# 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 the Maine Office of GIS hydrography  data, which has historically been stored and managed by 1:24,000-scale  quadrangles and ArcInfo Librarian.  ArcInfo Librarian was used to  extract the hydrography library layers (streams, ponds, rivers, and  coast), append the tiles together, and merge like polygon features  together.  The 8-digit Hydrologic Unit Code (HUC) boundary was obtained  from the State NRCS office to clip features from the paneled coverage  that fell partially or entirely within the boundary.  Where necessary,  the HUC boundary was slightly modified to completely include or exclude  features that incorrectly overlapped the boundary.  Substantial  alterations to the HUC boundary were confirmed on the topographic  maps and with NRCS.  DRGCLIPs and MEDOQs were used as a reference to  revise the current hydrography data by edge matching between quads and digitizing photo-revised features.  Features were modified to the DRGCLIPs and MEDOQs only where compelling evidence of change existed.   The National Wetlands Inventory (NWI) was used to confirm connectors  through wetlands with none of the existing NWI linework being  incorporated into the NHD data.  Arcs from the extracted coverages  were grouped in order to examine the connectivity of the dataset for  flow determination.  In some cases it was necessary to correct  digitizing errors.  Using available evidence or cartographic judgment,  lines called connectors were added to join features that were deemed  to have flow between each other.  These features are coded with the feature type of connector.  All arcs were directed downstream and the nodes were prepared to help create artificial paths through 2-D water bodies to complete the flow through the hydrography network.  The artificial path coverage was combined with the single line stream network to create the drainage network.  The drainage network was grouped again, and each group was directed downstream.  Feature codes (fcodes) were assigned to landmark, network,  waterbody features through a crosswalk that converts 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 24K dataset.  Names for the 24K drainage network  were interactively transferred from the vector GNIS coverage.   Additional GNIS names for point and waterbody features were also  added.

AttributeAccuracyreport:
Attribute accuracy was tested by visual comparison of the source or symbolized display of digital files.  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  June 2002 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 June 2002 Geographic Names Information System  names extract, however, operator error could in some cases  apply a name to a wrong reach.  Please report errors to either  the Maine Office of GIS or USGS.

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 amoung areas do not exist.  All areas close.  Spatial topology meets the Maine Office of GIS Data  Standards.  Label errors and node errors have been resolved.   Spatial topology is clean and free of errors.  The coverage was  built with polygon topology.

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:
Approximate horizontal accuracy is 12 meters, assuming source data meets 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.  The data  retains the edge-matching discrepancies existing in the source.

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

DataSetCredit:
U.S. Geological Survey, in cooperation with U.S. Environmental Protection Agency and Maine Office of Geographic Information Systems

Address:
Mid-Continent Mapping Center - 1400 Independence Road


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


ProcessDescription:
1:100,000 scale medium-resolution stream gage shapefiles obtained from the U.S. Geological Survey Nation Water Information System and 1:24,000 scale high-resolution watercourse digital data sets collected by the U.S. Geological Survey, National Geospatial Technical Operations Centers (NGTOC), were used to linear reference the medium resolution 0d stream gages to the corresponding high-resolution watercourse geometry.  Quality Assurance was preformed to guarantee that each gage was properly indexed to the watercourse geometry and that the correct spatial address and location on the network were obtained.  The position of the high-resolution gages was not further enhanced based on 1:24,000 scale sources such as DRGs or DOQs.


ProcessDescription:
Create high-resolution NHD Dam features and events from the National Inventory of Dams by snapping NID position to the appropriate position on the appropriate NHDFlowline and obtaining the network address.  Since dams are located on the network, they may be offset from the actual physical position.  Dams that cannot be logically associated with a NHDFlowline are not included.  Dams under a size threshold of 2,400 acre-feet normal storage capacity are generally not included

DataSetCredit:
U.S. Geological Survey, National Geospatial Technical Operations Center

Address:
U.S. Geological Survey, National Technical Operations Center, P.O. Box 25046


Address:
U.S. Geological Survey, National Geospatial Technical Operations Center, P.O. Box 25046


ProcessDescription:
Update GNIS ids and names to match the current GNIS ids/names.


ProcessDescription:
NHD High Resolution Maintenance Lite II by Sub Region.  Procedures include the following: Topology is checked for:  NHDWaterbodys must not overlap; NHDWaterbody must not overlap NHDArea; and NHDAreas must not overlap. Check all reaches to ensure that they have MValues (measures). Remove branched GNIS names. Check entire extent of GNIS name for gaps. Check all WBAreaComIDs and correct or add as necessary. Check all coastlines (coincident with 2D features) and correct as necessary. Extract transactional updates (XML) from updated personal geodatabase and load updates into original personal geodatabase for final transaction review. Re-check data integrity based on previous Sub Region Maintenance Lite.

Address:
U.S. Geological Survey, National Geospatial Technical Operations Center, 1400 Independence Road


ProcessDescription:
Updated major areal (2-D) features to match current 2008 NAIP imagery. Added lake/ponds 500,000 sq meters or larger. Water surface elevations are not collected on new lake/ponds.  The shoreline for these lake/ponds is date of photography. Modified position of lake/ponds; greater than 1.0 sq km, that do not have a value for elevation in the data, if the shorelines were off by more than 500 ft.  Lake/ponds that have controlled water levels, indicated in the data by a value for “elevation” and “stage”, are not modified.  The elevation represents and average water level for the lake/pond and that elevation is maintained as the most common position of the shoreline over the years. Realigned areal (2-D) stream/rivers; greater than 100 ft wide, when the position of the banks had moved more than 1000 ft.  These areal stream/rivers were corrected to within 200 ft of the image.  If necessary, artificial paths and/or 1-D stream/rivers that were related to or in proximity to the revised 2-D features were edited to maintain flow and conform to the rules of the National Hydrography Dataset (NHD).  These updates were completed by USGS personnel as part of a national update program begun in 2009 to help align prominent features with the orthoimages being used for US Topo product.  After the 2-D features were modified, the standard QA/QC checks were run and any errors were corrected as part of this process.  This QA/QC step generally checks the flow network and topology of the dataset.  The most common edits are for flowlines with incorrect flow direction, invalid WBComIds on Artificial Paths and reach delineation problems.


ProcessDescription:
Maintenance of known errors to the NHD using 2009 NAIP imagery. Maintenanace includes the change in attribution and geometry of connectors, reservoirs, and other flowlines and waterbodies as reported by user input. Some additional flowlines added from internal databases.

DataSetCredit:
New Hampshire Geological Survey/New Hampshire Department of Environmental Services


# NHDSourceCitation

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) and  Maine Office of GIS (MEGIS)


SourceCurrentnessReference:
Date the revision process step was completed


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

SourceContribution:
Reach codes and flow direction attributes


# NHDFCode

Description:
Underground Conduit: Positional Accuracy = Definite


Description:
Underground Conduit: Positional Accuracy = Indefinite


Description:
Underground Conduit: Positional Accuracy = Approximate


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


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


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


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


Description:
Swamp/Marsh: Hydrographic Category = Intermittent


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:
Swamp/Marsh: Hydrographic Category = Perennial


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


Description:
Stream/River: Hydrographic Category = Ephemeral


Description:
Canal Ditch: Canal Ditch Type = Stormwater


# NHDPointEventFC

Source_DataDesc:
National Water Information System (NWIS)


