Ch. 17] SAVANNAH HARBOR, SAVANNAH RIVER 309 



considerably more expensive to construct in nature than would plan 

 1 ; therefore it was recommended that plan 1 be installed in the river. 

 Plan 1, now known as the Pennsville Dike, was constructed in the 

 river during the period April, 1942, to June, 1943. A study of the 

 effects of this dike on prototype shoaling during the period June, 1943, 

 to November, 1946, has been made by the Philadelphia District Office 

 of the Corps of Engineers. During this period, it was found that Deep- 

 water Point Range shoaled at an average annual rate of 1,470,000 

 cubic yards, or a reduction in shoaling of 48 percent from the average 

 rate before construction of the dike. The predicted decrease in shoal- 

 ing for this structure, as obtained from the model study, was 47 per- 

 cent. Construction of the dike effected some increase in the rate of 

 shoaling in the lower end of Cherry Island Range, a short distance 

 upstream from the Pennsville Dike; however, the increased shoaling 

 in that locality was considerably less than one-half the reduction in 

 Deepwater Point Range effected by the structure. Taking into ac- 

 count the initial cost of the structure, interest thereon, and the cost of 

 maintenance, as against the cost of dredging material which would 

 have deposited in Deepwater Point Range except for the dike, the 

 actual monetary saving amounted to approximately $67,000 annually 

 at the cost levels then prevailing. The study, conducted on an exist- 

 ing model of the Delaware River, cost somewhat less than $12,000 to 

 perform. 



SAVANNAH HARBOR, SAVANNAH RIVER 



A problem somewhat related to the Deepwater Point Range prob- 

 lem, but nevertheless different in its basic features, is that of deposition 

 of suspended silt in portions of tidal rivers and estuaries in which 

 salinity and salinity currents play an important role in the process 

 of sedimentation. As an example of an investigation of this type of 

 problem by means of hydraulic models, the study of Savannah Har- 

 bor has been selected. 



Savannah Harbor (see Fig. 7) comprises the lower 22 miles of the 

 Savannah River and forms the navigable waterway from the port of 

 Savannah, Georgia, to the Atlantic Ocean. At the time of the model 

 study the channel was maintained to a depth of 30 feet below mean 

 low water over a suitable width and was subject to shoaling in sev- 

 eral reaches of the harbor. A large part of the silt carried by the 

 Savannah River is in the form of colloidal or semi-colloidal suspen- 

 sion. An important property of these particles in suspension is that 

 they exhibit no tendency to ball together and form deposits on the 

 river bed, for the reason that the outer layer of each particle is 



