I began to read Toby Hemenway's Gaia's Garden in the winter of 2012/13, when we still lived in our old house an hour's drive south of here. It is a very practical guide to planning one's yard, and one that impressed upon me the importance of water conservation (among other things).
In the book, Hemenway illustrates the usefulness of swales in reducing water runoff on slopes. The idea is to dig a trough of one to two feet deep (in my case, much closer to ONE backbreaking foot deep!):
Although it looks like I have put the swale running downhill, the actual slope that we lose most of the runoff from is to the left of the trench I dug.
See what I mean? This is facing uphill, where snow melt and rain runoff had actually worn deep gullies into the soil before we harrowed (carrying away my valuable topsoil). But back to the swale. Into the bottom my helpers and I deposited first, gravel. We topped that with sand because, hey, they had loaded their John Deere trailer and I hated to disappoint ;)
The next layer was straw (or rather long dead grass out of the bushes). It was straw-like and more plentiful than the bit of straw I swiped from the farm for my compost. We quickly covered it before the wind blew it away. Looks like the helpers are conspiring...
Ah, yes, they moved on to more exciting adventures and left mommy to finish the job. As usual ;)
The point of the swale is to catch water as it moves down the slope and give it somewhere to go (rather than gushing downhill in soil depleting rivers). When the water hits the swale (and the slight berm that is on the downhill side of the swale...difficult to photograph...) it should soak in and travel along the gravel bottom before soaking slowly and more deeply below-ground--the width of the swale.
I had high hopes that we might get three or even four swales installed because our yard is sloping in every direction. Alas, I managed only this one poor lonely swale by the sweat of my own brow. We are short on time and very short on horse power, but if there is a chance this fall after my cover crops get turned under I hope to try another.
Have you any water conservation strategies in place in your garden? Or is the rainfall plentiful enough that you haven't the need?