Doubts cast on riparian buffers
RIPARIAN BUFFER ZONES ARE SEEN AS THE ANSWER TO preventing sediment ending up in our water ways, but doubts are being cast on their effectiveness.
Scion researchers have been studying riparian buffers in forests and discovered that many of them are “ineffective”.
One of the Scion team members, Chris Phillips, told the Forest Growers Research Conference in Christchurch that sediment will often go through the buffer to a stream via concentrated flow paths, even though the area is densely planted.
He says the steepness of the slopes is the over-riding factor in sediment flows and water will always find a way through, carrying sediment with it, if the slope is steep enough. Trees and shrubs may trap some of the sediment, but not all of it.
Steep land sites that have just been harvested continue to be the most vulnerable to sediment flows, as there is even less planted material to inhibit water and debris flows.
Dr Phillips says buffer zones created on flat, or gently sloping land appear to be more effective in trapping sediment than those created on steep land. He says there is a need for more in-depth research to determine how to better manage sediment flows.