tag:blogger.com,1999:blog-28875506.post959763997381487358..comments2022-02-28T18:47:55.551+01:00Comments on permaculture in brittany: Stuart and Gabriellehttp://www.blogger.com/profile/07886622731103783384noreply@blogger.comBlogger3125tag:blogger.com,1999:blog-28875506.post-5325961249033812712009-06-14T22:13:36.998+02:002009-06-14T22:13:36.998+02:00Wait a second...
If those calculations are correc...Wait a second...<br /><br />If those calculations are correct, than a bumblebee can't fly...<br /><br />Albert,<br /><a href="http://trochronicles.blogspot.com/2009/05/know-your-limitiations-ii.html" rel="nofollow">Almost Neutered</a>Albert A Raschhttps://www.blogger.com/profile/11431765456546701021noreply@blogger.comtag:blogger.com,1999:blog-28875506.post-55208146475588488612009-06-14T21:55:42.555+02:002009-06-14T21:55:42.555+02:00erratum: "the height of your swale [...] shou...erratum: "the height of your swale [...] should be at least THE SQUARE ROOT of twice [...]", otherwise the units are inconsistent.kristenhttp://www.arpentnourricier.orgnoreply@blogger.comtag:blogger.com,1999:blog-28875506.post-13338233934087398952009-06-14T21:47:57.936+02:002009-06-14T21:47:57.936+02:00For those who do not speak French but do get math,...For those who do not speak French but do get math, I can explain the sizing formula here: h ~ sqrt(2rDp). Literally, it means : "the height of your swale above the initial terrain should be at least twice the maximum downpour rainfall (r) times the horizontal distance D between swales, multiplied by the initial slope (p)" (with a 1-p/q correction if your terrain has steep slopes) [note: all values in metric units, évidemment]<br /><br />What it essentially means is that for instant summer downpours, your terrain can be considered impervious: therefore your swale has to be able to store all the water that falls between itself and the next uphill swale.<br /><br />In fact, this is a worst-case assumption, when your soil is really impervious over a two-hour timescale. This might be the case if you inherit barren land that has been extensively plowed, but should not happen with healthy soils full of worm holes, tap roots and mole tunnels, even when they have a very high clay content and an impervious rock bed less than two feet below the surface like mine: last week we had a 50mm (2 inch) downpour over three hours and I believed I would find my swale half full (according to the above formula). In fact, it was dry: there had been absolutely no runoff.kristenhttp://www.arpentnourricier.orgnoreply@blogger.com