variety of natural environments. The natural hydrology of the basin is affected by the operation of five U.S. Army Corps of Engineers navigation locks and control structures, which control the impoundment of winter runoff for irrigation use in the summertime. This helps maintain a freshwater reservoir for agricultural use while preserving the basin’s sensitive environments from the detrimental effects of saltwater intrusion from the Gulf (US Army Corps of Engineers, n.d.). The Vermilion-Teche basin’s drainage area covers approximately 4,047 square miles. Land cover types within the basin range from the upland pine forests, northwest of Alexandria, to agriculture lands consisting primarily of corn and soybeans, in its northern portion, and rice and sugarcane in its central and southern portion (Baker, 1988). The coastal zone is mostly freshwater marsh from Bayou Cypremort eastward to Bayou Sale. Intermediate and brackish marsh occupy the entire coastal zone west of Bayou Cypremort with small areas of salt marsh (Baker, 1988). Bayou Teche and the Vermillion River were historically supplied with fresh water from the Atchafalaya River via Bayou Courtableu. A system of flood protection levees, constructed by the U.S. Army Corps of Engineers to parallel the Atchafalaya River after the major flood of 1927, severed this connection. Water from the Atchafalaya River is currently diverted into the Vermilion-Teche River Basin through the Bayou Teche water project. Authorized by the Flood Control Act of 1966, this structure allows the diversion of supplemental fresh water from the Atchafalaya River upstream of Krotz Springs to the head of Bayou Teche at Port Barre. The supplemental fresh water is distributed among Bayou Teche, the Vermilion River, and the west side borrow pit along the Atchafalaya basin protection levee for municipal, industrial, irrigation, and waterquality control uses (Lester et al., 2005). The Vermillion River Basin covers approximately 1,836 square miles and the Bayou Teche Basin covers approximately 2,211 square miles. The hydrology of the Vermilion River is affected by the geographic features of the basin, the diversion of water from other river basins into the river, the physical characteristics and configuration of drainage channels, and the actions of tides and winds. The river is a coastal stream that flows through the relict deltaic deposits of the Atchafalaya and Red Rivers. Interest in the hydrology of the Vermilion River stems partially from the prevalent use of the streamflow as a water resource and the inadequacy of the river to provide that resource. Water availability for rice irrigation and the dilution of effluents are the major concerns in the Vermilion River basin (Baker, 1988).
Water Balance Results Overall, the water budget shows a surplus of total water resources (including surface and groundwater) of 8,838,203 acre-feet/year, or about 45.4% of the total water input to the study area (Table 10). Excesses were calculated using Equation 3 in all four watersheds – Bayou Teche, Vermillion, Mermentau Headwaters, and Mermentau (Figure 12). Due to the magnitudes of the surface and groundwater supply differences (surface water supply in the SWLA study area is 45 times greater than the groundwater supply), the overall surplus shown is dominated by the surplus of surface water. This surplus of surface water is considered an upper bound, as minimum in-stream and coastal ecological flows were not calculated as part of this effort. These minimum ecological flows would put constraints on the amount of usable water in the study area, and require further study to quantify.
Water Resources Assessment for Sustainability and Energy Management
46