Design Systems for Liberty: Capturing Hard Surface Runoff (part one)

  Water is the elixer of life. I don't need to explain its importance to you, if you have made it this far in life you probably have a good grasp on what water means to your health. The sources of fresh water are diverse in Cascadia, from the unsustainable bottled water we see on store shelves to a crisp spring freshet rolling down a hillside in the majestic old growth forest. One thing they all have in common is they wouldn't exist if it was not for the copious amounts of rainfall the bioregion is blessed with, though increasingly unpredictable in volume.
Currently many watersheds in Cascadia are under immense pressure from industry and urban sprawl. Local boil water advisories are becoming the norm as seasonal inundation paired with poor logging practices and snow melt due to unseasonal warm conditions scrape topsoil from the mountain slopes. The resulting turbidity can last for weeks after the rain event. Households are often forced to boil water for drinking, a costly waste of energy and time. The sad hilarity in this is that the answer is literally falling from the sky, in permaculture design "the problem is the solution".
I have been working on the design of my newly purchased property and decided to include a hard surface runoff calculation as part of the site analysis. This is a very easy thing to do and I am going to explain how I got my numbers. First of all I measured my roof surface to get the total area. You can do this from the roof or architectural drawings of your home. You can achieve close numbers by measuring the foundation of your home but you must be able to calculate for slope, unless you have a flat roof the surface area of your roof will be greater than the area of your building footprint. My roof is 173 m2. Next you need to find the average rainfall calculations for your town. You can get this information through Environment Canada or NOAA in the USA (other sources are likely available). At the Comox airport an average yearly rainfall of 1100mm can be expected. To get volume you simply multiply your surface area by the amount of measured precipitation. In my case 173 m2 × 1100mm = 190,300 litres. Can't do metric? You should learn! (Sq' × inches=gallons) Now that you know what is possible it's time to calculate losses. Every building material will have different losses due to saturation and evaporation. Our asphalt shingle roof loses 10%. This gives us a 0.9 coefficient of loss that we must multiply against our total to achieve a more accurate number. So 190,300 × 0.9 = 171,270 litres. As a family of four this number ends up being 117.3 litres per person per day. The average Canadian uses over 250 L/day according to gov't studies taken from household water metering. You can bet the US figures are similar, given the almost identical 'quality of life' of the two countries. We tend to take fresh water for granted, I believe 100 litres per day to be more than ample to supply a person with all necessary hygienic and cooking needs. We will discuss methods of water conscious living in a future blog post.
   When designing a life of liberty we must take all necessary inputs into account and realize that freedom does require us to work a little. The distractions put forward by corporate media and government often leave us forgetting what we really need to do to provide our families with a healthy living environment that is both sustainable and resists stresses forced onto it by the modern world. We need to apply holistic post modern design strategies. Providing your own water is a great place to start.
Stay tuned as we discuss storage and conservation methods in part two of our discussion on Catching Hard Surface Runoff.