Streams and Waterbodies in Louisiana

The National Hydrography Dataset

This map displays the pattern of different surface water feature types across the
state of Louisiana, 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. No streams in
the state have yet been classified in the ephemeral category (data current as of
October 2009). The map highlights the predominance of intermittent and
ephemeral streams across the state. Of the 103,320 miles of linear streams in
Louisiana, 57 percent (58,458 miles) are intermittent or ephemeral. Seventeen
percent of streams are ditches (17,473 miles), which are not classified by their
flow duration in the dataset.

The water features on the map are from the National Hydrography Dataset (NHD)
at high resolution (1:24,000 scale or higher). 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.

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