Reconsidering Infiltration Potential in the Auckland Region

Infiltration practices have the potential to ‘return’ excess stormwater runoff from developments back into the ground. Infiltration offers a multitude of benefits resulting in extensive implementation nationally and internationally and offers an opportunity to implement Low Impact Design (LID). This practice is frequently eliminated prematurely in the Auckland region in many stormwater management best practicable options (BPO) assessment due to the presumption that it is not feasible on the predominantly clayey Waitemata series. Other concerns include contaminant accumulation and mobilization; groundwater contamination; early clogging or failure; and accuracy of the minimum infiltration rate for determining the preliminary feasibility of infiltration devices.

These concerns are investigated and analysed to ascertain their weight; followed by approaches to manage these concerns, and a depth specific safety factor design chart for clogging. The points of diminishing returns were ascertained from size of footprint and construction costs.