The beach and dunes of Humboldt Bay National Wildlife Refuge are at the vanguard of sea level rise and other climate impacts. The foredune is an important feature that buffers the effects of extreme storms, and the entire dune system protects the estuarine systems behind it. UFSWS and its partners have posed the question of what our dunes will do in response to sea level rise and extreme events, and what measures we can take to increase resiliency. To answer these questions, the refuge has engaged in a collaborative, six-year research project known as the Humboldt Coastal Resilience Project (formerly, Climate Ready Project). The project has been funded by the State Coastal Conservancy, Bureau of Land Management, and the Ocean Protection Council. Geographically the project spans the Eureka littoral cell. A littoral cell is a stretch of coastline characterized by a closed sediment circulation cell, i.e. sediment does not enter or leave the cell. The Eureka littoral cell stretches from Trinidad to Centerville beach.

Topographic Transects

A total of 73 transects were established along the littoral cell. Transects begin on the beach and extend inland for various distances. Transects are parallel with prevailing wind direction. There are points on the transects at 2-4 m intervals at which vegetation and elevation are measured. Crews visit the transects twice a year, in summer and winter. Each crew consists of a “rover” and a vegetation person. The rover takes elevation measurements using a real time kinematc (RTK) GPS (each transect is tied to a benchmark of known elevation). Following behind the rover, the vegetation person places a quadrat over the elevation point and takes vegetation measurements including vegetation type, cover, and height.  The data from these transects will ultimately be used in a model to predict climate-driven changes.

Adaptation Sites 

A total of three Adaptation Sites have been established. The purpose of these sites is to test methods that can potentially increase resilience of the dunes to climate impacts. The Lanphere adaptation site was established in 2015. It originally consisted of a foredune dominated by invasive Ammophila arenaria. Ammophila was removed by the California Conservation Corps. The foredune was then replanted using 3 different configurations of native plants: Elymus mollis (the native dune grass), dune mat, and a mix of the two. The purpose of this adaptation site is to test the hypothesis that restoration to native species increases the resilience of the foredune. Monitoring of the site occurs twice annually in May and October. Terrestrial Lidar scanning is used to collect detailed topographic data over the entire site. Change detection can then be used to quantity changes. To date, the data show that removal of Ammophila reestablishes the sediment budget, allowing sand to once again reach the backdune.

A second adaptation site was established at The Wildlands Conservancy’s property on the South spit of the Eel River. This is an area of sediment deficit, and the foredune has been breached in several places allowing sand to bury a drainage ditch serving agricultural lands to the east. A new foredune was constructed in one of the breaches. This was accomplished using heavy equipment and moving sand from the overwash fan, recontouring the foredune. Although this is not a long term solution to the sediment deficit problem, it allows for a short term response while landowners make plans for the long term.

The third adaptation site is located north of the Lanphere adaptation site, Similarly, it was covered by Ammophila arenaria. Methods of removal differed, with the Ammophila burned and then, after it greened up, sprayed with herbicide (imazapyr). This adaptation site will not be planted, in order to assess whether planting is a necessary part of this adaptation method.

Sediment Budget 

A critical part of understanding climate impacts to dunes is understanding the littoral cell sediment budget. Do we have enough sediment reaching the beaches to maintain our beaches and dunes? Past work on the sediment budget has been found to overestimate the sand inputs. This task will use existing data on sediment transported by our rivers and creeks, and develop updated sediment budget numbers.

Shoreline Change Analysis 

The behavior of the beaches over the long and short term contributes to our understanding of shoreline change. In this task historic photos going back to the 1930s were examined, and the shoreline traced. Specialized software is then used to calculate the rate and direction of change. Based on this analysis, we identified erosional hotspots on the North Spit just north of the jetty, and the entire south spit of the Eel River.

Vulnerability Assessment 

Vulnerability assessments are tools used to prepare for climate change impacts. The VA will look at multiple measures of vulnerability and rank them. For example, LiDAR imagery shows detailed topographic data for the littoral cell. The VA will conduct a change analysis for the 2010 and 2015 data sets to see where erosion or accretion is occurring. The shoreline change analysis will also contribute, as will data from the topographic transects. The VA will include natural features, infrastructure, and cultural resources.

Stakeholder Involvement 

Doing research in a vacuum will not lead to successful implementation of adaptation strategies. The Coastal Conservancy will spearhead a stakeholder engagement group both to convey results from this research and to elicit feedback.

Public Outreach 

The Friends of the Dunes will make results of the research available to the public through their website and newsletter.