Atmospheric rivers spark debate over Washington state flood management

Atmospheric rivers spark debate over Washington state flood management

A series of storms dumped unprecedented rainfall in the northwest corner of Washington last November, leaving small communities in the Nooksack Valley severely inundated and asking questions about how to prevent flood damage in the future. But finding a solution to the flood isn’t easy. The area is home to a variety of stakeholders, including indigenous tribes, community leaders, gravel mining companies and agricultural landowners, whose interests, such as the protection of fish habitat, commercial enterprises and private property, often conflict directly with flood control measures .

Winter storms are produced by a series of atmospheric rivers—long, narrow regions of the atmosphere that carry water vapor from the tropics. When these rivers reach land, they can dump large amounts of precipitation in localized areas. In November, Whatcom County, where the Nooksack River empties into the vast valley, is right on the bullseye of the atmospheric river.it records approx. rainfall 13 inches. Of those, nearly six inches fell in just three days, causing the river to overflow into nearby areas.Flood damage can be as high as $50 millionaccording to Whatcom county officials.

Shocking images from Sentinel-2 show flooding along Washington’s Nooksack River https://t.co/CaAiGukfbk pic.twitter.com/ohiiBT1Q0y

— Joshua Stevens (@jscarto) November 19, 2021

The solution may seem simple. Deeper rivers will carry more water downstream, reducing overflow during extreme precipitation events. This will require dredging the river by removing gravel and sediment from the bottom of the channel. But dredging can have a devastating impact on the ecology of the watershed, destroying the habitat of salmon species—an important natural and cultural resource for the local Lummi and Nooksack Indian tribes. treaty rights Harvesting and co-managing salmon populations in the Nooksack River in partnership with Washington State.

Nooksack begins with three rivers: North Fork, Middle Fork and South Fork, which originate from the peaks of North Falls. The North Fork absorbs melting snow and receives input from two other forks in the Cascade Foothills, sweeping across the vast floodplain in the Whatcom County lowlands and continuing west into Bellingham and Puget Sound. Along the way, the river transports a large amount of sediment from glaciers on the north side of Mount Baker. of the Nooksack River annual sediment load That’s 1.4 million tons — the second-highest of all rivers flowing into the Puget Sound region, according to the U.S. Geological Survey.

Nooksack River commercialized for nearly half a century mined Gravel used for construction, mainly downstream between Linden Township and Everson Township. But mining was eventually stopped in 1997 due to concerns among local indigenous tribes that mining was adversely affecting fish habitats. In the wake of recent floods, the idea of ​​removing gravel from rivers to mitigate flood risk has resurfaced.Some farmer For example, Nooksack Valley owners believe that gravel removal is an effective way to lower or maintain the riverbed and prevent their lands and properties from flooding each winter.

in a community meeting On Nov. 24, in the town of Everson, a week after devastating floods, local county officials sat on the stage at Nooksack Valley High School to listen to community members, some of whom lost their homes and businesses. “Some people can’t go home tonight because they don’t have a bed. Some people can’t go home because they don’t have a house to go home to,” a community member said. Dredging has dominated, even as local leaders have tried to focus discussions on short-term solutions to the flooding. “We have to dred the river. Stop shouting ‘climate change’ when you haven’t dredged the river,” another community member demanded, drawing cheers from the crowd behind them. Although the meeting ended with a thank you to the volunteers who helped the area recover, many questions about flood control remained unanswered.

But even if rivers are dredged, too much sediment is carried along the river each year to effectively prevent flooding, Oliver Grah, water program manager at the Nooksack Indian Tribes Department of Natural and Cultural Resources, told GlacierHub. Accumulation of sediment and gravel is likely to increase with climate change. He added that when glaciers retreat as temperatures rise, more material is exposed, which can accumulate downstream, build up in riverbeds and cause flooding. “[Dredging] is a huge cost and has little effect. “

On December 7th, former Whatcom County Councilman Rud Browne, whose term ended in January this year, introduced a solve At Whatcom County Council Natural Resources Committee meeting. Brown proposed removing sediment from the river’s dry upland meanders. In an interview with GlacierHub, Browne explained that the project will include digging holes above the waterline to prevent flooding. In theory, these water holes would replenish the river during dry summer months when river flows are much lower, he added.

But his resolve was quick submitted Other council members asked for further input from tribal and county flood and river staff. According to Brown, this is because “people are often lost on dredging issues,” although he stressed that this is not dredging advice, but something else entirely. While burrowing requires removal of vegetation and gravel around river habitats, he said it would not have the same impact on fish habitats as dredging, including the removal of gravel and sediment below the waterline.

in a letter The resolution at Brown prompted Whatcom County Council to say that Lummi Nation does not approve of any form of gravel removal. “To be clear, Lummi Nation was not consulted on the proposed resolution,” the letter said, calling for a collaborative approach based on “sound science” and “indigenous insight” for long-term flood management plans. “

“the best method [to prevent flooding] is to remove or move back all flood protection structures so that the river can return to its historic floodplain,” explained Grah. It is believed that the river ecosystem also Mitigate your own floodsHe noted that as long as there is enough space and capacity to do so, it can benefit every stakeholder involved. An example includes replanting areas of frontier watersheds for commercial deforestation, which will improve water quality and reduce flood risk by retaining more soil moisture and slowing runoff after heavy snow and rainfall events.

Grant Gutierrez, a doctoral candidate at Dartmouth College, echoed this sentiment. Gutierrez, who studies the Skagit River south of Nooksack, explained that over the past 150 years, settler colonialism has transformed flooding, whether by removing log blockages and large wood debris that affect river flow, or Change the configuration of the river by installing dikes, levees and dams. Its valley changed when early settlers developed the area around Nooksack for agriculture in the late 1800s and early 1900s. Land is cleared for farming, forests are cut down for timber, and rivers are straightened. These modifications only made the flood worse. But Gutierrez added that humans still rely on a fantasy that they can “fix” their way out of the flood.

The North Fork Nooksack River shows heavy sediment loads. Source: Andrew Enns/Wikimedia Commons

Warmer air contains more water, increasing rainfall intensity during atmospheric river events. That intensity increases as the region’s dynamics change, Guillaume Mauger, a research scientist with the University of Washington’s Climate Impact Group, explained in an interview with GlacierHub.For example, the most recent one analyze Forecasts from Lawrence Berkeley National Laboratory suggest that annual snow cover in the Cascades could decline by nearly a quarter by 2050 and by nearly three-quarters by the end of the century. As the snow line receded up the mountain, more areas would get rain than rain, and the rain ran faster, exacerbating flooding. Mauger concluded that the events of November show that Washington communities are not well adapted to the current climate or the future climate.

Despite his resolution, Browne hopes that future flood management in Whatcom County will proceed with an open mind. “There’s an old saying that the definition of insanity is to keep doing the same thing, but expecting a different outcome,” he concluded. “We will only address these issues if we are willing to discuss every option.”