Ground Water and Geologic Structure of Natchitoches Area, Louisiana

Abstract

The municipal water supply of the city of Natchitoches has been obtained for many years from shallow wells screened in fine-grained sands of the Wilcox formation. These sands have been over-developed and the supply of water stored in the sands has been depleted gradually as the recharge from rainfall has failed year by year to equal the withdrawals by wells. An exploratory program designed to locate an adequate supply of ground water was initiated in the fall of 1943 by the City of Natchitoches. This program, directed by the Geological Survey, United States Department of the Interior, included the drilling, electric logging, and testing of nine exploratory wells which penetrated water sands of the Sparta sand and of the Wilcox formation. Geological and hydrological data obtained from the test drilling suggest that the city of Natchitoches may be situated on a downthrown fault block defined on the southwest by a fault along Youngs Bayou and on the southeast by a fault extending from Old River toward Cane River Lake. Salt water, unlike connate sea water in composition, is present in the sands underlying most of the city. A similarity of topographic, geologic, and hydrologic conditions in this area to those in salt-dome areas in near-by parishes is evident. Southwest of the city, abundant supplies of soft water were found in the Sparta sand and in the sands of the Wilcox formation. These sands crop out in a narrow band extending from Natchitoches into Texas, and generally yield moderately large quantities of potable water in the areas immediately south of their outcrops. A supply of at least 1,000,000 gallons a day for the city of Natchitoches may be obtained from three to five properly developed supply wells in Secs. 10, 56, and 57, T. 8 N., R. 7 W. Additional water for increased needs of the future may be provided by extending this well field toward the west.