Climate Change Amongst Other Flood Hazard Uncertainties: Marlborough Case Studies

Knowledge of the performance of a floodway or river is an ongoing challenge for engineers working towards managing flood hazard. Furthermore the New Zealand climate is changing, which presents a new uncertainty in defining the standard of flood control works into the future. Other uncertainties also cloud the ability to define both the existing and future flood hazard standards. These uncertainties include flood hydrology, channel hydraulics, aggradation, joint probability of high outlet levels and other parameters.

Marlborough has a long history of flooding and river control works. The Marlborough District Council still has a programme of monitoring and further upgrading of the river control works despite nearly 150 years of previous effort.

The paper scopes how the various uncertainties affect assessing flood hazard standard for four case study rivers. The new climate change uncertainty is considered in the context of comparison with these other uncertainties that are site specific for each river.

Monitoring and review of flood events is identified as a sound way of dealing with climate change and the other uncertainties, with upgrading as and when required. This supports the principle of adaptable design; river control schemes should be designed so that they can be readily upgraded when further information comes to hand on the various uncertainties, including the uncertainty of climate change.