Comparison to Previous Maintenance Dredging Capabilities Assessment

Comparison to Previous Maintenance Dredging

Capabilities Assessment

In December 1998, the MVN published a document entitled "Assessment of

Coastwide Louisiana Maintenance Dredging Capabilities under the Federal

Standard."1 In this document, MVN assessed the need and economic feasibility

of adding maintenance hydraulic dredging capability in the District. The assess-

ment also identified opportunities for providing cost reduction in channel main-

tenance and enhancing the level of beneficial use of dredged material. The

assessment concluded that a large dustpan dredge (30- to 38-in.-diam discharge)

with a flexible discharge would best provide the capabilities needed and achieve

cost savings. Such a dredge would also provide environmental benefits associ-

ated with the creation of wetlands from dredged material not otherwise being

beneficially used.

In the MVN report, eight evaluation factors were used in assessing various

dredge types for required maintenance dredging capabilities. The evaluation

factor criteria are compared to corresponding results obtained from the

Beachbuilder demonstration below.

Past experience with dredge type

Values in the assessment were assigned based on the level of historical

experience with the various dredge plants. The MVN has past experience with

dustpan dredges. The flexible-discharge dustpan demonstration project using the

Beachbuilder provided MVN personnel with additional experience and baseline

production and maneuverability data on the capabilities of a dustpan with a

flexible discharge and extensive pumping resources.

Utility of dredge type and size across projects

Under this factor, the dredge is required to provide both overboard placement

and long distance pumping capabilities with ease in switching between modes. In

the MVN report, the overboard discharge pumping distance requirement was

3,000 ft, and the long distance pumping requirement was 15,000 ft through com-

bined floating, submerged, and shore line. While the 15,000-ft pumping distance

was not achieved during the demonstration, the maximum distance Beachbuilder

did pump was 10,820 ft (1,320 ft floating hose, 7,920 ft submerged line, and

1,580 ft shore line). This production was accomplished using the ladder pump

and only one of the two deck pumps. Weeks Marine personnel stated that with

the second pump in operation, the Beachbuilder would be able to meet the

15,000-ft pumping requirement plus another approximate 5,000 ft (the ultimate

line length would depend on the type and classification of material). Overboard

placement was not demonstrated in this project, but switching between modes

could be accomplished. For the shorter 3,000-ft overboard placement option, the

pipeline configuration might be changed. Both the long and short pumping

Ibid.

Chapter 6

Feasibility Analyses