Flats residents find stronger dikes, more storage capacity

With about three weeks left in flood season, Skagit County Dike District 1 commissioners are feeling pretty good.

Fields are soggy, but no “pineapple express” storm has overwhelmed the Skagit River system.

If one comes, the dikes will be in good shape – and a new agreement will help prevent future flooding by keeping more water behind Ross Dam, northeast of Newhalem.

Each year District 1 invests two-thirds of its annual budget in maintenance and reinforcement of dikes on the west side of the Skagit River between Avon Allen Road and the North Fork Skagit River bridge on Best Road.

“Almost everything downstream from the west Mount Vernon bridge now has a seepage berm in place and we are about 50% done with widening the dike,” said Commissioner Jason Vander Kooy. The section between Marsh Lane (east of Beaver Marsh Road) and the Pioneer Potatoes shed at the corner of Calhoun and Penn Roads has just been completed.

Built of heavy rock and fabric, a seepage berm filters out sediment from water that naturally seeps through the dike. “If we see dirty water running through the bottom of the dike, we know it’s taking material from underneath the dike,” said Vander Kooy.

Thousands of yards of heavy clay are placed on top of the new rock foundation. More mass makes the dike stronger, wider and safer for District 1 personnel.

“It’s kind of sketchy up there in the middle of the night when the bank is no wider than your pickup,” said Vander Kooy, who with other commissioners monitors the river during flood alerts and warnings. Where clay-covered seepage berms are in place, the top of the dike is now “almost a two-lane road.”

The dry land side of this section of the dike has also been regraded. The new, gentler slope will slow down water that overtops the dike. The previous steep slope could trigger a “waterfall-type fall, which would erode the dike,” Vander Kooy said.

During a flood, the ability to store water behind dams on the Skagit River is critical. Right now, plenty of storage is available. More is expected when Seattle City Light’s Skagit River Hydroelectric Project is relicensed by the Federal Energy Regulatory Commission in 2025 or 2026.

As reported by Adam Sowards on the Skagitonians to Preserve Farmland blog, representatives from Skagit County government, the Skagit Dike District Partnership, and the Skagit Drainage and Irrigation Districts Consortium collaborated with SCL to increase the amount of water that can be stored during a flood.

The new agreement, not yet in effect, calls for increasing storage from 120,000 to 140,000 acre feet, and to make the space available by Nov. 1. The current agreement has a Dec. 1 deadline.

“Since 1990, all of the major floods in the Skagit River have occurred in October and November,” said Daryl Hamburg, chair of the Skagit Dike District Partnership. Climate change is expected to trigger earlier floods.

To make space for 140,000 acre-feet of water, Ross Dam must drawdown – release – some water from storage.

“The earlier drawdown in important to ensure Ross has the full amount of flood storage available when the risk of floods occurring is greatest,” Hamburg said.

When a flood threatens, the U.S. Army Corps of Engineers takes over control of Ross Dam and coordinates with a variety of governmental entities to ensure decisions are well informed. That last happened in 2021, when Skagit River flooding caused $14.8 million in damage to property and infrastructure.

Flood season 2024 will be a wrap by Christmas.

To Vander Kooy, and everyone else who works to keep the Skagit Flats safe and dry, that’s the best present of all.