Revamping the rip rap

One large bend on the Mendenhall River is restored to help the flora and fauna, prevent erosion

“We’re wrapping up some rip rap with a little reveg’ on the revetment,” John Hudson said smiling.


It may sound like a mouthful, but actually it’s quite simple.

One bend on the Mendenhall River, fortified by a reinforced slope of large shot rock called rip rap, was overhauled this summer with a revegetation effort by the U.S. Fish and Wildlife Service.

Hudson, a habitat restoration and coastal program biologist with Fish and Wildlife, said the bend hadn’t changed much over the course of the past few decades. He and his crew of SAGA volunteers where aiming to change that by turning the 300-foot wide swath of jagged rock into a restored area lush with cottonwood and spruce trees, willows and perhaps a few clumps of fireweed.

Located on a tight curve by Riverbend Elementary School, the rip rap had been laid back in the 1980s to protect the adjacent property on Postal Way from erosion, which includes some housing units and the valley post office. He said floods that decade continued to damage the revetment and it was rebuilt in 1996.

Since that time, the only life that has recolonized those sharp, jagged rocks were lichens and mosses.

“It’s pretty much nonfunctional as habitat because it’s just bare rock,” Hudson said.

Until now.

On a sunny day in June, Hudson stood on the bank, which was now covered in 100 cubic feet of soil that had been moved in by hand. The nooks and crannies had been filled in and green shoots peppered the landscape. In a container, he held up what looked like a stick poking out of damp soil. Near the top, three heart-shaped green leaves shone new and glossy in the noon day sun.

“These were just started from cuttings; they’re about six weeks old,” he said, gesturing to the tiny cottonwood tree.

“The beauty of this,” he said, “is (these cuttings were) taken from trees that will be cut down for the Brotherhood Bridge project. So we went in there and salvaged them. You just put them in a pot of soil, keep them moist and they sprout leaves and, as far as we can tell, they’ll make it.”

Not far away were more shoots. These were willows that had also been started from cuttings and alders that had been salvaged from the City and Borough of Juneau’s sand and gravel quarry behind Costco.

“Alders grow in sand and gravel quite easily because they make their own nitrogen,” Hudson said.

That’s important in an area not terribly rich in organic material, like the Mendenhall River bend revetment.

“We were also able to salvage Sitka spruce from the right of way on Glacier Highway, at the Auke Recrecation Area bypass.” Hudson said. “It just grows like a weed over there and they just mow it over, keep it small and so you can just dig it up in big batches. And occasionally, we’ll add some fireweed to just diversify it a little bit.”

Overall, Hudson said, the goal is to bring some life back into this zone.

The effort was well on its way, that’s for certain.

Huge shot rock was now cloaked in a solid layer of dirt and the deep crevasses were now filled with the infant plants.

Hudson painted a picture of what they hope will be forthcoming.

“The trees will provide wonderful cover, nesting habitat, foraging habitat for small birds and small mammals,” he said. “The small mammals will be able to use the lower portions around the rock and near the base of the trees and the birds will use the willows and alders. A lot of aquatic insects emerge from this river and the first thing on their mind is find some vegetation to hide in and look for a mate.”

In just a few short years, they will have a place to hide. Those insects in turn, will provide an important food source for migratory birds, Hudson said.

Even the leaf litter is important.

“The leaf litter falls into the stream and fuels the benthic food web, where invertebrates process that leaf litter and turn it into insect biomass that then emerge and come back to the riparian zone, which is what we’re trying to restore here. And that cycle continues ... the birds eat the insects and so on.”

But the efforts of the team are not all about beautification and providing a resource for birds, mammals and insects.

“Vegetation is really good at slowing water velocity,” Hudson said.

It also helps the stream bank resist erosion. Hudson said the big root systems of spruce trees, for instance can actually help to cement the rock revetment together, rendering it stronger than before.

That will be important when the first glacial outburst flood rips through. Mix that natural occurrence with a high tide and Hudson said there could be a problem.

“One thing I’m seriously worried about is the next outburst event,” he said. “ ... how big it will be, how high the water will rise ... if there’s a high tide at the same time the water will be that much higher. We could lose all this stuff.”

He said the crews have revegetated the bank down to the historic high water line, but it’s entirely possible water levels could go higher. So to prevent all this hard work from literally washing away, Hudson said he would come back a day or two later and spread grass seed over the entire area. That, he said, will provide some natural erosion control.

In all, work to complete the project took about a week. Members of the SAGA crew assigned to help were upbeat about the experience, on working in the sunshine and for these young adults from all over Alaska and the United States, the effort was worth it.

Yet, Hudson doesn’t want to stop with this project.

“We want to make this standard practice,” he said. “(This project is) a demonstration of sorts, to kind of show people what can be done. Fish biologists often get really worried when they hear something is going to be armored with large rock because of the natural functions that are lost, but in instances where large rock may be the only practical way to prevent loss of property or infrastructure, let’s just put some soil on top of it — you know, lipstick on a pig — plant it and eventually it will look like some of the upper parts of the revetment where you can’t even tell there was rock there. So it’s a nice win-win. You get the stability of the rock, but you plant trees.”

In many ways, Hudson and his team are just speeding up what Mother Nature would have done on her own over many decades.

Hudson said the next application might be the Brotherhood Bridge project.

“I’ll provide some specifications and details to the Department of Transportation once we finish this project,” he said. “There are, I think, ten or more revetments on this river. Most of them, however, are on private land. It would be nice to work with those homeowners to see if they’d be willing to dress it up and make it more functional.”

Other areas that could use a similar treatment, according to Hudson, include the Sunny Point Bypass and large swaths — hundreds and hundreds of feet — along the banks of Lemon Creek.

“So there’s opportunity,” Hudson said.

• Contact Outdoors Editor Abby Lowell at 523-2271 or


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