Mad River Slough – Wadulh Lagoon Restoration Project

Wadulh Lagoon Tidal Wetland Enhancement Project

The Wadulh Lagoon Restoration Project aims to revitalize tidal wetlands and rejuvenate riparian forests along Mad River Slough in Humboldt County, Humboldt Bay. The initiative involves converting diked agricultural working lands with marginal and subsiding pasture into a diverse wetland environment, encompassing salt marsh, brackish marsh, mudflat, and subtidal/intertidal eelgrass habitat. Additionally, it seeks to establish ecological connections between Mad River Slough and the forested wetlands at the Lanphere Dunes’ base, reinstating full tidal hydrology. The project focuses on enhancing habitat conditions for resident and migratory neotropical birds, shorebirds, and aquatic species while safeguarding existing forested wetlands from saltwater impacts. Key objectives include minimizing wetland conversion to mudflat, supporting eelgrass through appropriate hydrologic conditions, ensuring the long-term sustainability of fringing salt marsh, and protecting adjacent properties and the Refuge Access Road from tidal flooding.

Project Background

Wadulh is the word for dunes in the Wiyot language, and the name Wadulh Lagoon was selected in recognition of the Wiyot Tribe’s significant cultural connection to the Project area. The Wadulh Lagoon Restoration Project is located in the Lanphere Dunes Unit of the Humboldt Bay National Wildlife Refuge, just south of the Lanphere Road Bridge, west of Arcata, CA. Initially intended as a wetland mitigation bank for highway construction impacts, the 78-acre Wadulh Lagoon parcel was acquired by Caltrans and later donated to the US Fish and Wildlife Service (USFWS) in July 2021 due to non-compliance with Caltrans’ mitigation credit requirements. Previously the project area, located adjacent to the Mad River Slough, was converted to agricultural land use through the construction of a levee on the west bank of Mad River Slough, the establishment of drainage ditches, and the installation of a tide gate. Historical mapping from 1870 reveals that a large portion of the low pasture area was intertidal mud flat or sub‐tidal with a band of salt marsh vegetation adjacent to the forested wetlands prior to diking and draining.

30% Project Design Plans (not for construction)

Construction Actions

Existing Conditions

Habitat Projection

Construction Actions