4.1.12.B+pd.2

There are a few levels of of watershed divisions in the united states. The first level is divided into 21 divided regions. All of these divisions drain into a main water source, such as a river, and then into a an even bigger water source. After the 21 major divisions there are 221 subregions. A subregion involves the area drained into the river. All of the streams and tributaries that drain into a certain river are involved in that subregion as well. The third level of divisions are the 378 hydrologic accounting units. After the accounting units come the 2264 cataloging units. All watersheds are included in a hydrologic unit. There is no set size for the regions that are divided. They just need to be able to fit the requirements of a watershed, which would most importantly be that it drains into one area or body of water(Hydrologic Unit Geology 2006)
 * Watershed Relationships in the United States**



__Water-resources regions of the ____United States ____(U.S. Geological Survey, 1982) __. USGS Diagram. USGS. __usgs.gov__. 16 May 2008  <[|http://water.usgs.gov/‌wsi/‌images/‌water_resources_regions.gif>.]

[|national watersheds] 4.1 Watersheds pd2