IV-436 



freshwater to salt water in the harbor area was such that a definite 

 interface developed which moved longitudinally up and down with the 

 tide. The dense saltwater was overlain by the freshwater inflow. 

 As the freshwater flow increased to 15,000 c.f.s., the bottom flood 

 currents became greater in duration over the bottom ebb currents. 

 The effect was to create a net upstream movement of the bottom 

 currents in the saline region of the harbor area, a condition which 

 created a trap at the bottom of the estuary preventing the movement 

 of settling materials out to sea. 



At about the same time the Santee-Cooper Project began operations, 

 the project depth of the Charleston Harbor was changed from 30 feet 

 to 35 feet. This further complicated the dredging problem for two 

 reasons: first, the Corps had 5 additional feet of depth to 

 maintain and second, the dredging itself loosened the accumulated 

 silt outside of the shipping channels and allowed it to slip into 

 the channels. The Corps maintained, however, that the natural 

 depth of the Charleston Harbor had exceeded 35 feet, and that the 

 greater project depth in itself would not have constituted much of 

 a problem. 



From its study of the shoaling problem in the Charleston Harbor, 

 the Corps estimated that the Santee-Cooper Project was responsible 

 for approximately 85 percent of the shoaling in the harbor. The 

 rest, they said, would have occurred without the project. 



