# NHDFCode

Description:
Reservoir: Reservoir Type = Disposal; Construction Material = Earthen


Description:
Reservoir: Reservoir Type = Disposal; Construction Material = Nonearthen


Description:
Canal/Ditch: Canal/Ditch Type = Aqueduct


Description:
Dam/Weir: Construction Material = Earthen


Description:
Dam/Weir: Construction Material = Nonearthen


Description:
Lake/Pond: Hydrographic Category = Intermittent


Description:
Lake/Pond: Hydrographic Category = Perennial


Description:
Lake/Pond: Hydrographic Category = Intermittent; Stage = High Water Elevation


Description:
Lake/Pond: Hydrographic Category = Intermittent; Stage = Date of Photography


Description:
Lake/Pond: Hydrographic Category = Perennial; Stage = Average Water Elevation


Description:
Lake/Pond: Hydrographic Category = Perennial; Stage = Normal Pool


Description:
Lake/Pond: Hydrographic Category = Perennial; Stage = Date of Photography


Description:
Lake/Pond: Hydrographic Category = Perennial; Stage = Spillway Elevation


Description:
Inundation Area: Inundation Control Status = Not Controlled


Description:
Inundation Area: Inundation Control Status = Controlled


Description:
Inundation Area: Inundation Control Status = Controlled; Stage = Flood Elevation


Description:
Pipeline: Pipeline Type = Aqueduct; Relationship to Surface = At or Near


Description:
Pipeline: Pipeline Type = Aqueduct; Relationship to Surface = Elevated


Description:
Pipeline: Pipeline Type = Aqueduct; Relationship to Surface = Underground


Description:
Pipeline: Pipeline Type = Aqueduct; Relationship to Surface = Underwater


Description:
Pipeline: Pipeline Type = General Case; Relationship to Surface = At or Near


Description:
Pipeline: Pipeline Type = General Case; Relationship to Surface = Elevated


Description:
Pipeline: Pipeline Type = General Case; Relationship to Surface = Underground


Description:
Pipeline: Pipeline Type = General Case; Relationship to Surface = Underwater


Description:
Pipeline: Pipeline Type = Penstock; Relationship to Surface = At or Near


Description:
Pipeline: Pipeline Type = Penstock; Relationship to Surface = Elevated


Description:
Pipeline: Pipeline Type = Penstock; Relationship to Surface = Underground


Description:
Pipeline: Pipeline Type = Penstock; Relationship to Surface = Underwater


Description:
Reservoir: Reservoir Type = Decorative Pool


Description:
Reservoir: Reservoir Type = Tailings Pond; Construction Material = Earthen


Description:
Reservoir: Reservoir Type = Tailings Pond


Description:
Reservoir: Reservoir Type = Swimming Pool


Description:
Reservoir: Reservoir Type = Cooling Pond


Description:
Reservoir: Reservoir Type = Filtration Pond


Description:
Reservoir: Reservoir Type = Settling Pond


Description:
Reservoir: Reservoir Type = Sewage Treatment Pond


Description:
Reservoir: Reservoir Type = Water Storage; Construction Material = Nonearthen


Description:
Reservoir: Reservoir Type = Water Storage; Construction Material = Earthen; Hydrographic Category = Intermittent


Description:
Reservoir: Reservoir Type = Water Storage; Construction Material = Earthen; Hydrographic Category = Perennial


Description:
Reservoir: Reservoir Type = Water Storage


Description:
Reservoir: Construction Material = Earthen


Description:
Reservoir: Construction Material = Nonearthen


Description:
Reservoir: Reservoir Type = Water Storage; Hydrographic Category = Perennial


Description:
Reservoir: Reservoir Type = Evaporator; Construction Material = Earthen


Description:
Rock: Relationship to Surface = Abovewater


Description:
Rock: Relationship to Surface = Underwater


Description:
Special Use Zone: Special Use Zone Type = Dump Site; Operational Status = Operational


Description:
Special Use Zone: Special Use Zone Type = Dump Site; Operational Status = Abandoned


Description:
Special Use Zone: Special Use Zone Type = Spoil Area; Operational Status = Operational


Description:
Special Use Zone: Special Use Zone Type = Spoil Area; Operational Status = Abandoned


Description:
Stream/River: Hydrographic Category = Intermittent


Description:
Stream/River: Hydrographic Category = Perennial


Description:
Sounding Datum Line: Positional Accuracy = Approximate


Description:
Sounding Datum Line: Positional Accuracy = Definite


Description:
Special Use Zone Limit: Positional Accuracy = Definite


Description:
Special Use Zone Limit: Positional Accuracy = Indefinite


# NHDMetadata

ProcessDescription:
Replaced branched and disjoint (disconnected) reaches with linear reaches in NHDFlowline.  This change occurred during the conversion to the geodatabase model.  Each NHDFlowline that was part of a branched or disjoint reach was assigned to a new reach.  The ComID of the NHDFlowline was unchanged   The change information from the old reach to the new reach was captured in the NHDReachCrossReference table.  Each new reach has M values assigned from 0 to 100.


ProcessDescription:
Merged and/or split area features (NHDWaterbody, NHDArea, region.wb, region.lm) and updated associated artificial path WBAreaComID (wb_com_id) values.  This change occurred during the conversion to the geodatabase model.  If adjacent or overlapping area features had identical classifications, including ReachCode where applicable, the features were merged.  If an area feature exceeded 100 sq. km. (25 sq. km. for canal/ditch, stream/river, or submerged stream) and crossed a subbasin boundary, the feature was split at the subbasin boundary.  If any sliver polygons of a size of less than 5 sq. km. adjoined the split features, the slivers were merged back into the larger area feature.  Merged or split area features were assigned a new ComID.


ProcessDescription:
Updated WBAreaComID (WB_COM_ID) on NHDFlowline (route.drain) where the associated area features were assigned new ComIDs from merge or split during the conversion to geodatabase.


ProcessDescription:
Create high-resolution NHD from USGS/WRD hydrography data.  This process started with the acquisition of two sources of  vectors provided by USGS NMD.  Existing 1:24,000-scale USGS  Digital Line Graph data was available.  Feature code attributes  present in the DLG major and minor codes were used to populate a  temporary working coding scheme used by WRD.  For the remaining  quadrangle files, NMD provided unattributed vector data, from  scanned Mylar 1:24,000-scale hydrography separates.  The quads  were then converted into ArcInfo coverages and projected into  the Vermont State Plane coordinate system (VTSP, NAD83, meters).   Having the data in VTSP allowed for the draping of the vector  data with the State of Vermont's projected Digital Raster Graphic  Images (source: USGS).  Quadrangle-based hydro coverages were  then edge-matched, where arcs 12 meters of each other along the  neatline were snapped together if the feature types were the same.   Next, the 12-digit Hydrologic Unit Code (HUC) boundary was  obtained from the State's NRCS office.  The 12-digit HUC coverage  was manually interpreted from USGS, 1:24,000-scale, 7.5'  topographic maps.  The HUC boundary was used to break up the basin  into tiles based on the 12-digit HUCs which defined the basin  boundary.  Paneling the hydrography according to the 12-digit HUCs  allowed for systematic processing using a logical approach and  manageable format.  Where necessary, the HUC boundary was slightly  modified or the hydrography was corrected to completely include or  exclude features that incorrectly overlapped the HUC boundaries.   Substantial alterations to the HUC boundary were confirmed on the  topographic maps (DRGs).  Using available evidence or cartographic  judgement, lines called connectors were added to join features  that were deemed to have flow between each other.  Artificial  paths were digitized on-screen, manually, through 2-D waterbodies  using the waterbody geometry to digitize a centerline through the  features.  Next, arcs from the extracted coverage were grouped in  order to examine the connectivity of the data set for flow  determination.  In some cases it was necessary to correct  digitizing errors.  Next, feature code attributes were assigned  for all arcs which did not already have coding assigned.  Feature  codes were assigned using WRD's coding scheme.  Next, arcs from  the extracted coverages were grouped in order to examine the  connectivity of the data set for flow determination.  The  individual hydro files were then appended back together into one  single hydrography coverage.  All arcs fnode to tnode topology  were corrected to insure all arcs in the network pointed in a  downstream direction.  Last, all WRD feature codes were  transferred over into the NHD fcode scheme, and projected into  the NHD common projection (Albers, NAD83, meters).  Feature codes  (fcodes) were assigned to landmark, network, waterbody features  through a crosswalk that converts DLG-3 attributes to fcodes,  where an fcode is a five digit integer that encodes a set of  feature type characteristics.  Reach codes and associated  attributes were conflated from the 100K NHD data to the 24K  drainage network and 2-D waterbodies.  Several checks were  performed to validate the reach transfer process.  Any reach  codes that could not be maintained are tracked in the Reach  Cross Reference table.  New reaches that do not exist in the  100K data were defined according to reach delineation rules  (See http://nhd.usgs.gov/chapter1/index.html).  New waterbody  reaches were assigned to 2-D lake/pond and reservoir features  that do not exist in the 100K NHD.  New reaches were assigned  reach code values that are sequentially ordered to 2-D and then  1-D reaches.  New 24K reach codes are larger than any existing  100K reach code in the associated Catalog Unit.  Additional  Geographic Names that exist in the Geographic Names Information  System (GNIS) were added to reaches in the 24

AttributeAccuracyreport:
The accuracy of the attributes of the source Digital Line Graph data is estimated to be 98.5 percent. One or more of the following methods were used to test attribute accuracy: manual comparison of the source with hardcopy plots; symbolized display of the digital line graph on an interactive computer graphic system; selected attributes that could not be visually verified on plots or on screen were interactively queried and verified on screen. In addition, software validated feature types and characteristics against a master set of types and characteristics, checked that combinations of types and characteristics were valid, and that types and characteristics were valid for the delineation of the feature. Feature types, characteristics, and other attributes conform to the Standards for National Hydrography Dataset - High Resolution (USGS, 1999) as of the date they were loaded into the database. All names on the 1:24,000-scale reaches were validated against a April 1999 extract from the Geographic Names Information System. The entry and identifier for the names match those in the Geographic Names Information System. The association of each name to reaches has been interactively checked against the April 1999 Geographic Names Information System names extract, however, operator error could in some cases apply a name to a wrong reach.

LogicalConsistencyReport:
Points, nodes, lines, and areas conform to topological rules. Lines intersect only at nodes, and all nodes anchor the ends of lines. Lines do not overshoot or undershoot other lines where they are supposed to meet. There are no duplicate lines. Lines bound areas and lines identify the areas to the left and right of the lines. Gaps and overlaps among areas do not exist. All areas close.

CompletenessReport:
The completeness of the data reflects the published USGS topographic quadrangle, usually supplemented by Digital Orthophoto Quadrangles (DOQs). Features found on the ground may have been eliminated or generalized on the source map because of scale and legibility constraints. In general, streams longer than one mile (approximately 1.6 kilometers) were collected. Most streams that flow from a lake were collected regardless of their length. Only definite channels were collected so not all swamp/marsh features have stream/rivers delineated through them. Lake/ponds 100 feet or greater in the shortest axis were collected. Note, however, that these general rules were applied unevenly among maps during compilation. Transport reaches are defined on nearly all features of type stream/river, canal/ditch, artificial path, and connector. Waterbody reaches are defined on all lake/pond features. Detailed capture conditions are provided for every feature type in the Standards for National Hydrography Dataset - High Resolution (USGS, 1999), available online through  http://mapping.usgs.gov/standards/.

HorizPositionalAccuracyReport:
Statements of horizontal positional accuracy are based on accuracy statements made for U.S. Geological Survey topographic quadrangle maps. These maps were compiled to meet National Map Accuracy Standards. For horizontal accuracy, this standard is met if at least 90 percent of points tested are within 0.02 inch (at map scale) of the true position. Additional offsets to positions may have been introduced where feature density is high to improve the legibility of map symbols. In addition, the digitizing of maps is estimated to contain a horizontal positional error of less than or equal to 0.003 inch standard error (at map scale) in the two component directions relative to the source maps. Visual comparison between the map graphic (including digital scans of the graphic) and plots or digital displays of points, lines, and areas, is used as control to assess the positional accuracy of digital data. Digital map elements along the adjoining edges of data sets are aligned if they are within a 0.02 inch tolerance (at map scale). Features with like dimensionality (for example, features that all are delineated with lines), with or without like characteristics, that are within the tolerance are aligned by moving the features equally to a common point. Features outside the tolerance are not moved; instead, a feature of type connector is added to join the features.

VertPositionalAccuracyReport:
Statements of vertical positional accuracy for elevation of water surfaces are based on accuracy statements made for U.S. Geological Survey topographic  quadrangle maps. These maps were compiled to meet National Map Accuracy  Standards. For vertical accuracy, this standard is met if at least 90 percent  of well-defined points tested are within one-half contour interval of the  correct value. Elevations of water surface printed on the published map meet  this standard; the contour intervals of the maps vary. These elevations were  transcribed into the digital data; the accuracy of this transcription was checked by visual comparison between the data and the map.

MetadataStandardName:
Content Standards For Digital Geospatial Metadata, ver.2

DataSetCredit:
U.S. Geological Survey, in cooperation with U.S. Environmental Protection Agency and U.S. Forest Service


ProcessDescription:
Added flow relationships between subbasins and other updates as appropriate.


ProcessDescription:
Updated GNIS_Name and GNIS_ID to reflect corrections to names data in the Geographic Names Information System.


DataSetCredit:
U.S. Geological Survey in cooperation with U.S. Environmental  Protection Agency

Address:
Mid-Continent Mapping Center - 1400 Independence Road


# NHDSourceCitation

Originator:
U.S. Geological Survey in cooperation with U.S. Environmental  Protection Agency

SourceContribution:
Reach codes and flow direction attributes


Title:
Geographic Names Information System Oracle Database

SourceContribution:
Names for reaches and areal water bodies


Originator:
U.S. Geological Survey (USGS) in cooperation with Natural Resources Conservation Service (NRCS).


SourceCurrentnessReference:
Date the revision process step was completed


# Subbasin

HU_8_Name:
Upper Androscoggin. Maine, New Hampshire.


# Subwatershed

HU_12_Name:
Coaticook River-headwaters to Averill Creek


HU_12_Name:
Clyde River-headwaters to Echo Lake stream


# Watershed

HU_10_Name:
Passumpsic River-headwaters to Moose River


HU_10_Name:
Connecticut River-Johns River to Ammonoosuc River


