building, ecology, erosion, farm, Fleurieu Coast, permaculture, revegetation, seasons, soil, water, waterways, winter
Some of the challenges of our landscape regeneration efforts have been both working to restore eroded badlands in some parts of the property, as well as to arrest continuing erosion. To make matters more complex, some sections of the property have “dispersive” subsoil. While the topsoil is relatively stable, when the subsoil becomes saturated it dissolves and begins to move, hollowing out tunnels beneath the surface that ultimately collapse into sinkholes, and eventually gullies. Of course, because it’s all happening underground, tracking or predicting which areas are vulnerable, or already cavernous is tricky.
Over the last seven years, we’ve been gradually working our way around the property installing erosion control structures, based on the work of permaculture-based landscape restoration folk like Craig Sponholtz and Bill Zeedyk. Hailing from the dry southwest of North America, Sponholtz and Zeedyk advocate applying small and slow interventions that use local materials to slow water flows and gradually heal erosion. In the permaculture spirit of viewing problems as solutions, our junk-filled erosion gullies have provided a seemingly inexhaustible supply of demolition rubble, concrete chunks and segments of brick walls that are ideal material for these structures.
One of the sections that we’ve avoided is a notorious headcut that our DIY soil tests showed us boasted slaking soil that disintegrates when moist and subsoil that was also more saline than other locations around the farm. With saline subsoil, most plants wanted to avoid getting their stabilising roots down. Tree-planting was also fraught, survival rates in the saline subsoil and cracking grey topsoil were low and the very process of digging a small hole for a seedling can be enough to expose the subsoil so that next time there was a downpour, a sinkhole would open and swallow the seedling, tree guard and all. With the headcut moving about a metre a year and also widening, we thought it was time to get stuck in. At the very least, we’ve discovered that doing something is better than doing nothing and the act of getting in there and digging around allows for more accurate monitoring and effective intervention. Continue reading