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When it comes to culverts, bigger is better

by: ISABEL GAUTSCHI - In the past, dams prevented gravel from Mt. Hood from being washed through Clackamas River and its tributaries. Gravel provides safe places for endangered salmon species to spawn. It also houses vital food sources for fish. Mt. Hood National Forest Biologist Tom Horning lifts a rock to show the algae and insects on it that a fish might eat.A culvert is a drain or pipe that allows water to flow under a road, tunnel, railroad or other similar embankment or obstruction.

But you probably already know that.

Passing by, a culvert can seem pretty unremarkable.

But for Tom Horning, the Mt. Hood National Forest district fish biologist for the Clackamas River, it’s not just a culvert.

A properly sized culvert is the salvation of endangered fish species such as coho and chinook salmon and steelhead and bull trout.

Properly sized culverts also keep roads from caving in.

Horning has a 2004 photo ready to illustrate his point: One lane of the Sam Creek crossing of Forest Road 57 caved in when a beaver dam plugged the site’s small culverts.

When there was enough water pressure to push out the blockage, the force of the flow washed out the road.

The moral of that story? When it comes to culverts, bigger is better.

Horning is thinking forward to the next big flood.

“We know sometime in the future we’ll have another 100- year flood, so a lot of this work is to upgrade those culverts to be able to handle that.”

The work he’s referring to is the “Forestwide Aquatic Organism Passage and Road Related Restoration” projects approved for implementation in April.

In Horning’s district, most of the projects involve replacing small culverts that date to the 1950s, ‘60s and ‘70s with larger ones.

by: ISABEL GAUTSCHI - Sam Creek would greatly benefit from a larger culvert. There are two small culverts, one on top of the other, in place now. However, when the lower culvert gets blocked, water shoots so forcefully from the upper culvert that it erodes soil and debris in its flow downstream. In the event of a large flood, it could potentially dislodge boulders and cause the sides of the creek bed to collapse.Horning hopes to do just that with the upper Sam Creek culverts on the 5720-120 Road.

One must climb a precariously steep bank to even get a good look at the culverts.

High above the creek bed, two small culverts; maybe 36 inches in diameter, if that, jut out from the bank, one on top of the other.

“You never want an ‘over-under’ culvert,” Horning warned.

The logic behind the over-under culverts was that if the lower culvert plugs, then water may still pass through the upper culvert.

However, when this happens water shoots out of the upper culvert with such force that it carves out the creek bed carrying dirt, sediment and potentially boulders or roads with it.

As soon as the Forest Service can find the funding, Horning hopes to replace the upper Sam Creek culverts with one much larger culvert that will allow all debris to pass through without jamming.

by: ISABEL GAUTSCHI - The Mag Creek culvert was a successful project completed in 2011. Now, Mag Creek is an excellent habitat for fish to spawn and other acquatic species to thrive. Mt. Hood National Forest hopes to implement larger culverts in other sites to get similar results.He points to the Mag Creek culvert, completed in 2011, as a success story.

Mag Creek once had an undersized culvert above a series of timber and gabion step pools.

Not only was the culvert easily blocked, but salmon had great difficulty swimming up stream over the step system.

The Forest Service had been planning to replace the little culvert for 10 years, but had to wait for the funding to do it.

The project was finally completed in 2011. Mag Creek now has an approximately 15-foot-wide culvert and the step pools are gone.

The successful implementation took a lot of work.

Part of the highway was removed during construction and a temporary dirt road was put in.

The Forest Service partnered with many local contractors and subcontractors for the project.

“It was good for local contractors and the local economy,” Horning said of the approximately $800,000 project.

He explained that after the new, larger culvert had been successfully implemented volunteers came to plant black cottonwood cuttings on the creek banks in an effort to rapidly restore vegetation to the site.

Black cottonwood trees are known for growing quickly.

The improved water flow at Mag Creek makes for an extremely fish-friendly environment.

Horning explained how small woody debris such as branches and small logs can pass through the culvert and either flow through or settle naturally in the creek.

Woody debris provides hiding places for fish in the effort to avoid predators.

The large, natural gravel in the creek bed is ideal for spawning fish to lay their eggs.

Adult salmon typically return to the streams where they were hatched to spawn their eggs.

The improved water flow will allow salmon to reach their spawning grounds more easily.

Improving creek, stream and river conditions for fish also benefits creatures such ospreys, fish hawks, great blue herons, otters and mink which depend on fish in the Clackamas River area as a major food source.

Funding for the Mag Creek Culvert came primarily from Legacy Roads and Trails Program, which is money that Congress appropriates to the U.S. Forest Service.

The Forest Service hopes to replace the Winslow Creek culvert in the near future; they are striving to have the project under contract this summer.

However, Horning pointed out that funding is much harder to come by these days.

“Multi-funding of these restoration projects for stream crossings is probably the wave of the future,” he wrote.

Funding will likely come from Portland General Electric mitigation funds, timber sales on Forest Service land and Eugene Water and Electric Board mitigation funds.

In addition to the upper Sam Creek culvert, the Forest Service hopes to replace two other culverts in the Oak Grove Fork watershed and a culvert in the Upper Clackamas watershed as soon as there is funding.



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