The graphic below shows the river system of the Trinity Basin color coded by HUC unit. The NHD describes naturally occurring and constructed bodies of water and their paths. The organization of the NHD river system is broken up into two components, features and reaches, with each element having unique common identifier. Features represent hydrographic elements such as paths through water flows and bodies of water. They are each classified by a specific Feature Type, which has its own unique Feature Code.
Features can be either points, lines, or areas.
Groups of features then form reaches. Reaches are composed of hydrographic entities which have similar hydrologic characteristics. Each reach also has a unique identifying reach code. Transport reaches represent the conveyance of water through the river network. Coastline reaches are located along the major coastlines of the United States and they allow for the storage of information necessary to coastlines.