The New Hampshire Hydrography Dataset (NHHD) is a feature-based database that
interconnects and uniquely identifies the stream segments or reaches that
make up the state's surface water drainage system. The NHHD, developed at
1:24,000 scale, is an extract from the high-resolution National Hydrography
Dataset (NHD) housed at the US Geological Survey.
The NHHD Shapefile Extract contains the NHDFlowline, NHDWaterbody and NHDArea feature
classes from the original NHHD geodatabase. These shapefiles cover the extent of the
sixteen cataloging units that intersect the State of NH, and contain reach codes for
networked features, stream order, flow direction, names, and centerline representations
for areal water bodies. Reaches are also defined on waterbodies and the approximate
shorelines of the the Atlantic Ocean. However, because this data is no longer contained
in the original geodatabase, the networking capabilities of the NHDFlowline has been lost.
These data may be used to construct municipal, regional or statewide base maps.
Attribute definitions may be found in the file, NHHD_Geodatabase.pdf. This file was
obtained from the USGS National Hydrography Dataset website.
Currentness_Reference: publication date
Maintenance_and_Update_Frequency: None planned
Theme_Keyword: Surface Water
Theme_Keyword: Artificial Paths
Theme_Keyword: Transport Arcs
Theme_Keyword: Reach Codes
Theme_Keyword: Stream Orders
Place_Keyword: United States
Place_Keyword: New England
Place_Keyword: New Hampshire
Stream order as determined by the Strahler method is dependent upon the scale and accuracy of the
hydrographic network that is being ordered. The primary data source for assigning stream orders
to the 1:24,000-scale vector flowlines was the USGS digital line graphs (DLGs), representing blue
line features on the 1:24,000-scale topographic maps. Given the acknowledged inaccuracies in the
attribution of intermittent versus perennial hydrographic features as depicted on these maps, all
blue line features were included as part of the drainage network and subject to ordering. This
approach is consistent with the Strahler method as originally proposed. However, some of these data
were subsequently modified in an attempt to account for known differences in drainage density in
limited areas of the state where density differences could reasonably be attributed to cartographic
representation by the DLGs and not physical differences in geology and/or hydrology. Specifically,
areas where DLGs were digitized from provisional 1:25,000-scale 7.5x15-minute metric source maps
exhibited a significantly higher drainage density than contiguous areas. Strahler stream order is
very sensitive to drainage density and the overall consistency with which blue line features are
defined and mapped. To enforce consistency in drainage density in those areas with provisional map
coverage, the drainage network was systematically “pruned” based on an empirical upstream drainage
area threshold value that was representative of the initiation points (network starts) of blue line
features in neighboring areas. Ordering was performed on the “pruned” network in these areas. The
resulting order values represent the best characterization possible given the limitations in the
currency, accuracy and resolution of the source data, and serve the expressed goal of providing a
meaningful parameter that can support hydrologic assessments of relative stream discharge and
classifications of channel geometry.
The 1:24,000-scale flowline network has not been subject to rigorous ground-truthing and, therefore, is
subject to significant errors of omission, inclusion, and connectivity. Users of these data should be
aware that any such error has the potential to significantly affect the stream order of downstream reaches.
Furthermore, errors in the network have been discovered since the ordering was completed and additional
errors are likely to be identified over time as more and more users with local hydrographic knowledge
reference the dataset. The vector flowlines will be revised accordingly, but no plan exists to maintain
the associated stream order attributes to be consistent with modified geometry. Significant differences
exist between stream orders as assigned in this dataset and those assigned in an earlier version (1995) by
the NH Office of State Planning (now the Office of Energy and Planning). Users should carefully consider
their objectives when deciding which dataset to reference, given that some limitations apply in both cases.
An understanding of the specific data sources and methods, as documented above and in the accompanying
metadata records, is critical for appropriate application of the stream order dataset.
Contact_Organization: Complex Systems Research Center, University of New Hampshire
One or more of the following methods were used to test
attribute accuracy of the source USGS Digital Line Graph
data: 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 (FCODEs) 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 (USGS, 1999) as of the date they were loaded
into the database. All names were validated against a current
extract from the Geographic Names Information System (GNIS). The
entry and identifier for the names match those in the GNIS. The
association of each name to reaches has been interactively checked,
however, operator error could in some cases apply a name to a wrong
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.
Data is complete for the hydrologic cataloging unit.
The completeness of the data reflects the content of the source (the
published USGS topographic quadrangles). The USGS topographic quadrangle is
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 having an area greater
than 6 acres were collected. Note, however, that these general rules were
applied unevenly among maps during compilation. Reach codes are defined on
all features of type stream/river, canal/ditch, artificial path, coastline,
and connector. Waterbody reach codes are defined on all lake/pond and most
reservoir features. Names were applied from the GNIS database. Detailed
capture conditions are provided for every feature type in the Standards for
National Hydrography Dataset available online through
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.
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.
DLG files were converted to ArcInfo coverages and projected
to the New Hampshire State Plane coordinate system
(NHSP NAD83 Feet). Attributes were standardized to ensure
consistent number of MAJOR/MINOR pairs. Attributes were
also verified, using one or more of the following methods:
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. The DLG coverages were edgematched
using a 40 foot snapping tolerance. Features outside the
tolerance were not moved; instead, a feature of type connector
was added to join the features.
Using a suite of tools provided by the USGS, the DLG quads for
each 11-digit CU were paneled into one coverage and arcs within
40 feet of each other along the neatline were again snapped
together if the feature types were the same. Next, the 11-digit
Hydrologic Unit Code (HUC) boundary was used to extract features
from the paneled coverage that fell within the boundary. Next,
arcs from the extracted coverage 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 contour
lines from the New Hampshire Digital Raster Graphics, lines called
connectors were added to join features that were deemed to have
flow between each other. All arcs were directed downstream and
the nodes were prepared to help create artificial paths through
2-D waterbodies and 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. The data was then appended to conform to the 8-digit
CU boundaries. Feature codes (fcodes) were assigned to network
and 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. At ths point, all
spatial and attribute data were QC'd by staff at both CSRC and the
NH Department of Environmental Services.
Then, 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
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 waterbody features were also added.
Due to a higher feature density resulting from a smaller mapping
scale in Southwest NH and the White Mountain National Forest, the
stream network generated from pre-conflation in these areas was
"pruned" prior to the stream ordering process. This was
accomplished through the following steps using ArcInfo and Grid tools:
- Burned the stream network into a Digital Elevation Model.
- Ran the FLOW ACCUMULATION command using a threshold value that
produced a rasterized stream network matching the 1:24000 scale
stream density representative of the majority of the state.
- The grid resulting from the FLOW ACCUMULATION was visually compared
to the stream network in the high density areas to determine which streams
would not receive a stream order. Streams that were not to be ordered
were retained in the data, but were "pruned" by assigning a flag value.
Using the Strahler method, stream orders were manually assigned to the
"pruned" pre-conflation data using ArcEdit tools. The following
additional rules were applied to the stream ordering process:
- Artificial paths in lakes and reservoirs received the value of the
outflowing stream. The out flowing stream (and artificial paths) were
coded one order higher if two streams of the same order flowed into the
- Divergent paths received the order of the stream immediately upstream
from the divergent path. Stream order only increased if a tributary of
higher or equal order flowed into a divergent path.
- Features that did not receive a stream order were "pruned" streams,
coastline arcs and pipelines.
- Streams that originate in tidal wetlands were coded as first order streams.
Stream orders were QC'd by staff at CSRC and NHDES.
Once the NHD was certified and downloaded from USGS, the streams orders
were spatially joined and transferred to the NHDFlowline feature class.
However, due to spatial edits to the NHD during the conflation process,
the stream order data required editing to spatially match the NHD before
the attribute could be transferred. Modifications were made in ArcGIS,
using standard editing tools.
The NHDFlowline, NHDWaterbody and NHDArea feature classes were extracted
from each geodatabase and mosaicked into a statewide dataset in ArcSDE.
These feature classes were then exported back out of ArcSDE into shapefiles.
Grid_Coordinate_System_Name: State Plane Coordinate System 1983
Enumerated_Domain_Value_Definition: "pruned" - no stream order
Enumerated_Domain_Value_Definition_Source: CSRC/NHDES (see process steps)
The information encoded about the NHHD Shapefile Extract includes a
feature date, classification by type, a unique common identifier and
the feature length or area. For reaches, encoded information includes a
reach code. Names and their identifiers in the Geographic Names Information
System are assigned to most feature types. Attribute definitions can be
found in the file, NHHD_Geodatabase.pdf.
Contact_Organization: Complex Systems Research Center, University of New Hampshire
Contact_Person: GRANIT Database Manager
Contact_Position: GRANIT Database Manager
Address_Type: mailing and physical address
Address: Morse Hall, University of New Hampshire
Hours_of_Service: 8:30AM-5PM. EST
Resource_Description: Downloadable Data
Digital data in NH GRANIT represent the efforts of the
contributing agencies to record information from the cited
source materials. Complex Systems Research Center, under
contract to the NH Office of Energy and Planning, and in
consultation with cooperating agencies, maintains a
continuing program to identify and correct errors in these
data. OEP, CSRC, and the cooperating agencies make no claim
as to the validity or reliability or to any implied uses of