The record-breaking rain and devastating flooding we experienced in November 2021 caused widespread damage and devastation, especially to people who live in the Nooksack River flood overflow corridor including the communities of Everson, Nooksack, and Sumas.  People are understandably concerned and looking for what can be done to prevent this from happening again. Some are advocating for “dredging the river” as the principal way to prevent future flooding, yet experience has shown that this may not provide the relief people want to see.  

“Dredging” (or, more accurately, gravel removal), will not by itself prevent flooding. To have any sort of meaningful impact on the kind of flooding we saw in November 2021, vast amounts of sediment would need to be removed. It could actually increase flood risk in other areas. These impacts must be carefully considered and compared against other flood reduction methods that may be more effective and protect more people overall.  While gravel removal alone will not prevent flooding, it is not “off the table” and could be an effective method to reduce flood risk in certain situations when used alongside other flood prevention methods. 

The following Frequently Asked Questions regarding gravel removal provide information on what it is and why it is not the principal solution to reduce Nooksack River flood risk.

Gravel Removal FAQ’s

What is dredging?

Dredging is the removal of sediments from the bottom of lakes, rivers, harbors, and other bodies of water. These sediments can include gravel, sand, silt, and clay. Dredging usually implies the removal of sediment from below the water surface and is often done in water bodies to allow for navigation. The Nooksack River has not been dredged in this manner in recent history.

But wasn’t the Nooksack River dredged into the 1990s? 

In the past, gravel and sand were removed from exposed bars along the river above the water line. This type of sediment removal, often called “gravel bar scalping,” was conducted by various commercial gravel companies from approximately the 1960s until the mid to late-1990s. This work was not performed as a flood reduction effort. It was done to provide gravel for adjacent landowners and as a commercial aggregate (gravel) source. 

Did it prevent flooding?

No. Gravel bar scalping did not prevent flooding in November 1990 in the Everson, Nooksack and Sumas areas, when one of the biggest floods to date caused widespread damage, nor did it prevent flooding in 1989 and 1995. See: Floods of November 1990 in Western Washington, U.S. Geological Survey  

Why did gravel bar scalping stop?

Gravel bar scalping by commercial gravel companies stopped in the late 1990s. This was due in part to increased permitting requirements including a mid-1990s ruling that a U.S. Army Corps of Engineers (USACE) permit would be needed to ensure the protection of water quality under the federal Clean Water Act. This was followed in 1998 by the listing of three fish species (bull trout, Chinook salmon, and steelhead) as “threatened” under the Federal Endangered Species Act. The increased permit scrutiny, mitigation requirements, and the extra handling costs needed to transport scalped material to an upland stockpile location all contributed to increased costs of scalping to the point where it was not commercially viable compared to mining from nearby sand and gravel pits. 

Why aren’t the agencies involved in river management pursuing gravel removal more aggressively? 

The Nooksack River produces a tremendous amount of sediment.  It’s estimated to carry 1.4 million tons of sediment (including gravel, sand, and silt) per year (source: USGS Fact Sheet 2011-3083 Sediment Load from Major Rivers into Puget Sound and its Adjacent Waters). How gravel moves through a river system is not well understood. River systems are dynamic and there currently are no computer models that can predict how sediment moves during and between floods with any degree of reliability, though research is currently underway at the University of Washington. The river’s response to weather events and human intervention is not always predictable. If actions are taken without a thorough understanding of river processes, unintended consequences may result. If the river is starved of gravel in one reach because too much gravel was removed, it may result in more erosion downstream as the river has the ability to carry more sediment.

Shouldn’t we at least study the benefits of gravel removal to see if it is effective?

We have studied it a number of times over the past few decades.  Most recently, in 2013, Whatcom County sponsored a gravel removal pilot study to look at the potential benefits of gravel removal. The results of this study showed that gravel removal would have negligible benefits even at smaller flood flows. The study also showed that other factors, such as a constriction in the levees downstream of the pilot area gravel bars, had a much greater effect on flood heights than gravel accumulation. The study showed that opening up constrictions on the river and reconnecting the floodplain would reduce flood heights by a greater amount and would not have to be repeated every year.  

What permitting is required for gravel removal from the Nooksack?

Removing gravel from any river or stream requires permits from local, state, and federal agencies. The U.S. Army Corps of Engineers (USACE) is the lead federal agency who reviews and approves permits to remove river gravel. The USACE consults with the U.S. Fish and Wildlife Service and the National Marine Fisheries Service on impacts to threatened or endangered species. The USACE is also required to consult with local tribes. The Washington Department of Ecology issues approvals related to protecting water quality. The Washington Department of Fish and Wildlife issues a Hydraulic Project Approval with conditions necessary to protect aquatic life. Whatcom County Planning and Development Services reviews permit applications for compliance with local codes such as Clear and Grade, Shorelines and Critical Areas. Each permitting agency conducts their own reviews and consults with outside agencies as is necessary before issuing their permit. Each permitting agency may require mitigation for impacts that may occur although a single mitigation plan can satisfy multiple permitting agency requirements. The permitting process could take 1-2 years or more depending on the specifics of the proposal . 

Could gravel removal have impacts in other locations? 

Yes. Increases in river channel capacity that may result from gravel removal in one location will send more water downstream and result in more impacts in areas such as Lynden, Ferndale, and the Lummi Reservation.  Those potential impacts would need to be evaluated to make sure we are not transferring risk from one community to another.  

In addition, removing gravel in one spot may increase bank erosion and result in scour around bridges, roads, pipelines, or fields in other locations.  If too much gravel is taken out over time, infrastructure such as levees, bridges, and pipelines can be undermined.

How would gravel removal affect the Nooksack River’s ecosystem? 

Removing gravel from the Nooksack River can negatively affect fish and fish habitat, including that of three species on the Endangered Species Act list: the Nooksack winter-run steelhead, Chinook salmon, and bull trout.  A gravel removal project may prompt the need for an Environmental Impact Statement through the State Environmental Policy Act (SEPA) and/or the National Environmental Policy Act (NEPA) to determine what impacts, either detrimental or beneficial, may occur.  The applicant would need to demonstrate that any detrimental impacts are fully mitigated and that impacts to the threatened species will not occur. 

If gravel removal isn’t the best way to reduce flood risks, what is?

Managing flood risk requires that we use all the tools at our disposal to reduce harm to people and property throughout our entire community. Single-tool solutions most often transfer risk to others downstream. Tools to reduce harm during a flood include:

• Strategically designing and improving the river’s connections to its floodplain where floodwaters can spread out over a larger area and slow down, taking advantage of natural flood storage and conveyance.
• Maintaining a levee system that allows the river to overflow at predictable locations without damaging the levee.
• Setting back existing levees to provide more space along the channel to handle flood flows without overtopping the levee system, allowing for some channel movement without damaging levees. 
• Elevating or removing structures in flood-prone areas and flood-proofing infrastructure to handle floods safely without sustaining damage.
• Removing or alleviating artificial constrictions that raise upstream flood elevations, for example, bridges or places where levees narrow the channel.
• Identifying specific places where strategic removal of gravel can help convey more water through constrictions during high water.  The Flood Control Zone District, in partnership with the City of Everson, is constructing a pilot project this year near the bridge in Everson that will strategically remove gravel at the inlet to an existing channel in the gravel bar to encourage the river to increase the capacity of the side channel. See the Nooksack River Side Channel Enhancement Pilot Project page.  
• Constructing ring dikes and interior drainage systems for population centers to route floodwaters safely around the areas where people live and work. The FCZD is working in partnership with the Cities of Everson, Sumas, Nooksack, Lynden and Ferndale and other stakeholders to investigate the feasibility of a large-scale flood hazard reduction project for the Everson-Sumas overflow corridor that would utilize these types of measures.