Turning Constraints into Innovative Flood Mitigation Opportunities

Parts of Epsom and Mt Eden in Auckland suffer from regular urban flooding. Auckland Council is investigating options to deliver long term benefits in these areas; however, they recognise the need to deliver a solution that will reduce the frequency of flooding in the absence of a catchment-scale solution that may be many years away.

Generally the flooding is a legacy of development in overland flowpaths, reliance on poorly performing soakage and limited existing stormwater infrastructure. A series of additional constraints including; no natural outfall, high groundwater, rock ground conditions and the location of existing services limit opportunities to deliver a cost effective scheme.

This paper outlines the design of a stormwater scheme that includes taking one of these constraints – a large diameter abandoned watermain – and turning it into an opportunity that sustainably re uses an asset that was believed redundant. The scheme also includes turning a local reserve into a multi-functional stormwater storage area and using an existing sewer for the attenuated discharge of stormwater. The scheme provides a cost effective and sustainable solution to manage flood risk to residents which can be readily adapted to provide an improved level of service in the future should the opportunity arise.