ERF1-2 -- Enhanced River Reach File 2.0

This report describes the process of enhancements to the stream reach network,
ERF1, which is an enhanced version of EPA's RF1. The U.S. Environmental
Protection Agency's reach file (RF1) is a database of interconnected stream
segments or "reaches" that comprise the surface water drainage system for the
United States. A variety of attributes have been assigned to each reach in
support of spatial analysis and mapping applications. ERF1-2 was designed to be
a digital database of river reaches capable of supporting regional and national
water-quality and river-flow modeling by the water-resources community. ERF1,
on which ERF1-2 is based, is used at the U.S. Geological Survey to support
national-level water-quality monitoring modeling with the SPARROW model (see
Alexander and others, 2000; Smith and others, 1997). In the current and earlier
analyses, the reach network is used to determine flow pathways between the
sources of point and nonpoint pollutants (e.g., fertilizer use, municipal
wastewater discharges) and downstream water-quality monitoring locations in
support of predictive water- quality models of stream nutrient transport.
Acknowledgements

The authors would like to thank Richard Smith, a co-developer of the SPARROW
approach, Kristine Verdin, and Stephen Char, all of the U.S. Geological Survey,
for providing technical assistance. The reviewers of this report, Dave Stewart,
and Mike Wieczorek, are also acknowledged for their significant contributions.

The digital segmented network based on watershed boundaries, ERF1-2, includes
enhancements to the U.S. Environmental Protection Agency's River Reach File 1
(RF1) (USEPA, 1996; DeWald and others, 1985) to support national and
regional-scale surface water-quality modeling. Alexander and others (1999)
developed ERF1, which assessed the hydrologic integrity of the digital reach
traces and calculated the mean water time-of-travel in river reaches and
reservoirs. ERF1-2 serves as the foundation for SPARROW (Spatially Referenced
Regressions (of nutrient transport) On Watershed) modeling. Within the context
of a Geographic Information System, SPARROW estimates the proportion of
watersheds in the conterminous U.S. with outflow concentrations of several
nutrients, including total nitrogen and total phosphorus, (Smith, R.A.,
Schwarz, G.E., and Alexander, R.B., 1997). This version of the network expands
on ERF1 (version 1.2; Alexander et al. 1999), and includes the incremental and
total drainage area derived from 1-kilometer (km) elevation data for North
America. Previous estimates of the water time-of-travel were recomputed for
reaches with water- quality monitoring sites that included two reaches. The
mean flow and velocity estimates for these split reaches are based on previous
estimation methods (Alexander et al., 1999) and are unchanged in ERF1-2.
Drainage area calculations provide data used to estimate the contribution of a
given nutrient to the outflow. Data estimates depend on the accuracy of node
connectivity. Reaches split at water- quality or pesticide-monitoring sites
indicate the source point for estimating the contribution and transport of
nutrients and their loads throughout the watersheds. The ERF1-2 coverage
extends the earlier ERF1 coverage by providing digital-elevation-model
(DEM-based estimates of reach drainage area founded on the 1-kilometer data for
North America (Verdin, 1996; Verdin and Jenson, 1996). A 1-kilometer raster
grid of ERF1-2 projected to Lambert Azimuthal Equal Area, NAD 27 Datum (Snyder,
1987), was merged with the HYDRO1K flow direction data set (Verdin and Jenson,
1996) to generate a DEM-based watershed grid, ERF1_2WS. The watershed
boundaries are maintained in a raster (grid cell) format as well as a vector
(polygon) format for subsequent model analysis. Both the coverage, ERF1-2, and
the grid, ERF1-2WS are available at:
"http://water.usgs.gov/orh/nrwww/sparrow_section5_nolan.pdf". 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 ArcInfo
format, this metadata file may include some ArcInfo-specific terminology.