal values in the attribute table are a result of double precision calculations while significant digits are considered in defining the attribute measurement resolutions. Therefore, the smallest unit increment for area values and elevation is assumed to be 1 meter and 0.01, respectively.
The purpose of this shapefile is to calculate the mean elevation for each marsh unit and its vegetated component. Analysis of marsh elevation is part of a comprehensive assessment to identify the factors and their weights in determining the vulnerability and resiliency of salt marshes. Elevation distribution in the Hudson Valley and New York City salt marsh complex is given in terms of mean elevation of conceptual marsh units. The elevation data is based on the 1-meter resolution Coastal National Elevation Database (CoNED).
This process step was performed by Robert Welk, in ArcMap (ver. 10.7.1) using tools from ArcToolbox, unless otherwise stated. For complex operations, names of specific tools used are given in CAPITAL letters (any critical parameters used are given in parentheses, separated by a semicolon, immediately after the tool name). The input and output file names are provided in [square brackets] when necessary. Units for length and area calculations are meters (m) and square meters (m^2) unless otherwise stated.
a) Set the data frame coordinate system and projection to NAD 1983 UTM Zone 18N. Prepare elevation dataset to be clipped to the boundaries polygon. MOSAIC TO NEW RASTER(Pixel type=32 bit float; Mosaic operator=Mean; Cellsize=1 m) the entire CoNED raster to a new raster dataset with 1 meter resolution [elev_mosaic.tif].
b) Calculate values for each marsh unit. DISSOLVE(Input features=[CMU_HvNYC]; Dissolve field=FID_CMU; Statistics field=ATOT_M2 and FLG with Statistics type= First) to dissolve the vegetated and unvegetated classes in each marsh unit. FLG flags anomalous marsh units based on absence of vegetation, elevation and surface area, and is set to (-1) no vegetated area; (-10) marsh unit elevation higher than the 99.8 percentile; (-100) marsh unit elevation less than 0.2 percentile; (-1000) marsh unit surface area less than 900 m^2; and (0) no flag. Combination of negative values indicate a combination of flags. For example, -1001 indicates no vegetated area and area less than 900 m^2. PROJECT(Input coordinate system=WGS 1984 Web Mercator Auxiliary Sphere; Output coordinate system=NAD 1983 UTM Zone 18N; Geographic transformation=WGS 1984 (ITRF00) to NAD 1983) the feature dataset to obtain dissolved marsh units [mu_diss.shp].
c) Clip the raster with the polygon features by using EXTRACT BY MASK to obtain [elev_idw_mu.tif].
d) ZONAL STATISTICS AS TABLE(Feature Zone Data=[mu_diss.shp]; zone field=FID_CMU; Value Raster=[elev_idw_mu.tif]; Output Table=mu; Statistics type=MEAN)
e) ADD JOIN(Layer name=[mu_diss.shp]; Input join field=FID_CMU; Join Table=mu; Output join field=FID_CMU) to marsh units layer based on the "FID_CMU" field
f) Export dataset as a shapefile [mu_elev.shp] and keep the 'mu_MEAN" and "mu_ATOT_M2" fields from the join operation.
g) Calculate elevation of the vegetated areas only. SELECT BY ATTRIBUTES FROM [CMU_HvNYC] where "CLASS"= 'vegetated'. Follow steps (c) to (f) using the selected features to export [veg_elev.shp].
h) JOIN FIELD(Input table=[mu_elev.shp]; Input join field=mu_FID_CMU; Join table=[veg_elev.shp]; Output join field=vg_FID_CMU; Join fields=vg_AVEG_M2,vg_ATOT_M2,vg_MEAN). Change the field names to VG_ELEV and MU_ELEV respectively for the fields with the mean elevation for the vegetated area only and mean elevation for the entire marsh unit. Set VG_ELEV to -9999 if there is no vegetated area in the marsh unit. Name AVEG_M2 and ATOT_M2 for vegetated and total area, respectively, and export to a new shapefile. [mu_elev_HvNYC.shp].
i) Calculate metrics that quantify the distribution of marsh unit elevation values. SKWNSS is the measure of skewness of the elevation distribution in the vegetated part of a marsh unit. Positive skewness values, i.e. right-skewed distributions, indicate clustering of elevation distributions towards lower elevations. Negative numbers indicate a left-skewed distribution and clustering towards higher elevations. LOW3RD is the percent of elevation values that fall within the lowest third of the elevation range within the vegetated part of a marsh unit. SKWNSS and LOW3RD parameters are calculated by applying the formulation of Raposa et al. (2016) to the elevation raster within the vegetated part of each marsh unit.
j) SELECT BY ATTRIBUTES FROM [CMU_HvNYC] where "CLASS"= 'vegetated', and join field "APGN_M2" from CMU_HvNYC.shp on the feature dataset [mu_elev_HvNYC.shp].
k) Rearrange field names and change the projection for better performance of web services with online base maps. PROJECT(Input coordinate system=NAD 1983 UTM Zone 18N; Output coordinate system=WGS 1984 Web Mercator Auxiliary Sphere; Geographic transformation=WGS 1984 (ITRF00) to NAD 1983) the feature dataset to obtain the final elevation data set [mu_elev_HvNYC.shp].
Raposa, K. B., Wasson, K., Smith, E., Crooks, J. A., Delgado, P., Fernald, S. H., et al. (2016). Assessing tidal marsh resilience to sea-level rise at broad geographic scales with multi-metric indices. Biological Conservation, 204, 263–275. https://doi.org/10.1016/J.BIOCON.2016.10.015
Person who carried out this activity:
How well have the observations been checked?
Marsh units and water and land boundaries inherit their horizontal accuracy from the accuracy of the source data, the Hudson Valley and New York City marsh units, and their vertical accuracy from the 2016 U.S. Geological Survey Coastal National Elevation Database (USGS CoNED).
How accurate are the heights or depths?
Because the elevation values are averaged over delineated polygons, vertical accuracy depends on both the horizontal accuracy of the NWI dataset and the vertical accuracy of the source elevation data, CoNED. CoNED vertical elevation accuracy is 0.2 meters.
Where are the gaps in the data? What is missing?
The results are specific to the marsh polygons as defined within the boundaries of the Hudson Valley and New York City salt marsh complex. A detailed on-the-ground analysis of a single site may result in a different interpretation of the wetland and marsh unit boundaries.
The mean elevation for each marsh unit is defined for scientific research purposes and should not be used as a sole source of reference for any regulations and policy making. Public domain data from the U.S. Government are freely redistributable with proper metadata and source attribution. Please recognize the U.S. Geological Survey as the source of this information.
Neither the U.S. Government, the Department of the Interior, nor the USGS, nor any of their employees, contractors, or subcontractors, make any warranty, express or implied, nor assume any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, nor represent that its use would not infringe on privately owned rights. The act of distribution shall not constitute any such warranty, and no responsibility is assumed by the USGS in the use of these data or related materials. Any use of trade, product, or firm names is for descriptive purposes only and does not imply endorsement by the U.S. Government. Not for navigational use.