CONTROLLING EROSION

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As an engineering venture, you should build your structures as if they were going to last forever. Perhaps they will. But as a spiritual venture you should treat the whole thing as if success or failure of the structures is totally irrelevant. Make sure the process is human and loving, have fun, and open your eyes to the here and now. Saving soil is important, but not at the expense of losing a group of kids or a group of friends.

HOW EROSION HAPPENS

In the following sections I tell you what deeds you must do to fight erosion. But before you put on your coat of armor and rush out of the house, let's stop for a minute to examine the nature of the beast. Here is a model of atypically eroding watershed.

To begin at the beginning, drops of rain fall down. Plip, plip, plip. They hit the ground at a speed of about 30 feet a second. If your land is healthy and the raindrops fall onto a thickly carpeted meadow, a wonderful thing happens. It is something you have to see to appreciate fully. The next time it begins to rain, try to forget everything your mother taught you about "catching your death of cold," lie down on your belly, nestle your chin into the grass, and get a frog's-eye view of how raindrops fall. You'll see how the raindrops hit the individual blades of grass, causing them to bend down. This bending absorbs the energy of the raindrop, and the raindrop slides gently off the blade of grass, which immediately springs up again, waiting to catch another raindrop. Perhaps it's just my own sense of humor, but the sight of hundreds of blades of grass bowing down and popping back up like piano keys strikes me as one of the merriest sights in the world; I've spent embarrassing amounts of time rolling around on wet meadows in the rain, laughing at the wonderful antics of the blades of grass.

After the energy of the raindrop is taken up by the grass, the raindrop slides gently to the ground. On a healthy meadow with lots of humus, the ground is spongy and absorbent and the raindrop quickly sinks out of sight.

A similar thing happens in a forest. As every kid knows, the best place to run when a sudden rain comes is under a tree — unless, of course, there is thunder and lightning. The leaves of the tree break the raindrops into a fine mist. What moisture does fall through the canopy is easily absorbed by the understory, the leaf litter, and the humus, and it too sinks gently into the ground.

But let's say that the ground has been logged, grazed, burned, cultivated, or otherwise disturbed. There are now bare patches of earth. When the raindrops hit a bare spot, they strike full force, like tiny hammers, and splatter the soil. This splattering breaks up clods of earth into fine particles. The raindrops hold the fine particles in suspension. As the water sinks into the soil, these fine particles get filtered out and soon clog up and seal the passageways through which the water would ordinarily flow. The clogging and sealing effect is very important: Clear water percolates through the soil ten times faster than muddy water. After a brief time the soil becomes crusty and impenetrable, and the water can no longer sink in. Instead, it forms puddles on the surface.

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