(6) Purpose of Model Study . The model study was conducted to 

 determine the influence of modified freshwater inflow on the salinity 

 regimen of the Delaware River estuary. 



(7) The Model . The existing Delaware River model (Fig. 3-56) 

 was used; model scales were 1:1,000 horizontally and 1:100 vertically. 



(8) Test Procedures . A detailed salinity reverification of the 

 Delaware River model was accomplished before conducting the tests, using 

 freshwater inflows and salinities measured in the prototype between 1 

 March and 30 November 1965. In the test to determine the effects of 

 Tocks Island Dam on salinity conditions in the estuary, the observed 

 1965 freshwater hydrograph was modified to reflect the program of stor- 

 age and release that would have been followed if Tocks Island Dam had 

 been in operation during 1965. 



(9) Summary of Test Results . When all necessary field measure- 

 ments were available, tests were conducted in the Delaware River model 

 to determine what revisions (if any) were needed to reproduce the actual 

 rate of advance of the salinity front and the maximum upstream location 

 of the 250 isochlor for conditions of the 1965 drought. During this 

 drought, a prolonged period of very low flow (about 2,000 cubic feet per 

 second) occurred. After the initial check showed unsatisfactory agree- 

 ment with the maximum extent of salinity intrusion, the U.S. Army Engi- 

 neer District, Philadelphia, determined that an additional 200 cubic feet 

 per second entered the river between Trenton and Torresdale as ground- 

 water and well-water discharges. This is an insignificant part of the 

 12,000 cubic feet per second mean Delaware River flow at Trenton. How- 

 ever, 200 cubic feet per second is critical when drought flows occur on 

 the order of 2,000 cubic feet per second. The model was found to correctly 

 reproduce both the rate of advance and the maximum location of the 250 

 isochlor when this additional freshwater was introduced into the model. 



With the exception of short-term fluctuations in prototype salinities, 

 caused primarily by winds and other meteorological effects not simulated 

 in the model tests, the agreement between model and prototype salinities 

 was very close throughout the test period. Figure 3-81 shows a comparison 

 of the location of the 250 parts per million chloride concentration (iso- 

 chlor) in the model and prototype for the duration of the test with the 

 natural 1965 hydrograph. The solid line in the figure shows the exact 

 location of the 250 isochlor at high water slack in the model throughout 

 the test, as determined from measurements made every second tidal cycle; 

 the solid black points represent the locations of this concentration at 

 high water slack in the prototype, as determined by the U.S. Army Engi- 

 neer District, Philadelphia, on a monthly basis. The open points in 

 Figure 3-81 represent the approximate locations of the 250 isochlor as 

 determined from surface salinity profiles made in the prototype by sev- 

 eral agencies during the test period. Comparison of model and prototype 

 salinity time histories at selected stations for this reverification are 

 shown in Figure 3-34. The agreement between model and prototype salin- 

 ities was well within acceptable limits for the entire period of the test. 



175 



