Technical Integrity / Collaboration / Exceptional Results

Santa Cruz Harbor, Inner Harbor Dredge Monitoring

Santa Cruz Harbor, Inner Harbor Dredge MonitoringIn fall 2005, Integral scientists, under prior employment, designed and conducted a monitoring program for the Santa Cruz Port District’s inner Santa Cruz Harbor dredging cycle. The program was the third in a series of inner harbor dredge monitoring programs that examined sediment conditions during different seasons and weather conditions over the course of 5 years.Santa Cruz Harbor, located in the Santa Cruz Bight of northern Monterey Bay, California, experiences sediment accumulation in two locations that require dredging. The Harbor was permitted to dredge a mixture of 40 percent sand and 60 percent mud from the upper harbor into the surf zone at a local beach. However, this fine-grained dredging event challenged EPA’s “80/20 guideline,” which states that dredged, nontoxic sediment released into the surf zone should contain at least 80 percent sand. Before these dredge monitoring programs were in place, it was considered too great a risk to release sediment containing more than 20 percent mud into the surf zone, because it might have damaging effects on the coastal environment.

The project goal was to determine if sedimentary changes occurred on the beaches and in nearshore benthic habitats of the Santa Cruz Bight during the dredging period. A variety of data were collected to monitor the experimental dredging event as well as natural conditions in the Santa Cruz Bight, including local stream flow, wave and current data, beach and offshore sediment sampling, pre- and post-dredging multi-beam surveys and benthic habitat mapping, and numerical sediment transport modeling.

Monitoring program data showed that the Santa Cruz Bight experiences high wave and current energy that can efficiently transport silt, clay sediment, and sand-sized material away from Santa Cruz Harbor. These results imply that the Santa Cruz Bight could accommodate a larger volume of inner Santa Cruz Harbor dredge sediment.

The project team developed a state-of-the-art field and modeling approach to nearshore disposal assessment that effectively addressed regulatory concerns. This approach was developed in close collaboration with local stakeholders and scientists to ensure a rigorous evaluation was completed. The project included effective public outreach to gain project acceptance.

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