How to Plan an Ecological Water-Harvesting System for Your Home

By Toby Hemenway, Chelsea Green Publishing. Posted May 18, 2009.

The secret of storing water in a pond is depth since the smaller surface area needed by a deeper pond to store a given volume means less evaporation. A twelve-by-twelve-foot garden pond that's four feet deep instead of the usual two can store over 4,000 gallons of water. Obviously, if you're pulling water from the pond for irrigation, you will have to develop some strategies for protecting plants and fish when the water level drops toward the bottom. One possibility is to have one pond strictly for irrigation and a second, smaller one for finny and leafy inhabitants.

A typical garden pond is lined with flexible plastic and edged with flat rocks. In nature, you'll never see a pond that looks like this -- a tidy opening in the ground rimmed with an even border of flagstones -- and that design creates problems. Birds, small mammals, and many insects can't drink from a pond with such a sheer rock edge. Earle Barnhart, a landscape designer on Cape Cod, has evolved a more natural pond edge, replacing some or all of this abrupt rock drop-off with a gently sloping beach, as shown in Figure 5-5 (below). Small animals can sip at the water's edge in this design. One warning: Larger animals, such as dogs and children, may also be attracted to this backyard beach, with possibly messy results.

To see how a pond can be both a landscape focal point and a practical water source for the garden, let's look at what forestry consultant and permaculturist Tom Ward did in his Ashland, Oregon, yard. Tom built a 3,000-gallon pond on the uphill side of his vegetable garden. “After we dug the hole for the pond,” Tom told me, “we added three coats of a product called plastic cement, troweled onto bird netting, for reinforcement.” He could have used a rubber or plastic liner but chose a less-expensive but more labor-intensive method since he's got plenty of friends to help him build. The pond is fed by downspouts from the house next door and from a shed in the lot behind Tom's. Both neighbors responded readily to his request for their runoff water.

The pond was new when I visited, but Tom intended to stock it with edible fish and a variety of useful and attractive plants. However, the pond's benefits extend beyond its boundaries. A swale runs alongside the pond. Overflow dribbles out of the pond, down a rock waterfall, and into the swale. The water is captured by the level swale and sinks into the soil. Tom's vegetable garden is just downhill from the swale, and the expanding lens of subterranean wetness from the swale moves down the slope toward the crops like a slow underground tide. The pond and swale thus form a subsurface irrigation system for the nearby garden. Once again, placing the pieces in the right relationship lets nature do the work and substantially cuts Tom's reliance on municipal water.

At the outlet end of the swale, about twenty feet from the waterfall inlet, Tom planted blueberry bushes. Any water that flows the entire length of the swale and spills out the far end is captured by these shrubs.

This is a fine example of ecological design. The pond harvests rainfall from his neighbors' roofs, the swale collects any surplus from the pond, and the garden and blueberries benefit from moisture taken in by the swale. Tom has integrated a pond into his garden that is attractive and practical and that connects once-separate elements -- even from beyond his own property -- into a healthy, smoothly functioning whole.

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