Specialist flood hazard modelling for development of reserve land by Gisborne District Council, Hicks Bay

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Description: The Gisborne District Council's Parks & Reserves department was looking to develop a park in the Hicks Bay area along the banks of the Nukutaharua Stream.  The stream has a notable catchment and has been known to flood in the lower reaches.  GDC engaged e2 to perform a hydrology model and a 2D overland flow modelling to assess potential flood hazard and thus develop mitigation works if required.

 

Our expertise: Being a DHI MIKE Flood shop, we modelled the entire catchment in MIKE Urban, complete with local parameters, to get an understanding of normal and design runoffs that could be expected in the lower reaches.  This hydrology was used as input to a 2D flexible mesh MIKE Flood model to quantify the impact of flooding in the proposed park development area.

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An infrastructure failure scenario was also run to understand where overland flow might be directed in the case of a culvert or bridge blockage during a flood event.

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Outcome: The model results revealed that the lower end of the park development area was susceptible to minor flooding during an intense runoff event.  This was less of an impact then what was expected by the Parks & Reserves department; however, these results aligned with locals' experience during past flood events.  These results were used to help progress the development of the park area.