Being involved with permaculture helps one develop a mild obsession (and that’s putting it mildly) with water. Long before I was a certified designer, just an avid reader of permaculture texts and articles, and a compulsive watcher of Geoff Lawton YouTube videos, I was looking at landscapes completely differently, with an eye that begged for contour lines and took aim at potential dam sites. I imagined this water feature connected to that one, which fed another downslope when it overflowed across a level sill, the entire countryside dotted with water storage and well-hydrated food forests.
One of the ideas I’ve always been excited about but never quite got my head around was using hard surface runoff from roads and/or polluted areas. It seemed counterintuitive to spend so much time developing natural, chemical-free permaculture sites then funnel tainted water onto them. Of course, in certain environments, any drop of water available is worthy of collection, but still… how could we? Well, I was recently watching some videos from the upcoming earthworks course with Geoff Lawton, and I finally got an answer.
We can set up natural water harvesting and filtration systems to make the most of dirty hard surface runoff, as well as provide us with both clean water and rich compost for our forest gardens.
The water catchments in this situation need to centre around soakage rather than storage. In other words, we don’t want to catch the dirty water in dams and allow the pollutants to remain in the water. Instead, we want the water to gather and soak into the landscape, where natural elements like soil and plants can begin to clean it.
What these catchments look like are marshes and mangroves, the natural way of handling this situation. We can install shallow ponds on contour, leaving them unsealed and lining the bottoms of them with gravel to allow water to soak into the landscape. We can do the same with long swales (or, even better, connect the two), lining the bottom with wood chips or gravel. These catchments stop the polluted water from entering the site with contaminants.
Rather than fearing a possible problem uphill, this is how we begin to make the strategic move of both keeping our site clean and making the most of natural resources despite what those around us are doing.
Whether it’s a pond or a swale or both, the entire catchment should be planted to reeds. Reeds are a large family of aquatic plants that include cattails, bulrushes, and papyrus, and these plants specialise in soaking in excess nutrients and/or toxins from water. These species will form a dense mat of roots, so much so that the system will eventually clog. That means they are taking in all the bad stuff and letting filtered water through into the earth, so just thin them out and let the process repeat.
The berms of swales and banks of these ponds should be planted to “mop crops”, as Geoff calls them, such as willows and fountain grass (pennisetum), as well as more reeds. Bamboo might work as well. We want plants with hairnet root structures that grow into thick mats and lock soil into place. They should be thirsty for water and hungry for nutrients, so they will thrive in semi-aquatic areas like these. They’ll also take in what’s bad and let the rest filter through into the landscape.
Most of these plants and trees are fast-growing and provide a lot of carbon material that can be collected and composted periodically, both thinning out the reed beds and opening up the tree line canopy.
There are some obvious issues with plants grown on contaminated water (we don’t want to grow our potatoes with it), so in this case, we still have another step to go: composting. After thinning out the reeds, willows, and fountain grass, it can be stacked into compost piles and allowed to rot down over time. It’s in this process that we finally can nullify the pollution and move on.
During decomposition, toxins get locked into long-chain molecules and become inert. In simpler terms, as contaminants move through the compost cycle, being processed by microorganisms and heated within the pile, they become less problematic, chemically speaking. This isn’t true for large concentrations of pollutants or for certain agro-chemicals, but by and large, the compost process eliminates most dangers that would be found in our “mop crops”.
The compost, then, is useful and safe for forest gardens, or if any worry remains, they can be added to other types of crops, which don’t evolve eating, such as coppiced firewood stands or evergreen privacy hedges.
Meanwhile, as the chemical residue or concentrated nutrients are soaked up into the plants and enveloped in carbon pathways, the filtered water permeates into the earth for further cleaning as it moves through sand, rock and clay. It may later emerge as sparkling springs, just as happens in naturally hydrated landscapes, or it may be absorbed by trees and plants further down slope to receive more natural filtration via transpiration (evaporation from plants).
Even for those wet climatic zones that don’t necessarily need more water, instigating this process is still worthwhile because it keeps the contaminants out of the natural stream of things and buffers for unexpected droughts, all too common in these days of climate change. As Geoff explains in his course, while nature has the ability to clean the water, and in fact does so in marshes and mangroves, but in developed situations, it’s our strategic designs that can stop this problem right as it starts.
We may not be able to control what other people are doing on their land, or what chemicals municipalities use when building roads, but we can set up our sites to naturally remediate the toxic situation.
So, why wouldn’t we?