National Basin Delineation

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National Basin Delineation

• Project Team Ken Howard
• Ami Arthur
• Gina Cox
• Dave Slayter
• Nathan Kuhnert
• Cooperative Institute for Mesoscale
  Meteorological Studies (CIMMS)/
• National Severe Storms Laboratory (NSSL)

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National Basin Delineation

• Project objective
• To delineate flash flood basins using a
  minimum drainage area threshold of 2 mi2 for use
  in the Flash Flood Monitoring and Prediction
  (FFMP) program.

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FFMP Basin Data Set Shapefiles

• / (main directory)
• 1) _orig_basins
• A polygon shapefile of the original small basins
  (before aggregation).
• 2) _aggr_basins
• A polygon shapefile of the aggregated basins
  within the radar coverage area. These are the
  basins for which the FFMP average rainfall values
  are calculated.
• This is one of the two shapefiles required by
  FFMP. Any basin customization should ultimately
  result in a file named _aggr_basins with the
  specific attributes required by FFMP.

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FFMP Basin Data Set Shapefiles

• 3) _str_gen
• A polyline shapefile of the synthetic stream
  lines generated from the DEM.
• 4) _bins
• A point shapefile of the radar bin center points
  with the associated Pfafstetter basin IDs
  (aggregated).
• This is the second shapefile required by FFMP.
• 5) _nhd_rch
• A polyline shapefile of stream lines from the
  National Hydrography Dataset (NHD).
• 6) _reg_nhd
• A polygon shapefile of NHD waterbodies including
  lakes, reservoirs, ponds, and swamps.

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FFMP Basin Data Set Shapefiles

• /custom/
• 1) _ref_basins
• A polygon shapefile of the original basins
  (before aggregation) with the necessary
  hydrologic connectivity attributes for use with
  the AMBER Basin Customization Extension in
  ArcView.
• 2) _ref_sl
• A polyline shapefile of the synthetic stream
  lines (generated from the DEM) with the necessary
  hydrologic connectivity attributes for use with
  the AMBER Basin Customization Extension. There
  is a one-to-one relationship between stream lines
  in this shapefile and basins in the
  _ref_basins shapefile.

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FFMP Basin Data Set ShapefilesAttributes in
_aggr_basins

• a) Pfaf_id
• 13-character Pfafstetter basin ID
• b) Streamname
• Stream name as available from the NHD
• c) Huc
• 8-digit HUC ID
• d) Huc_name
• Name of the 8-digit HUC

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FFMP Basin Data Set ShapefilesAttributes in
_aggr_basins

• e) X-outlet
• Longitude of the basin outlet
• f) Y_outlet
• Latitude of the basin outlet
• g) State
• Two-character state abbreviation (based on basin
  outlet)
• h) CWA
• Three-character county warning area ID (based on
  basin outlet)

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FFMP Basin Data Set ShapefilesAttributes in
_aggr_basins

• i) Countyname
• Name of the county
• j) FIPS
• Five-character FIPS ID
• k) RFC
• Five-character River Forecast Center ID (based on
  basin outlet)
• l) Modified
• Flag to indicate whether a basin has been merged
  with other basins. 0 indicates a basin in its
  original state, 1 indicates a merged basin.

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FFMP Basin Data Set ShapefilesAttributes in
_aggr_basins

• m) Reservoir
• Flag to indicate whether a basin intersects a
  lake or reservoir according to those water bodies
  included in the NHD. 0 indicates no intersection
  with a reservoir, 1 indicates an intersection.
• n) Area_sq_mi
• Basin area in square miles
• o) Flow_acc
• An approximate flow accumulation value (in
  thousands of grid cells).

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FFMP Basin Data Set ShapefilesAttributes in
_aggr_basins

• p) X_centroid
• Longitude of the basin centroid
• q) Y_centroid
• Latitude of the basin centroid

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FFMP Basin Data Set ShapefilesAttributes in
_orig_basins

• The _orig_basins shapefile contains the same
  attributes as the _aggr_basins shapefile,
  with one additional field
• Pfaf_aggr
• Pfafstetter ID of this basin in the
  _aggr_basins shapefile
• In addition, the _orig_basins Pfafstetter ID
  field is named Pfaf_orig to distinguish it from
  the Pfaf_id field in _aggr_basins.

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FFMP Basin Data Set ShapefilesAttributes in
_bins

• a) Azimuth_dg
• Azimuth of the radar bin center point in degrees
• b) Range_km
• Range of the radar bin center point in kilometers
• c) X_coord
• Longitude of the radar bin center point
• d) Y_coord
• Latitude of the radar bin center point
• e) Pfaf_id
• Pfafstetter ID of the associated FFMP basin
  (aggregated)

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FFMP Basin Data Set ShapefilesAttributes in
_ref_sl and _ref_basins

• These two shapefiles have the same attributes as
  the _orig_basins shapefile plus the following
  hydrologic connectivity attributes
• a) Basin_id
• The integer basin ID assigned by the AMBER Basin
  Customization Extension
• b) Parent_id
• The Basin_id of the immediate downstream basin
• c) Length_mi
• Length of the synthetic stream reach in square
  miles
• d) Flow_acc
• Area in square miles of the upstream contributing
  drainage area
• e) Upstream
• The Basin_id of the immediate upstream basin(s)

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FFMP Basin Data Set Shapefiles
Hydrologic Connectivity Attributes
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FFMP Basin Data Set ShapefilesProjection
Information

• Projection Geographic (lat/lon)
• Datum NAD83
• Units Decimal Degrees
• Spheroid GRS80

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FFMP Basin Data Set Shapefiles
The _orig_basins shapefile contains all small
basins in the HUCs covering the area. There is
one stream reach per basin.
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FFMP Basin Data Set Shapefiles
The _aggr_basins shapefile contains
aggregated basins within the radar coverage area.
There may be multiple stream reaches per basin.
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FFMP Basin Data Set Shapefiles
The NHD reach and water body shapefiles are
included for all HUCs covering the area. These
are a good reference for "the real world".
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FFMP Basin Data Set Shapefiles
The _ref_basins and _ref_sl shapefiles
contain the hydrologic connectivity attributes
necessary for use with the AMBER Basin
Customization Extension in ArcView.
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Basic Basin DelineationProcedure

• Begin with a Digital Elevation Model (DEM)
• A digital map of terrain
• Gridded or "raster" format
• Rows columns of elevations
• Integer elevation values

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How are DEMs created?
Created from various scale maps.... 124000 11000
00 1250000
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A Bunch of Blocks to Represent the Earth
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A DEMWhat the Computer Sees What You See
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Other Views
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DEM (90-meter)
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Basins Derived from the 90-meter DEM
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DEM (30-meter)
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Basins Derived from the 30-meter DEM
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The National Elevation Dataset (NED)

• Produced at the USGS EROS Data Center
• A 30-meter resolution seamless mosaic of
  7.5-minute DEMs for the U.S.
• Base DEMs have been edge-matched to ensure there
  are no gaps or missing data

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The National Elevation Dataset (NED)
Filtering techniques have been applied to
minimize artifacts from the original DEM creation
methods.
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The National Elevation Dataset (NED)
The NED is a dynamic dataset-updates are made
when better quality or higher resolution DEMs are
available.
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NSSLs Partnership with the USGS EROS Data Center

• NSSL assisted EROS with the blind pass"
  processing for Stage 1 of their Elevation
  Derivatives for National Applications (EDNA)
  project.
• This involved producing a hydrologically
  conditioned (filled) DEM, flow direction and flow
  accumulation grids, slope, contours, basins, and
  synthetic streams from the NED.
• Access to the NED and basin delineation scripts,
  along with the guidance and expertise of several
  EROS scientists ensured the highest quality basin
  delineation attainable from a blind pass process.

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Begin with the USGS 8-Digit Hydrologic Cataloging
Units of the U.S.
Delineation Methodology
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8-digit Hydrologic Unit Code (HUC) basin with a
25000-meter buffer.
Delineation Methodology
NED tiles covering the buffered area are merged
and clipped.
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Delineation Methodology
The DEM must be projected from Geographic
coordinates to the Albers Equal Area projection
with units in meters. Note Basins should not
be delineated in Geographic coordinates (lat/lon)
because flow direction may be incorrectly derived.
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Delineation Methodology

• Projection Information (CONUS)
• Projection Albers Equal Area
• Datum NAD 83
• Units Meters
• Spheroid GRS1980
• Parameters
• 1st standard parallel 29 30 0.000
• 2nd standard parallel 45 30 0.000
• Central meridian -96 00
  0.000
• latitude of projections origin 23 00 0.000
• false easting (meters) 0.00000
• false northing (meters) 0.00000

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Delineation Methodology

• Filling the DEM
• Sinks in the DEM are filled to remove small
  imperfections in the data.
• A sink is a cell with undefined drainage
  direction (all neighboring cells are higher
  elevations).
• Sinks are filled to a point where water will flow
  out of the cell.
• The pour point is the boundary cell with the
  lowest elevation for the contributing area of a
  sink.

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Delineation Methodology

• Flow Direction
• Derived from the filled DEM
• Each cell flows to a neighboring cell based on
  the steepest slope.

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1
2
4
8
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Delineation Methodology
Flow Direction Grid
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Delineation Methodology
Flow Accumulation

• Note that each grid cell flows into another grid
  cell and so forth.
• One could tally or keep track of the total number
  of grid cells that flow into each downstream
  grid cell.
• This is generally known as a flow accumulation
  data set.
• Grid cells with high flow accumulation values are
  areas of concentrated flow and are identified as
  stream channels according to the specified flow
  accumulation threshold.
• Grid cells with flow accumulation values of zero
  are topographic highs or ridges.

This grid cell has a flow accumulation value of
15.
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Delineation Methodology
Flow Accumulation Grid
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Delineation Methodology
Stream Network

• Derived from the flow accumulation grid.
• Based on the specified minimum flow accumulation
  threshold.
• Cells with flow accumulation greater than the
  threshold are designated as "stream channel"
  cells and will form the stream network.
• A minimum flow accumulation threshold of 5000
  grid cells (1.74 mi2) was used to delineate the
  FFMP basins.

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Delineation Methodology
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Delineation Methodology
Outflow Points

• Outflow points are the cells with the maximum
  flow accumulation along a stream segment.
• Derived from the flow accumulation and stream
  link grids.

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Delineation Methodology
Catchments

• Basins are delineated to each outflow point.
• Derived from the flow direction and outflow point
  grids.

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National Basin Delineation Project Related
Websites

• National Basin Delineation Project
• http//www.nssl.noaa.gov/wrd/wish/basins
• National Elevation Dataset (NED)
• http//ned.usgs.gov
• Elevation Derivatives for National Applications
  (EDNA)
• http//edna.usgs.gov
• National Hydrography Dataset (NHD)
• http//nhd.usgs.gov
• Pfafstetter Basin Codification System
• http//edcdaac.usgs.gov/gtopo30/hydro/P311.html