On Aug. 29, Brig. Gen. John S. Kem, Commanding Officer of the Northwestern Division, U.S. Army Corps of Engineers, gave final approval for a plan to dredge the Grays Harbor Navigation Channel from the South Reach upstream to Cow Point to its fully legislatively authorized depth of -38 feet MLLW. The project covers approximately 14.5 miles of the 27.5-mile channel.
The dredging plan has been in the works for more than a year, including development of a proposed plan that included three alternative actions, the completion of environmental impact studies and public and agency review.
The Grays Harbor federal navigation deep draft channel is 250 feet wide at Cosmopolis, increasing to 1,000 feet over the Bar at the mouth of Grays Harbor. The currently maintained channel depth is -36 feet Mean Lower Low Water (MLLW) from the South Reach to the Cow Point Reach, where Port of Grays Harbor Terminal 4 is located. The channel then decreases to -32 feet MLLW through Cosmopolis.
Alternatives
Three alternative dredging plans were considered:
• Alternative 1 - No Action, meaning that channel maintenance would continue a -36 Feet Mean Low Low Water (MLLW) and placement of the dredged material at a variety of open-water beach nourishment and upland beneficial use sites.
• Alternative 2 – Deepen the Channel to -37 Feet MLLW. The Point Chehalis aquatic site for dredged material would have been shifted 1,000 feet to the north-northwest during the construction year, 13,500 cubic yards of unsuitable material would be transported and disposed in a confined upland location, and any material deposited at the Point Chehalis Revetment Extension mitigation site would be hydraulically pumped via marine pipeline.
• Alternative 3 – Deepen Channel to -38 Feet MLLW: Alternative 3 will deepen relevant reaches of the navigation channel an additional two feet compared to baseline conditions. Following deepening, the channel will thereafter be maintained at the new design depth of -38 Feet MLLW.
Project purpose
According to the final approval document, “Alternative 3, based on the economic and environmental analysis conducted for the reevaluation, is the plan that maximizes net benefits for National Economic Development (NED). The Port of Grays Harbor requested deepening the channel to the legislatively authorized depth of -38 feet MLLW to better accommodate current vessel traffic for existing Port tenants and commodities.
As a result of the current channel depth of -36 feet MLLW, and the narrow tidal windows, deep-draft vessels calling at Grays Harbor have to be partially loaded or experience tidal delays due to insufficient channel depth.
Alternative 3 addresses that problem.
The two-foot deepening is neither designed nor intended to facilitate access for any new vessel classes or commodity types that could not currently utilize Port facilities.
Dredge spoils placement
According to the Alternate 3 plan, approximately 22,400 cubic yards of sediment that will be drudged during construction from the Cow Point Dredged Material Management Subunit 32a are unsuitable for open-water disposal. This material will be dredged via clamshell bucket, transported to a dock via walled barge with filtered scuppers to eliminate loss of sediment, transferred dockside to trucks and transported to an upland disposal site slated to be located at the former City of Hoquiam wastewater treatment lagoon for permanent disposal.
Suitable dredged material will be placed at the following existing placement locations: The South Jetty dispersive placement site, the Half Moon Bay and South Jetty nearshore beneficial use sites, and upland at the Point Chehalis Revetment Extension mitigation site.
As a result of a site capacity analysis, the Corps will institute a 1,000-foot north-northwestern shift in the Point Chehalis aquatic placement site. This placement site shift will not increase the size of the Point Chehalis Site and will be a temporary one-time shift to accommodate the volumes of material to be placed during the construction year by taking advantage of deeper water and more dispersive hydrodynamics.
The site will be shifted back after the construction year’s activities of deepening are completed.
A second clamshell dredge will be employed in the inner harbor reaches. Any material deposited at the Point Chehalis Revetment Extension mitigation site would be hydraulically pumped via marine pipeline and a long-reach excavator may be necessary to break up firm dredged material in the Cow Point Reach for removal by a clamshell dredge.
Doubling dredged material initially
The Corps maintains the waterway now by dredging the deep draft channel annually at an average cost of $9 million, removing an average annual volume of about 1.7 million cubic yards of material.
Initial deepening of the channel by two feet will require excavation and placement of an additional 1.972 million cubic yards of sediment, to be removed in the same dredging season as present annual maintenance dredging, for a total construction year volume of approximately 4 million cubic yards.
Annual maintenance volume up 5%
Subsequent annual maintenance volumes are estimated to increase by 107,000 cubic yards over Alternative 1 levels. This represents an increase in annual maintenance dredging volumes of 5% to maintain the channel at -38 feet MLLW.
Environmental impacts
According to the SEIS, “Although Alternative 3 will have a marginally greater adverse effect on the environment, the environmental consequences analysis presented in the SEIS determined that the effects of Alternative 3 will be minor or not adverse and appropriate mitigation measures will be implemented to reduce potential environmental impacts”
Dredge history
According to plan documents, “Planning studies for the Navigation Improvement Project to deepen the channel began in 1957. An Interim Feasibility Report/Environmental Impact Statement (FR/EIS) was completed in September 1982 and approved in May 1985. During the interim, biological assessments and impact mitigation studies were developed focusing on salmon and Dungeness crab.
“The 1982 FR/EIS evaluated deepening and widening the channel to a depth of -38 feet MLLW, addressed the design refinement reflected in the General Design Memorandum, as well as the environmental studies previously conducted, and assessed the impacts of dredging and disposal on biological communities, water quality and commercially significant fish and shellfish resources.
“Congress authorized deepening of the relevant portion of the Grays Harbor navigation channel to -38 feet MLLW in 1986, but a 1989 economic evaluation found that dredging only to -36 feet MLLW was economically justified at that time.
“Through updated economic and environmental analysis, the recently completed study evaluated implementing the previously authorized -38-foot depth through a Limited Reevaluation Report and a Supplemental Environmental Impact Statement (EIS), building on the original 1982 EIS and its 1989 Supplement.
“The June 2014 SEIS assesses the incremental effects of deepening the channel to its legislatively authorized depth in its present alignment, and it updates the 1982 EIS and 1989 EISS with the description of effects that are expected to result from subsequent maintenance of the channel, as modified through the changes in channel design.
