Witwatersrand National Botanical Garden, Roodepoort, Gauteng. Diagram 22: Erosion by stormwater runoff reduced by laying down wire netting (section). Diagram 23: Erosion by stormwater runoff reduced by laying down willow mats (two sections, one showing willow mat during installation, and one showing willow mat after two growing seasons. Notes on the prevention of erosion from stormwater runoff. Extract from report.