Plan 1-40

Plan 1-40 would involve deepening the Savannah Harbor channel to an authorized depth of -40 feet mlw between Station 0+000 (mile 0.0) and Station 103+000 (19.5), including Kings Island Turning Basin. The jetties channel would be deepened to an authorized depth of -40 feet mlw between Station 0+000 and the end of the jetties at Station -14+000B (mile 0.0-2.7B), then to -42 feet mlw in the bar channel between Stations -14+000B and -60+000B (mile 2.7B-11.4B).

All new work material dredged from the harbor channel and Kings Island Turning Basin, approximately 715,780 cubic yards, would be placed in existing disposal areas. The new work material could be used to improve and increase the heights of the dike systems of the existing disposal areas. Future O&M quantities from the harbor channel would not increase significantly, and Plan 1-40 would not adversely affect future O&M costs. O&M costs may be reduced by Plan 1-40, since material for dike improvements will not have to be obtained from some other source.

New work material from the jetties channel and bar channel, approximately 255,405 cubic yards, would be carried to the ocean disposal site. This would result in a slight reduction in the capacity in the ocean disposal site; however, due to the dispersive nature of the site, this would be a short term impact. There would be no increase in O&M costs due to ocean disposal. Plan 1-40 assumes that all maintenance dredging for the present 38-foot channel would be completed prior to the new work dredging, including advance maintenance and overdepth dredging, where applicable. Plan 1-40 also retains present advance maintenance criteria for Savannah Harbor.

Plan 1-40 would result in a maximum increase in salinity of 0.34 ppt above U.S. Highway 17 and 1.02 ppt below Highway 17. This increase in salinity is not considered to be significant. Plan 1-40 would also potentially impact any cultural resources located within and alongside the channel and the Oysterbed Island light structure located in the existing disposal area on the island. The South Carolina State Historic Preservation Officer recommended that archival research be conducted for the existing disposal areas to identify the locations of buried resources, and this study is now in progress. Impacts to the CSS GEORGIA would be avoided by narrowing the channel in that area as was previously indicated. Total initial cost for Plan 1-40 is estimated to be approximately $17,162,600, including interest during construction. The average annual cost would be $1,483,900 and average annual benefits would be $4,529,500. The net annual benefits would be $3,045,600 and the overall benefit/cost ratio would be 3.1 to 1.

Plan 1-42

Plan 1-42 provides for deepening of the harbor channel to an authorized depth of -42 feet mlw between Station 0+000 (0.0) and Station 103+000 (mile 19.5), including Kings Island Turning Basin. The jetties channel would be deepened to an authorized depth of -42 feet mlw between Station 0+000 and the end of the jetties, Station -14+000B (mile 0.0-2.7B), then to -44 feet mlw in the bar channel between Stations -14+000B and -60+000B (mile 2.7B-11.4B). All new work dredged material from the harbor channel and Kings Island Turning Basin, approximately 4,375,000 cubic yards, would be placed in existing disposal areas.

The impacts of this plan are essentially the same as those for Plan 1-40, except for the impact on salinity levels in the river and potential impacts on cultural resources. Plan 1-42 would result in a maximum increase in salinity of 0.0-0.68 ppt above U.S. Highway 17 and 0.0-2.0 ppt below Highway 17 at flows of 6,000 cfs. At flows of 12,000 cfs, there would be a 0.03 ppt increase above Highway 17 and 1.72 ppt below Highway 17. The difference in the salinity impacts of the two plans essentially equates to a 0.5 mile upstream shift in predicted maximum salinity levels due to the additional 2 feet of deepening. Therefore, Plan 1-42 has the potential for impacting approximately 300 more acres of marsh than Plan 1-40 by limiting its conversion from brackish/saline marsh to freshwater marsh.

Plan 1-42 would result in a similar potential for impacts to cultural resources as Plan 1-40. However, the potential for impact would be greater, especially in the vicinity of Station 60+000 (mile 11.4) where the CSS GEORGIA, Confederate crib obstructions, Old Fort Jackson, Battery Lee, and Turnbull's Tavern are located. In accordance with 33 CFR Part 800, a Programmatic Memorandum of Agreement has been developed to identify and to avoid or mitigate impacts to any`significant historic or cultural resources within the deepening impact area. Impacts to the CSS GEORGIA would be avoided by narrowing the channel in that area.

New work material from the jetties channel and bar channel, approximately 1,551,915 cubic yards, would be dredged and transported to the ocean disposal site. This would result in a slight reduction in the capacity in the ocean disposal site; however, this impact would be short term due to the dispersive nature of the site. There would be no increase in O&M costs due to ocean disposal of this material. Plan 1-42 assumes that all maintenance dredging for the present 38 foot channel would be completed prior to the new work dredging, including advance maintenance and overdepth dredging where applicable. Plan 1-42 also retains present advance maintenance criteria for Savannah Harbor.

Total initial cost for Plan 1-42 is estimated to be approximately $40,434,500, including interest during construction. The average annual cost would be $3,496,100 and average annual benefits would be $5,432,900. The net benefits of the project would be $1,936,800 and the overall B/C ratio would be 1.6 to 1.

Plan 5-40

Plan 5-40 provides for deepening the harbor channel to -40 feet mlw from Station 0+000 to Station 103+000 (mile 0.0-19.5), including Kings Island Turning Basin; deepening the jetties channel from Station 0+000 to Station -14+000B (mile 0.0-2.7B) to -40 feet mlw; and deepening the bar channel from Station -14+000B to -60+000B (mile 2.7B-11.4B) to -42 feet mlw. The plan involves use of towboats and dump scows, or barges, to transport the total dredged material, approximately 971,185 cubic yards, to the ocean disposal site. A shuttle system would be made with tows and barges leaving the dredge and heading for the disposal site at regular intervals. Two dump scows would be handled by each towboat. Scows would have split hulls and be capable of bottom dumping at the disposal site. A mooring facility would be built to moor the scows and tows during non-working hours.

Use of a convoy of tow boats and dump scows to constantly carry material to the ocean disposal site, as called for in Plan 5-40, has never been done in Savannah Harbor. It seems likely that due to the amount of harbor traffic Plan 5-40 would generate and the narrowness of the channel, particularly upstream of the Fig Island Turning Basin, problems could arise with safety in the harbor and disruptions to shipping schedules. Plan 5-40 would have no effect on the existing system of upland disposal sites; however, it would result in a short term decrease in capacity of the existing ocean disposal area.

This plan would have a greater impact on water quality at both the dredge and disposal sites. The greater impact at the dredge site would be from the overflow filling of scows, which would be necessary to efficiently perform the work, and the greater impact at the disposal site due to the use of unconfined disposal.

The potential for cultural resource impacts would be the same as Plan 1-40, except for potential impacts associated with dredged material disposal. Future O&M quantities from the interior channel would not increase significantly. Additional O&M costs would be realized due to the increased monitoring effort which would likely be required at the ocean disposal site. Plan 5-40 assumes all maintenance dredging for the present 38-foot channel would be completed prior to new work dredging, including advance maintenance and overdepth dredging where applicable. This plan retains the present advance maintenance criteria for Savannah Harbor.

Total initial cost for Plan 5-40 is estimated to be approximately $34,024,300, including interest during construction. The average annual cost would be $2,802,100 and average annual benefits would be $4,529,500. The net benefits of the project would be $1,589,800 and the overall benefit/cost ratio would be 1.6 to 1.

No Action

The adoption of the No Action Alternative would mean that nothing would be done to change existing channel depths and conditions in Savannah Harbor. This alternative obviously fails to meet planning objectives, since shipping delays and expenses would continue. Savannah Harbor would not increase its efficiency for shipping and might lose a part of its competitiveness on the southeast coast. This would affect the local economy as well as the economy of the region and the State of Georgia. Vessels requiring a harbor deeper than -38 feet mlw would conduct their shipping operations at other ports.

No action would also mean there would be no adverse impacts on fish and wildlife or cultural resources due to project construction. Salinity levels would remain at their present levels in the Savannah River.

Benefit/Cost Analysis

Table 34 presents a summary of the benefits, costs, and the benefit/cost ratio for the three plans.