Attribute_Accuracy:
Attribute_Accuracy_Report:
Marsh units and water and land boundaries inherit their horizontal accuracy from the accuracy of the source data, the conceptual marsh units, and their vertical accuracy from the elevation datasets (primarily: USGS CoNED, for NC: NOAA NC DEM). Mean tidal range is calculated from the VDatum database, then interpolated on a raster surface and averaged at each marsh unit. If a marsh unit does not overlap with any raster cell center, it is assigned the value of the raster cell with the largest overlap.
Logical_Consistency_Report:
Polygons do not overlap and mean tidal range is positive. During processing of conceptual marsh units, small polygons (less than 9 m^2) were assumed to be marginal and were assigned the classification from the surrounding majority value.
Completeness_Report:
The marsh polygons are bound to the borders of the Chesapeake Bay estuarine intertidal areas that include: 1) emergent wetlands, 2) scrub-shrub areas, 3) rooted vascular aquatic beds, 4) organic unconsolidated shores, and 5) channels of open water that are narrower than 10 meters.
Sliver polygons of open salt water along the marsh edges may also be included in some instances as a result of geoprocessing (e.g., marsh unit 36608).
In a few cases, linear marsh unit features that are artifacts of the NWI dataset are retained (e.g., marsh units 17309, 17310, 20453).
Occasionally, marsh units are retained in this dataset even though the imagery displayed extreme change (e.g., partially or completely converted to water) from the NWI wetland delineation (e.g., marsh units 18150, 36504).
In some marsh units there are small sliver gaps due to coupling of artifacts of the NWI (e.g., NWI polygons for ditches that are classified as riverine) and geoprocessing when the marsh polygons were closer than 10 meters at a specific section that is followed by a wider distance (e.g., access roads, fringing forests, etc.). The effect of these sliver gaps on the calculations is negligible (e.g., south of marsh unit 19742).
In a few marsh units there are small gaps that inadvertently did not get incorporated into the marsh unit; the effect of these gaps on the calculations is negligible (e.g., marsh unit 33957).
A detailed on-the-ground analysis of a single site may result in a different interpretation of the wetland and marsh unit boundaries than those established through this analysis.
At Colonial National Historic Park, Virginia, palustrine emergent persistent wetlands (with freshwater tidal modifiers) were included to ensure complete coverage of the estuarine and palustrine emergent wetlands within the Park boundaries.
In region CB16 (at the VA-NC border), the methodology was changed slightly to include estuarine and marine wetland polygons that are completely surrounded by salt marsh (see process step e.3).
In region CB08A (Aberdeen Proving Ground, in northern Chesapeake Bay), Worldview-2 imagery was used due to the unavailability of NAIP imagery.
Positional_Accuracy:
Horizontal_Positional_Accuracy:
Horizontal_Positional_Accuracy_Report:
Horizontal accuracy for the polygon boundaries is inherited from the source layer, the conceptual marsh units, and is considered to be +/- 6 meters. The point cloud used for calculating tidal range with VDatum had a 0.0005 arc degree (~50-meter) resolution that was interpolated over a 0.0001 arc degree raster prior to clipping and calculating the mean value for each marsh unit.
Vertical_Positional_Accuracy:
Vertical_Positional_Accuracy_Report:
The maximum cumulative uncertainty for the Chesapeake Bay operational VDatum region is 0.0277 meters, for Maryland and Virginia areas, and 0.0468-0.0507 meters for North Carolina areas. See VDatum's "estimation of vertical uncertainties" for more information (
https://vdatum.noaa.gov/docs/est_uncertainties.html).
Lineage:
Source_Information:
Source_Citation:
Citation_Information:
Originator: Ackerman, K.V., Defne, Z., and Ganju, N.K.
Publication_Date: 2022
Title: Conceptual marsh units of Chesapeake Bay salt marshes
Geospatial_Data_Presentation_Form: vector digital dataset (polygon)
Publication_Information:
Publication_Place: Reston, VA
Publisher: U.S. Geological Survey
Online_Linkage:
Type_of_Source_Media: Digital
Source_Time_Period_of_Content:
Time_Period_Information:
Single_Date/Time:
Calendar_Date: 2022
Source_Currentness_Reference: publication date
Source_Citation_Abbreviation: CMU_CB
Source_Contribution:
Used conceptual marsh units to delineate marsh unit boundaries and areas of vegetation.
Process_Step:
Process_Description:
This process step and all subsequent process steps were performed by the same person, Kate Ackerman, in ArcGIS Pro (ver. 2.8.2), unless otherwise stated. For simple operations the name of the geoprocessing tool used is given in capital letters; for complex operations, the name of geoprocessing tool used is given in capital letters and 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.
b) Establish marsh unit boundaries. Dissolve the vegetated and unvegetated classes in each marsh unit to have only one class for each marsh unit. DISSOLVE(Input features=[CMU_CB.shp]; Dissolve field=FID_CMU; Statistics field=ATOT_M2 and FLG, with Statistics type= First). PROJECT(Input coordinate system=WGS 1984 Web Mercator Auxiliary Sphere; Output coordinate system=GCS NAD 1983) the feature dataset to obtain dissolved marsh units [mu_diss.shp].
Source_Used_Citation_Abbreviation: CMU_CB
Process_Date: 2022
Source_Produced_Citation_Abbreviation: mu_diss.shp
Process_Contact:
Contact_Information:
Contact_Person_Primary:
Contact_Person: Kate Ackerman
Contact_Organization: U.S. Geological Survey
Contact_Position: Geologist
Contact_Address:
Address_Type: mailing address
Address: 384 Woods Hole Road
City: Woods Hole
State_or_Province: MA
Postal_Code: 02543
Country: US
Contact_Voice_Telephone: 508-548-8700 x2331
Contact_Facsimile_Telephone: 508-457-2310
Contact_Electronic_Mail_Address: kackerman@usgs.gov
Process_Step:
Process_Description:
Generate a point cloud of coordinates indicating calculation locations for the mean range of tides (MN).
a) CREATE CONSTANT RASTER with 50 m spacing (Constant value= 0; Output cell size: 50) that surpasses the marsh unit boundaries by 300m.
b) RASTER TO POINT to generate an array of points [pts.shp]. PROJECT [pts.shp] to GCSNAD 1983. Calculate latitude and longitude of each point [pts.shp]. Export the shapefile to a text file (TABLE TO TABLE (output table= [Tidal_Points.txt]). This text file includes latitude, longitude and height (set to zero).
Process_Date: 2022
Source_Produced_Citation_Abbreviation: Tidal_Points.txt
Process_Step:
Process_Description:
Calculate Mean Range of Tides (MN) using the VDatum (v.4.4.1) database covering this region. Mean range of tides (MN) = mean high water level (MHW)- mean low water level (MLW) in the VDatum database. Interpolate MN to the point dataset.
a) Input point cloud file [Tidal_Points.txt] to VDatum. Set the REGION (Chesapeake/Delaware Bay), HORIZONTAL INFORMATION (Reference Frame (UGS14-use ITRF2014), Coordinate System (Geographic)) to be the same for the source and target. Set the VERTICAL INFORMATION (Source Reference Frame: MHW (meters); Target Reference Frame: MLW (meters)). Choose ASCII FILE CONVERSION (exclude NODATA points) and save output [MN.txt]. The resulting text file includes latitude, longitude and MN.
Source_Used_Citation_Abbreviation: Tidal_Points.txt
Process_Date: 2022
Source_Produced_Citation_Abbreviation: MN.txt
Process_Step:
Process_Description:
Create a raster surface dataset from the feature points.
a) Convert points from [MN.txt] to a shapefile using MAKE XY EVENT LAYER (Z field= Value; Spatial Reference: GCS_NAD_1983; Layer Name: MN_lyr) and COPY FEATURES [MN.shp].
b) Create a raster surface with inverse distance weighting. IDW (Input point features: [MN.shp]; Output Cell Size=0.0001 degree; Power=2; Search Radius=Variable; Number of Points=12; Input barrier polyline features – if necessary) to obtain [MN_raster_idw.tif]. After running this tool, it may be apparent that input barrier polyline feature(s) need to be created to separate areas of unrelated tidal range data (e.g., where values from one body of water cross land to another body of water); in those cases, this tool was re-run with the input barrier polyline features specified. Input barrier polyline features were created in southern VA and northern NC.
Source_Used_Citation_Abbreviation: MN.txt
Process_Date: 2022
Source_Produced_Citation_Abbreviation: MN_raster_idw.tif
Process_Step:
Process_Description:
Clip the raster to marsh boundaries. A buffer zone is created around the marsh boundaries to facilitate alternative interpolation and clipping options in future studies.
a) Create 300 m buffer around the marsh units polygons [mu_diss.shp] to create a clipping mask [mu_buff300m.shp]. BUFFER(Side type= Full; Method =Geodesic; Dissolve type= All).
b) CLIP the raster [MN_raster_idw.tif] with the clipping mask. EXTRACT BY MASK (Mask=[mu_diss.shp]) to obtain [MN_IDW_MU.tif].
Source_Used_Citation_Abbreviation: mu_diss.shp
Source_Used_Citation_Abbreviation: MN_raster_idw.tif
Process_Date: 2022
Source_Produced_Citation_Abbreviation: MN_IDW_MU.tif
Process_Step:
Process_Description:
Calculate mean tidal range value for each marsh unit and flag the marsh units that have tidal range values that are extrapolated.
a) ZONAL STATISTICS AS TABLE(Feature Zone Data=[mu_diss.shp]; zone field=FID_CMU; Value Raster=[MN_IDW_MU.tif]; Output Table=[mn]; Statistics type=MEAN).
b) JOIN FIELD(Input table=[mu_diss.shp]; Input join field=FID_CMU; Join Table=[mn]; Output join field=FID_CMU; Join Field= MEAN). Export dataset as a shapefile [mu_MN_CB.shp] and change “MEAN” to “MN.”
c) Identify marsh units that are greater than 25 m from the VDatum data. SELECT BY LOCATION (Input feature= [mu_diss.shp]; Relationship=within_a_distance; Selecting Features: [MN.shp]; Search distance= 25m; Selection type= New_Selection; Invert Spatial Relationship). Assign the marsh units with a distance greater than 25 m from VDatum data a tidal range value of -9999 and a “flag” of -10000.
d) Add field "FLG" to flag anomalous marsh units based on absence of vegetation, elevation, surface area, and tidal range extrapolation. The flags are calculated in their respective shapefile (i.e., elevation flags are calculated in the elevation shapefile). Set FLG to: (-1) no vegetated area in the marsh unit; (-10) marsh unit elevation higher than the 99.8 percentile; (-100) marsh unit elevation less than the 0.2 percentile; (-200) greater than 25 percent of the marsh unit elevation is hydro-flattened; (-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 indicates a combination of flags; for example, -1001 indicates no vegetated area and area less than 900 m^2.
e) Rearrange field names and change the projection for better performance of web services with online base maps. PROJECT(Output coordinate system=WGS 1984 Web Mercator Auxiliary Sphere) the feature dataset to obtain the final mean tidal range dataset [mu_MN_CB.shp].
Source_Used_Citation_Abbreviation: MN_IDW_MU.tif
Process_Date: 2022
Source_Produced_Citation_Abbreviation: mu_MN_CB.shp
