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)

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

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.

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.

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.

FFMP Basin Data Set Shapefiles Attributes 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

FFMP Basin Data Set Shapefiles Attributes 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)

FFMP Basin Data Set Shapefiles Attributes 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.

FFMP Basin Data Set Shapefiles Attributes 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).

FFMP Basin Data Set Shapefiles Attributes in ****_aggr_basins p) X_centroid Longitude of the basin centroid q) Y_centroid Latitude of the basin centroid

FFMP Basin Data Set Shapefiles Attributes 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.

FFMP Basin Data Set Shapefiles Attributes 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)

FFMP Basin Data Set Shapefiles Attributes 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)

FFMP Basin Data Set Shapefiles Hydrologic Connectivity Attributes

FFMP Basin Data Set Shapefiles Projection Information Projection: Geographic (lat/lon) Datum: NAD83 Units: Decimal Degrees Spheroid: GRS80

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.

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.

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".

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.

Basic Basin Delineation Procedure Begin with a Digital Elevation Model (DEM) –A digital map of terrain –Gridded or "raster" format Rows & columns of elevations –Integer elevation values

How are DEMs created? Created from various scale maps.... 1: : :250000

A Bunch of Blocks to Represent the Earth

A DEM What the Computer Sees & What You See

Other Views

DEM (90-meter)

Basins Derived from the 90-meter DEM

DEM (30-meter)

Basins Derived from the 30-meter DEM

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

Filtering techniques have been applied to minimize artifacts from the original DEM creation methods. The National Elevation Dataset (NED)

The NED is a dynamic dataset- updates are made when better quality or higher resolution DEMs are available.

NSSL’s 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.

Begin with the USGS 8-Digit Hydrologic Cataloging Units of the U.S. Delineation Methodology

8-digit Hydrologic Unit Code (HUC) basin with a meter buffer. NED tiles covering the buffered area are merged and clipped.

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.

Delineation Methodology Projection Information (CONUS) Projection: Albers Equal Area Datum: NAD 83 Units: Meters Spheroid: GRS1980 Parameters: -1st standard parallel nd standard parallel Central meridian latitude of projection’s origin false easting (meters) false northing (meters)

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. Delineation Methodology

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

Delineation Methodology Flow Direction Grid

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

Delineation Methodology Flow Accumulation Grid

Delineation Methodology 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 mi 2 ) was used to delineate the FFMP basins. Stream Network

Delineation Methodology

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

Basins are delineated to each outflow point. Derived from the flow direction and outflow point grids. Delineation Methodology Catchments

National Basin Delineation Project Related Websites National Basin Delineation Project National Elevation Dataset (NED) Elevation Derivatives for National Applications (EDNA) National Hydrography Dataset (NHD) Pfafstetter Basin Codification System