Digital data sets were compiled by the U. S. Geological Survey (USGS) and used as input for a collection of Spatially Referenced Regressions On Watershed attributes for the Chesapeake Bay region. These regressions relate streamwater loads to nutrient sources and the factors that affect the transport of these nutrients throughout the watershed. A digital segmented network based on watershed boundaries serves as the primary foundation for spatially referencing total nitrogen and total phosphorus source and land-surface characteristic data sets within a Geographic Information System. Digital data sets of atmospheric wet deposition of nitrate, point-source discharge locations, land cover, and agricultural sources such as fertilizer and manure were created and compiled from numerous sources and represent nitrogen and phosphorus inputs. Some land-surface characteristics representing factors that affect the transport of nutrients include land use, land cover, average annual precipitation and temperature, slope, and soil permeability. Nutrient input and land-surface characteristic data sets merged with the segmented watershed network provide the spatial detail by watershed segment required by the models. Nutrient stream loads were estimated for total nitrogen, total phosphorus, nitrate/nitrite, amonium, phosphate, and total suspended soilds at as many as 109 sites within the Chesapeake Bay watershed. The total nitrogen and total phosphorus load estimates are the dependent variables for the regressions and were used for model calibration. Other nutrient-load estimates may be used for calibration in future applications of the models.
This spatial data set was created and used by the USGS in the initial applications of the SPARROW models in the Chesapeake Bay watershed. Revised and updated digital spatial data sets will be created and distributed by the USGS as planned enhancements and applications for the SPARROW models are completed.
Any use of trade, product, or firm names is for descriptive purposes only and does not imply endorsement by the U.S. Geological Survey.
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. Users are cautioned not to be confused by this terminology. This metadata file should contain enough information to eliminate any confusion caused by the use of ARC/INFO-specific terminology.)
A digital segmented network was created using approximately 1,300 stream reaches modified from 1:500,000 scale (River Reach File 1 (RF1), DeWald and others, 1985) and a flow direction grid (Verdin, 1997) derived from a 1-kilometer grid cell DEM (Verdin and Greenlee, 1996). The modified stream-reach data contain a unique identification number (erf1##).
Stream reaches were split into two separate reach segments at the location of the flow collection sites. A new identification number (erf1##) was calculated for each split reach up and down-stream of the sampling location. Stream reaches representing shorelines of major estuaries within the watershed were also split at arbitrary locations along the shoreline and attributed with erf1##. These reaches representing shorelines did not include any other attributes and were not included in SPARROW model applications.
The stream reach coverage (erf1_1) was projected into a lambert projection with the following parameters:
A 1-kilometer cell size raster grid of stream reaches was generated and used with the flow direction raster grid to generate a 1-kilometer cell size raster grid of watershed boundaries for each stream reach (ESRI, 1992). This process was done by using the watershed function in Arc/Info's GRID, using the grid of stream reaches as pour points. In some cases, watersheds were not created for small reaches and had to be added manually. The watershed boundary grid was attributed with the unique erf1## number and converted to a polygon vector format and projected into an Albers Equal Area projection.
CBWS.PAT:
COLUMN ITEM NAME WIDTH OUTPUT TYPE N.DEC ALTERNATE NAME
1 AREA 4 12 F 3
5 PERIMETER 4 12 F 3
9 CBWS# 4 5 B -
13 CBWS-ID 4 5 B -
17 ERF1## 4 8 B -
21 OLDERF1## 4 5 B -
ERF1## - New unique reach identifier. Values of -9999 represent No Data
OLDERF1## - Original unique reach identifier
For the GRID data set...........
** OLDERF1## is not contained in GRID data set. The VALUE of the
GRID represents ERF1##. Values of -9999 represent no data.
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.
Generated by mp on Tue Sep 22 13:02:21 1998