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.
The data set ERF1_1 represents the 1:500,000-scale stream data used to create the digital segmented watershed. It was modified from enhancements to the U.S. Environmental Protection Agency's River Reach File 1 to ensure the hydrologic integrity of the digital reach traces and to quantify the time of travel of river reaches and reservoirs [see U.S.EPA (1996) for a description of the original RF1] )(Alexander and Brew, 1996).
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.
Addition of reservoir centerlines: (b) ArcEdit functions were used to create centerlines within the RF1 shoreline boundaries. A separate coverage of the shoreline segments was superpositioned as a backcover in ArcEdit and used as a guide in the manual positioning of the centerlines. The downstream nodes of tributary reaches were moved (using the VERTEX MOVE Arc command) and joined with other tributary nodes to form centerlines. The VERTEX ADD Arc function was applied to centerline reaches in ArcEdit to ensure that the new arcs approximated the thalweg of each reservoir.
[Note the attributes listed in the ERF1_1.AAT file may not be accurate for centerlines because these reaches were created from reservoir tributary reaches.]
Verification of reach connectivity: Using the Arc TRACE function, the connectivity of reaches was determined by navigating upstream from all terminal reaches. Disruptions in navigation resulting from disconnected nodes or, more commonly, improperly oriented arcs were corrected in ArcEdit by joining nodes or "flipping" the arc direction, respectively. To conform with TRACE requirements, from-nodes (FNODE#) were located at the downstream end of each reach and to-nodes (TNODE#) were located at the upstream end of the reaches. This node orientation is maintained in the final version of ERF1.
Fewer than 10 disruptions were detected in navigation in each of the water-resources regions. Additional edits were performed to correct a few instances of circular reaches (identical to- and from-nodes) and inaccurate digital representations of rivers.
Estimation of reach time-of-travel: The reach time-of-travel (RCHTOT) in units of days was computed as the quotient of reach length and reach velocity for reaches with positive values of velocity such that
RCHTOT = C1 * LENGTH / MEANV
where C1 is a conversion factor of 0.00003797, LENGTH is the length in meters of the Arc reach segment, and MEANV is the mean velocity in feet per second. Reaches with missing time-of-travel are assigned a value of zero.
Estimation of reservoir time-of-travel: (a) ERF1 centerlines were digitally associated with the RF1 shoreline digital features and attributes (i.e., reservoir name in PNAME and unique reservoir code in PNMCD) by converting reservoir shoreline segments to polygons and intersecting these polygons with the centerlines in Arc.
(b) These centerline reaches were digitally matched with reservoirs identified in the USGS reservoir file (Ruddy and Hitt, 1990) by linking each reservoir to the nearest centerline within 10 kilometers using the Arc NEAR function. The USGS reservoir file consists of 2,728 reservoirs with normal capacity of at least 5,000 acre-feet or maximum capacities of at least 25,000 acre-feet and that were completed as of January 1, 1988. These reservoirs are digitally represented by points in an Arc coverage [see Web location cited in references for Ruddy and Hitt (1990)].
Manual verfication of reservoir-RF1 reach links were completed by comparing the river and reservoir names in RF1 to those in the USGS reservoir file, and by visual inspection for agreement between the centerlines and reservoir shoreline boundaries.
A total of 815 reservoirs were matched with RF1 shorelines features (350 unmatched RF1 water bodies). Of these 815 reservoirs, there are 19 pairs of reservoirs that match the same RF1 water body (i.e., duplicate PNMCD-RES values in the file ERF1.RESINT), and 2 RF1 water bodies that match the same USGS reservoir RESERVOIR##=1004). Reservoir residence time (i.e., time-of-travel or RESTOT) in units of days was computed for 810 reservoirs with available values of normal capacity and outflow such that
RESTOT = NORMCAP / MEANQ-OUT * C2
where NORMCAP is the normal capacity in acre-feet from the USGS reservoir file, MEANQ-OUT is the mean streamflow for the immediate reach downstream of the reservoir, and C2 is a conversion factor of 0.50416. Reservoirs with missing time-of-travel values are assigned a value of zero.
(c) Remaining reservoirs in the USGS reservoir file were initially matched to RF1 reaches located outside of the RF1 shoreline boundaries using the Arc NEAR criterion of 10 kilometers described previously. Manual verification of links was initially completed by comparing the river names with those in the USGS reservoir file.
An automated graphical display Arc aml was created to allow visual verification and correction of the remaining reservoir-reach links and previous links that were in question. USGS topographic maps were used in combination with the display aml to obtain accurate reservoir-reach matches.
A total of 1,322 reservoirs were matched to 1,245 RF1 reaches external to RF1 shoreline boundaries (RESCODE = 3, 4, or 5). Multiple reservoirs were linked to 67 reaches (2 reaches with 4 reservoirs each; 6 reaches with 3 reservoirs each; and 59 reaches with 2 reservoirs each). Reservoir residence time in units of days (RESTOT) was computed for 1,296 reservoirs with available values of normal capacity and streamflow such that
RESTOT = NORMCAP / MEANQ * C2
where MEANQ is the RF1 reach mean streamflow.
MODEL_R.AAT:
COLUMN ITEM NAME WIDTH OUTPUT TYPE N.DEC ALTERNATE NAME
1 FNODE# 4 5 B -
5 TNODE# 4 5 B -
9 LPOLY# 4 5 B -
13 RPOLY# 4 5 B -
17 LENGTH 4 12 F 3
21 MODEL_R# 4 5 B -
25 MODEL_R-ID 4 5 B -
29 HUC 8 8 C -
37 SEG 3 3 C -
40 RESCODE 4 5 B -
44 ERF1## 4 5 B -
48 OLDERF1## 4 5 B -
52 STAID 15 15 C -
67 MEANQ 4 10 F 2
71 MEANV 4 10 F 2
75 RCHTOT 4 12 F 5
79 RESTOT 4 12 F 3
** REDEFINED ITEMS **
29 RR 11 11 C -
HUC - 8 Digit Hydrologic Unit Code
SEG - EPA RF1 reach segment number
RESCODE - Reservoir type code:
= 0 No reservoir on reach.
= 1 Arc is interior to RF1 shoreline features
for a reservoir with a large length to width ratio.
= 2 Arc is interior to RF1 shoreline features
for a reservoir with a length to width ratio
of approximately one.
= 3 Arc is exterior to RF1 shoreline features; the arc is the
outlet reach for a reservoir with RF1 shorelines but without
interior arcs.
= 4 Arc is exterior to RF1 shoreline features; no shoreline
features are present for this reservoir in RF1 coverage.
ERF1## - New unique reach identifier
values > 9000 and < 80000 are reaches that were split
values > 80000 are shoreline reaches of major estuaries
OLDERF1## - Original unique reach identifier
STAID - USGS streamflow data collection site identification number
MEANQ - Mean streamflow (ft3/sec)
MEANV - Mean velocity (ft/sec)
RCHTOT - Reach time-of-travel (days)
RESTOT - Reservoir time of travel (days)
RR - RF1 river reach code
MODEL_R.NAT:
COLUMN ITEM NAME WIDTH OUTPUT TYPE N.DEC ALTERNATE NAME
1 ARC# 4 5 B -
5 MODEL_R# 4 5 B -
9 MODEL_R-ID 4 5 B -
13 CENTER 4 5 B -
Center = 1, center line node
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 13:02:24 1998