Utilising Stormwater Runoff to Meet Non-Potable Water Demands at Auckland Zoo: A Quantitative and Qualitative Assessment

Auckland Zoological Park uses substantial quantities of water in their daily operation; for visitors and staff sanitary purposes, animal welfare and cleaning, through to irrigation in summer. Up to 2/3 of the demand is for non-potable quality water. The merits of stormwater runoff to meet this demand was evaluated at a desktop level for the period from 2010-2014.

Stormwater runoff was calculated using a simple event based model utilising historic daily rainfall statistics from NIWA’s Cliflo database. The watershed was divided into subcatchments and each was analysed based on Auckland Regional Council’s TP108 methodology. Stormwater runoff for the 16.4 ha site was calculated to be 45ML to 86ML per annum for the study period. Reservoir storage is required to bridge the periods between rainfall. A reservoir capacity of 14ML achieved 72% volumetric reliability over the study period whereas a volume of only 1.2ML still achieved 59% reliability. An uncharacteristically dry period in 2013 skewed the results and meant that large increases in reservoir volume resulted in only incremental improvement in volumetric and temporal reliability.

Water quality demands for the end user are high as a result of the potential to ingest pathogen or toxins by visitors, staff and animals. Heavy metal pollutants from vehicles in the carpark make this sub-catchment a poor quality option for stormwater harvest and levels of pathogens in runoff from exhibits means that stormwater requires a degree of filtration and sterilisation before re-use. Qualitatively, a ‘one type fits all’ approach for non-potable water use limits its viability as a potable water substitute.

The capture, filtration, storage and distribution of non-potable water for multiple end users is challenging. This study highlights some of the opportunities but also the difficulty in implementing stormwater re-use schemes and perhaps explains why the uptake of water re-use strategies is not prevalent.