USA: Proactive Strategy for “Dredge-Ready” Operation and Maintenance at Low-Use Navigation Projects
This Coastal and Hydraulics Engineering Technical Note describes a collaborative strategy with a Federal navigation project sponsor for conducting operation and maintenance (O&M) dredging and disposal activities. A collaborative strategy increases opportunities for securing funding to conduct maintenance dredging and promotes responsiveness to local sponsor needs and capabilities. Dredge-ready or shovel-ready maintenance dredging plans compete well and may possibly be more competitive for future Federal funding presently unavailable through U.S. Army Corps of Engineers (USACE) for low-use navigation projects.
The governing criteria for obtaining Federal O&M funding to conduct routine dredging is based on commerce statistics. Typically, low-use navigation projects fall below a budgeted funding cutoff line, resulting in deferred maintenance that severely impacts local users and the associated economy.
The USACE, Seattle District, (hereafter, Seattle District) is responsible for 23 active navigation projects with 15 of them ranked as low-use projects (Figure 1). Willapa Harbor, WA, navigation project features are representative of low-use projects located in a highly dynamic coastal inlet on the southwest coast of Washington state (Figure 2). Included is a small, low-use deep-draft navigation channel at Toke Point Marina (Figure 3) sponsored by the Port of Willapa Harbor (hereafter, Port). In 2006, the Port expected to abandon the project unless they could use hydraulic pipeline maintenance dredging with “flowlane” disposal at a site located in a nearby deep natural channel with strong tidal flow.
Flowlane disposal is placement of dredged sediment in a natural inlet thalweg such that it is transported out of the area without harm elsewhere. Flowlane disposal is beneficial in returning sediment that was trapped in a harbor or navigation channel to the littoral system and, therefore, can be part of a regional sediment management plan. At Willapa Harbor, the flowlane dispersive disposal is an alternative to more costly and traditional clamshell dredging with bottom-dump barge transport 4 miles south to an open-water dispersive disposal site. In the river setting, flowlane disposal has been called thalweg disposal, “the placement of dredged material in a deepwater portion of the channel thalweg where it will become a natural element of the sediment transport system and will be assimilated into the system with minimal impacts to either the sediment transport system or the environment”.
Since initial pipeline dredge construction of the Toke Point Marina navigation project in 1958, it has been challenging to fund periodic maintenance dredging of the Federal entrance channel and Port berthing area. Periodic maintenance dredging was performed by hydraulic pipeline dredge with confined disposal at local sponsor-furnished upland disposal sites located close to the Toke Point Marina. By the 1970s, there was increased difficulty in locating and permitting upland sites of sufficient capacity for continued pipeline maintenance dredging. In the 1980s, the Seattle District, in cooperation with resource agencies, designated dispersive open-water disposal sites near Goose Point and Cape Shoalwater in Willapa Bay. Availability of these sites allowed continued clamshell maintenance dredging and bottom dump barge disposal use. The open-water sites were preferable because they were readily available and avoided disposal-impact issues and possible delays.
However, there was increased local concern about the high costs for ocean-going equipment mobilization and unit costs of clamshell dredging and bottom dump barge disposal. Efforts to minimize the Federal entrance channel and Port berthing area footprint helped, but were not sufficient. By 2006, six small, Southwest Washington ports including the Port of Willapa Harbor were desperate for responsive, less-costly maintenance dredging as Federal funding for small, low-use navigation projects continued to decline.
LOW-COST DREDGING AND FLOWLANE BENEFICIAL USE DISPOSAL:
Stakeholder consensus is that low-cost dredging is essential for viability of marina and continued maintenance dredging. The capability to adequately address some of the coordination issues about flowlane disposal stems from comprehensive USACE studies (Kraus 2000, Kraus et al. 2002), observations, and numerical modeling of Willapa Bay (Shepsis 2008). Flowlane disposal may be feasible at other sites, although placement at sites with complicated wave, tide, longshore, and cross-shore currents such as open coast inlets must be carefully evaluated to ensure that rehandling of dredged sediment is minimized. For Willapa Bay, previous studies provided a foundation for improved understanding of the sediment and current dynamics, and the studies demonstrated knowledge to obtain required agency approvals for future O&M dredging that is essential to the small fishing based economy and navigation at the Toke Point Marina.
COORDINATION HURDLES CLEARED:
The joint permit application process facilitated options intended to avoid permit delays regardless of which entity (Seattle District or Port) obtained the required O&M funding first. The Port and its consultant were successful in satisfying initial fisheries objections to flowlane disposal with receipt of State Hydraulic Project Approval (HPA) and State Ecology 401 Water Quality Certification Order #6297 dated January 7, 2009. A condition of the HPA was mitigation for potential crab entrainment mortality associated with pipeline dredging in the Federal entrance. The Seattle District may not have agreed to such mitigation for Federal maintenance dredging; however, the Port negotiated a mitigation plan that paid $4,000 to place 237 cy of oyster shell on Washington State Oyster Reserves at Willapa Bay.
TEN YEAR CORPS PERMIT ISSUED AND PORT BUYS NEW DREDGE:
Seattle District permit approval of 2009-2019 maintenance dredging for the Tokeland Marina and the Toke Point Federal Entrance was issued on August 7, 2009. The Port applied State grants and loans to purchase a new 10-inch Ellicott cutterhead pipeline dredge in September 2009 (Figure 6). The first of four Port maintenance dredging events scheduled over the 10-year permit period started on October 9, 2009. Initial dredging began in October 2009 and was completed on March 5, 2010 with flowlane disposal.
Dredged volumes are modest for the Toke Point Marina. This chronology of dredging through 2019 shows a return to least-cost pipeline dredging which would not have been possible without better understanding of sediment transport dynamics at Willapa Bay:
• 1958 New Construction: 184,000 cy Pipeline with upland disposal
• 1964 O&M 12,000 cy pipeline with upland disposal
• 1970 O&M 16,500 cy pipeline with upland disposal
• 1974 O&M 14,000 cy pipeline with upland disposal
• 1987 O&M 27,800 cy clamshell with open-water disposal
• 1991 O&M 27,100 cy clamshell with open-water disposal
• 1998 O&M 27,650 cy clamshell with open-water disposal
• 2009 O&M pipeline with flowlane and beneficial use disposal
(underway and funded by Port of Willapa Harbor)
Federal Channel Port Berthing Areas
20,000 cy 45,000 cy
• 2012 O&M 15,000 cy 40,000 cy
• 2015 O&M 15,000 cy 40,000 cy
• 2019 O&M 15,000 cy 40,000 cy
CONCLUSIONS AND FUTURE CHALLENGE:
Collaborative strategies were complimented by access to appropriate technical studies, which allowed the Port of Willapa to overcome challenges for accomplishing maintenance-dredge-and-disposal operations at a Federal, low-use navigation project. The next challenge for the Port is to seek congressional authority and grants for future Federal funding of Port dredging of the Federal entrance channel. As a bottom line for the Toke Point low-use project at Willapa Harbor, the Seattle District initially took the lead, but now the local sponsor has to assume that role to meet its dredging needs.
Source: usace, December 16, 2010; Image: ellicott