Project Description - trchl04-30015

Project Description

Site Location

The dustpan dredge demonstration project was conducted at the HOP on the

Mississippi River (Figure 1). MVN established the dredging limits for the

demonstration project between Mile 1.0 above HOP and Mile -0.5 below HOP

(Figure 2). Mile 1.0 is located approximately 1 mile downriver from Pilottown.

This area includes the bend where the navigation channel enters Southwest Pass.

The project channel width in this area is 750 ft with a design depth of -45 ft

MLG. The project area was divided into three dredging reaches. Reach 1

extended from Station (Sta) 3+00 to 18+00 (or Range 26 to Range 21) (Figure 3);

Reach 2 extended from Sta 42+00 to 61+00 (or Range 15 to Range 10); and

Reach 3 extended from Sta 69+00 to 84+00 (or Range 8 to Range 4). Reach 1

was selected as the starting location for demonstration of equipment mobility, as

it presented the least difficult navigational area. The project plan specified

working Reach 1, Reach 2, and Reach 3 in sequence to minimize downtime for

moving the "hard point" and adding submerged line.

The marsh creation area where the dredged material was to be placed was

located on the west side of the river at Mile 1.6 above HOP. The area was in

open water immediately west of the dike/adjacent pasture upland and existing

wetlands (see Figure 2). The distance across the upland and wetlands to reach

this area was relatively small, minimizing the amount of discharge pipe required

to reach the placement area. MVN requested that a minimal amount of open

water be left between the wetlands and placed dredged material.

Site Conditions

During the demonstration project, the Mississippi River was at above-

average high stages due to heavy rains on the Ohio River Valley in late spring

2002. The maximum measured current during the project was approximately

7 ft/sec. The high sediment load resulted in the continuous deposition of large

amounts of sediment at the HOP causing rapid formation of shoals. Four hopper

dredges were working continuously in this area to remove shoals before they

could impact navigation. The largest amount of shoaling was predominantly on

the inside of the bend. MVN survey results from 5 June 2002 illustrate this point

by showing maximum shoaling of approximately 6 ft in Reach 1, and 20 feet in

Reaches 2 and 3 (see Figure 3).

Chapter 2

Project Description