Thursday, August 6, 2020

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!

Thursday, July 2, 2020

What Have We Been Up To ...

Our projects to mitigate the effects of roads on amphibians on the west coast of Vancouver Island are still underway. We invite you to read about our recent work in our annual newsletter - the SPLAT UPDATE for 2019-2020.

Friday, September 6, 2019

2018-19 SPLAT Update

This past year we moved a short distance away from roads to work on preventing toads from being trampled on shorelines. We've written about the toad project and our continuing work to mitigate the effects of roads on amphibians in our annual activity report - SPLAT Update for 2018-19.

Wednesday, July 25, 2018

2017-18 SPLAT Update

We're continuing to monitor the movements of frogs and salamanders through two culverts under Highway 4.  Read an update and learn about some of our other conservation work in the annual newsletter.

Friday, September 23, 2016

SPLAT Project in documentary Striking Balance

The SPLAT Project is part of a documentary TV series called "Striking Balance" which explores Canada's UNESCO Biosphere Reserves. The series presents stories about how people interact with nature and several episodes examine the problem of roads for wildlife, including the first episode on the Long Point UNESCO Biosphere Reserve on Tuesday, October 4, 2016 at 9:00 PM on TVO. SPLAT will be part of the Clayoquot Sound episode broadcast the following Tuesday, October 11 at 9:00 PM.  Here's a preview.

Tuesday, March 31, 2015

You can lead a Treefrog to an underpass, but you can't make it enter...

We tested the effectiveness of our new fence design using wildlife cameras. Two cameras took time-lapse photographs of our fences at the entranceway of the culvert. Surveillance started in September 2014 but we did not get a chance to look through the images until this winter.

For the most part, Northern Red-legged Frogs and Northwestern Salamanders moved without hesitation along the ground at the base of the fences into the culvert. We counted more of them moving through to the other side on peak nights than in previous years.

Northern Pacific Treefrogs, however, did not take the culvert in stride. Our September surveillance period showed dozens of juvenile treefrogs climbing the fences just outside the entranceway.

The young tree frogs were not only good climbers, they also found the weak points where the fences joined the culvert. There was a cut in the fabric on one side, and a bunched fold on the other side. At each spot the overhanging fabric came close to touching the upright wall and gave the climbing frogs a relatively easy escape hatch. It was remarkable to watch so many of them follow the same route around the overhanging lip and over the top!

After realizing the flaws, we braced the overhanging fabric with wood at the joins.

We set out the cameras again in February to see if we had made the fence more escape-proof. Granted, a week of surveillance in February is not the same as a week of surveillance in September. There were no juvenile treefrogs around to test our improvements. Instead, we watched a few adult treefrogs and a salamander climb the fences. We were happy to see that none of them escaped. We will have to wait until next September to see whether our fix is also effective for the next generation of juvenile treefrogs.

Making an escape-proof fence for treefrogs is useful in reducing the number killed by traffic. We also hoped it would guide them to take the safe passageway under the highway. It was too difficult to detect juvenile treefrogs in the grass to track the number that actually did enter and move through the culvert. Perhaps some did, however seeing so many treefrogs climbing begs the question: are culverts effective in connecting habitats across roads for these climbers? 

We're not the first to wonder about this problem… Kenneth Dodd and colleagues showed that culverts and concrete barriers helped other amphibians, but not Green Treefrogs or Squirrel Treefrogs, cross a busy highway in Florida.

Various researchers in Europe have also noted that treefrogs do not readily move through culverts. A Dutch publication on Boomkikkers (the Dutch word for treefrogs) recommends not interrupting connections between breeding and foraging habitats across the landscape when new roads are planned.

The fence installation and effectiveness monitoring were financially supported by the B.C. Ministry of Transportation and Infrastructure, the Clayoquot Biosphere Trust and the Government of Canada, as part of the National Conservation Plan.