Inspection and Compliance

Conversely, it is much more difficult to control the rate sand is dis-

charged from a split-hull barge. Based on the Seattle District's experience

using split-hull barges to place caps, Parry (1994) recommends discharge

rates of 30 to 42 m3/min to reduce the size of the end pulse caused by

bridging to about 5 percent of the load. At higher discharge rates, say

600 m3/min, Parry (1994) notes that the size of the pulse can be up to

33 percent of the total load. Nelson, Vanderheiden, and Schuldt (1994)

report discharge rates of 41 to 70 m3/min using a split-hull barge at the

Eagle Harbor in situ capping project.

Controlling and monitoring extended discharge from a split-hull barge

is a nontrivial matter. The small barges, typically about 1,000 m3 used by

the Seattle District, are opened 6 to 8 deg to start sand flowing. Discharge

rate can be monitored by change in draft measured by pressure sensors

radio linked to a display on the tug, and with experience it can be done

visually. As the load is lightened, the barge has to be opened more to

continue a constant flow of sand.

Inspection and Compliance

Proper tracking of dredged material placement prior to capping includes

adequate records of barge position, environmental conditions, vessel head-

ings and velocities, start/end times of discharge, and load/draft of barge.

In most cases, dredging contractors keep records detailing much of this

information in their dredge logs.

The information from the inspector 's or contractor 's logs can be useful

in identifying volumes of material placed, locations of placement, and cor-

relation of material placement with hydrographic survey results. Dredge

logs can also be the primary source of information for locating material

that is short-dumped. Short-dumping can result for various reasons including

human error, inadequate positioning information, malfunction of electronic

positioning instruments, and safety. When material is short-dumped, it

usually ends up outside of the specified disposal site, and postdisposal sur-

vey information may be limited or nonexistent. However, the dredged ma-

terial must still be capped, and the more information that is available

(from dredge logs), the better the capping job that can be done. In one in-

stance on the Port Newark/Elizabeth project, a short dump of one barge

load of material (2,300 m3) was covered with 31,000 m3 of cap material

because of a substandard positioning system (LORAN-C), lack of knowl-

edge of the tug/barge offset (the antenna was on the barge not the tug),

and incomplete records.

Dredged material placement inspection can be conducted by onboard

personnel provided by either the USACE District or dredging contractor.

Many USACE dredging projects already require onboard inspectors to

document proper dredging location, volumes dredged, and appropriate

depths attained. For capping projects, both the New England Division and

the New York District use inspectors. New England Division inspectors

are contractors (but not employees of the dredging company). The New

York District uses Corps employees as inspectors.

Chapter 5 Equipment and Placement Techniques