Newsletter:20070223/Welcome
From EcoReality
Dam, WWOOFers Highlight EcoReality News
It's been an interesting couple of months at EcoReality. (Sorry we haven't had a proper newsletter since December, 2006!)
Some beavers got in our neighbor's pond and tried to dam up the outflow. Our neighbor broke up the beaver dam, which flowed downhill into (you guessed it) our pond, plugging up our outflow. The water then raised up to the dam spillway, which was improperly constructed, and the dam washed out.
James discovered it: "Hey, do you know the pond is empty?" he asked. "Oops," I thought to myself. The neighbor had told me what he did to the beaver dam, but he neglected to mention that perhaps the debris might affect our dam, and I hadn't given it adequate thought.
So now we have a dam pond with a trickle of water in it, and a poorly-constructed dam that needs to be repaired.
The original earthen dam was reinforced with some poorly-cemented rocks, and a culvert at the outflow level. When that dam culvert blocked, the water raised up above the outflow, and began to attack the dam spillway, causing the dam earth to erode and eventually wash out.
So the proper way to fix it is with an outflow that is fed from nearer the center of the pond, with some pipe coming up to the surface. If we use something that can be extended, we can adjust the water level at will. We also want to put in a second outflow of six-inch PVC pipe, which can eventually be hooked up to a low-head micro-hydropower system.
But first things first -- the most important thing is the geometry of the dam pond, and re-constructing the dam spillway. The inside slope should be set at 1:2 (rise over run), but it was much steeper than that at the breach, causing dam material to migrate down the inside of the dam. The spillway needs to be fairly impervious to outflow, but the failed spillway was just a concrete pour on the top of the dam, allowing water to eat away at the weakened earth below the spillway. The outside of the dam should be sloped at 1:3, but it was way too steep at the spillway, contributing to the breach. The inside of the spillway should be lined with rocks, not just the outside, which is how the original dam spillway was constructed.
Blame the blackberries
The biggest issue with the dam repair project -- and a big reason why the beaver-dam debris problem wasn't readily detected -- is that the place is totally overrun with dam blackberries -- a special, insidious variety that only grows where you need to work. If you don't know much about blackberries, you should at least understand that a two-meter (six foot) thick patch of blackberries is a powerful deterrent to exploration, and I plead guilty to not having closely inspected the dam. If you don't understand how something works, it will eventually fool you.
So this is where the WWOOFers come in. Anyone who has battled blackberries knows it is a tedious, labour-intensive process. Dave Atkins, our very first WWOOFer (and we were his very first WWOOF site!) and I got a good start on fighting back the dam blackberries, and Candice Duchesse and Galaad Perrier, our second and third WWOOFers, continue to make steady progress against the dam blackberries. I must say that, we are totally pleased with our dam WWOOFers so far!
Once we've gotten rid of the blackberries and repaired the dam, we will plant a multi-story, edible guild of plants, from reeds at the water's edge, to an under story of fruit and nut bearing plants, to an overstory of willows that will keep the pond shaded and reduce evaporative loss. With a multi-story complementary planting in place, the blackberries should be out-competed, and easily controlled. And all those different roots will help keep the dam in place better than the dam blackberries did.
If any of this sounds interesting, come on down to help us repair the dam! Remember to bring your wellies!
More good news this month: we've qualified for an energy efficiency grant with City Green, and will be getting over half the cost of insulating our floor back. I estimate the pay-back time on the insulation to be about three years.
