Issues

The estuarine main channel has widened and shallowed from excessive sediment delivery linked to land use upstream and destabilization of channel banks from removal of riparian vegetation;

The loss of approximately 90 percent of original wetland habitat and tidal prism is from land conversion and the affects of levees and tide gates. The network of levees and tide gates in the Eel River estuary has reduced channel connectivity and blocked the ebb and flood of the ocean tides;

Swickard (1899) estimated a reduction of tidal prism of about 877,000 cubic yards (about 543 acre feet) that was caused by the early damming the southern salt marshes;

The diking which occurred east of McNulty Slough probably reduced the tidal prism even more than did the actions addressed in Swickard’s deposition;

The reduction in salt marsh habitat area and loss of channel connectivity and complexity has altered the natural ecosystem process involved with nutrient cycling, food production, and resulted in a loss of habitat area and diversity.

Findings Related to Issues

A loss of channel connectivity due to levees and tide gates adjacent wetlands and sloughs, limits rearing area, nutrient cycling, food production, and habitat diversity available to salmonids and other valuable fishery resources;

A loss of channel depth may limit the carrying capacity for adult salmon holding in the estuary before rains allow passage upstream to spawning areas;

The reduction of tidal prism limits available wetland habitat and limits scour potential needed to maintain slough channel functions;

A relative paucity of woody debris in the estuary may limit shelter habitat needed by juvenile salmonids during large winter runoff flows and also limits cover to escape from predators.

Recommendations

Flow and Water Quality Improvement Activities:

Insure the supply of freshwater inflows are provided for maintaining estuarine habitat diversity and to drive ecosystem processes that fish, wildlife, and vegetative communities depend on for part or all of the life history cycles;

Use levee set backs, reconfiguration, or levee removal strategies to develop a wider flood plain that restores natural sinuosity, improves connectivity with sloughs and adjacent wetlands in North Slough channels or other areas constricted by levees;

Increase tidal prism by modifying tide gates and/or removing leveesto restore tidal and riverine flow and connectivity between the main channel and slough channels and adjacent wetlands;

Continue to prevent or reduce cattle waste and agricultural and dairy by-products from entering stream and slough channels;

Take measures to ensure that water treatment facilities in Fortuna, Fernbridge, Loleta, Ferndale and other nearby areas do not contaminate estuarine waters.

Erosion and Sediment Delivery Reduction Activities:

Land managers should work to maintain and/or establish adequate streamside protection zones to encourage growth of riparian vegetation to help stabilize stream banks;

Increase slough channel scour potential by restoring tidal prism in historic tidal wetland areas;

Continue efforts such as road improvements, good maintenance, and decommissioning and other erosion control practices associated with all land use activities throughout the Eel River basin to reduce sediment delivery to the estuary;

Armour eroding banks near Fernbridge or other such areas with bioengineered techniques that secure large wood pieces into banks and integrate live trees into the stabilization project.

Riparian and Instream Habitat Improvement Activities:

Where feasible, restore or improve width of riparian vegetation stands with native vegetation (Sitka spruce, cottonwood, redwood, alder willow) along the banks of lower Eel River and slough channels;

Work to restore natural functioning tidal and drainage patterns within the McNulty Slough portion of the Ocean Ranch Wildlife Area and other north slough area channels and wetlands. The project should address water temperature, water flow regimes and other parameters needed to promote seasonal and/or year round use by fishery resources;

Candidate sites for levee removal include both sides of McNulty Slough and its tributaries, and the land west of McNulty slough. The northwestern delta should be expanded rapidly outward from earlier project sites;

Consider conservation easements or land acquisitions that would promote the removal or modification of tide gates and levees in order to restore tidal prism and tidal wetlands;

Develop policy or regulations that prohibit or reduce wood removal from within the estuarine channel banks (0.25 mile upstream from Fernbridge to the river’s mouth) and out to 50 feet from the high tide shore line of the North Bay. Such regulations should protect wood pieces on stream banks needed to reduce potential from further bank and beach erosion, provide instream shelter during high flows for fish, and protect bank restoration projects;

Develop plans to eradicate or control the spread of invasive Spartina densiflora. An optimal strategy for low to medium sized budgets is to remove Spartina in areas where it grows in low density subpopulations.

Education, Research, and Monitoring Activities

Develop an inclusive estuarine ecosystem management and monitoring plan that works with natural processes to restore tidal connectivity to wetlands and increases tidal prism;

Investigate potential impacts form sea level rise, increased storm intensity and other impacts to the estuary related to climate change;

Add to baseline data regarding habitat utilization by all estuarine species;

Study and assess the status of estuarine conditions needed to complete specific life history requirements for salmonids and other estuarine dependant fish and invertebrate species;

Continue and expand water quality monitoring (including temperature and D.O).of nutrient levels that may be elevated from runoff from cattle pastures, sewage treatment facilities or other sources;

Monitor the progress of natural succession (biotic and abiotic) and fish and wildlife resource utilization within the Ocean Ranch wildlife area. This should include the estuarine area and the fresh water impoundment;

Determine the percentage of adult Chinook returning to the Eel River that show extended estuary rearing patterns by using scale analysis or other means;

Investigate operations of tide gates on McNulty Slough, Hawk Slough, Centerville Slough and others to determine effects and/or loss of properly functioning saltwater/freshwater ecotone;

Investigate dynamics of breaching the seaward levee at the south end of McNulty Slough to increase tidal prism and develop connectivity between wetlands and other sites to restore wetland connectivity.