This document provides a description of the standard operating procedure of Basin Analysis. The document was based on a discussion on May 19, 2010 between PSU and NWCC team members at USDA-NRCS-NWCC office.
1. Basic Layers Compilation
NWCC provides the following layers (this step is done for the upper Colorado basin):
* snotel sites shapefile (with elevation in feet or meters)
* active snow course sites shapefile (with elevation in feet or meters)
* forecast points shapefile (with name and the watershed area (acres) the point represents)
2. Identification of Supplemental Layers
NWCC specifies the supplemental layers to be incorporated in the basin analysis. The layers identified include:
* Forest service road shapefile
* NLCD Land cover raster grid (2001)
* Forest canopy density
* (please add to this list if there is any layer you want to use in the basin analysis)
Please note that the following layers are automatically added to the AOIs for basin analysis:
* PRISM precipitation layers (monthly, quarterly, and annual)
* snotel and snow course sites
* DEM and its derivatives (slope, aspect, hillshade, flow direction, flow accumulation)
* AOI boundaries
* Stream channels (the model can generate the shapefile from the flow accumulation raster)
3. BASIN List Compilation
NWCC provides a list of "large watersheds" for the preparation of BAGIS BASINs. The watersheds are identified using the ID and name of the forecast points. The average size of the basins is around 5000 square miles. (Note to
Gus: I created a basin with a size of 60000 sq miles without any issue). The upper Colorado basin has around 10 to 15 BAGIS BASINs.
4. BASIN Creation
PSU creates BAGIS BASINs by delineating rectangular boundaries that encompass the complete watersheds of the identified forecast points. A map showing the BASIN boundaries is submitted to NWCC for review.
5. BASIN Verification
NWCC reviews the BASIN boundaries and identifies AOIs in each BASIN. The AOIs are identified using the ID and name of the forecast points. If PSU is not notified by NWCC, AOIs are delineated for all forecast points in a BASIN.
6. AOI Creation
PSU creates the AOIs. The location of the forecast point (i.e., the pour point of the AOI watershed) is determined based on the maps published on the USGS Water-data site information webpage (http://waterdata.usgs.gov/nwis/si). The area of AOI is verified using the area information published on the same webpage. NWCC might provide additional GIS layers showing reference AOI boundaries. When the AOI delineation is completed, PSU submits a map showing the AOI boundaries and a table of the AOI areas to NWCC for review.
7. AOI Verification
NWCC reviews the AOI boundaries. PSU conducts basin analysis for the delineated AOIs.