How Do We Reduce Harm During Flooding?

Natural Resources

With flood recovery efforts estimated as high as $50 million and nearly 1,900 structures reported damaged, many families and businesses are displaced and recovering from the devastating flooding events across Whatcom County in November.

Individuals impacted by the flood are calling for solutions to prevent the next disaster. The quick-fix solution at the tip of many tongues? Dredging the Nooksack River. Proponents of dredging suggest removal of sand, sediment, and gravel with the intention of deepening river channels and increasing water capacity during high flow events.

Mountainous watersheds, like those that drain the volcanoes of the North Cascades, are naturally sediment-rich systems, especially as glaciers are receding and major flooding events are becoming more common.

“The Nooksack River is the second largest contributor of sediment to the Puget Sound Basin,” said Mike Maudlin, Nooksack’s Forest and Fish Specialist/Restoration Geomorphologist. “It contributes nearly 1.5 million tons of sediment per year, which is over 20% of the total load to the basin.” Due to climate change, melting glaciers expose more ground to erosion, he explained, and warmer winter weather means more precipitation falling as rain rather than snow, further increasing flooding and erosion. It is estimated that this latest flood may have washed up to two-years’ worth of sediment down the river in a single event.

The mainstem of the Nooksack River downstream of the Cedarville Bridge at Nugent’s Corner on November 17, 2021. Nooksack Natural & Cultural Resource staff member Lindsie Fratus-Thomas captured the flooding event during a helicopter ride to survey damages.

Proposals to remove sediment through dredging, however, are not new. Over the decades, gravel companies have tried to convince officials to allow sediment extraction from the Nooksack River for a profit. In 1990, gravel removal was widespread in the river, though its removal is not credited with impacting the historic flood event that occurred that same year. On Dec. 7, 2021, a proposal was brought to the County Council suggesting $250,000 for sediment studies, legal remedies, and negotiations for dredging the river, with the hopes of extraction and export to new markets. Neither the Nooksack Tribe nor Lummi Nation were consulted in bringing forward the proposal, though it included tribal properties. Both tribes voiced concerns, and the proposal was then tabled at the County Council committee level.  

A cultural concern is the exposure of historic tribal villages, if a dredging process were to take place in the river, said George Swanaset Jr., Natural & Cultural Resources Director. Sediment removal could, for example, uncover ancestral remains as the Nooksack Tribe has historic village sites up and down the riverbank.

Even with extraction, Nooksack’s Natural & Cultural Resource staff are among the voices who think sediment removal would not have been enough to prevent the impacts of the November 2021 flood.

“Our understanding is that the bigger the flood, the less effective sediment removal is for reducing flood levels,” said Ned Currence, Fisheries and Resource Protection Program Manager for the Tribe. “We had a big flood among a series of successive floods. It is doubtful sediment management would have prevented it.”

In fact, research suggests sediment removal is not proven to be an effective flood management strategy at this level. Using US Geological Survey reports, approximately 50,000 cubic feet per second of water was flowing in the Nooksack River on November 15, approximately 46,000 cubic feet per second of water above the average flow. Meaning, you would need an additional 142 dump trucks per second of sediment removed from the river to equal a normal river flow. Removing an amount of sediment to be significant is unrealistic as well as detrimental.  

Marine Drive bridge over the lower Nooksack River on November 17, 2021. Lindsie Fratus-Thomas.

Dredging also presents a major problem. The Nooksack River supports three Endangered Species Act (ESA)-listed species, including the Nooksack winter-run steelhead, Chinook salmon, and bull trout, who use the river for spawning, rearing and migration. A proposal to dredge could trigger an environmental impact statement.

Dredging can negatively impact habitat and offer direct damage to incubating eggs, rearing juveniles, and migrating fish, said Currence.

“Our salmon resources are in deep trouble, and we cannot support more negative impact to habitat. These Treaty-protected species are important to the Nooksack Tribe’s culture and its fishers.”

The latest proposal to the County Council suggests removing sediment from dry upland beds, to discourage impact on salmon habitat. However, the Nooksack River is constantly changing and shifting, especially during high flooding events. Dredging can have unpredictable consequences both upstream, as sediment backfills extraction holes, as well as downstream, as sediment disruption settles.

Homes flooded along Marine Drive on November 17, 2021, looking north towards the lower Nooksack River. Lindsie Fratus-Thomas.

Solutions & Actions to Reduce Harm

How does Whatcom County move forward? Can floodplain management integrate the needs of fish, agriculture, cities and towns, and be cost-effective flood protection?

“We still believe an approach that integrates salmon recovery with flood management, as was agreed to in the 2005 WRIA 1 Salmon Recovery Plan, is the best course of action,” wrote Nooksack Chairman Ross Cline, Sr. in opposition to the recent dredging proposal before the County.

With this, Whatcom County has taken the lead in developing a Flood Integration Planning (FLIP) process to update the Comprehensive Flood Hazard Management Plan, which brings together diking districts, federal, state and local regulatory agency staff, technical experts, landowner representatives and the tribes to integrate the needs of salmon, agriculture, cities and towns. This process began in 2017 and includes developing goals, management strategies, alternatives, and projects to reduce flood risks on the Nooksack River. Several pilot projects from this process are currently in the design phase, demonstrating that it is leading to on-the-ground action.

“We believe it is important to review what we have learned in the FLIP process as well as better understand this most recent flood, before planning remedial actions,” said Ned Currence, who is also on the Flood Integration Planning steering committee. FLIP receives funding and support from the Washington Floodplains by Design program, which has funded several flood risk reduction projects throughout the state.

However, there is not one fix-all solution to reducing flood risks. Even after the flood, many questions remain as to its full impact upon the landscape. Further research will help better understand pinch-points and the hydraulic outcome of this historic flood. Any actions moving forward will require careful review.

“While we share the County’s desire to mitigate the impacts associated with future flooding,” wrote William Jones Jr., Chairman of Lummi Indian Business Council, “we urge the County to take a measured and deliberate approach, that takes proper account of the important ecological aspects associated with the functioning of the Nooksack River and the needs of the native fish.”

“Our understanding is that the bigger the flood, the less effective sediment removal is for reducing flood levels.”

Once the results of the flood can be better understood, considering why the changes are occurring will help lead to better outcomes. Scientists at the Nooksack Tribe still have questions. To what extent are certain levees or bridges constricting the river? Where are the pinch-points? Can improved or restored sediment routing make a significant contribution? How do we plan for a variety of river bed elevations (aggradation and degradation) over time? As the upper mainstem degrades, will it work its way down to Everson? 

“If we can review what we know, answer some outstanding questions, and continue to try to work collaboratively to address needs without harming salmon, through FLIP for example, optimally that will improve longer-term conditions for salmon,” said Ned Currence.

“Long-term flood management and salmon recovery planning are critical to the future of Whatcom County and the Lummi Nation,” Chairman William Jones Jr., wrote opposing the proposal for dredging. “We believe a collaborative, cooperative approach based on sound science and informed by Indigenous insight is what is needed.”