unavailable. The tests may be necessary because of the high cost of 

 obtaining field data (compared to the cost of obtaining the data in an 

 existing model), or because the transient and uncontrollable prototype 

 conditions prohibit the definition of quasi-steady-state conditions from 

 field data. Such studies obviously cannot be made until the hydraulic 

 and salinity verifications of the model have been completed. 



Salinity intrusion in the Delaware River estuary constitutes a serious 

 problem when freshwater discharge conditions are such that saltwater in- 

 trudes upstream beyond the Delaware-Pennsylvania State line, since up- 

 stream from this point the river water is used extensively for industrial 

 purposes. The maximum salinity concentration that can be tolerated by 

 certain industries located on the river is on the order of 50 parts per 

 million of chlorine (50 isochlor). When the salinity of the river water 

 at the plant sites exceeds this value, either the water must be treated 

 chemically to remove the objectionable constituents or water of satis- 

 factory quality must be obtained from another source. Either method is 

 very expensive because of the large quantities of water involved. 



(6) Purpose of Model Study . A series of tests was conducted in 

 the Delaware River model to determine the effects of each principal factor 

 known or believed to affect the nature and extent of salinity intrusion in 

 the estuary. 



(7) The Model . The Delaware River model (Fig. 3-56) was a fixed- 

 bed type with scales of 1:1,000 horizontally and 1:100 vertically. 



(8) Test Procedures . For most of these tests, constant fresh- 

 water inflows were used. 



(9) Summary of Test Results . It had long been recognized that 

 freshwater discharge into the Delaware River estuary was the major factor 

 governing the extent of salinity intrusion therein, since saltwater has 

 intruded as far upstream as Philadelphia during periods of extremely low 

 freshwater discharge and has been forced as far downstream as Artificial 

 Island during large floods. However, the proper correlation of the ex- 

 tent of salinity intrusion with freshwater discharge has never been possi- 

 ble, since the freshwater discharge in the prototype rarely, if ever, 

 remains stable for a sufficient period of time to produce an equivalent 

 stable salinity regimen. Therefore, one of the problems for the model 

 study was determination of the relationship between sustained freshwater 

 discharge and stable salinity conditions over a fairly wide range of 

 freshwater discharges. The results of such tests would show the sus- 

 tained freshwater discharge required to hold the critical salinity con- 

 centration (50 isochlor) at the Delaware-Pennsylvania State line. 



Six tests were conducted in the model to determine the relationship 

 between sustained freshwater discharge and salinity distribution through- 

 out the estuary for mean tide conditions. These tests involved reproduc- 

 tion of sustained freshwater discharges in the Delaware River including 

 the Schuylkill River of 5,000, 7,000, 9,000, 10,600, 13,000, and 16,475 

 cubic feet per second. 



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