The CMP comes out of the embankment on the downstream side about 20 feet below the inlet, so a siphon ought to be possible. Alan suggested garden hose and I went to fetch those, but I saw this flexible drainspout hose and brought it back instead. We stuck one end down the pipe and struggled for quite a while to establish a siphon, but never really came close. The hose was too flexible in volume and too large in diameter to hold a charge of water after we filled it and shoved one end down the CMP. As soon as we released that end of the hose, water drained out faster than we could lower it, so the siphon never caught. But we worked our hands raw in the icy water. The sensation of cold was...notable.
Our discussion returned briefly to the garden hoses, but it would have required more than a half-dozen of them to move very much water. We had no way to keep them from clogging, and they were stiff and brittle in the cold in any event.
We were bested. Our hands were chapped and scraped and took three days to heal.
We called the pump rental place.
The last half-inch is the hardest:
Alan brought home a 3" trash pump, which we estimated could lower the pond by six inches within a couple of days. We set it up on the top of the embankment – you can see that it is quite steep, and the vibrating contraption would have jiggled into the pond if we tried to put it on the slope.
We had a bit of a challenge priming the pump – with the inlet and outlet running steeply downhill, it took a lot of water to fill the pump and the inlet hose and enough of the outlet hose that the pump would keep operating once started, and until we got the inlet into the pond. By elevating and filling the hoses and the pump, then flinging the inlet into the pond as the engine caught and the pump turned, we began to move water.
The inlet hose barely extended to the water, and kept clogging with all the muck in the shallow water near the bank.
You can see that the outlet flow doesn't amount to much, compared to the flow shown in the previous post when we pulled out the old riser.
Alan worked diligently to keep the pump inlet clear of muck, but we would have been doing this for the next 48 hours. How to get better performance out of the pump?
You can see how low the pond is. This image looks south along the dam and the lane. We call this area the Isthmus. Just beyond the falling snag is the emergency spillway, and the dam is designed to impound water to nearly that level, about three feet above where it is now. If we can fill it again to that level by installing a primary spillway that doesn't leak, we can increase the area of the pond by a good third, maybe a half – a huge difference.
We needed a construction barge and at Alan's inspiration, I shipped the anchors on the Deck Dock and poled it from the beach to the work site.
Now we could get the inlet into deep water where it wouldn't clog, and run the pump at full capacity.
The outlet hose wasn't long enough. We tied it and duct-taped it to the failed siphon drain hose, and ran that down over a layer of geotextile to prevent erosion of the embankment, and into the channel at the outlet works. You can see how much more water we were moving now. We ran the pump until 9:30 p.m. and the pond level was down a couple inches, below the bottom of the CMP.
The next day we ran the pump another four hours, and that afternoon installed the new primary spillway. Now we wait for the pond to rise again.