Land-use change and sedimentation

Land-use change and sedimentation

Simulations showing the spread of fine sediment in Whaingaroa Harbour over 5 hours, after heavy rain.

Sedimentation of estuaries and inshore environments is a serious environmental issue in some areas around New Zealand’s coastline. Changes to land use may affect the amount of sediment being transported to the coast, and planners and developers need to know how proposed landuse change will affect sedimentation, so risks and suitable mitigation strategies can be assessed.

NIWA is continuing to develop systems which model the dispersal of eroded sediment in coastal receiving waters. By coupling together a hydrodynamic model with a mudtransport module, it is now possible to simulate a combination of tidal, wind-driven, and density-driven currents, and associated fine-sediment dispersal and deposition.

"We are proving the model’s capabilities by using a hindcast – data which looks back in time – of Whaingaroa (Raglan) Harbour, obtained during a severe storm in 2006," says NIWA’s Malcolm Green. "The data from the hindcast comprises measurements from the catchment, the freshwater stream network, and the harbour. The model captures the interaction between freshwater and saltwater in the tidal creeks at the head of the harbour, the spreading of sediment plumes, and loss of a significant fraction of the land-derived sediment to the adjacent coastal ocean."

The simulations are already being used by environmental managers to underpin risk assessments to aid prediction of sediment effects.

Research subject: Oceans