an oxbow lake formed from a cutoff of the Mississippi River in northeastern Louisiana, is a popular recreational lake widely used for water-based activities such as water skiing, fishing, boating, and swimming. Lake Bruin is a source of drinking water for several small communities surrounding the lake. The following amounts of water were withdrawn from the lake during 1994: the Newellton Water System, 0.25 Mgal/d (million gallons per day); the Lake Bruin Water System, 0.038 Mgal/d; and the Tensas Water Distribution Association, 0.281 Mgal/d (P.M. Johnson-Thibaut, U.S. Geological Survey, written commun., 1998). An understanding of current hydrologic conditions of Lake Bruin and other lakes and reservoirs in Louisiana is essential to the management and protection of these valuable natural resources. Water quality and quantity are important concerns to those who use the lakes for municipal, recreational, agricultural, or industrial purposes. Current and accurate information regarding the physical and chemical-related properties and conditions of freshwater lakes in Louisiana is fundamental to planners and managers for evaluating these resources. In October 1996, the U.S. Geological Survey, in cooperation with the Louisiana Department of Transportation and Development, began a study to conduct a bathymetric survey and determine the physical and chemicalrelated properties of Lake Bruin.The purpose of this report is to present the results of the bathymetric survey and the results of vertical profiles of physical and chemical-related properties, including depth, water temperature, dissolved oxygen, specific conductance, and pH, which were measured at three sites on the lake. Hydrographic surveying software was used for combining differential global positioning system (DGPS) information with digital survey fathometer data to accurately map the bathymetry of the lake. The bathymetric map was produced using geographic information systems (GIS), and contour lines were reviewed and edited for accuracy and consistency. On-site physical and chemical-related properties were measured at the three strategic locations using a water-quality sampler. This report is one in a series of planned map reports describing current bathymetry and physical and chemical-related properties of lakes and reservoirs in Louisiana.
Description of Study AreaLake Bruin ( fig. 1) Lake Bruin has a drainage area of 21.4 square miles, and receives some inflow from a canal that drains Big Pond and from Bayou Bruin, both entering at the western end of the lake at the shallow slough Brushy Lake. The lake level is controlled by a structure on Routh Ditch at U.S. Highway 65; the crest elevation is 61.00 feet above sea level. Neither the Mississippi River nor ground water appear to be a source of water to the lake, and fluctuations in lake level are closely associated with rainfall and runoff (Demas,