In order to achieve economies of scale offered by the newer ships, it is common practice for arriving vessels to wait offshore, adjust their steaming speed, or change vessel itineraries in order to meet optimum channel depth requirements for the operating draft. Conceptually, this involves increased time at sea, at the vessel's hourly operating cost times the number of hours delayed awaiting favorable tides. In the case of departing vessels, the operating cost of the vessel in port times the delay time equals the delay cost.

To capture these benefits in this analysis, the traffic was divided first by trade route (Europe or Far East), since the fleet varies in composition between the two. Next, the percentage of inbound and outbound vessels operating fully laden or light loaded (from one to six feet) was determined from the Transportation Savings analysis. Finally, the time of availability of each foot of tide was determined in order to develop a probability distribution of vessels requiring tidal assist.

When the channel depth is compared with the operating draft of any vessel (less underkeel clearance required), a required tide depth can be determined, along with the time such a tidal advantage can be expected to prevail during a 24 hour period (adjusted for the average 2.5 hour channel transit). Because arrivals and departures occur in a random fashion, compared to the state of the tide, the probability of arrival or departure during this period is simply the number of hours of tidal availability divided by 24. probability of a tidal delay is one minus this probability.

The

From this process, a distribution of all delayed vessels was developed, and a delay cost assigned to each. The total cost of delays with the existing 38-foot channel was compared cost of each alternative channel. The differences are the delay savings for each alternative. The annualized results are shown in Table 26.

Benefit/Cost Ratio and Net NED Benefit Comparisons

The three plans analyzed are summarized in Table 27. The Interest During Construction is based upon a construction period of 13-1/2 months. Both the 40 and 42-foot channel deepening alternatives are economically feasible. Based on a 50-year planning horizon, results indicate that the NED plan, the plan with highest net benefits, is the 40-foot channel depth. Over time, the 40-foot channel will enable shippers to operate their fleets with the most efficient distribution of vessels.

Source: Calculated by Savannah District, Corps of Engineers.

$209,900

$1,936,800

Sensitivity Analysis

A detailed sensitivity analysis was conducted which tested the traffic forecasts and fleet forecasts, which are the key variables in the benefit analysis. Appendix A includes a detailed discussion of these tests. However, the analyses revealed that the NED Plan does not exhibit extreme sensitivity to either critical variable. Under a "worst case" scenario, the NED Plan is economically sound.

Benefit/Cost Ratio Update Plan

Economic benefits of the alternative deepening plans are largely determined by the following four factors:

(1) Vessel operating costs;

(2) Discount rate used for water resource projects;

(3) Commodity projections for Savannah Harbor; and

(4) Vessel operating characteristics.

The first two factors, operating costs and discount rate, are updated annually and are provided by the Corps of Engineers, Office of the Chief of Engineers. This information can easily be incorporated to update transportation savings. Yearly updates of commodity tonnage movements are also available from "Waterborne Commerce Statistics". These data can be used to check the validity of project tonnage movements of the benefitted commodities, which include general cargo and grains.

Public sources of data on vessel operating characteristics at the level of detail desired for a feasibility study are scant. The Georgia Ports Authority can and does provide some of this information to the Savannah District, using their on-line access to the PIERS database.

ECONOMIC IMPACTS

Benefits

The benefits attributable to proposed harbor modifications were evaluated in separate increments. Since channel widening was authorized for construction by P.L. 99-662 in 1986, a Local Cooperation Agreement for sharing construction costs has been signed, and construction is underway. This improvement is considered part of the Without Project condition. Deepening the channel was evaluated from its currently authorized 38-foot depth to 40, 42, or 44 feet, assuming the widening project was in place.

Channel Deepening

The economic benefits of channel deepening were estimated using the economic analysis rationale previously discussed.

Costs

The principal cost component common to all five plans is the cost of dredging the channel. Plan 2 also contains the cost of providing disposal areas for the new work dredged material.

The sunken vessel CSS GEORGIA has been accurately located on the river bottom just outside the channel prism proper. Maintenance dredging operations have been able to avoid disturbance of the wreckage, and any dredging up to 42 feet could be accomplished with no impact on the main wreck. Therefore, deepening the channel to 40 feet would not affect the wreck, itself, with the exception of scattered parts which have fallen into the channel bottom. Impacts to the scattered parts of wreckage in the channel could be mitigated by mapping, possible recovery, and conservation.

The deepened channel is not expected to make any change in the annual maintenance quantities for Savannah Harbor. The salinity/sediment model indicated that there would be no significant changes in shoaling patterns or quantities. Therefore, there would be no increased cost to maintain the deepened channel. Also, disposal of new work material for all of the plans was designed to have no adverse impact on present maintenance disposal areas and procedures. Thus, there are no future O&M costs assigned to any of the harbor deepening plans.

a

Plans 1 and 2 call for dredging the harbor channel with cutterhead dredge and pumping the material by pipeline to the disposal areas. The jetties channel and bar channel would be dredged with a hopper dredge or other equipment and the material carried to the ocean disposal site. Plan 1 is much less costly than Plan 2 because it makes use of the shorter pumping distances by moving the material to the nearest existing disposal area, plus it does not require obtaining a new disposal area for the new work dredged material.

Plan 5 calls for dredging the harbor channel, jetties channel, and bar channel with a cutterhead dredge and pumping the material into dump scows. The dump scows would be towed to the ocean disposal site for deposition of the new work material.

Only Plan 2 includes a cost for a disposal area. The estimated cost to provide the new disposal area for one-time use for the new work dredged material is $3,953,000.

ENVIRONMENTAL IMPACTS

Water Quality

Plans 1 and 2 would involve the excavation of interior sediments by hydraulic dredge, with subsequent disposal in either existing diked disposal areas or a new diked area near the South Channel. Several tests were conducted to determine the pollution potential of these interior sediments.

Thirty sediment grab samples were taken throughout the harbor and analyzed for the 129 priority pollutants, as designated by the EPA. Seventeen of these samples were taken from the channel and in the immediate vicinity where deepening would occur. The results of the analysis of these samples were published in a 1982 report prepared by Environmental Systems, Inc., titled "Chemical Analysis of Sediments Collected in the Savannah Harbor, Chatham County, Georgia". Although the sediment samples did not reveal organic contaminants in concentrations that would be of concern, some trace metals were detected in elevated concentrations. These metals included chromium, cadmium, copper, lead, nickel, silver, thallium, and zinc. Arsenic was also detected at several sample locations in the area of deepening.

Although these contaminants are present, this does not necessarily mean these contaminants would be released during dredging or disposal activities. Research conducted during the U.S. Army Corps of Engineers' Dredged Material Research Program (DMRP) indicates that most metals are released in only small concentrations for short periods of time. The results of this research were further verified during the Savannah Harbor Comprehensive Study. Sediment samples were subjected to standard elutriate tests, with the analysis concentrated on the above trace metals. None of these contaminants were released from the sediments at levels above recommended EPA criteria.

In addition, sediment samples were subjected to sediment fractionation studies, which provided an indication of the distribution of constituents in sediments, as well as an idea of their mobility. These tests showed the trace metals and other contaminants to be primarily in phases of the sediment (residual, moderately reducible, organic + sulfide) where they would be less likely to be released. These test results were published in a 1983 report prepared by the Savannah Laboratories and Environmental Services, Inc., titled "Elutriate and Sediment Fractionation Characteristics of Sediment from Four Stations in the Savannah

Harbor, Georgia".