Southwest Washington Littoral Drift Restoration Project

Introduction

Sediment analysis has shown that the sand beaches of the Washington coast, from the mouth of the Columbia River north to Grays Harbor, are all composed of the same type of sand. These sands originate from the Columbia River and have been carried to the mouth of the river and deposited on the Columbia River Bar over the past 10,000 years. Wave action and longshore currents have gradually re-worked these Columbia River sediments, carrying them northward (Sternberg 1986) and creating the beaches of the Washington coast. The term littoral drift refers to the process of waves and currents carrying sand along the shore.

Man-made changes to the Columbia River and to the mouth of the Columbia River (MCR) have contributed to a reduction in the sand supply to the Pacific Northwest's coastal system by a factor of three from 5.6 million cubic yards per year between 1878 to 1935 to 1.4 million cubic yards for the period 1958 to 1997 (Gelfenbaum et al. 1999). Ongoing erosion of the mid-continental shelf and nearshore at the MCR, including Peacock Spit to the north and Clatsop Spit to the south, are resulting in increasing nearshore wave energy, increased shoreline erosion, and increased risk of jetty undermining and breaching (Allan 2002). Long-term net removal of littoral sediment from the Columbia River system by dredging amounts to 3.3 million cubic yards per year for the period 1939 to 1999 (Allan 2002). Under the proposed channel deepening and maintenance project, the USACE would continue to dredge and dispose of approximately 4.5 to 5.7 million cubic yards per year. A major concern with existing disposal practices is that much of the dredged sediment is disposed in water that is too deep to allow efficient return to the nearshore by coastal processes. As a result, significant quantities of sediment are effectively lost from the littoral system.  

The Littoral Drift Restoration (LDR) Project is a long-term strategy for disposal of dredged sediment at the MCR. The purpose of the project is to restore significant quantities of sediment directly to the littoral drift on the Washington Coast to the north of MCR. The objective of the project is to place dredged sediment directly into the intertidal zone on Benson Beach on the north side of the North Jetty. A project vicinity map is shown below.

The LDR Project is consistent with the origin, objectives, and intent of the US Army Corps Regional Sediment Management (RSM) program (e.g., Martin, 2002). The concept of RSM originated with the notion of coordinating coastal dredging activities for the purpose of retaining sand in the littoral zone in order to foster more balanced, natural system processes, and reduced project costs. The project under development is intended to promote sustainability principles through an approach that considers competing demands for sediment resources, accommodates multiple objectives, and adopts a long term perspective to develop, demonstrate, and implement a dredging and placement program and achieve acceptable cost efficiencies.

Demonstration Project

The Coastal Communities have requested an addition to the Corps of Engineers Operations and Maintenance, Regional Sediment Management Program, budget for FY ’05 with language directing the funds be used for a demonstration project using a sump re-handling to pump sand over the North Jetty at the Mouth of the Columbia River (MCR) in associated with the annual dredging program.

Technical analysis shows that a re-handling sump is a likely cost effective method to efficiently move a sufficient quantity of sand for a long-term restoration project (Pacific International Engineering 2004). The demonstration project proposed for implementation during the 2006 dredging season is intended to provide information on sump/re-handling operations to assess the feasibility of placing much larger volumes of sand into the littoral system at Benson Beach. The demonstration project will involve removal of approximately 500,000 cubic yards of sand from the sump and placing the material in the intertidal zone at Benson Beach. The actual volume of material to be re-handled will depend on available funds and the construction bids received.  

A sump zone has been defined by considering navigation and operations, aquatic species and habitats, and sump and jetty stability. The identified sump zone and a potential sump location are shown in the figure below. The potential sump footprint measures 3,000 ft x 600 ft; the depth of the sump will be limited by the choice of dredging equipment and the desired volume of material from a given footprint, and is expected to be less than -75 ft MLLW. It is anticipated that the sump will have side slopes of approximately 5:1. As depicted, the sump could provide up to 1 million cubic yards of dredged material. Obtaining enviornmental clearances for a zone larger than the actual sump will allow the dredging operators flexibility in approach, promoting efficiency and reducing costs. One restriction that will be placed on the sump construction within the zone is that it must form a contiguous area (i.e., the sump cannot be composed of several separate excavations).

A pipeline dredge will be deployed to dredge sand from the sump area and the dredged material will be pumped through a 16- to 30- inch diameter pipeline over the top of the North Jetty onto Benson Beach. The area for placement of sand on Benson Beach extends from approximately 1,500 ft north of the North Jetty to a point approximately 4,500 ft north of the jetty. It is likely that the material will be placed in "strips" measuring approximately 150 ft by 2,000 ft. The strips will be placed by beginning at the southern end and moving to the north by incrementally extending the pipeline. The process will then be repeated until all the material is placed. The preferred pipeline route extends along the edge of the upper beach scarp, or the seaward edge of the vegetation in areas where there is no scarp, to the point of deposition. The pipeline will likely be buried in at least some locations to mitigate safety risks to beach users. Some re-working of the placed material with bulldozers will be required. The constructed profile will be relatively flat with a front slope on the order of 20:1 from approximately +14 to -10 ft MLLW.

Conceptual illustrations of the sand placement are shown below.

Refilling of the sump will be achieved by bottom dumping from hopper dredges. This refilling will be performed either concurrently with or following the excavation of the sump. The dredging contract will clearly specify that the sump must be refilled prior to the end of the dredging season.

The project will be conducted concurrently with Portland District dredging and disposal operations at the MCR, which typically occur between June and September. The timeframe for excavating the sump and placing the material will likely range from 1 to 2 months, depending on the equipment used and weather and wave conditions encountered during operations. During periods of bad weather, the pipeline dredge may need to be withdrawn from the sump area to the more sheltered area in the northeast corner south of the North Jetty or to a location east of Jetty A. It is likely that the pipeline dredge will be anchored to the seabed in the sump area using a four-point anchoring system.

Baseline data are being collected on site that will allow project performance to be assessed. Measurements of waves, currents, and suspended sediments will be obtained in the proposed sump and placement areas. Measurement locations are chosen to characterize physical processes in the sump area and on Benson Beach. The measurments will determine hydrodynamic conditions forcing movement of sediment in these areas and allow validation of models for dispersal of sediment from the placement area and potential for sediment movement in the sump area. Sediment sampling will be conducted in the placement area for comparison with sump area and dredged sediments to ensure that grain size, mineralogy, and shape are consistent; project monitoring may also include a sediment tracer analysis to provide information on the trends of dispersal of sediment from the placement area. The nearshore and littoral system response to the sand placement will also be monitored by aerial photography and regular surveys using RTK GPS. The surveys will provide approximately monthly maps of the intertidal topography, and nearshore bathymetry before, during, and for several months after, the demonstration project. The areas surveyed will include the sump area, the sand placement area, and the areas south and the north of the placement area including all of Benson Beach and portions of Long Beach. This information will be supplemented by video remote sensing of portions of Benson Beach with the Argus video monitoring system installed at North Head. Longer term monitoring will involve quarterly surveys of beach profiles in the project area and on beaches to the north. Numerical sediment transport models will also be applied to evaluate the short term and long term dispersal patterns and fate of sediment placed on Benson Beach.

Project sponsors:

Pacific County and Coastal Communities of Southwest Washington

Portland District, US Army Corps of Engineers

References

Allan, L.C. 2002. Columbia River Littoral Cell Technical Implications of Channel Deepening and Dredge Disposal. Open File Report O-02-02. Oregon Department of Geology and Mineral Industries.

Gelfenbaum, G., C.R. Sherwood, C.D. Peterson, G.M. Kaminsky, M. Buijsman, D.C. Twitchell, P. Ruggiero, A.E. Gibbs, and C. Reed. 1999. The Columbia River Littoral Cell: A Sediment Budget Overview. Proceedings of the Coastal Sediments '99 Conference. American Society of Civil Engineers, pp 1660-1675.

Martin, L.R. 2002. Regional Sediment Management: Background and Overview of Initial Implementation. IWR Report 02-PS-2. Prepared as part of the U.S. Army Coprs of Engineers Institute for Water Resources Policy Studies Program.

Pacific International Engineering. 2004. Dredging Operations and Sand Placement Alternatives, Southwest Washington Littoral Drift Restoration Project, Mouth of Columbia River, North Jetty. Draft report prepared for the Coastal Communities of Southwest Washington.

Sternberg, R.W. 1986. Transport and Accumulation of River-derived Sediment on the Washington Continental Shelf, USA. Journal of the Geological Society of London. Vol. 143, pp. 945-956.

Downloadable Reports

Pacific International Engineering, 2006. Littoral Drift Re-handling Sump: Evaluation of Geotechnical and Structural Effects on the North Jetty – Version 2.0: Southwest Washington Littoral Drift Restoration Demonstration Project. Prepared for the Coastal Communities of Southwest Washinton.

Pacific International Engineering. 2005. Dredging Operations and Sand Placement Alternatives, Southwest Washington Littoral Drift Restoration Project, Mouth of Columbia River, North Jetty. Report prepared for the Coastal Communities of Southwest Washington.

Pacific International Engineering, 2003. 2003 Field Monitoring Report – Waves, Currents, and Sediment Transport at North Jetty: Evaluation of Dredged Sediment Re-handling: Mouth of Columbia River , North Jetty, Report prepared for the Coastal Communities of Southwest Washington.

Appendix B - 2003 Field Monitoring Report

David Evans & Associates, 2003, Benson Beach Phase III - Geophysical Invesitgation, Report for the US Army Corps of Engineers, Portland District, CENWO-OP-NWH, Contract DACW57-01-D-0001.

Williams, G.D., Pearson, W.H., Evans, N.R., Anderson, M.G. 2003 Benson Beach Demonstration Project: Composition and Abundance of Biota at Three Alternative Sump Sites. PNNL-14522. Prepared for Portland District U.S. Army Corps of Engineers under a Related Services Agreement with the U.S. Department of Energy Contract DE-AC06-76RLO 1830

Kaminsky, G. and Ferland, M. 2003. Vibracores at the Mouth of the Columbia River. FY2003 Initial Report Prepared in support of US Army Corps of Engineers and Washington Department of Ecology Cooperative Agreement. Ecology Publication #03-06-031

Monthly Littoral Drift Restoration Newsletters
Beginning in March 2005 Pacfic International Engineering began producing a monthly newsletter as another means of communicating information on the Littoral Drift Restoration project. If you would like to be added to the mailing list for this newsletter, please send an email to Marie Garrett at marieg@piengr.com. You can also download a copy of the past newsletters by clicking the links below.

LDR News March 2005

LDR News April 2005

Littoral Drift Restoration Project Meetings

Click here to download the Memorandum for Record for December 9, 2005

Click here to download the Memorandum for Record for November 3 , 2005

Littoral Drift Restoration Meeting Scheduled for July 27, 2005
The next meeting on the Southwest Washington Littoral Drift Restoration (LDR) project is scheduled for July 27, 2005. The meeting was to review environmental clearances for the 2006 demonstration project, discuss authority and funding issues and review project schedule. Download the Memorandum For The Record for the July 27 Meeting.
Click here to download the Memorandum for Record for July 27 , 2005

Littoral Drift Restoration Project Meeting Scheduled for July 13 , 2005
The next meeting on the Southwest Washington Littoral Drift Restoration (LDR) project is scheduled for Wednesday, July 13, 2005. This meeting will be held on-site at Benson Beach to allow the group an opportunity to view the sand placement area proposed as part of the 2006 demonstration project.

We plan to meet at the Cape Disappointment State Park registration booth at 11:00 a.m. and will head to the beach from there. We will try to wrap up the meeting no later than 2:00 p.m.

Driving directions:
From Seattle, take I-5 south to SR 8. Follow SR 8 west to Montesano. From there, take SR 107 south to U.S. Hwy. 101 and continue south to Long Beach Peninsula. Follow signs to Ilwaco and the park.

From Portland, take I-5 north to Longview, then SR 4 west to U.S. Hwy. 101. Then drive south to Long Beach Peninsula. Follow signs to Ilwaco and the park.

Please contact me at marieg@piengr.com or 509.669.1800 if you have any questions or need more information.

Littoral Drift Restoration Project Meeting Scheduled for June 22, 2005
The next monthly meeting of the project team with regualtory agencies is scheduled for June 22 (10 AM-noon) at the Port of Longview offices at 10 Port Way in Longview. The main topic of discussion will be the Argus system at North Head and the physical monitoring program for the demonstration project. For further details, please contact Marie Garrett, Project Coordinator (marieg@piengr.com, 509-669-1800).

Click here to download the Memorandum for Record for June 22 , 2005

Littoral Drift Restoration Project Technical Meeting Scheduled for May 25, 2005
The next technical meeting is scheduled for May 25 (1 PM) at the Portland District offices.  The Coastal Communities and Corps technical team, along with representatives from the Department of Ecology, will discuss new work on questions concerning stability of the sump area and the development of a comprehensive monitoring program for the physical and engineering elements of the demonstration project.  A future technical meeting will focus on development of a biological monitoring program. For further details, please contact Marie Garrett, Project Coordinator (marieg@piengr.com, 509-669-1800).

Littoral Drift Restoration Project Meeting Scheduled for May 10, 2005
The next monthly meeting of the project team with regualtory agencies is scheduled for May 10 (10 AM-noon) at the Port of Longview offices at 10 Port Way in Longview. The main topic of discussion will be placement of dredged material at Benson Beach for the demonstration project. For further details, please contact Marie Garrett, Project Coordinator (marieg@piengr.com, 509-669-1800).

Click here to download the Memorandum for Record for May 10, 2005

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