Date/Time
Date(s) - Wed 26 August
12:00 - 13:00
Braided rivers across New Zealand have often been impacted by the reduction of their braid plain with dramatic consequences on hydrology and riverbed morphology. In extreme cases, rivers have transitioned from dynamic braiding to stable meandering channels. Channel stabilization and incision is inevitably followed by weed invasion of gravel bars. Introduced predators then move in and the last of braided river functions and biodiversity are lost.
Many of Southland historically braided rivers have, or are close to reaching that point, especially in lowland areas. Within the last 50 years, the Aparima River has transformed from bare gravel bed with multiple braids to a single deep, meandering channel flanked by steep and vegetated point bars. River bird habitats have almost entirely disappeared and introduced mammals are rampant. Within that time, gravel extraction techniques and regulations have also changed with unforeseen consequences.
A new gravel extraction approach combining commercial harvest with braided river restoration has been tested locally and effects on biodiversity are closely monitored. By stripping weeds and sediment overburden, lowering point bars to recreate side braids and islands, gravel extraction can attract birds back on the river. However, this project also highlights the ongoing issues that such restoration work faces, and how to work on ways to address these.
Presenter: Clement Lagrue is a Senior Science Advisor with New Zealand’s Department of Conservation (DOC).