Spillway Update

On the 7/11/2021, a couple hundred bareroot slips were used on a large dam spillway as a stop-gap measure to prevent stepping back of an erosion problem.

The dam for reference.

A photo of the February flood flow with long pasture grass visibly flattened over young hedge.

Come 7/07/22, unfortunately, a lack of promised maintenance of pasture grass directly beside the young Vetiver planting caused shading and then after a record wet season, the longer grass was pushed over the Vetiver, covering them and then catching silt and other debris. Maintenance of surrounding weeds is critical to allow the Vetiver to grow in the initial stages.

Once the problem was discovered, the long vegetation and mud was removed from the young Vetiver to expose it to the sun. One or two Vetiver slips were possibly killed by this swamping event. Plants that were swamped are noticeably smaller than ones that weren’t, causing the hedge to not be homogenous in size.

On 26/08/22 as the weather began to warm, I returned to check the progress of the hedge and trim it in preparation for the growing season. This involved some tweaking of mud and debris as the spillway was still actively flowing. The surrounding pasture was cut with a brushcutter and some handweeding of herbs and other grasses where appropriate.

On 31/10/22, I stopped in to check growth. After the record flooding and nutrient inflows into dam, an Azolla Water Fern flush had occurred and then subsequently been washed out after another downpour over the wet catchment. This has caught, in places, over 22cm in depth of a mulch layer of mostly Azolla and other aquatic plants.

As the flow of water has been non-stop since November of last year, there are still areas struggling to stand up and a couple of gaps will probably not close due to the initial lack of maintenance.

All in all, for a one year old, poorly maintained hedge to resist record floodings from a massive dam catchment and still catch significant amounts of debris is a clear example of the versatitily of Vetiver hedges for silt and erosion control. No other native or exotic plant could do what has been done here.