River brings researchers together
Researchers from four countries have arrived in Gisborne to study the Waipaoa River, as part of a collaborative project
in river sediment management.
The Waipaoa River (south of Gisborne) stems from an erosion-plagued catchment, and has one of the highest sediment loads
of any river in the world. This silty, muddy sediment is either washed out to sea or deposited onto the Waipaoa valley
floodplains, where it builds up and can reduce the flood capacity within the stopbanks.
Landcare Research is hosting the visiting researchers, and will hold a public workshop on sediment management on
Wednesday. The workshop will be opened by Mr Philippe Perez, Cultural and Scientific Counsellor to the French Embassy.
Participants and attendees will include Gisborne's mayor Meng Foon, Gisborne District Council staff, tangata whenua and
other river users, and representatives from NIWA. The workshop will cover topics including how best to handle such
sediment-prone rivers, and how changing land uses and river courses affect local people and businesses.
Landcare Research programme leader Dr Noel Trustrum says the workshop is part of a wider project sponsored by the French
government. Dr Trustrum says the researchers' visit reciprocates a trip to the Drôme River catchment in southeast France
by Landcare Research scientists and others from a range of countries.
"The land around the Drôme River gives a glimpse into the future of the Waipaoa River," Dr Trustrum says. "The Drôme
River catchment has many similar problems to the Waipaoa catchment, but has had them for much longer. For example, the
Drôme area was deforested 2-300 years ago compared to 120 years ago for Waipaoa. In the Drôme River valley, as in the
Waipaoa valley, sediment from eroded land has built up on the floodplains, increasing the flood hazard and changing the
course of the river. "However, due to forest plantings and hillslope erosion control commencing 150 years ago, the Drôme
River has recently started to cut back into the floodplains. Many had thought this would be a desirable process, helping
to return the area to its pre-deforestation condition. In practice, however, the more the river eats into the floodplain
around it, the lower the groundwater drops, which lowers the overall aquifer. This can have negative effects on water
availability for nearby horticultural and viticultural operations.
"We can learn many lessons from how the French are managing this problem, lessons that can be passed on to our own
horticulturists, viticulturists, land managers and engineers."
Dr Trustrum says while New Zealand researchers are getting a glimpse into the future of the Waipaoa catchment, the
French are gaining a retrospective view of their catchment, which helps them to better understand how they can change
their landscape to manage sediment. "For example, land use changes can affect the size of sediment particles that enter
river channels, which in turn can alter the future behaviour of the river itself."
The visiting researchers will be in New Zealand for 10 days. As well as participating in the workshop, they will visit
various parts of the Waipaoa and Waiapu River systems, looking at erosion processes, sediment sources, and aspects of
river behaviour, such as when and how it changes its course. The researchers will inspect areas damaged by Cyclone Bola
in 1988, and talk to tangata whenua about community issues including hapu catchment management plans, and threats to a
marae caused by coastal erosion processes. They will also visit the Montana vineyard at Patutahi to discuss viticulture
issues in relation to floodplain management.
Media are welcome to attend the public workshop, from 5pm, Wednesday, February 12, at the Rose Room, Lawson Field
Theatre, Fitzherbert Street, Gisborne.