Case Study: Floodplain histories

Mapping and coring river floodplains provides information on longer-term river behaviour and response to environmental change. Reconstructing the history of floodplains and valley floors helps contextualise present river behaviour, as well as better understand future potential river behaviour in response to predicted climate change. By understanding responses to past climate patterns, predictions can be made regarding future trajectories of river behaviour.

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Floodplain investigation sites, Northland

Research in Northland is investigating Holocene (last 10, 000 years) floodplain development using a number of sites throughout the region. This shows two major periods of floodplain development. The first occurred around 3000-4000 years BP and was connected with catchment disturbance associated with climate deterioration. The second represents substantial valley floor infilling associated with post-settlement land clearance, with rates of floodplain sedimentation far exceeding natural levels, even associated with the climate disturbance at 3000 years BP.

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Post-settlement alluvium, Wairua River.

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Increased sedimentation rates post-settlement

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Waimamaku catchment with Waimamaku study site planform map and floodplain morphology and chronology identified at coring sites. Ages are derived from radiocarbon dating of organic material preserved in the floodplain sediments.

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