300 Miles 75 150 Miles Alaska Streams and Waterbodies in the United States The National Hydrography Dataset, High Resolution This map displays the pattern of different surface water feature types across the country, including perennial, intermittent and ephemeral streams. Perennial streams generally contain water throughout the year, except for periods of extreme drought. Intermittent streams contain water for only part of the year, while ephemeral streams flow only in response to precipitation events. Although the intermittent and ephemeral stream classifications are distinguished from each other in the dataset, many ephemeral streams are included in the "intermittent" category. In addition, some ephemeral streams in the Southwest have been classified as washes. Only recently, and mainly on U.S. Forest Service land, have streams been added to the dataset under the "ephemeral" category, so very few streams are indicated as such. The map highlights the predominance of intermittent and ephemeral streams across the country. Of the 7,339,124 miles of linear streams in the U.S. (including Puerto Rico), 77 percent (5,661,337 miles) are intermittent or ephemeral. Five percent of streams are ditches (348,674 miles), which are not classified by their flow duration in the dataset. i------- v. ^ :/ , J ; \ ^ ¦ r * \s» V / ' / ¦> ; A ¦ v This map relies exclusively on USGS data for mapping water resources such as streams and other waterbodies. Due to the resolution of the map, it does not distinguish effectively between land and water and thus makes waters appear more prevalent than is actual. This map does not depict the scope of waters protected under the Clean Water Act or the scope of waters that would be protected under the Army/EPA proposed rule. This map has not been used for any regulatory purpose. SURFACE WATER FEATURES ~ STREAM/RIVER - PERENNIAL ~ STREAM/RIVER - INTERMITTENT ¦ STREAM/RIVER - EPHEMERAL ~ STREAM/RIVER - UNCLASSIFIED EI CANAL/DITCH ¦ LAKE/POND OR RESERVOIR ~ SWAMP/MARSH ¦ PLAYA ~ WASH Prepared by INDUS Corporation under contract with U.S. Environmental Protection Agency Office of Water - Washington, DC October 2013 The water features on the map are from the National Hydrography Dataset (NHD) at high resolution (1:24,000 scale or higher) (data current as of October 2009). Alaska is mapped at the 1:63,360 scale. Many smaller waters are not included in the NHD because they could not be detected on the original aerial photos used to create the dataset or were excluded from the maps from which the dataset originates. The majority of perennial and most intermittent streams are captured at this resolution. However, most ephemeral streams are not captured unless they are in the arid west. Additional information on the NHD can be obtained from the NHD website at https://nhd.usgs.gov. ^EDST"^ HU8GS (m) science for a changing world A/^L Pfj0le0<> EZ STATE BOUNDARY 0 25 50 Miles \4*?t Puerto Rico ------- |