Digital data sets compiled by the U.S. Geological Survey were used as input for a collection of Spatially Referenced Regressions On Watershed (SPARROW) attributes for the Chesapeake Bay region including parts of Delaware, Maryland, New York, Pennsylvania, Virginia, West Virginia, and the District of Columbia. These regressions use a nonlinear statistical approach to relate nutrient sources and land-surface characteristics to nutrient loads of streams throughout the Chesapeake Bay watershed. A digital segmented-watershed network serves as the primary framework for spatially referencing nutrient-source and land-surface characteristic data within a geographic information system.
Flow direction and flow accumulation generated from a 30-meter cell-size Digital Elevation Model and attributes from 1:500,000-scale stream data were used to generate stream and watershed networks. Spatial data sets representing nutrient inputs of total nitrogen and total phosphorus from the early 1990's were created and compiled from numerous sources. Data include atmospheric deposition, septic systems, point-source locations, land use, land cover, and agricultural sources such as commercial fertilizer and manure. Some land-surface characteristic data sets representing factors that affect the transport of nutrients also were compiled. Data sets include land use, land cover, average-annual precipitation and temperature, slope, hydrogeomorphic regions, 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 SPARROW. Stream-nutrient load estimates for 132 sampling sites representing the early 1990's (103 for total nitrogen and 121 for total phosphorus) serve as the dependent variables for the regressions. These estimates were used to calibrate models of total nitrogen and total phosphorus depicting 1992 land-surface conditions. Examples of model predictions consist of stream-nutrient load and source percentages contributed locally to each stream reach, as well as percentages of the load that reach Chesapeake Bay.
The data set ERF1_2 represents an attributed stream network generated from digital elevation data (USGS NED, 1999) and existing stream information used to support SPARROW for the early 1990's (Version 2.0) in the Chesapeake Bay watershed.
The dataset ERF1_2 was created specifically to enhance the application of SPARROW in the Chesapeake Bay watershed. Generated to represent a stream network comparable in scale and attributes to other modified virsions of the EPA River Reach Files (Alexander and Others, 1999: Brakebill and Preston, 1999), ERF1_2 represents stream channels determined by flow direction and flow accumulation based on 30-m digital elevation data. Watershed boundaries for each stream segment, generated using an automated process, were used to aggregate nutient input and land-surface characteristic information necessary for the SPARROW models.
Revised and updated digital spatial data sets will be created and distributed by the USGS as planned enhancements and applications for SPARROW are completed.
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. Arc/Info specific commands are in
ALL CAPS.
USGS 30-m DEM's were acquired from the National Elevation Data Base
(USGS NED, 1999) for the Chesapeake Bay watershed. The elevation data
was in a .bil format and was converted into an integer GRID using
the Arc/Info IMAGEGRID command. The elevation data was organized
by 4 digit hydrologic units, (0205, 0206, 0207, and 0208. 0205 and
0206 were split into 2 separate units) so there were 6 major
watersheds, (catalog units) in the Chesapeake Bay watershed.
Flow direction was calculated for each hydrologic unit using the
FLOWDIRECTION function. Flow accumulation was then calculated using
the FLOWACCUMULATION function. Using the output GRID from the
FLOWACCUMULATION function, a stream network was generated for
each unit using a threshold of 5,000 upslope cells that flow into
each cell. The number 5,000 was chosen as a threshold because it
yielded the best results in test areas that were comparable to the
desired final scale of 1:500,000, or comparable to the ERF1
(Alexander and others, 1999).
The above processes generated more stream reaches than were
necessary to build a network to support version 2 of SPARROW
in the Chesapeake Bay watershed. A Flag in the dataset
was attributed if the existing stream (Arc) coresponded to a modified
RF1 1:500,000 scale reach (Brakebill and Preston, Modified Stream-
Reach Data, 1999). This "main channel" was then selected out of the
dataset to produce a subset of stream reaches, and the dataset
ERF1_2.
Arc Macro Language (AML) was used to attribute (E2RF1##) for each
stream reach (segment) with the same unique identifier (ERF1##)
that exists in the 1987 (Version I) stream reach file (Brakebill and
Preston, Modified Stream-Reach Data, 1999). For any reach that
contained a sampling location from Version 1, the downstream ERF1##
value was used. Attributing E2RF1## provided a crosswalk,
or a "related item" between the two data sets (ERF1## and E2RF1##).
Attributes of mean flow, mean velocity, hydrologic unit code,
primary stream name, traveltime for reaches with reservoirs, and
stream segment number were transferred to ERF1_2 using RELATE and
CALCULATE.
In earlier reach files (RF1, ERF1, ERF1_1), one ARC was equivalent
to one reach. The process of converting the raster stream network to
a vector coverage exceeded the 500 vertices per arc limitation for
some reaches. Therefore, since the attribute data is reach based, it
was necessary to duplicate some information on an ARC level.
Traveltime estimates were calculated for all ARCS except for
shoreline reaches of an E2RF1## value > 80000.
LRCHTOT = C1 * Length / Velocity
where C1 = .00003797 ft-day/meter-second
traveltime was estimated for shoreline reaches (E2RF1## > 80000)
were calculated based on watershed characteristics and estimated
stream lengths.
An example of one reach represented by multiple arcs would be
reach 4278 (E2RF1## = 4278). Three arcs represent this reach. The
traveltime for the reach is represented in the RCHTOT attribute,
and is duplicated for each ARC record (cover# number). Since time
of travel is a function of length, local traveltime (LRCHTOT)
was also calculated for each ARC. The sum of LRCHTOT for each ARC
with the same reach number (E2RF1##) would give you the time of
travel (RCHTOT) for that reach. Other than having multiple reach
numbers, LRESTOT and TOTLEN are affected by this limitation.
ERF1_2.AAT: Arc Attribute Table
COLUMN ITEM NAME WIDTH OUTPUT TYPE N.DEC
1 FNODE# 4 5 B -
5 TNODE# 4 5 B -
9 LPOLY# 4 5 B -
13 RPOLY# 4 5 B -
17 LENGTH 8 18 F 5
25 ERF1_2# 4 5 B -
29 ERF1_2-ID 4 5 B -
33 ERF1## 4 5 B -
37 E2RF1## 4 5 B -
41 MAINC 1 1 I -
42 STAID 15 15 C -
57 RESTOT 4 12 F 5
61 LRESTOT 4 12 F 5
65 RCHTOT 4 12 F 5
69 LRCHTOT 4 12 F 5
73 TOTLEN 4 12 F 3
77 MEANQ 4 10 F 2
81 MEANV 4 10 F 2
85 TERMFLAG 1 1 I -
86 HUC 8 8 C -
94 SEG 3 3 C -
97 HECTARE 4 12 F 3
101 PNAME 30 30 C -
** REDEFINED ITEMS **
86 RR 11 11 C -
LENGTH - Length of ARC, in map units (meter)
ERF1## - Unique reach identification number from ERF1_1
data set used in Version I, 1987 (Brakebill
and Preston, 1999) Used as relate item to transfer
attributes.
E2RF1## - Unique reach identification number for Version II, 1992.
STAID - USGS station identification number of flow location
RESTOT - Reservoir traveltime (Days)
LRESTOT - Arc Reservoir traveltime (Days)
RCHTOT - Reach traveltime, (Days)
LRCHTOT - Length of arc, in meters
TOTLEN - Total length of reach based on E2RF1## Value (meter)
MEANQ - Mean Flow for reach (E2RF1##) from ERF1_1, ft3/sec
MEANV - Mean Velocity for reach (E2RF1##) from Erf1_1, ft/sec
TERMFLAG - Terminal Reach Flag, 1 = Terminal Reach
HUC - 8 digit USGS Hydrologic Unit Code
SEG - EPA River Reach Segment number
HECTARE - Area of watershed for reach (E2RF1##) in hectares
PNAME - Primary stream name
RR - River reach file, redefined from Huc & Seg
** A reach represents any arc(s) with the same value of E2RF1##.
ERF1##, RESTOT, MEANQ, MEANV, HUC, SEG, PNAME, and RR were added from
the ERF1_1 data set (Brakebill and Preston, Modified Stream
Network, 1999). RCHTOT was re-calculated based on total length of
reach (TOTLEN).
.00003797 * LENGTH / MEANV
ft-day/meter-second * Meter / ft/second = DAYS
MAINC.NAT:
COLUMN ITEM NAME WIDTH OUTPUT TYPE N.DEC
1 ARC# 4 5 B Associated Arc ID
5 MAINC# 4 5 B Internal ID
9 MAINC-ID 4 5 B User defined ID
13 STAID 15 15 C Same as above
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 version 2.2.5 on Tue Mar 13 14:05:23 2001