Flood hazard evaluation for subdivisions in areas of coastal inundation hazard

Stormwater Conference

This paper discusses the outcomes of a recent resource consent hearing and environment court decision for a subdivision consent application for a proposed 66 lot subdivision on low lying land adjacent to the Kaipara Harbour in Auckland. The initial consent application was refused on grounds that the applicant had designed the subdivision to have all building platforms above the future coastal inundation 100 year ARI flood level, but the hazard arising from future coastal inundation on footpaths, roads and reserves had not been appropriately avoided, remedied or mitigated. The decision found that the potential adverse effects would be significant, unacceptable and more than minor. A subsequent appeal to the environment court resulted in the consent being granted subject to raising the road levels to avoid flooding to more than 500 mm depth of water. This was considered acceptable to mitigate the hazard for vehicles and pedestrians in the event of inundation from flooding from the harbour due to extreme tide and wind conditions. The paper discusses the hazard at the site due to coastal inundation, including allowance for future sea level rise. This discussion includes how flood hazard is generally addressed by engineers from consideration of the depth and velocity of floodwater. It also discusses other considerations such as the nature of potentially affected population, their likely expectations of protection against flooding and how their activities might interact with a flood event. It discusses the possible implications of the consent order on planning and engineering practice with respect to assessing acceptable coastal flood hazard for subdivisions.

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Mark-Brown Flood Hazard Evaluation.pdf

632 KB
26 Apr 2017