Conservation, Demonstration Sites, Food Forests, Irrigation, Land, Potable Water, Regional Water Cycle, Rehabilitation, Soil Conservation, Soil Erosion & Contamination, Storm Water, Swales, Water Contaminaton & Loss, Water Harvesting — by Chris McLeod September 29, 2012
I always thought that rain was a nurturing and gentle aspect of nature. You know how it is, you get a bit of rain and it helps all of the plants to grow, provides water for us and the animals and generally stops the place from drying out. That was my thinking back in an urban environment. In that area, the drainage infrastructure had been developed and maintained over the past 120 years and it just worked. In fact, the infrastructure was so good you never really thought about it.
In a rural location however, there is usually little to no infrastructure, so any change you make to the landscape will change the way water interacts with that landscape. Winter rain here is usually quite gentle with many hours of sustained drizzle and relatively high humidity. These conditions generally don’t present too many challenges. Or so I thought.
Rainstorm running along the valley below
When I started building my house on my rural block, I had the earthworks done over winter by a 20 tonne excavator which produced a level house and small garden site on the sloping land. Then I started building the house.
By spring, the rains had picked up in both frequency and intensity. The building site was looking good and the drainage was working OK, so I patted myself on the back and thought, “job well done!” Then just before New Year’s Day, 85mm (3.3 inches) of rain fell in under an hour. The valley below flooded, but of more immediate concern to me was the several cubic metres of my building site that had washed away down the slope, dumping silt and clay right through my growing food forest.
Erosion of building site
It was the rain that provided the energy to erode several cubic metres of soil, but it was changes that I had made to the landscape that allowed that energy to concentrate with such destructive force. The rain had merely collected and concentrated on a small shed on which I had not yet set up systems which could handle such a large volume of water. From hindsight, it was clear that the storm, although large, was not an unusual circumstance.
Just in case I didn’t treat the lessons of that day seriously, nature has conspired to prove a point by providing the wettest couple of years in a row since records began around here in 1870. What a wet year here means is about 1,400mm+ (55+ inches) of rain per year in a cool temperate environment. As an extreme example illustrating just how wet it has been, one stretch of rain during summer a few years back dumped in excess of 250mm (9.8 inches) of rain over just five days.
Tree frog on the veranda, sheltering from the excessive rainfall.
Yet for a couple of years prior to this recent wet period, drought conditions prevailed for around a decade. Clearly water can be both a destructive influence as well as a resource to be treasured.
Food forest growing during the drought
It was only after careful observation, much reading and investigation that I came to learn that rainfall generally runs over hard, bare or compacted surfaces.
A previous article, Food Forests – Part 3: Closing the Loop, described how originally the soil here was compacted clay, where rainfall ran over the surface rather than penetrating into the soil. Under these circumstances, that rainfall also serves to further compact the clay by repeatedly pounding the surface. It also washes away any accumulated organic matter. The result of all of these actions is that soil is either lost or does not get the chance to develop. Without at least some top soil, it is very hard to grow anything and this is a common problem with soils right across the globe.
As discussed in that earlier article, soil repair can only occur by breaking up the clay to allow water to penetrate it when it rains. This work has to be done at the same time as accumulating organic matter onto the surface to prevent further compaction and eventually nature will do the rest.
However, it is not always desirable to have vegetation covering all areas of the landscape (eg. Roads, paths and driveways). In addition, a site may have additional specific issues which require excluding vegetation from an area. In my case, it would be unwise to have vegetation in close proximity to the buildings as this would increase the risk of damage to buildings during a bush fire.
Sometimes hard surfaces are a necessary evil and this will mean that most places will have to have some sort of systems to manage this water during rainfall. I like to either collect this water for later use or store that water in the ground where it can be utilised later by the vegetation.
Here at the farm, after much observation, trial and error, plus some failures, I have employed a variety of systems to harvest all of the water that runs off these hard surfaces. These systems include:
Water Tanks: Roofs are great places to collect water during rainfall. Most houses in rural areas in Australia rely on their roof to collect water for all purposes including drinking water. It is usually collected from the roof in gutters and gravity piped via PVC or steel pipes to water tanks for later use. Even in urban areas, people are regularly installing water tanks to collect water from their roof for use in the garden. I even collect the rainfall from my chook shed and garden shed roof in separate water tanks, not wanting to waste a drop.
Mulch pits: This is a cheap method of getting water into the ground. It makes use of some of the properties of mulch which is its ability to hold water and also its porous nature. I use this method to capture water collected from a pit near the driveway. I use a large quantity of mulch (about 1m3 or 35ft3) and build a mounded structure resembling a volcano (which acts like a round swale) and have the water released into the cone.
Mulch swales: This is a similar structure to a swale, however it is much smaller. A small ditch is dug on contour with mulch being added and mixed in to the soil on the mounded side to slow the movement of the water and improve the infiltration of it into the soil.
Swales: There are plenty of articles on this website describing swales. They are really useful for managing very large flows of water and here I have two swales for this purpose.
Mulch lips: These work similarly to mulch swales, but are small mounds of mulch placed along the top of any sudden drop or incline. The mulch works by slowing the movement of water across the landscape as well as increasing infiltration of that water into the soil. This method would probably have reduced the damage to my building site.
Food forest and herbage: As mentioned previously, diverse and well established vegetation can absorb most rainfall.
Combinations of the above systems: I also combine the various systems to ensure that if one system is overwhelmed by the volume of water and fails, then another system can absorb the excess water. For example, I have both a mulch pit and a mulch swale located inside the food forest.
As a final word on water systems, passive systems are the most effective when it comes to water systems. Over the years, I’ve noticed that many people tend to be excited about water systems that involve pumps, yet these systems tend to fail during extreme storms when there is a possibility of power outages making those pumps useless at the time when they are needed the most.
Water is both a life giver and a destroyer and over the years it has shown me just how much power it can wield. I now have a healthy respect for it, so that whenever I change any aspect of the landscape I consider the potential impact that will have so that I can improve its force as a life giver rather than suffer its wrath.
Addendum 1: For those that are technically inclined, you can calculate how much water you will have to manage from a certain amount of rainfall. The general formula for this is:
1mm of rainfall over 1m2 of land provides 1L of water.
As an example, 25mm of rain (1 inch) over 10m2 (107.6ft2) of land provides 250L (66 gallons) of water.
Addendum 2: In mainland Australia, water is best stored in the ground as when it is stored on the surface the water is subject to evaporation over summer. It may surprise people to learn that there are very few large permanent natural lakes on the mainland as most are artificial.Comments (0)
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