Roy L Hales/ Cortes Currents - As the second year of the Dillon Creek wetland restoration project on Cortes Island is coming to an end, project manager Miranda Cross gave an overview of the creek’s natural history and ways to restore it.
She explained how European settlement brought changes to the landscape.
“It’s very, very hard to find an unaltered stream in British Columbia or around the world,” said Cross.
When the pioneers dug ditches to drain the water from where they wanted to farm or live, they unintentionally changed the water table.
“When you dig a ditch, the elevation of water that's stored in the soil is reduced to the bottom of the ditch. So if you have a one metre deep ditch, then you're lowering the elevation of the water table by one metre. In some cases at Linnaea farm (where the Dillon Creek Wetlands Restoration project is taking place), the ditches are three metres deep. That's a very, very deep ditch,” explained Cross. “So the capacity of the soils to store water, as well as carbon, has been reduced greatly.”
Prior to its being transformed into pasture, the mouth of Dillon Creek would have been a patchwork of wet meadows, with “Fen and open water areas and then these big cedar forested swamps or possibly cottonwood.” The rains would periodically cause the creek to rise and spread over the land, where it slowed down and filtered into the soil.
This natural process was terminated when heavy equipment was employed to move the creek to the side of the fields. A deep ditch was dug, which both prevented the water from spreading across the floodplain and channeled it into Gunflint Lake.
“You have this narrow channel, that has steeped vertical sides. The stream doesn't have access to its flood plain. So rather than spreading out and slowing down, it has high shear stresses on the size of that ditch or stream. And it erodes the banks, particularly when there's a highly erodible soil like this glacial till that we have in the valley,” said Cross.
In other parts of Cortes Island, like Carrington Bay, they dragged logs out though the streams. This was relatively easy with a skid, but Cross pointed out it also straightened and ‘ditched’ the streams, so they continue to incise and erode today.
“In upper Dillon Creek, I don't think they did that because the stream is quite sinuous. It’s actually quite intact and healthy looking up there,” said Cross.
Rocks and fallen logs act as vertical grade control, slowing down the flow of the water.
“There is usually a little pool down below them, So it's great habitat for fish and frogs,” said Cross.
Ditches disturb the natural vertical grade control.
“If you see a little waterfall, that's just soil that is moving and it's deepening and widening the stream channel as it's moving,” added Cross. “These little waterfalls are moving their way up stream and they're putting at risk the forests surrounding them.”
She said they are not sure what they will be doing in the upper creek area yet, but there are ways to repair the damage to Dillon Creek.
