Water in the Landscape

On a slope, water is the whole economy. It arrives on the high ground, decides where the soil stays and where it leaves, and carries the season to the roots below or takes it off the property entirely. Get the water wrong and nothing else on the farm works. Get it right and the ground does the pumping for free.

P.A. Yeomans, an Australian mining geologist, published The Keyline Plan in 1954 and set out the Keyline Scale of Permanence in The Challenge of Landscape in 1958. His order for planning land is: climate, land shape, water, roads, trees, buildings, fencing, soil. Soil sits last on purpose, because good soil is destroyed faster than a fence post rots, and can be rebuilt faster than people expect. Read that order once. Water is third, ahead of roads and buildings, and every structure on the farm is fitted into the water lines rather than the water fitted around the buildings.

The contour is the master line

Everything water-shaped hangs on the contour, the line of equal height across a hill. A swale dug on a true contour fills, then sinks its water into the ground below the bank. A swale dug three degrees off contour runs to one end and empties, and both the work and the water are lost.

Find contour without instruments. An A-frame of three stakes and a string with a weight marks equal height as you walk it across the slope, and a length of clear hose filled with water does the same job. Stake the line before you dig, and re-check it as you go.

Swales, ponds, and the keyline

A swale is a level ditch on the contour, with the excavated soil thrown downhill to form a bank. It is a store and a soak, not a drain. The trough holds the rain and lets it seep into the ground on the downhill side, feeding the roots below the line for weeks after the storm. A chain of swales down a slope turns dry ground into a series of watered bands.

A pond is the battery. Put it high, on the contour above the fields it will water, so gravity delivers it. Size it for the worst summer rather than the average one, because the dry year is the one the pond exists for. Seal it properly, plant its edge to cut evaporation, and it will hold.

Yeomans's keyline is the pattern that ties these together. On a valley or a broad slope, the keypoint is where the slope changes from convex to concave, and the keyline runs from that point across the land. Graded channels along the keyline spread water from the wet valleys out toward the dry ridges and feed the high dams, so one storm waters ground it never reached. You do not need Yeomans's machinery to use the idea. You need to see where the slope changes and put the water line there.

Roof catchment and greywater

The cheapest reservoir is the roof you already have. One inch of rain on 1,000 square feet is about 623 gallons. A 1,200 square foot roof in a 47-inch year catches roughly 35,000 gallons, which is more than a household garden drinks. Run the downspouts to a tank, a swale, or a planted basin rather than to the road, and the house becomes part of the waterworks.

Greywater, the used water from sinks, showers, and laundry, can irrigate perennial plantings and fruit trees. Keep it away from leafy greens and root crops eaten raw, use greywater-safe soaps, and let the soil and its biology do the filtering. It is a supplement to the design, not the design.

The mathematics of storage

Two stores do the work: the tank and the soil. Take the soil first, because it is the larger and the one you build for free.

The USDA's Natural Resources Conservation Service reports that each one percent increase in soil organic matter lets soil hold up to 20,000 more gallons of water per acre. That is about three quarters of an inch of water. The same ground at 4 percent organic matter holds more than twice the water of the same silt loam at 1 percent.

Turn that into a bridge across a dry spell. At this site peak summer demand runs about 0.18 inches a day. A shallow tilled soil holds around 1.8 inches, about ten days. A high-organic-matter soil with a 24-inch root zone holds near 4.8 inches, about 27 days. Against 131 years of measured rainless runs, the deep rich soil carries a rainfed crop through the worst five years roughly 98 to 100 percent of the time, while the shallow tilled ground fails in all five and has about a one in five chance even in an ordinary year. Nothing here needs irrigation. It needs organic matter and root depth.

The tank maths is simpler: gallons equal roof area times rainfall, with one inch over 1,000 square feet giving 623 gallons. Size the tank to the gap you are trying to bridge, not to the roof.

The ancients drew this map first

Water-finding, cisterns, and graded channels are not new. They are the oldest infrastructure on earth.

The medieval estate kept the same habit. Crescenzi, through Palladius, told farmers to find springs by the spirals of damp air rising from the ground at dawn, and named willow, alder, reeds, and ivy as water indicators, then gave aqueducts a fall of a foot and a half over sixty to a hundred feet. The Geoponica had the orchardist heap mould around each tree and cut a basin around the heap "for the reception of rain-water," a micro-catchment at the root. The pattern has not changed: read the ground, catch the rain where it falls, store it above the fields, and let gravity do the carrying.