How Do I Find The Keyline?
When the geology of an area has had time to settle down, when all the exposed rock faces have weathered away the final result is gently undulating country.
The topographical form of that gently undulating country, the fundamental “shape” of that country is always exactly the same in every country on every continent on the whole planet.
Big rivers are fed by smaller rivers. The smaller rivers are fed by even smaller rivers and they in turn are fed by hundreds of creeks. Then finally the creeks are fed rain water from the thousands of small primary valleys that feed into them. The primary valleys are the end of the chain, or really the beginning of the chain of rain to the sea. for the floor of a primary valley only receive the water from the sides of that valley and nowhere else. That the start.
Walk up the floor of a primary valley and at first it is fairly flat, just a gentle slope. Then suddenly it gets steeper. And where it suddenly gets steeper is the Keypoint of that valley. And a contour line passing through the Keypoint of a valley, is the Keyline.
When plowing up the hill, parallel to the Keyline, rain falling in the furrowers will tend to drift out towards the adjacent ridge. And the weird thing about the Keyline is that plowing parallel to the Keyline and moving down from the Keyline, we find again that rain falling in the furrowers will tend to drift out towards the adjacent ridge.
A contour that passes through the steep valley floor will continue out to where the adjacent ridge is steeper and a contour passing through the flatter part of the valley floor will continue out to where the adjacent ridge is steeper. It always happens that way. The relative steepness pattern swaps at the Keyline. That was my father’s peculiar and amazingly insightful discovery. (Indecently, it was me who came up with the name “Keyline”. Around 1950 it was.)
Between the river’s outlet into the ocean and the primary valleys way upstream, the shape of the rivers and creeks are like fractals. Where every pattern is an enlarged version, or conversely a reduced version of every other pattern.
But geological movements and reshaping never stops so very often the formation of these inevitable fractal valley patterns are disturbed and the weathering has to start all over again. So classic, well defined Keylines don’t always exist.
But that doesn’t matter for the principal of pegging a contour and plowing parallel up from that line, or paralleldown from that line, can always be used to control the drift of rain water across the land and prevent its concentration.
Viscous, earth gouging erosion, needs big volumes of water moving fast. The flow has first to become concentrated. Keyline pattern deep working does two things. It allows the rain to soak in fast and secondly it prevents what doesn’t soak in from concentrating into tiny fast flowing rivulets.
Keyline means you keep the water and, you stop erosion.