Development of Multi-catchment Flood Reduction Alternatives in Auckland

Auckland faces major stormwater drainage issues including flooding, growth pressures and ageing infrastructure. Historically, stormwater management within the Auckland City isthmus has been undertaken on a catchment-by-catchment basis. Development of multi-catchment solutions to address existing and future drainage issues requires a shift from the individual stormwater catchment management approach. A major strategic objective is to protect all habitable floors from flooding in a 50 year average recurrence interval (ARI) event by 2043 and as a significant portion of the City relies on soakage for the primary stormwater disposal method, this will be difficult to achieve without consideration of crossing drainage basin divides. Some of these soakage catchments are centrally located within the City and are closed basins. A GIS-based City-wide flood map was developed as a tool to investigate potential, holistic, multi-catchment stormwater solutions. The mapping effort included compilation of known flooding problems and complaints, field observations, flood hazard mapping results, soakage potential, planned and conceptual improvements, and other available information. Stormwater flows and initial pipe sizes were based on a simplified and verified design storm flow calculator which provides the ability to assess at a strategic level what flood protection can be achieved.