Exploring the Wodehouse Karst
Although we take it for granted here in the valley, the Wodehouse Karst is actually one of the most interesting karst geology sites in all of Canada. Wodehouse Creek arises in massive springs forming a large creek immediately and drains downstream about 8 km., disappearing into a group of sinkholes. It re-emerges on the west slopes of the escarpment in the Beaver Valley in several springs that you can see from the Bruce Trail, and drains down into the Beaver River.
That’s the simple story; the complete story is a lot more complex.
For most of the year, Wodehouse Creek is a tiny little stream that flows east a bit further, and then south into the sinkholes.You can spot the creek at several road crossings. Intriguingly, the stream seems to get smaller as it flows downstream!
The sinkholes are not the spectacular gaping holes you sometimes see in newspaper reports from Florida! Here they are simply cracks in the bedrock, the Amabel Dolostone that forms the cliffs of the Niagara Escarpment. These allow the water to drain away underground. If you keep in mind that this geological formation was once an ancient coral reef, you can relate to the fact that it has strong, solid sections, with weak zones in between.
The term “karst” refers to a landscape, usually formed of limestone or dolostone, where chemical dissolution has formed underground channels through which water can flow. Acidic rainwater dissolves the calcium carbonate in the dolostone, widening cracks to allow underground drainage, starting in the sinkholes. The entire east and west side of the Beaver Valley north and south of Kimberley is a karst landscape. The property where the main cluster of sinkholes is found is owned by the Grey Sauble Conservation Authority, and is known as Wodehouse Karst.
Of course, water that plunges into the ground usually emerges again somewhere downstream. In this case, the main spring is on a Bruce Trail Property, Kimberley Springs, immediately east of the karst property, but down over the slope of the escarpment. Today, the main Bruce Trail passes directly upslope of the springs, and wanders down the north side of the emerging creek, where you can get a great look at the stream tumbling downhill, eroding a steep-sided ravine in the Queenston Shale. At this point the stream is known as Bill’s Creek.
Over the coming summer, the Beaver Valley Bruce Trail Club plans to create the Wodehouse Karst Side Trail here that will link the sinkholes with the springs, and extend west to a new entry point on the Conservation Authority’s Wodehouse Karst property. A new small parking lot is planned on the 7th Line, which will enable you to walk in and see both the sinkholes and the springs. Or with two cars, you’ll be able to leave one at the top of Talisman, and walk in the side trail and out the main trail to the north.
However, this is just the simple version of the Wodehouse Karst story; the creek disappears into sinkholes, and reappears as springs. But some fascinating changes occur every year during the spring flood. At this stage, the sinkholes are not large enough to take away all the water, so it backs up forming a lake, overflowing onto the fields to the south, and joining the much smaller Lower Wodehouse Creek, normally a tiny separate watershed that disappears in a small sinkhole at the Beaver Valley Ski Club.
In this picture, taken last year at the height of the flood, you can see the entire valley south of Sideroad 7, flooded and overflowing into the fields to the south. The sinkholes are under the closest part of the darker blue lake, while the part curving out to the right is a perched pond. The new side trail will cross this view from west to east; obviously it will be impassible at a certain stage in the spring!
The flood swells the normally tiny Lower Wodehouse Creek into a significant torrent which flows right across some further small sinkholes, fills a normally dry glacial riverbed, and forms an ephemeral waterfall plunging into Bowles Gully at the Beaver Valley Ski Club. This is the route the original post-glacial river took, when it carved out the deep valley that is today labelled Bowles Gully (it was on the old Bowles family farm), and is now home to the deadly steep Avalanche ski run.
The entire pattern of drainage south along the top of the escarpment until it reaches this point is caused by a large ridge along the edge of the slope, which is an ancient glacial moraine, the Banks Moraine. Otherwise the creek would simply have run straight east and over the edge into the valley; it actually detours a long way to the south.
The ephemeral waterfall might last as little as a few days, or as long as 6 weeks, depending on winter snows and spring runoff. This picture was taken in November after 3 weeks of steady fall rains when a small waterfall formed for a few days. Then the creek subsides, the water disappears down the several sinkholes, and the system moves back to normal, a landscape of sinkholes and springs for the next 50 or so weeks of the year.
But there are still two continuing mysteries of the Wodehouse Karst. First, there’s the perched pond. Right beside the main final sinkhole sits a large pond, but it sits nearly 20 feet higher than the sinkholes, making it hydrologically separate from the creek and sinkholes. Where does it get its water supply? Well, it turns out that it is refilled every spring by the spring flood, which is high enough to fill the lake about 24 feet deep at this point, and extend right over the ridge you can walk on in the summer, to include the pond.
I suspected that this might be the case when I found a small dead fish on the trail in early spring several years ago, high and dry above the water level of the creek. I proved this to my own satisfaction two years ago when a friend and I paddled in on the flooded creek and measured how deep the water was. You could paddle directly from the flooded lake over the sinkholes into the perched pond.
The final mystery of Wodehouse Karst is the impression I have that the stream gets smaller as it flows downstream. Somewhere, more water is disappearing underground. And there are six springs flowing out of the escarpment to the east of the small Wodehouse watershed, so there are obviously other underground channels taking water away from the creek and feeding these springs in addition to the main cluster of sinkholes.
This topographic map where I’ve highlighted the creek and the springs shows the overall pattern. The creek flows mostly north to south, but the springs flow west to east. The gaps on the map reveal where the water flow is entirely underground. In the case of the southern three springs, you can guess where the flow from sinkhole to spring goes, but for the northern three springs, it’s not so clear. But add them all together, and you have a substantial underground flow through multiple bedrock channels, all ending up in the Beaver River far below.
So when our new side trail opens linking the Wodehouse Karst sinkholes and the Kimberley Springs, I hope you get out to take the walk and appreciate the uniqueness of this remarkable karst landscape right here in the valley.