Pondology
news from the waterfront by Tim Matson

JUST SAY NO

A couple of weeks ago I arrived at a pond site scheduled for excavation, took a look around, and advised my client not to build. He was very dissapointed. But I left feeling good. (Nope, I'm not a sadist.) I felt good because I knew that while his dreams of a swimming and irrigation future were going away, so was a future of shelling out thousands on a pond that would never fill, along with the uncountable hours of frustration that often accompany efforts to turn around an irreversible mistake. How did I know to say no? Test pits.

Let's take a look at the common path that leads many landowners to spend so many days planning and nights dreaming about swimming and fishing in their sparkling new pond. It usually begins in spring walking around a wet area soggy with ground water and watershed runoff. Whether the owner has been on the land a short time or many years, those wet spring walks often lead to thoughts of a pond. And in many cases, based on those spring puddles, a pond gets built. But in many cases, after the pond is built and summer arrives, the ground water table drops and the pond doesn't fill. It's true that a new pond can take months to fill (after all we're talking about filling a very big hole)and new ponds can be very soil pervious (leaky), and it can take a few years for a nice layer of sediment to settle and help seal off the seepage. Let's say the pond does finally fill in the fall with post summer rains, or during the winter, or commonly, at least by spring. Success!

Not so fast. Suddenly the pond starts to drop. And just when you want it to be full, mid summer, it's empty. A few years of that, and the unhappy pond owner will begin trudging another familiar path: the trail of pond rescue remedies.

It's possible that the owner will find the ingredient that was missing at the start: supplementary water, a soil sealant, a liner. But all that takes time, and money, and often just as much luck as was needed in the first place, because if there's one true thing about all ponds, it's that in addition to all the established elements, pond building is a gamble, and luck can make the difference between success and chronic trouble.

 

 

To avoid the disappointments and expense of a failed pond construction effort, I strongly advise my clients to begin with test pits. Whether you dig test pits in spring or summer, you will want to monitor them in dry summer weather, when ground water is at its lowest. If you have empty test pits in dry summer, you know you have a problem with your ground water supply. To make up for that deficit you may need supplementary water (springs, a well, a stream feed, runoff from roof structures, drainage piping). Or, if your supplementary supplyis limited, you may need to install a membrane liner in the pond to eliminate seepage/leaks of any kind.

Test pits are usually dug with a backhoe, about 8-10 ft deep. Often several holes around the site just the width of the bucket will tell you plenty about the site. In addition to preparing you to observe ground water in dry weather, test pits reveal soil type (is there enough clay to help hold water?) and presence of ledge (ledge can obstruct digging as well as contain fissures that can drain a pond).

Sometimes test pits are left open to monitor for several months; or for safety reasons, they are backfilled after soil and ledge exams, with a monitor pipe installed so you can check ground water depth with a dip stick.

But back to the hillside pond site. To the owner it had looked like a promising place for pond...in spring. There were puddles of surface water all over the place, and a small stream of water flowing off the hill above the site. He could imagine a place for swimming as well as an irrigation source for gardens and fruit trees and grape vines planted downhill. I suggested he dig test pits later in the summer, for a true test of the ground water. In August five borings were done. As they were dug the soil revealed an encouraging amount of clay. But no water, not a drop in pits as deep as eight feet. Sometimes it takes a while for ground water to fill test pits, but after a week, these holes were still bone dry. The stream had also dried up. Needless to say there were no puddles of water on the surface.

Looking at the empty test pits, the owner and I discussed methods of overcoming the water shortage. Drill a well, which would require running electricity over one hundred yards from the house, with no guarantee of well capacity. Pump up water from a stream downhill? State regulations would likely nix that. The best bet looked to be a membrane liner to leakproof the entire pond, which would still require a water source. But liners are expensive in themselves, and so is the special construction involved. And some folks are simply opposed to a plastic liner. Too much like a swimming pool.

And so the pond was scratched off the to-do list. So was an expensive exercise in frustration.

October 1, 2015

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