Watershed attributes that are considered to describe nutrient input conditions are included as source variables in the regression equation; the nutrient-source variables to be tested in the SPARROW model for the SAGT area include atmospheric deposition, fertilizer application to farmland, manure from livestock production, permitted wastewater discharge, and land cover. Watershed attributes that are considered to affect rates of nutrient transport from land to water are included in the regression equation as land-to-water transport variables; the nutrient-transport variables to be tested in the SAGT SPARROW model include characteristics of soil, landform, and climate. Channel attributes considered as nutrient transport variables in the SAGT SPARROW model include reach time of travel and reservoir hydraulic loading. Datasets with estimates of each of these attributes for each individual reach or catchment in the reach-catchment network are presented in this report.
The dataset "MRB2_CAT" represents the watersheds that drain to each stream segment in the stream network within the SAGT SPARROW model area. The National Elevation Dataset, resampled to 100 meter cell size, was used to develop elevation derivatives that could be used to create watersheds around each stream segment. The "erf1_spar" streams coverage was burned in to define the flow to each of the streams within the network.
The "MRB2_CAT" dataset, along with the "erf1_spar" dataset, is the foundation for the SPARROW model. Together they define the flow pathways and overland flow to the network for estimating loads and transport within the study area.
The ERF1_2 reach set was further enhanced for the SAGT nutrient SPARROW model by inserting 433 segment boundaries, which was accomplished by splitting 433 reaches into two segments each. The locations of the added boundaries, and thus of the added model computation nodes, correspond with the locations of sites where mean annual nutrient load could be estimated from monitoring data. Methods similar to those used by Brakebill and others (2001) for the Chesapeake Bay SPARROW model were used to create the additional reach segments: (1) load estimation sites were identified on the ERF1_2 stream network; (2) for sites located in the middle of a stream reach, the reach was split at that location; and (3) a unique node and reach was added to the upstream portion of the split reach. The segments added to the ERF1_2 through this procedure were assigned values between 65,747 and 66,462 for the unique reach identifier (the attribute "e2rf1##" or "wshed").
Once the network was defined, the watersheds were created for each segment as follows:
1. Resampled 100m National Elevation Dataset elevation data was merged to create a continuous surface in the study area. NIBBLE command was used to clean up edge nodata areas.
2. AGREE was run to burn in the ERF1_SPAR stream network. Flowdirection and flowaccumulation grids were created.
3. The WATERSHED function was used to create watersheds around each unique segment of the ERF1_SPAR flow network.
4. Drainage areas were checked for each SPARROW model LOAD station to determine if upstream areas were close to recorded drainage area.
28 sites still have da greater than 10% different from LOAD station. This can be for a number of legitimate reasons - primarily because the LOAD station uses the NWIS flow station drainage area for comparison, and that site may or may not be colocated.
5. Check against the ERF1_SPAR stream network to make sure that all stream segments have catchments (watersheds) delineated for them.
11 stream segments do not have catchments delineated. These 11 are:
MRB_ID LENGTH 10689 65.90251 10708 21.40166 10752 42.50294 10751 43.02711 10745 32.05836 10212 39.07375 10703 75.21178 65611 8.41966 10740 46.49769 81233 1231.59392 65516 15.65830Of the 11 stream segments, 10 have lengths less than 100 meters. Because the cell size of the elevation data surface was 100 square meters, the stream segments were not long enough to have a watershed created for them.
E2RF1## LENGTH 10689 65.90251 10708 21.40166 10752 42.50294 10751 43.02711 10745 32.05836 10212 39.07375 10703 75.21178 65611 8.41966 10740 46.49769 81233 1231.59392 65516 15.65830Of the 11 stream segments, 10 have lengths less than 100 meters. Because the cell size of the elevation data surface was 100 square meters, the stream segments were not long enough to have a watershed created for them.
Polygon Attribute Table, MRB2_CAT.PAT:
COLUMN ITEM NAME WIDTH OUTPUT TYPE N.DEC ALTERNATE NAME
1 AREA 8 18 F 5
9 PERIMETER 8 18 F 5
17 MRB2_CAT# 4 5 B -
21 MRB2_CAT-ID 4 5 B -
25 DEMIAREA_RAW 8 18 F 2
33 WSHED 4 8 B -
37 MRB_ID 6 6 I -
43 DEMIAREA 4 9 F 2
Item Name Description
DEMIAREA_RAW Incremental drainage area for a given reach,
based on the cumulative area for each reach's
catchment. In square kilometers.
WSHED Unique identifier for each reach used in the
SPARROW model
MRB_ID Unique identifier for each reach used in the National
SPARROW model - reaches that were edited to split and
add stations have been differentiated by multiplied
the WSHED id by 10.
DEMIAREA Incremental drainage area for a given reach, in square
kilometers. This value is used in the SPARROW model.
May not be equal to the DEMIAREA_RAW field because the
DEMIAREA may be manually adjusted to reflect know
drainage area values that do not match the calculated
values from the GIS analysis.
Any use of trade, product, or firm names is for descriptive purposes only and does not imply endorsement by the U.S. Government.
Generated by mp version 2.8.12 on Mon Aug 10 11:01:08 2009