Tuesday, December 23, 2008

Keeping Water

A few years ago I learned that in decades past a small stream had flowed down from the hill to the east and through the lot on its way down to the still small, but larger, Amazon Creek. This made sense to me in light of the sheer amount of water that ‘wanted’ to be on the lot, sometimes in awkward places.

So, my original plan was to restore at least the contours of the old creek as a means of re-enabling better drainage which would in turn allow for earlier gardening, better management of storm runoff, etc.

However, my permaculture friends have convinced me to explore a different basic strategy for water which uses contour-line bed as a means of actually holding as much water on the lot as possible. Rather than reinstating creek bed across contour lines, I now plan to use drainage swales between beds, running parallel to contour lines as a means of managing water. The primary objective behind this strategy is water storage.

In southern Oregon, we basically have a sort of mild monsoon climate. From a precipitation point of view there are more or less two seasons: a wet one beginning from November to May and a dry one from June to October. My own water bill reflects this pattern almost perfectly: my water bill for any one month between July and September equals the total water bill for all other months between November and June. Most of that water is used for gardening. So, again, water storage is an important challenge.

I considered cistern or tank based storage of water. However, each time I did the calculations, I ran into the fact that storage of significant quantities of water requires significant space….a problem for my small lot and for my interest in density. Engineered approaches to the space problem also get expensive (or ugly) very quickly. Putting tanks in the ground or above the ground is difficult.

Soil, however, has a remarkable ability to hold water. So, I began looking at ways of keeping more water in the ground itself. That opened my ears to the suggestions of the ‘permaculturistas’ to consider contour-based beds and swales.

The swale system is not a complete solution. Surface soil still dries out. It’s also not an instant solution. Hydration of a piece of ground can take years, just as desiccation of a piece of ground or a watershed often occurs over decades. However, specifically for a garden plan based significantly upon perennials (e.g. permaculture), it holds promise. Perennials typically have deeper roots able to stretch down to find sub-surface moisture. Perennials also create shade that can conserve surface water for annuals.In the net, the ground level of the lot is going to rise a bit owing to my sheet mulching approach to bed building. This higher ground and the pathing I install in the swales will still enable me to move about in the garden without swimmies even during the wettest parts of the year…that’s the plan anyhow.

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