Introduction - trchl04-30009

Introduction

Purpose

The purpose of this report is to present the demonstration results of the dust-

pan dredge Beachbuilder using a flexible discharge at the Head of Passes/

Southwest Pass on the Mississippi River (Figure 1) in June 2002. The report

details and discusses the project activities, operational characteristics of the

Beachbuilder, and feasibility of using a flexible-discharge dustpan dredge to

augment the hydraulic dredging capabilities of the U.S. Army Corps of Engineers

(USACE) on the Mississippi and other rivers. The goal of this report is to use the

project results to identify potential opportunities for reducing overall costs for

channel maintenance and increasing beneficial use of dredged materials during

dredging Corps navigation projects.

Background

The navigation channel of the Mississippi River in the vicinity of the Head of

Passes (HOP) is an area where significant dynamic shoaling occurs (Figure 1). In

Fiscal Year (FY) 2002, approximately 5.5 million cu yd1 was placed in Pass A

Loutre. At HOP, the increased cross-sectional area provided by Pass A Loutre

and South Pass results in lower currents that allow much of the river's sediment

load to be deposited. During the traditional high-water period in the spring,

shoaling in this area occurs rapidly and can represent a hazard to deep-draft

vessel traffic. The shoaling must be removed rapidly to maintain adequate

channel depth. Currently, dredging of the channel at HOP is conducted using

hopper dredges, primarily due to their mobility. Hydraulic dredges with conven-

tional spudding systems and floating discharge pipelines, such as cutterhead

dredges, are considered a safety hazard in this area due to their inability to

rapidly move out of the way of vessel traffic. Unfortunately, hopper dredges

simply move the dredged material out of the channel and redeposit it in open-

water disposal sites at the heads of Pass A Loutre and South Pass. There are two

disadvantages to this technique. First, the disposal sites periodically become so

filled with material that the hopper dredges' drafts prevent them from dumping

dredged material at the sites. The dredged material must be handled again at

additional cost to provide sites for hopper disposal. Second, there is no beneficial

use of the dredged material. Hopper dredges can use direct pump-out to place

A table of factors for converting U.S. customary units to metric (SI) is presented on page vi.

Chapter 1

Introduction