Making Ponds from Borrow Pits

With the need for elevated home sites, borrow pit ponds are being constructed at an increasing rate. While elevating homes on fill material is not allowed in some areas, the technique is widely used in other flood-prone zones. Of course, check local and federal regulations before you build!

Borrow pit ponds typically are the result of excavating the maximum amount of soil from the smallest possible area. The result is a pond that is small, deep and with very steep sides. Homeowners often want to create a fishing pond out of the borrow hole, but are not always happy with the results. There are, however, a number of ways to improve your enjoyment of the pond:

1. Dig a fish pond instead of just a hole,
2. Add water control features, and
3. Add water quality features.

Dig a Fish Pond Instead of Just a Hole

First question: Will it hold water? The soil should have more than 20 percent clay to hold water. Most ponds in South Louisiana hold water just fine, but watch out for sand lenses during digging. Any sandy areas should be dug out and filled over with clay. Tree roots can also be a problem. Dig them out and pack extra clay in those areas.

Another major concern that must be addressed is safety. If livestock, a pet or a child falls into the pond, they must be able to easily climb out. This means that vertical pond walls are not acceptable – not even in a few places. If you do not have room on your lot to slope the pond sides at a 3-to-1 ratio (at the steepest), then you should consider having your fill brought from another site.

Pond size is also important. Basically, bigger is better. A one-acre pond will need far less intensive management that a one-tenth acre pond. Larger ponds can approach the level of a self-sustaining ecosystem – like a small lake. Very small ponds can provide an attractive landscape feature and a bit of fishing, but they require careful management – more like an aquarium.

Pond depth must be considered. Too often, borrow holes are nearly as deep as they are wide. In fish ponds, deeper is not necessarily better. In most cases, areas over 7 feet deep are little used by fish. At worst, very deep areas become totally devoid of dissolved oxygen. If a storm causes the oxygen-deficient water to mix with the surface layer, this rapid destratification causes a fish kill.

At the same time, avoid large areas of water less than two feet deep. It is almost impossible to keep these areas from becoming clogged with aquatic weeds.

Add Water Control Features

In some ponds, runoff control is needed. If rainwater moves across your property where the pond is located, you have two options: add levees around the pond or add water controls within the pond.

If levees are added to keep the runoff out of the pond (or if the pond is situated in a dry site), then a source of fill water will be needed. Without any method to add water, many ponds will get low during dry weather, with reduced capacity to keep fish alive. Most people choose to install a well or run a line from an existing well. Remember that well water has no dissolved oxygen content: adding lots of well water without aeration is a good way to kill your fish! A simple series of splash screens will solve this problem.

In-pond water controls include drainpipes and spillways. While watershed ponds in hilly areas need to have both, many ponds on flat terrain will need neither. Drainpipes are not an option for borrow ponds that are deeper than adjoining ditches. Ponds that catch runoff will need a spillway at the lower end of the property to divert overflow without causing erosion.

Add Water Quality Features

Many people who already have a small, deep borrow-pit pond find that aeration solves most of the basic problems. Pumped-air diffusion or turbulent mixing, or both, can be used. Aeration will prevent stratification, improve nutrient cycling and prevent problems from periodic low dissolved oxygen levels. Fountain-type aerators don’t generate the most efficient mixing, but in small ponds they provide an attractive feature and adequate aeration.

For more information on ponds, visit the LSU aquaculture Web site http://www.lsuagcenter.com/en/crops_livestock/aquaculture/, or the Louisiana Sea Grant aquaculture site http://www.seagrantfish.lsu.edu/aquaculture/index.html or request publication #2573: “Management of Recreational and Farm Ponds in Louisiana” from your parish AgCenter office.

For more information about flood risk and flood protection, visit http://www.LouisianaFloods.org.

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