Here comes spring! And with it many land owners thoughts turn to pond building. There's that wet spot in the field, or the sag in front of the house. What a landscape feature a pond would make. Fantasies arise: of size, shape, fish stocking, wildlife attraction, beach building, stonework, dock, waterfalls, even a zip line. But hang on, let's not overlook that most mundane and important first step in pond development. Test pits. Of the thousands of ponds I've seen, whenever there's been trouble, it's often due to neglecting that crucial first step: the test pit.
What is a test pit? Essentially it's a hole dug in the ground used to gauge soil quality, water table, and possible ledge rock. The cool thing about test pits is that as important as they are, the digging cost is low. Especially compared to the cost of ignoring them and then facing the problems of a poorly planned pond, and its repairs.
Test pits are mostly done nowadays with a backhoe or backhoe attachment on a tractor. Sometimes an excavator if it's handy or if the amount or size of test pits requires more ambitious digging.
Anyway, you start with a site that seems promising. A place that's consistently wet, perhaps receiving a feeder stream, water vein, spring, or watershed runoff supply. Maybe there's a high capacity well nearby that could feed a potential pond; or a supply of roof runoff that could be directed to the pond. Perhaps a stream or other body of water could be tapped, if legal.
Let's keep in mind here that we are shooting for a natural earthen pond, so test pits will be essential in evaluating pond soil and ground water levels. (A membrane liner pond needs less soil testing, because it doesn't rely on water retaining soil, or ground water; so test pits may be less important.) Test pits were once dug by hand with shovel or auger, but now backhoes make the work easier and potentially more revealing. The basic test pit dug by backhoe is often about 8 feet deep or more and the width of the backhoe bucket. Often several pest pits are dug in a prospective site, to yield a thorough mapping of soil type, water table, and ledge. Sometimes test pits are dug rather large essentially emulating a small pond. That can help gauge the effect of a bigger pond in the area.
Although test pits may be dug any time of the year, they yield the most accurate forecast of pond success if dug from late spring to fall. One of the crucial things you are looking for is the ground water level at the driest time of the year. That way you will know your worst case scenario for ground water supply, and be able to judge if extra water will be needed. It usually is, because the best quality pond water is often in a pond that overflows much of the time, and that usually requires water to supplement the ground water. Test pits dug in dry summer will give the best reading of ground water supply, or dug earlier/later, but monitored in dry weather.
Test pits dug in very wet weather may not only give a false reading of ground water levels, but the pit is likely to collapse, making evaluations of soil profile, ledge, etc., difficult to continuously monitor.
Many a successful pond begins with test pits that indicate good water retaining soil, reliable ground water supply, and no obstructions of leaky and excavation-blocking ledge rock. It was a promising test pit that gave me the confidence to build a pond, and after forty years it's never let me down.
Topics vary from month to month and provide great information when researching where you want to build a pond, or how to keep it clean. Other areas of interest are pond use for more than swimming, and how to keep fish happy in your pond.