The natural and adjusted hydrographs for the Delaware River estuary 

 are shown in the upper part of Figures 3-81 and 3-82. The lower part of 

 Figure 3-81 shows the changes in location of 250 isochlor for the test 

 period as a result of simulated operation of the reservoir; Figure 3-82 

 shows the change in salinity at high water and low water slacks at Dela- 

 ware Memorial Bridge, Chester, and Fort Mifflin. Note that both high 

 water slack (maximum) and low water slack (minimum) salinities at all 

 three locations were reduced by the regulated hydrograph, thus showing 

 that salinities would be reduced generally in the upstream part of the 

 estuary during the low flow season. The 250 isochlor was not moved as 

 far downstream during the high inflow period of the regulated hydrograph 

 as for the natural hydrograph; however, the maximum upstream location for 

 the 250 isochlor for the regulated hydrograph was almost 8 miles farther 

 downstream than for the natural hydrograph. Thus, while maximum salin- 

 ities in the upstream part of the estuary would be significantly reduced 

 by flow regulation (advantageous for water use) , minimum salinities in 

 the lower estuary would be increased (may be undesirable for marine life 

 and oyster predator control) . 



k. Freshwater Supply-Salinity Control — Vermilion Bay . 



(1) Project . Construction of a salinity control barrier in 

 Vermilion Bay. 



(1959), 



(2) Reference . U.S. Army Engineer Waterways Experiment Station 



(3) Laboratory . WES. 



(4) Test Period . December 1955 to December 1966. 



(5) Problem . Vermilion Bay (Fig. 3-83) is located on the 

 Louisiana coast between Morgan City and Lake Charles. The bay has a 

 deep and narrow connection to the Gulf of Mexico through Southwest Pass 

 on the south, and a second wide and shallow connection through West and 

 East Cote Blanche Bays and Atchafalaya Bay to the east and southeast. 

 The Vermilion River, a relatively small stream, discharges into the 

 northeast side of Vermilion Bay; the Atchafalaya River, which carries 



a large freshwater discharge at all times, and Wax Lake Outlet discharge 

 into Atchafalaya Bay. 



The Vermilion River is used extensively as a source of water for 

 irrigating rice. During dry seasons, when most irrigation water is used, 

 the rate of pumping from the Vermilion River often exceeds the riverflow, 

 and saltwater from Vermilion Bay moves rapidly upstream and eventually 

 reaches the pump intakes. Considerable damage to the rice crop may then 

 result, either from lack of water needed by the rice if pumping is cur- 

 tailed, or from the salinity of the water pumped into the ricefields if 

 pumping is continued. Historical salinity data show that the entire bay 

 complex is freshened during the high discharge season on the Atchafalaya 

 River, which usually extends from about February through June. After the 



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