White Slough Wetlands Enhancement

Restoration of Humboldt Bay National Wildlife Refuge’s White Slough Unit provides an opportunity to regain 40 acres of salt marsh in Humboldt Bay.

Restoration of White Slough provides an opportunity to regain 40 acres of salt marsh in Humboldt Bay.

The purposed of the wetland enhancement work on the White Slough Unit of the Humboldt Bay National Wildlife Refuge was to restore 40 acres of coastal tidal wetlands on diked historic tidelands, transforming the site from a near-monoculture of brackish wetland into a dynamic complex of salt marsh and brackish wetlands, providing ecological and climate adaptation co-benefits, including reducing the threat of dike failure and risk to the Highway 101 corridor.

During the late-nineteenth and early twentieth centuries, diking and filling reduced Bay tidal wetlands from an estimated 9,000 acres to only 900 acres today. Like much of Humboldt Bay’s shoreline, White Slough was separated from Humboldt Bay by a non-engineered historic earthen dike. The dike was in very poor condition, experiencing seepage, erosion, and occasional overtopping. Cut off from Humboldt Bay by this dike, the White Slough elevations subsided up to three feet below undisturbed native marsh plain elevations. Restoration of White Slough included placement of approximately 250,000 cubic yards of sediment to establish elevations suitable for tidal wetlands to reestablish and persist. Other restoration activities include lowering and breaching the dike in several locations to provide reconnection to Humboldt Bay and reconnecting Chism Creek to the project area to restore sediment deposition and accretion at the site, helping restored wetlands keep pace with sea level rise.

This project was funded by the State Coastal Conservancy, National Coastal Wetlands Conservation Grant Program, California Natural Resources Agency Environmental Enhancement & Mitigation (EEM) Program, and California Department of Fish and Wildlife Wetlands Restoration for Greenhouse Gas Reduction Program.

The final breach reconnecting White Slough to Humboldt Bay, August 2021
Tidal marsh reestablishing at White Slough , August 2021.