Detailed Shoaling Analyses

Detailed Shoaling Analyses

Background

Detailed analyses of the physical processes that occur in and around the

ship channel, coupled with a detailed analysis of dredging effectiveness

by season can provide approaches to reduce overall dredging volumes

and/or the need to dredge. At two locations within the United Kingdom

(UK), port authorities conducted such analyses that have had a major im-

pact on the routine maintenance required by the facilities. In England, the

port authorities are solely responsible for maintenance of their navigation

channels. Funding, contracting, or conducting the work is a port function.

Several ports have acquired dredges with crews, and conduct their own

dredging, while others choose to contract out their required maintenance.

The two examples used here are the Tees and Hartlepool Port Authority

and the Harwich Haven Port Authority. The Tees and Hartlepool Port

Authority conduct almost all of their own dredging with a private plant,

while Harwich Haven Port Authority contracts out its dredging needs.

Technology

The Port of Tees and Hartlepool is located in the northeast section of

England. The Port Authority (Port) currently conducts a majority of its

own dredging with two trailing suction hopper dredges. The Port has

taken a proactive approach to shoaling analyses to identify patterns and,

when possible, to reduce overall dredging requirements. Currently, berths

are dredged deeper than authorized channels so that deep-draft vessels can

come and go on high tide and remain at the dock during low tide. Dredg-

ing is coordinated with the vessels that are calling on the port. For exam-

ple, dredging is conducted in the shallowest area if a deep-draft vessel is

calling on port; otherwise, high shoaled areas are dredged. With this kind

of flexibility, the Port can and does assign dredging operations daily.

A careful analysis of the Port's projects indicates that the majority of

shoaled material originates from the North Sea and is transported up the

navigation channel by tidal action. The Tees River does not have a large

flow volume compared to flushing from the large tidal range of 3 to 5 m.

The analysis was developed over three broad areas. First, a detailed hy-

drodynamic and sedimentation study was conducted on the area to deter-

mine the sources of shoaling and flow patterns in the channel. Second,

modifications were made to the dredging operations, and third, the effec-

tiveness of the modifications were monitored.

Prior to the analysis, a majority of the dredging was conducted in the

upper portions of the channel and at the mouth. Sediment dredged in the

upper sections of the channel was placed in the midsections, near the S

curves, where dredging was not required. Since the midsection did not

need dredging, little consideration was given to the fate of this material.

It was determined that much of the material placed in the midsection of

the channel was migrating back to the upper portion, recycling the mainte-

nance material. The Port identified several actions which could help re-

Chapter 4

Detailed Evaluations