By late July this year we’ve already exceeded our entire rainfall for 2015, and for now, the rain shows no signs of abating. This is fantastic news for our revegetation efforts, and our dam is now almost full for the first time in two years. With heavy rains – we managed to top 100mm (4 inches) in a single day – it’s also a chance to test the effectiveness of the erosion control strategies we’ve employed.
With significant erosion in some key areas of the property, we’ve worked to adapt erosion control strategies such as those practised by Bill Zeedyk and Craig Sponholtz (see April’s Waterway Restoration workshop/working bee and our Resources page for more information). In particular, we’ve constructed Zuni bowls, for arresting headcuts, and One Rock Dams, to slow water flow, catch sediment and gradually lift the floor of erosion gullies. After the recent deluge, we toured the works to see how we went. The Zuni bowls have had mixed success: those in relative stable locations have been effective, those in dispersive soils have been unpredictable. The One Rock Dams (ORDs) have been generally successful, if swamped by sediment!
The impact of 100mm of rain in one day is significant: exposed areas lose significant amounts of soil (some areas of gully floor had almost 30cm of freshly deposited sediment), and areas of dispersive soil go berserk, collapsing in all directions. For some of these areas, we’re continually seeking further advice, but for those we can manage, we monitor and tweak over time, and try to “let the water do the work” in healing the landscape.