MAINTAINING YOUR POND

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If no supplementary stream or well is available, pond owners sometimes cut drainage ditches in the watershed above the pond. The ditches are usually filled with stone over perforated plastic pipe. As a last-ditch resort, an artesian well may be drilled for extra water, although hitting a rich vein is never certain. If leakage is suspected, balance the estimated cost of bringing in water against that of attempting to improve the pond's water-retaining ability.

Erosion of the feeder stream, and consequent siltation of the pond, is a common inflow problem. It's not unusual for ponds to require cleanouts near the inflow every five or 10 years. Poorly designed ponds, particularly if excavated during wet weather, can fill up with silt during their first year where the soil is unstable. Thus it's best to wait for dry weather for digging, and perhaps divert channel inflows away from the pond or through the basin via pipe during construction. When work is complete, the water can be returned to the pond after inflow channels are stabilized with riprap or piping. Riprap is effective where silt slows down stream flow. Such incoming water channels should be cleaned out and lined with stone to facilitate the flow, reduce erosion, and discourage algae.

In addition to using piping and silt basins, inflows can be stabilized by filtration. Hay bales are sometimes used in stream channels to retard the movement of silt. Establishing a vegetative strip may also help, whether it be native grasses or sod.

Rock riprap is one of the most common solutions to inflow erosion. Don't use large stones that leave wide gaps between them. In areas where the soil is especially silty and unstable, it may be helpful to lay down a bed of gravel before applying the riprap.

Ponds can also suffer from an inflow of too much water. A good example is the story of Runaway Pond in Glover, Vermont. In 1810, the operator of a grist mill in Glover decided that he needed a more reliable source of power for his water wheel, so he had a ditch dug from his existing pond up to another reservoir at a higher elevation. The idea was to channel the new pond into the original, but when the channel was complete and the water rushed down, the stream inundated the mill pond. The pond overtopped, the embankment blew, the mill was destroyed, and so was half the town. Moral: Don't add more water than your pond can handle. The miller's mistake was in not building a control gate on the higher pond so that he could regulate the inflow.

Excavated ponds that lie in wet lowlands may be damaged by flood waters. Fortunately, most excavated ponds, even if flooded, pose little threat downstream. Damage from flooding may involve siltation or contamination from upstream pollution, and loss of fish. It's possible to build a protective berm upstream as a barrier against flooding. The berm's effectiveness will depend on the height of the berm and the level of flooding. Material excavated during construction can be used to build the berm. A more natural look can be achieved by using earth excavated for the pond. This builds up a complete surrounding shore area a foot or two higher than the existing terrain. Like an island, the pond-shore complex sits above ground level, well-protected against flooding. Utilizing excavated material close to the pond, rather than trucking it away, may also save on construction costs.

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