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News Details

Humboldt Bay Maintenance Dredging

The City of Eureka (City) and Humboldt Bay Harbor, Recreation and Conservation District (District) are responsible for maintenance dredging of the public marinas, docks and boat launches in Humboldt Bay. The previous maintenance dredging was completed in 2007. As a part of the Coastal Development Permit for the previous maintenance dredging, the City and District were required to provide “annual reports detailing the efforts undertaken during the previous calendar year to prepare for future maintenance dredging in a manner that discontinues the past practice of nearshore disposal of dredged materials”. From 2008-2011, annual reports were provided to the Coastal Commission describing the securement of necessary properties, equipment and services for disposal of future dredged sediments at appropriate on-land disposal sites.

In 2012-13, there were changes made to the staff at the City and District overseeing dredge responsibilities. During this transition, there was an oversight of the permit condition requiring annual reporting to the Coastal Commission. No formal reports were sent to the Commission over the past four years. However, extensive resources and staff time have been spent over this time period to prepare for future maintenance dredging.

Dredging large volumes of material makes on-land disposal sites unfeasible. In order to make use of on-land disposal sites, there needs to be annual maintenance dredging so that the volumes are manageable. The only way to make this economically feasible was to make a capital investment so that all sampling and dredging can be done locally by staff. Over $1.5 million dollars have been spent on the purchase of a dredge, tender boat, work boat, piping, booster pumps and Vibracore sampling equipment. The costs for a sampling consultant and mobilization and demobilization by an out of the area dredge company annually would be cost prohibitive.

Including the capital investments over the past four years, the City and District have secured grant funding and worked with agencies on plans for dredge material disposal options. A Community Development Block Grant was secured to identify re-use options utilizing the District owned Redwood Marine Terminal facility. A Coastal Conservancy grant was obtained to also identify beneficial re-use options. And finally, staff worked to complete a draft Coastal Regional Sediment Management Plan which includes a Dredged Material Management Plan.

Along with these efforts, there has been new studies performed by the United States Geological Survey (USGS) in conjunction with the Coastal Conservancy and Ocean Protection Council which analyzed fine-grain sediment dispersal along the coast. The material being dredged from City and District facilities is approximately 70% fine-grain sediment and 30% sediment. Previously, there has been concerns expressed about the high ration of fine-grain sediment. The recent studies determined that fine sediment discharged onto the near shore did not result in observable deposition of fine-grained sediment on the beach or inner-continental shelf and that near shore dredge material disposal results in turbidity values significantly lower than those values observed during a large wave event or small flood. These studies are consistent with the monitoring data collected locally from previous dredge maintenance operations.

The Army Corps has estimated that 3 million cubic yards of material has been deposited into Humboldt Bay between the last two dredging projects of the main channels. Typically, there have been 1 million cubic yards. Due to this significant increase in sediment discharge into the Bay over the past two years, the associated problems at City and District facilities have become a safety and navigation concern.

At the Eureka Small Boat Basin Marina and Woodley Island Marina, the estimated volume needing to be dredged is ~100,000 cubic yards at each facility for a total of 200,000 cubic yards. Other facilities in need of maintenance dredging vary from 10,000 to 30,000 cubic yards. Because of the large volumes at the Marinas, on-land disposal options are not only cost prohibitive, but they are also more environmentally damaging. For the on-land disposal sites researched over the years, the maximum capacity is ~30,000 cubic yards. In order to dredge either of the Marinas utilizing an on-land disposal option, it would require a minimum of three separate dredging projects over three different time frames. This would not only increase the associated costs, but more importantly would significantly increase the associated environmental impacts.

Based on all of this, staff has developed a hybrid approach to future maintenance dredging which would start this year. Because of the environmental impacts and economic viability of on-land options for the two Marinas, there are three options for maintenance dredging which have less environmental impact. For the first two years, staff research identifies the disposal of the dredge material through a temporary outfall one-quarter mile off the coast, in-bay disposal or beach disposal. For subsequent maintenance projects, staff proposes disposal at an on-land location or the Redwood Marine Terminal.

Based on the results of sampling at both Marinas, the USGS studies and monitoring data from previous dredge maintenance projects, the research and data demonstrate that the beach disposal option for the two Marinas is the least environmentally damaging feasible alternative. Furthermore, the 60,000 cubic yards of sediment dredged that is not fine-grain from the Marinas will be beneficial to address some of the erosion concerns north of the jetty. The temporary outfall option would create turbidity impacts in the open ocean and not allow for mitigation and monitoring of unexpected trash and other material being discharged into the ocean. The in-bay disposal option would create similar concerns and also potentially effect the benthic community in the Bay as tides within the Bay may not transport the fine sediment adequately.

The City and District have received the testing results for sediment samples collected from both Marinas. Dioxin concentrations have decreased in these areas and are below any applicable regulatory screening levels. Metal data is below regulatory screening levels with the exception of total chromium which is consistent with naturally occurring concentrations. Polychlorinated biphenyls (PCBs) and Pentachlorophenol (PCP) concentrations were below laboratory detection limits, and Polycyclic Aromatic hydrocarbons (PAHs) were identified at low concentrations in the Small Boat Basin. The concentrations of PAHs present in the Small Boat basin were below any applicable regulatory screening levels.

Recently, staff and elected officials have heard concerns about “sludge” being deposited on the beach. The sediment from the Marinas is a black sludge with an odor. This material is not black and smelly because of any sort of contamination, but it is a nutrient rich material which is a result of the breakdown of organic material being deposited at the Marinas. As noted in the USGS studies referenced earlier, fine-grain sediment from dredge operations can be an important source of nutrients for estuarine ecosystems, the continental shelf and the California Current. The material from the Marinas is very similar to the material from a compost pile. It is a nutrient rich material that is the result of organic matter breaking down. Just like the dredge material, composted material smells and looks like “sludge”. As mentioned previously, the material from the two Marinas is no more contaminated than the sediment on a lawn, in a local park or on a public beach. As mentioned previously, the contaminant concentration levels in the sediment from the Marinas are below regulatory screening levels. The material in no way poses a public health concern.

In summary, City and District elected officials and staff have analyzed several disposal options and their impacts to the environment since the last maintenance dredging in 2007. During this 10 year period the most economical and environmentally responsible options have been identified using analysis from previous beach disposal monitoring, current sampling data and USGS reports. The nutrient rich material to be dredged is organic matter that enhances marine ecosystems and a portion of the dredge materials will be beneficial to address erosion concerns north of the North Jetty.

The City and District are committed to safely maintaining its Marinas by using the most scientific, economical and environmentally responsible dredging methods. The identified methods of dredging will allow for coastal access for all, while safely managing its docks and Marinas.

For additional information, please contact Miles Slattery at mslattery@ci.eureka.ca.gov or 707.441.4184