The New England SPARROW water-quality model utilizes the 1:100,000-scale NHD stream network as the framework of the SPARROW model. SPARROW is a spatially detailed, statistical model that relates concentrations of phosphorus and nitrogen (nutrients) in streams to pollution sources and watershed characteristics. The NHD stream network is used in conjunction with digital elevation model (DEM) data, to delineate watersheds, called catchments, for each unique NHD stream reach. SPARROW also requires the unique flow relationships found in the NHD to effectively model the downstream transport of nutrients delivered from sources found within each of the reach catchments. Tabular data of New England SPARROW model estimates of nutrient loads, catchment characteristics, and computed stream reach characteristics, can be linked back to the NHD for display and analysis (see DBASE files, n_inc_loads_yields.dbf, n_tot_loads_yields_conc.dbf, p_inc_loads_yields.dbf, and p_tot_loads_yields_conc.dbf).
The source NHD was obtained in an older NHDinARC format and is no longer available. NHDinArc is a set of complex ARC/INFO coverages, containing several feature data models. The framework of the NHD in Arc data model is built upon line and polygon feature classes. Linear stream network features are built upon the ARC/INFO line feature class with the Dynamic Segmentation Model of ARC/INFO (Environmental Systems Research Institute, 1995). The Dynamic Segmentation Model in ARC/INFO allows multiple line features that have similar attributes to be organized into unique linear features built as an ARC/INFO route. Multiple routes comprise a route-system. The original national 1:100,000-scale NHD has three route-systems built upon the underlying line feature class; NHD Route RCH, NHD Route Drain, and NHD Route LM. The NHD route-systems are composed of linear streams, ditches, canals, connectors, and artificial flow paths through 2-dimensional surface water bodies. The Route Drain system contains such attributes as feature types and feature codes, section route ids, and a unique reach code id (rch_com_id) which links the Route Drain system to the Route RCH system. The Route RCH system contains reach attributes such as the stream name, NHD reach code, and the unique numeric reach code id (com_id) used to link the NHD reach code to the Route Drain system and the NHD Rflow table. The NHD Rflow table contains the flow relationship needed for upstream and downstream navigation of the network. The NHD Route LM system is a landmark theme that categorizes certain line features as dams, rapids, or other hydrographic features not classified as part of a linear stream network.
Two-dimensional surface water body features in the source NHD coverage are built as Regions. Regions allow multiple polygons with similar attributes to be identified as one feature. For instance, stream network centerline flow paths divide a lake or pond into two or more polygon features. Regions built upon the polygon feature class allow the multiple polygon features defining a single lake as one region feature.
Because of the complexities of the NHDinArc format, spatial edits were applied to a simplified coverage of the data that lacked these regions. To utilize the NHD and make necessary modifications, the NHD Route Drain network was converted to a line feature class ARC/INFO coverage, named NHDDrain. Attributes in the NHD Route Drain system were carried into the coverage during the route-to-arc conversion in ARC/INFO. Many enhancements, corrections, and modifications were made to NHDDrain based on the methodology described in the Process_Description of this document. Corrections to the flow relationships defined in the NHD Rflow table were performed on the source NHD Rflow table using the source NHD data and the ArcView 3.x NHD Viewer toolkit. The modified NHDDrain arc coverage was then used to create a pseudo NHD-like data model. The NHD Route RCH and NHD Route Drain route-systems were rebuilt from NHDDrain using the arc attributes contained in coverage. Attributes from the original NHD Route RCH route network were transferred into the SPARROW NHD Route RCH network in the NHDDrain coverage. The NHDDrain coverage was renamed NHD, the same name as its source, to mimic the original NHD network data model. The modified NHD coverage contains the Route RCH and Route Drain networks only. No regions, polygons, or the Route LM system exist in the New England SPARROW model version of the NHD. However, the modified NHD data is compatible with the NHD ArcView 3.x Viewer toolkit, and the New England SPARROW Viewer Toolkit built specifically for the SPARROW project.
The New England SPARROW NHD version includes additional attributes not found in the original NHD. The attributes include required stream reach characteristics for SPARROW, such as mean annual streamflow and velocity and were computed during the model development.
The SPARROW NHD data are being made available for use with the New England SPARROW Viewer Toolkit for ArcView 3.(2,2a,3). Linked with corresponding reach catchments, the functionality of the New England modified NHD data and the toolkit will allow display of a selected reach's watershed. The NHD reaches and catchments can be linked with thematic tabular data from the New England SPARROW project for display and query. Related tabular datasets include a reach catchment characteristics database, reach watershed characteristics database, and SPARROW model estimates of nitrogen and phosphorus loadings and concentrations. The SPARROW NHD is not compatible with the ArcView NHD toolkit that is currently (2005) available from the NHD website.
Modifications applied to the SPARROW NHD have been submitted to the national NHD team for synthesis into the national NHD database. New reach codes in the SPARROW NHD were assigned generic reach address codes and are not present in the national NHD database. Because of the alterations of the SPARROW NHD, these data cannot be used as the NHD framework to index water-related data with, if one wishes to have reaches indexed to the national NHD reach code assignments. Outside of the SPARROW application, these data can be used for other hydrologic modeling applications requiring complete stream network connectivity and reach flow relationships.
Richard Moore Hydrologist U.S. Geological Survey Pembroke, NH (603) 226-7825 rmoore@usgs.gov
Certain disconnected reaches in the source NHD were reconnected to the network by digitizing connector reaches or extending existing reaches based on hydrography or topography depicted on USGS 1:24,000-scale Digital Raster Graphics. Some disconnected streams and canal/ditch/pipeline features existent in the source NHD are not included in this New England SPARROW NHD version. Most NHD intermittent stream reaches from the source NHD are also not included in the New England enhanced NHD data. Canadian reaches were added to the NHD stream network for the Connecticut River and St. Lawrence River Basins. Stream reaches in the St. Lawrence River Basin in Canada were digitized with the aid of 1:50,000-scale Canada Natural Resources National Topographic Database vector hydrography. Canadian reaches in the Connecticut River Basin were digitized from 1:100,000-scale USGS Digital Raster Graphic data. Canadian stream reaches were not integrated into the SPARROW NHD for the St. John and St. Croix River Basins.
Many stream reach attributes were not computed for reaches excluded from the SPARROW models. Excluded reaches include those reaches in the Upper St. John and St. Croix River Basins with contributing drainage from Canada. Lake Champlain, Lake Memphremagog and coastal shoreline reaches also do not contain many stream reach attributes as these reaches are not streams and are designated the terminal end reaches of transported nutrients through the network. Reaches less than 30 meters in length may not have had a catchment delineated for them due to the resolution of the catchment grid. Catchments were used to help derive mean annual streamflow, mean annual stream velocity, stream slope, tidal influence, and drainage area, thus without catchments these attributes could not be computed for the reaches. These reaches, with lengths less than 30 meters, were ignored in the New England SPARROW models.
Most intermittent streams were removed from the data to address inconsistent stream densities observed in the NHD files for New England. Inconsistent stream density problems can be traced to the source USGS Digital Line Graph (DLG) data used to create the NHD. Some intermittent streams were left in the data to retain connection of upstream features and retain intermittent features for areas with sparser stream density. Different USGS topographic map series of various source scales (1:24,000, 1:25,000, 1:62,500) were used to create the USGS 1:100,000-scale topographic maps and DLG data in New England. Intermittent streams were removed from NHDDrain by selecting all stream reach arcs coded as intermittent (fcode = 46001). Canal and Pipeline features without flow relationships were also removed from the data.
Disconnected networks were identified using the NHD Viewer Toolkit's "Upstream with Tribs" navigation tool. Many of the isolated networks were connected to the system by extending the isolated network outlet reach to the primary network. Topographic and hydrologic information from DRGs provided the flow path the digitized extension should make. In certain cases, a connector reach was added in place of the extension of a reach, such as when the connection was broken by man-made hydrologic divergences such as culverts through urban areas. Network attribute flow relationships were also updated to reflect the connections. Many isolated singular reaches were removed.
Existing 12-digit Hydrologic Unit watershed divides of the NRCS Watershed Boundary Dataset (WBD) were utilized to help find spatial errors in the NHD. NHD streams that crossed the WBD data were flagged and reviewed to determine if the intersection of the datasets were valid. The valid intersection points are those reaches that transport water from one 12-digit subwatershed to another. In some cases, more than one NHD reach was identified as transporting water to an adjacent subwatershed unit in error. Erroneous network connections were removed and the flow relationship attributes in the NHD.Rflow tables were corrected to reflect these changes. Other NHD connectivity problems were observed and corrected elsewhere within a 12-digit subwatershed unit. Most of these types of errors were found in the data, however it is possible that some still remain.
NHD headwater streams that crossed WBD divides were trimmed back to insure the NHD reaches and associated catchments would conform to the WBD data. Similarly, headwater reach starts were trimmed back if the reach was within a 30-meter distance from a WBD divide. The 30-meter distance was chosen to prevent the NHD streams from removing a section of the divide in the DEM processing to generate catchments.
Reaches were added to the network to provide adequate stream density for those areas lacking representation of stream features in the NHD. The areas lacking NHD stream features were identified by overlay with the NRCS 12-digit subwatershed data. Areas in need of reach additions were identified when a 12-digit subwatershed lacked any NHD linear stream features within the unit. In some cases, the only NHD features within a subwatershed unit belonged to isolated networks and required the addition of new reaches to connect them to the primary network. Reaches were added to the network using hydrologic information from the 1:24,000/1:25,000 digital raster graphics. The added reaches were generalized from the hydrography depicted on the 1:24,000-scale DRGs to match the density of the 1:100,000-scale NHD. Added reach codes and ids are generic and are not registered in the National NHD database system.
New reaches were also added for watersheds with contributing drainage from Canada. These watersheds include parts of the Connecticut River, St. Francois River, and Lake Champlain Basins. For Connecticut River reaches in Canada, the 1:100,000-scale Sherbrooke quadrangle DRG was used as the basis for added reaches. Natural Resources Canada 1:50,000-scale National Topographic Database (NTDB) digital vector hydrography was integrated into the NHD for the Lake Champlain, and St. Francois basins. The NTDB data were generalized to match the stream density of the NHD. Artificial flow paths were digitized through Canadian 2-dimensional water body features. Canadian reaches were not added for the Upper St. John and St. Croix River Basins in Maine because of the lack of existing data required for input to SPARROW.
Shoreline reaches represented in the source NHD linear route systems remain in this SPARROW enhanced version of the NHD; however the unique reach codes and ids for the coastal reaches have been reassigned one unique reach code. For shoreline reaches comprising Long Island Sound, the rch_com_id and rch_code values have been assigned a value of 888888888. For all other Atlantic Ocean coastline reaches, the value is 999999999. SPARROW did not model the coastline reach features. Artificial path reach features within the Great Bay Estuary in New Hampshire were combined to form one reach feature with rch_com_id and rch_code values = 999999998. Reaches in the St. John and St. Croix River Basins with contributing drainage from Canada were not used in the SPARROW model. The affected St. John and St. Croix reaches were reassigned a rch_com_id = 1000 to flag these reaches for the SPARROW model as terminal end reaches. All modified reach codes are generic values and are not part of the national NHD database.
Some NHD reach codes and ids were reassigned generic reach values for NHD features split as a result of added and extended reaches. Added and changed reaches are identified where rch_com_old is not equal to rch_com_id in the NHD route.drain system. Rch_com_id in the route.drain table is the corresponding number to com_id in the route.rch table. The reach ids were renumbered to a simpler numbering schema for use in the SPARROW model. The reassigned reach numbers are found in the database field, SPARROW_ID in the NHD route.rch attribute table.
Reaches added to the network may not contain populated values for all fields in the source NHD data. SPARROW required from the NHD, a reach code from the NHD Route RCH network, and reach flow relationships in the NHD Rflow table. Items such as feature code, feature type, and name were not needed for the SPARROW model. An effort however was made to populate the Feature Code, and Feature Type fields, but the fields are not completely populated for all new reaches.
Estimates of mean annual streamflow were checked with observed historical records from stream-gaging station data for 211 sites. Published drainage areas for 211 stream-gaging stations ranged in size from 0.04 to 9,660 square miles. Estimates of mean annual streamflow at 53 percent of the 211 sites fell within 5% of actual observed measurements. Estimates at 83 percent of the 211 sites fell within 10 percent of observed measurements. 17 percent of the sites had estimates greater than 10 percent difference with observed data, with 7 percent being greater than 15% difference and no higher than 28% difference. The estimate of mean annual streamflow is computed for the furthest downstream end of the reach.
A comparison of velocity estimates to measured velocity data was made using mean-annual flow conditions for five selected (relatively unregulated) New Hampshire stream reaches (Thor Smith, U.S. Geological Survey, written commun., 2002). These comparisons indicate that the velocity estimates may have as much as a 40 percent error. Further comparison of these estimates to RF1 velocity estimates reveal an improvement over the estimates associated with the RF1 stream network. The RF1 is a 1:500,000-scale stream network that includes estimates of velocity for each RF1 reach. The estimate of mean-annual velocity is most accurate at the furthest downstream point of the reach.
Jobson, H.E., 1996, Prediction of traveltime and longitudinal dispersion in rivers and streams: U.S. Geological Survey Water-Resources Investigations Report 96-4013, 69 p.
Since there was limited published information on tidal influence to New England rivers and streams, no thorough evaluation could be made to assess the accuracy of reaches identified as having tidal influence. Tidal influence estimates were based on published mean high tide heights available from the National Oceanic and Atmospheric Administration (NOAA), in conjunction with reach minimum and maximum elevation heights identified using the National Elevation Dataset (NED). Information on tidal influence for the Connecticut River was found from the Connecticut Department of Environmental Protection at <http://dep.state.ct.us/olisp/ramsar/sitedes2.htm#D.%20Hydrology>: The Connecticut River is tidal from the mouth of the Connecticut River to Windsor Locks (60 mile upstream). The SPARROW project-derived estimate for tidal influence of the Connecticut River compared well to the published information available. Along the New England Coast, mean high tide heights vary.