Visualising yearly rainfall distribution
This chart shows annual rainfall by month for the years 1990 - 2014 (and partial 2015). While there is a definite tenancy for rain to occur in June and July there is also obvious bumps in October, March and April. Wider areas of colour represent times of high rainfall while narrow regions are dryer.
It becomes clear that rainfall can occur at any time throughout the year and that dry years follow periods high rainfall. With this in mind it makes a lot of sense to be approaching water catchment and management with a multi year view of charging up soil moisture during wet times to carry us through periods of below average rainfall.
Data obtained from NIWA Ferniherst datasetSeptember 20, 2015
The way of the swale
A swale is a permaculture technique designed to improve water catchment and retention on slopes. Applicable to varying scales, a swale is basically a ditch or terrace created along a contour line with the removed soil piled on the downhill side. As rainwater drains down the slope above is is caught and absorbed by the swale. Plantings made along the swale will have access to additional moisture for extended period.
My first attempt at a small swale follows the contour line on a northwest facing slope below an existing track. Because of the small size I was able to dig this by hand over 2 periods, using an A-frame level. Over the course of the next few months we will be scattering the kitchen scraps along the length for the chooks to work over, adding their manure and nutrients from the kitchen. Finally it will be planted up in a variety of different plants from ground covers, bulbs and shrubs to fruit and firewood trees.June 12, 2011