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I love this article! Soil erosion is a fascinating part of nature nurture! It is something we can do both in the city and in rural areas. The result of this care of the land improves air quality, soil quality, and agricultural fertility...and it's SOOOO simple! Here are some starting points to help you think about erosion in a new, productive way. My hat is off to Malcolm Margolin for his informative article and book with such practical ideas for understanding and solving this widespread problem. I can see erosion projects started by families and teams of students, whether through a school, a summer program, or a scouting group. Becoming an Erosion Buster could become a lifelong mission with endless adventures and a tremendous sense of achievement!

Carolyn Allen

CONTROLLING EROSION

A visitor from outer space might have a good laugh at how we handle -- or don't handle -- erosion. Our homes have locks on the door, latches on the window, and insurance policies in the dresser drawer, and we support a huge police and prison system -- largely to protect a few cameras, watches, and other gewgaws. Meanwhile, outside our windows, every rainstorm carries away thousands of tons of valuable topsoil upon which we depend for our very survival. Our scale of values is pathetically confused, when you stop to think about it. With modern assembly-line methods, we could replace a stolen stereo in a few hours. Yet it takes nature almost a thousand years to rebuild one inch of topsoil.

Sheet erosion, according to the people who measure such things, causes 80% of all topsoil losses. Gullies cause only about 20%.

HOW EROSION HAPPENS

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.

On flat land, the puddles loiter around, grow bigger, and form temporary ponds. The soil structure is damaged somewhat, but there is no real erosion.

On slopes, however, the water flows downhill over the surface of the ground, evenly, like a sheet. It carries dirt particles dislodged from the tops of hills and deposits them below, creating what is known as sheet erosion.

Probably the worst thing that can happen at this point is that the flow of water becomes channelized, either because of the topography of the land or because of an accidental occurrence like a furrow, a tire rut, or a cow path running downhill. The water gathers speed and the particles of dirt act like sandpaper. The water soon cuts a small trench, or rill, which it may eventually widen and deepen into a gully.

As you can see, a gully is really the result of erosion — not the cause. Yet once the gully gets established, it brings about many severe problems. With each rainstorm, it gets deeper and deeper until it may even cut below the level of the groundwater, draining it and lowering the water table.

Within a few years, thousands of tons of topsoil are washed away, along with thousands of tons of subsoil. Where does it all go? Eventually, the gully probably drains into a stream. On a healthy watershed, a good cover of vegetation absorbs water, holds it like a sponge, and releases it gradually into the stream.

So far I've given you a model of a typically eroding watershed, which should help you to conceptualize what's happening on your land. If all you're going to do is think about erosion, you can stop here. But if you're going to do something about it, you'll need a gutlevel feeling for how erosion is happening on your land. This feeling, more than anything you read, will tell you where to plant, where to mulch, where to build check dams, and where to stay out of the way. It'll prevent you from building a matchstick structure to stop a raging torrent, and it'll save you the trouble of building a Hoover Dam to control a trickle.

FIGHTING EROSION WITH PLANTS

The only successful and lasting way to fight erosion is with plants. One of the nicest things about using plants is that plants want to fight erosion. In fact, they want to fight erosion even more than you do, and what's more, they know how to do it. Take a blade of grass. Grass depends for its survival upon topsoil, and over the last several million years it has developed ways of holding on to and increasing the earth's supply of topsoil. Grass intercepts raindrops; it forms a tough, tangled mat that prevents raindrops from flowing downhill; its fibrous roots embrace the soil and hold it together. Decaying roots create passageways through which water can penetrate, while transpiration allows the grass to pump water out of the soil before the soil gets waterlogged. At the end of its life, grass falls to the ground, decays, and becomes humus, which is the best of all possible elements in the topsoil. Plants depend upon a healthy soil, and they have learned how to serve and preserve that soil. Every time you drop a seed into the ground, you are introducing an ally with millions of years of genetic experience in fighting erosion and tremendous willingness to put that experience to use.

After seeding. If your land is relatively flat, you can seed and forget. But what if you're working on a steep slope where the soil is so unstable that you're afraid it will wash away, or where the land is so hard that you think the seeds might simply float down the hill? In such cases you'll have to devise some way of holding the seeds and earth in place -- at least until the seeds germinate, the roots work their way into the soil, and the green stuff rises up like flags of victory to tell you everything is going well.

Willow stakes. In the following sections I describe several structures that will hold the soil together for a while. You can use any materials to build these structures, but if you use willow cuttings, you will reap an extraordinary advantage. Not only will they serve a mundane mechanical function as posts or stakes, but they will very likely sprout, send down roots, help bind the soil, and carry on an exuberant and useful existence of their own. Willows are especially valuable wherever you're dealing with moist land and bad drainage.

In addition to willows, there are other cuttings you can use for living stakes or posts. In our part of California, for example, elderberries and "mule fat" sprout easily from cuttings. Under hard conditions they may last for only one or two seasons -- but while they last they'll do a lot of good.

CONQUERING THE SPLATTER

Solutions for erision include: