Creating a Path for Amphibians Over "Rip Rap" Armouring a Bridge

Summer 2020 is an eventful year for improving amphibian passage beneath Highway 4 on the west coast of Vancouver Island!

Parks Canada is installing three new box culverts close to the one we put in place with the BC Ministry of Transportation and Infrastructure in 2011. We're looking forward to sharing the design features of the Park culverts and fencing system once they are complete in a few weeks.

In the meantime, we have shifted our attention down the road to another crossing structure, a bridge over a tributary to Lost Shoe Creek. The bridge allows passage for Coho Salmon and Cutthroat Trout, as well as four-legged wildlife that can swim in the current or hop along the exposed shoreline. It's easy to move under the bridge at low water levels in summer but not during the rainy season. When water rises, flow increases and the shorelines become gnarly. The banks of the creek are armoured with large sharp angular rock, known as "rip rap". It protects the bridge abutments from scouring by heavy water flows. This is standard practice for bridge construction in British Columbia and other places, but it creates impediments to passage for smaller creatures like amphibians. They can get stuck in the cracks between the angular rocks! 

This particular bridge occurs at a hotspot for migrating Northern Red-legged Frogs. Several of their breeding ponds and forested habitats occur on opposite sides of the highway near Lost Shoe Creek. One of the habitats is an artificial salmon-rearing off-channel constructed in 2013. In 2014, we installed ~ 200 m of fencing to stop frogs and salamanders from being killed on the highway near the off-channel. Although the fencing works well to reduce the number killed, it blocks passage between habitats. 

That's where the bridge comes in... it could be the perfect habitat connector if we did something about the "rip rap". So that's what we're doing. Working with a crew of stream habitat restoration specialists from the Central Westcoast Forest Society, we spent the last two days creating a smoother path over the "rip rap" under the bridge. 

Our pictures tell the story:

Step 1. The crew reviewed how the amphibian fencing connects to the bridge abutments.

We explained the problem with the "rip rap", and our objective to create better pathways for amphibians under the bridge.

Step 2. We received a truckload of "pit run", a mix of coarse sand and rounded gravels from a local quarry. The truck delivered a quarter of the load to each corner of the bridge.

Step 3. The crew shovelled the "pit run" into wheel barrows and buckets so it could be carried under the bridge.

To prevent disturbance and ensure we didn't spill dirt into the stream, we did all the work by hand.

Many buckets and shovels full of dirt were transferred...

... to where it was placed to cover the "rip rap" bench above the high water line.

We raked to create a smooth pathway...

... then added more buckets to fill in gaps.

At one point we noticed a Northern Red-legged Frog sitting on a rock in the creek!  It seemed to be watching our progress. To see the frog check out the closest rock to the camera in the foreground.

Step 4. We measured the length of logs needed to place across each slope at the corners of the bridge.

We cut the logs...

... moved them to the bridge corners...

... and positioned them where they will help lessen the steepness of the approach from the ends of the fencing.

Step 5. To secure the logs, we drilled holes in the rocks, washed out the rock dust, and then inserted glue for cable.

After securing the cable in the rock holes we cinched it around the logs with staples.

Then covered the logs with landscaping cloth and poured more buckets of "pit run" on top.

We smoothed the surface to create a shallow slope from the ends of the fences around the bridge abutments.

Some of the fences were overgrown by alder trees so the crew used a powerful weed wacker...

... and cut back the alder to make a clear path for the amphibians to follow to the bridge.

We needed one more bucket of dirt to fill a steep section along one of the fences.

It felt good to deliver the last bucket!

The crew will take a break from this project for several weeks until it's time to plant. Then we'll use wildlife cameras to monitor the frogs and salamanders that move along the new paths and compare to what we saw moving over the "rip rap" last year.

We are grateful to the Habitat Conservation Trust Foundation and the BC Ministry of Transportation and Infrastructure for funding this work. 

We hope information that we share about the effectiveness of this project can help create smoother passageways for amphibians in other places!