THE DIGGER

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"Log pyramid pool digger" is the title the conservationists tagged their pond-making method, and it wasn't long before I saw how smoothly it worked. With my neighbors, Blake and Aletta, who live on the brink of Podunk Brook, I raised a barrier of logs and stones across the water, triggering a waterfall that carved out a pond. Now it flows like a self-propelled excavator and even sweeps itself clean every spring — a sorcerer's impoundment. We just call it the digger pond .

A sidehill pond is a bath; the digger is a whirlpool. Still-water ponds lie under ice half the year; the churning digger pond freezes for two or three of winter's coldest months, at most. The digger attracts native trout without trapping them, simultaneously stirring up a richly aerated pond suitable for cage-culturing fish.

As with all forms of pond making, success depends on tapping natural advantages of terrain. A stream has a way of hinting at the best site for a digger pond: a hollow that could be enlarged, a slow shallow flow between stable banks, or a pool already forming under existing falls. Banks should be at least three or four feet high and sites prone to flooding avoided.

The size of the digger basin will be limited by the breadth of the stream, so look for a site wide enough to let you stretch out — "Ample and large, that the arms spread abroad might not be hurt," as Cicero described the ideal pond — but not so wide that finding dam materials is difficult, or where watershed runoff will overload the structure. A stream spanning ten to twenty feet, catching runoff from less than ten square miles, works well. Dam materials should be close at hand. Our digger dam was built with trees felled at the site. Round timbers about a foot in diameter make the best structure, with hemlock, cedar, and tamarack topping the list. For longest durability the bark should be peeled. Stones can be used in place of timber, although the dam will be less effective, if quicker to build.

Dams are subject to a trio of wracking forces: sliding, crushing, and overthrow. A strong foundation will prevent sliding, and a tight structure will avert crushing and overthrow. The best foundation for a digger is bedrock or solid bottom. A base of sand or mud will undermine the structure. If you fail to find a solid base, it may be possible to create one using an old loggers' technique for building stream-driven dams: Drive a row of wooden pilings into the streambed to keep the bottom from washing away and to form a base to which the sills of the dam can be bolted.

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