Over the last two weeks we’ve been discussing solutions for a pond with a failing drainpipe. The alternative decided on was to do away with the drainpipe and have the pond simply drain out two spillways.
One was already there, built when the pond was made. Before work began building the second one from stone on the property, two steps were required. The first was to fill the dam hole. A truck operator dumped 10 tons of fill dirt into the hole, after I placed a small piece of PVC pipe in the bottom over the rusted-out gap in the horizontal drainpipe. The hole was fixed for $95.
Now the standpipe had to be capped. I wanted to get that accomplished first so the pond could gradually rise to its new level – a foot higher than before – while I was building the spillway.
Several options were explored, but concrete was clearly the best one. I built a “table-like” bracing structure that could be set down in the vertical standpipe, resting on the bottom, about 5 feet down. On top of the table, I attached a snugly fitting circle cut out of plywood as a form to pour the concrete on.
After test fitting it, I rented a pump for $45 per day, drained the pond several inches and inserted the form. Mixing the concrete furiously, I shoveled in six or seven bags of mortar and mortar-sand mix, smoothed off the top and the standpipe was sealed with a concrete plug for less than $75.
For strength, several rebars were placed in the form at angles extending out the top beyond the rim of the drainpipe, resting on the rim. They would prevent the concrete slab from slipping should it shrink slightly over the years.
I had plenty of time to build the spillway, since the pond would have to rise about a foot before it would flow out this spot. Since the spillway had been well-designed by the original pond builder, I simply dug out a lower area wide enough to hold the normal flow of water from the pond, about 4 feet wide, then laid rocks that brought it almost up to the spillway level, but a few inches lower to channel the water over the stones.
I also poured a 3x3 foot gradually sloping concrete intake pad where the water first flowed out of the pond. Mike Liskey had cautioned me to be sure the water didn’t flow under the stone spillway where it exited the pond and potentially erode it.
The stonework was grueling, but fun. I started laying just a flat channel, but almost immediately revised the design to widen it enough for side walls of rock 8-12 inches high on each border to keep from eroding the dirt there. If a pond only drained a small area with no significant creeks, these side panels might not be necessary. But my pond, according to the Conservation Service, drains 1,700 acres! That can mean a lot of water after heavy rains or snows, and I didn’t want the spillway to erode.
I was careful to swing the exit of the spillway away from the dam, to avoid possible erosion during heavy-water overflow situations. Then, after it curved away from the dam, I let it channel into a thick, weedy area. From there it would flow through a thin stand of switchgrass and back into the creek, 20 feet below the dam. With my small tractor helping out, I channeled the lower part of that drainage to make sure it flowed straight into the creek.
When the project was complete, the really hard part came – waiting for rain to see how it would work! Finally, after weeks and weeks, the pond rose to the spillway level. I was thrilled to be there watching when the first water trickled, then flowed through the stone channel. It was beautiful to see, like having a new stone-lined creek on the property.
The bigger test came when heavy rains arrived a few months later. The concrete plug held and the spillway worked perfectly.
If you’re faced with failing drainpipes under your dam, consider plugging the vertical standpipe connecting to it and switching to a spillway-only option. And if you’re building a new pond, give the spillway-only alternative some consideration as well – you might save thousands of dollars on drainpipe and excavating expenses. The switch to this type of pond-drainage system worked great for me and gave me a beautiful stone-lined stream to watch water splash through on hot summer days.
Of course each pond is different, and this may not be a viable option for yours. Drainpipes certainly have their place for many ponds. Consult with the appropriate government agencies such as the Soil Conservation Service and Natural Resources Conservation Service and a contractor or engineer before making any decisions.
Good luck with whatever pond building or drainpipe repair method you use. There are few greater pleasures a landowner can experience than building and enjoying your own tranquil private body of water for fishing, hunting, wildlife viewing and aesthetics.