Louisiana hydrologic atlas map no. 1: Mean annual runoff in Louisiana
The map shows the mean annual runoff from drainage basins in Louisiana exclusive of those in the coastal zone and the alluvial valleys of the Mississippi, Ouachita, and Red Rivers. The mean annual runoff for the State of Louisiana varies from 0.7 (cu ft/s)/sq mi in the Sabine and Red River basins to >2.0 (cu ft/s)/sq mi in the upper reaches of the Mermentau River. Factors that account for the three-fold variation in runoff across Louisiana include regional differences in rainfall, varying physical characteristics of the land, and differing land use patterns. The mean annual runoff was determined on the basis of continuing measurements of stage and discharge of uncontrolled streams. The periods of record from the 88 stations shown on the map vary from 5 to 25 yr. The 88 stations were grouped into seven categories of runoff. The boundaries for each region generally correspond to drainage boundaries or physiographic boundaries.