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Data format: Raster Dataset File or table name: inher_sw Coordinate system: State Plane Coordinate System 1983 Theme keywords: Inherenent Vulnerability, precipitation, land use, land cover, ground water contribution, slope, elevation, surface water |
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Abstract:
This data set represents the ratings applied to the watershed characteristics of surface water supplies. It is one of 6 data sets developed for the North Carolina Source Water Assessment Program. The data sets are used to rate the susceptibility of public water supplies in North Carolina to contamination.
The original dataset was produced in 2000. This version is updated to reflect new data sources.
The selected factors contributing to watershed characteristics
ratings are average annual precipitation, land-surface slope,
land cover, land use, and ground-water contribution. For
surface-water systems, the higher the inherent vulnerability of
a watershed, the higher the rating applied on a scale of
10 to 100. |
Metadata elements shown with blue text are defined in the Federal Geographic Data Committee's (FGDC) Content Standard for Digital Geospatial Metadata (CSDGM). Elements shown with green text are defined in the ESRI Profile of the CSDGM. Elements shown with a green asterisk (*) will be automatically updated by ArcCatalog. ArcCatalog adds hints indicating which FGDC elements are mandatory; these are shown with gray text.
This data set represents the ratings applied to the watershed characteristics of surface water supplies. It is one of 6 data sets developed for the North Carolina Source Water Assessment Program. The data sets are used to rate the susceptibility of public water supplies in North Carolina to contamination. The original dataset was produced in 2000. This version is updated to reflect new data sources. The selected factors contributing to watershed characteristics ratings are average annual precipitation, land-surface slope, land cover, land use, and ground-water contribution. For surface-water systems, the higher the inherent vulnerability of a watershed, the higher the rating applied on a scale of 10 to 100.
The purpose of this data set is to rate susceptibility to contamination for watershed characteristics of surface-water supplies.
The 1996 Amendments to the Safe Drinking Water Act require that each state prepare a source-water assessment for all public water supplies. States are required to (1) delineate source areas supplying wells and surface-water intakes, (2) inventory potential contaminant sources within the delineated source areas, and (3) determine the susceptibility of wells or intakes to the inventoried potential contaminant sources. In North Carolina, the lead agency charged with this task is the Public Water Supply Section (PWSS) of the Division of Environmental Health, Department of Environment and Natural Resources (DENR). North Carolina's Source Water Assessment Program (SWAP) provides assessments of each public drinking water intake in North Carolina. These assessments provide a relative susceptibility rating calculated using state-wide data. The U.S. Geological Survey (USGS) cooperated with the PWSS to provide components of the inherent vulnerability rating that was used with the contaminant rating to determine the overall susceptibility rating of source water supplies. To assist the PWSS with rating ground water inherent vulnerability, the USGS compiled the unsaturated zone rating based on the following characteristics: vertical hydraulic conductance, depth to water, land surface slope, land use and land cover. The watershed characteristic rating includes average annual precipitation, land surface slope, land use, land cover and groundwater contribution. The SWAP program has planned for updates to the initial ratings as conditions change and new data sources become available. The initial data used to calculate the unsaturated zone ratings and watershed characteristics ratings were compiled from sources from the late 1990's. Critical data layers have been updated since the ratings were calculated. These improved data layers need to be used in the ongoing update of the susceptibility ratings. Overlay and index methods for rating susceptibility to contamination of the unsaturated zone for ground-water suppplies, and watershed characteristics for surface-water supplies were derived for use by the State of North Carolina in assessing more than 11,000 public water-supply wells and approximately 245 public surface-water intakes. Factors that influence the inherent vulnerability of ground water and surface water were selected and assigned ratings on a scale of 1 to 10. These factors were then assigned weight to reflect their relative influence on inherent vulnerability and the reliability of the data. The values for each factor were obtained from geographic information system (GIS) data layers that were transformed into ARC/INFO raster data sets known as grids. These raster data sets have 30-meter by 30-meter cells, and each cell is assigned a weighted- factor value. Limitations -- The overlay and index methods of unsaturated zone and watershed characteristics ratings are broad-stroke methods that assess vulnerability on the basis of expert opinion. The methods aslo have limitations in the age and scale of the hydrologic and geographic data. But the most significant limitation of the methods used is that no statistical confirmation of the results have been performed. WATERSHED CHARACTERISTICS RATING-- The relative watershed characteristics rating is based on a combination of factors that contribute to the likelihood that contaminants from surface and shallow sources will reach a public surface-water supply intake by following the path of overland flow or shallow subsurface flow. The selected factors, which can be represented in the form of GIS spatial data layers, include average annual precipitation, land-surface slope, land cover, land use, and ground-water contribution. The values of each of these five factors are categorized, and the categories are assigned a rating on a scale of 1 to 10. A rating of 1 reflects a low contribution to inherent vulnerability and 10 reflects a high contribution. For example, the rating for land-surface slope is low (1) in areas of low slope (greater than 50 percent) and high (10) in areas of high slope (less than 2 percent) because increased runoff potential in steeper terrain leads to an increased likelihood of surface-water contamination. With the exception of land use, these factors describe influences on the physical transport of water, with or without contaminants. The land-use factor is included as a measure of the potential for generating nonpoint-source contamination at land surface. To determine the watershed characteristics rating, the five factors are weighted on the basis of weighted on the basis of importance of the factor in determining vulnerability. For each cell, the product of the factor weights and ratings are summed to determine the total rating for the cell, resulting in a relative numerical watershed characteristics rating that ranges from 10 to 100 for each cell. >Factors contributing to the watershed characteristics rating. > >Factor contributing to the watershed characteristics Weight >rating -- Description > >Average annual precipitation 3 >The average annual precipitation is a measure of the >amount of water (with or without contaminants) that >travels overland or through the shallow subsurface to >streams or lakes. > >Land-surface slope 2 >The inclination or slope of the land surface influences >the likelihood that precipitation will run off or >infiltrate into the ground. > >Land cover 1 >The type of material covering the land surface >influences the likelihood that precipitation will >run off or infiltrate into the ground. > >Land use 3 >The type of land use influences the likelihood >that potential non-point source contaminants will >be generated. > >Ground-water contribution 1 >The portion of surface water derived from ground >water influences surface-water quantity and quality. > Two datasets are created for the watershed characteristics rating. One with all five factors to visualize a statewide component. And one with only Average Annual Precipitation, Land-surface Slope, Land cover and Land use. This one is produced as the INTERMEDIATE watershed characteristics rating for use with the Public Water Supply Section's GIS system to combine ground-water contribution for each public water supply system. This allows the PWSS to create a custon data layer that includes only relevant stream segments for consideration in the groundwater contribution component. This data set is the Statewide Watershed Characteristics Rating layer. SELECTED REFERENCE: Eimers, J. L., Weaver, J. C., Terziotti, S., and Midgette, R. W., 2000, Methods of rating unsaturated zone and watershed characteristics of public water supplies in North Carolina: U. S. Geological Survey Water-Resources Investigations Report 99-4283, 31 p. North Carolina Department of Environment and Natural Resources, 1999, North Carolina source water assessment program plan: Raleigh, North Carolina Department of Environment and Natural Resources, Division of Environmental Health, Public Water Supply Section, [variously paged]. DISCLAIMER: Any use of trade, product, or firm names is for descriptive purposes only and does not imply endorsement by the U.S. Government. Although this Federal Geographic Data Committee-compliant metadata file is intended to document the data set in nonproprietary form, as well as in ARC/INFO format, this metadata file may include some ARC/INFO-specific terminology.
Ground Condition
Not to be used for site specific analysis
3916 Sunset Ridge Road
The authors are grateful to colleagues in the Public Water Supply Section of the Division of Environmental Health, North Carolina Department of Environment and Natural Resources (DENR) for their assistance in this collaborative project: thanks to Robert Midgette, Protection and Enforcement Branch Head; Amy Axon,hydrogeologist - Source Water Protection; and David Hammermann, Geographic Information Systems Specialist. The authors also thank the USGS report review team for their review of the update procedures: Jeanne Robbins, Surface-water Specialist; Melinda Chapman, Ground-water Specialist; Mary Giorgino, Water-quality Specialist; and Douglas Harned, ALBE-National Water Quality Assessment Project Chief.
visually verified against original source
Not applicable for raster data.
Completed for the State of North Carolina.
visually verified
methods for applying ratings
Create a floating point grid based on the weighted values of the contributing factors. INHER_SW = ( landcoversw * 2 ) + ( landusesw * 3 ) + ( precipsw * 3 ) + ( slopesw * 1 ) + ( ( gwcontrib) div 10 * 1 )
Metadata imported.
Internal feature number.
ESRI
>Value attribute table, INHER_SW.VAT: > >COLUMN ITEM NAME WIDTH OUTPUT TYPE N.DEC ALTERNATE NAME > 1 VALUE 4 10 B - > 5 COUNT 4 10 B - > Value is rating between 10 and 100. Count is the number of 30 meter by 30 meter cells that have the value in positive integers. In the final data set, the values range from 13 to 95. > >Summary statistics table, INHER_SW.STA: > >COLUMN ITEM NAME WIDTH OUTPUT TYPE N.DEC ALTERNATE NAME > 1 MIN 8 15 F 3 > 9 MAX 8 15 F 3 > 17 MEAN 8 15 F 3 > 25 STDV 8 15 F 3 > > MIN MAX MEAN STDV >13.000 95.000 31.127 8.895 Min is the minumum value. Max is the maximum value. Mean is the average value. STDV is the standard deviation.
none
3916 Sunset Ridge Rd.
Contact via email
Although these data have been used by the U.S. Geological Survey, U.S. Department of the Interior, no warranty expressed or implied is made by the U.S. Geological Survey as to the accuracy of the data. The act of distribution shall not constitute any such warranty, and no responsibility is assumed by the U.S. Geological Survey in the use of this data, software, or related materials.
3916 Sunset Ridge Road