Document ID: EPA-HQ-OW-2015-0174-0050
Agency: epa
Document Type: Supporting & Related Material
Title: 
Posted Date: 2015-09-14T04:00Z

Washington Criteria Rule
Percentage of Washington Waters that Flow into Oregon Waters via the Columbia River 
                              Calculation Summary
                                       
Purpose: Quantify the percent of Washington's fresh waters that could impact the water quality of waters under Oregon's jurisdiction. Waters that flow into Oregon only do so via the Columbia River, which forms the majority of the border between Washington and Oregon.  Since the two states share jurisdiction of the Columbia River, the water quality of tributaries to and portions of the Columbia River under Washington's jurisdiction can influence the water quality of waters under Oregon's jurisdiction.  
Numeric Results:
   * Stream miles that flow from Washington via the Columbia River into Oregon: 145,424 miles
   * Total stream miles in the State of Washington: 241,064 miles
   * Percent of Washington waters that flow into Oregon via the Columbia River: 60.3%
Data Sources:
   * Watershed boundaries in Washington were obtained from USGS Hydrologic Unit Maps, (https://water.usgs.gov/GIS/huc.html);
   * Streams in Washington  were downloaded from USGS National Hydrography Dataset (http://nhd.usgs.gov/wbd.html);
   * Washington State boundary was downloaded from the Washington Department of Ecology (http://www.ecy.wa.gov/services/gis/data/data.htm). This site provided the best most representative layer allowing for separation of land and water features in the state; and
   * Major streams in Washington (http://www.ecy.wa.gov/services/gis/data/data.htm).  The purpose for this layer was as a visual representation of streams and rivers for the map, not an all inclusive layer of streams; the USGS Hydrography Dataset was obtained for that purpose.  
General Steps:
   1. Identify the watersheds within the State of Washington, at the HUC 4 level. The HUC 4 level was used because it is an appropriate size to identify and delineate watersheds in a state the size of Washington.  
   2. Determine which major waterbodies potentially flow into Oregon, such as the Columbia River, the Snake River and any major tributaries. Since the Columbia River forms most of the boundary between the states of Washington and Oregon, streams, rivers and tributaries that flow into the Columbia River will ultimately flow into Oregon;
   3. Identify streams that flow into these major waterbodies;
   4. Limit stream lengths to the State of Washington (i.e., exclude sections of streams outside state boundaries). This was done by clipping the stream datalayer (NHD24Kst_l_wa) with the Washington state boundary shapefile;
   5. Calculate the total length of all streams within the state of Washington, using the clipped stream layer.  This was done in ArcGIS, in the attributes table, using the "calculate geometry" option.  The streams located in the HUC4 watersheds that do not drain into the Columbia River were selected and the total stream lengths were calculated.  The HUC4 watersheds that drain into the Columbia River, including the Columbia River, were selected and the total length of the streams was calculated. 
   6. Calculate a length ratio of the streams, identified in step 5, that flow into the Columbia River to total length of the streams in Washington ( both inclusive of the Columbia River). Due to limitations of GIS, some segments of some streams (<10%) are missing from the calculations.  
Map Illustration of the Data:
Main map of Washington includes: 
   * Major streams and rivers (purple lines);
   * Watersheds that contain rivers and streams that flow into Oregon via the Columbia River (orange watersheds);
   * Waters that do not flow into the Columbia River (yellow watersheds); and
   * Columbia River (teal line).
Inset map includes:
   * Detailed view of the streams and rivers in Washington (dark blue lines); and
   * Columbia River (teal line).