Temperature as a Contaminant in Streams in the Auckland Region, Stormwater Issues and Management Options

Elevated discharge water temperature is gaining international recognition as a contaminant of concern to receiving waterways. Maintaining suitable thermal conditions in waterways is critical to stream health, and guidance is required for the assessment and management of stormwater temperature effects on freshwater receiving environments.

Reference catchments representative of bush (pre-development state), pastoral, and urban catchments were studied to provide data on baseline temperature regimes in Auckland. Based on an ideal management scenario to prevent additional thermal enrichment and reduce existing background thermal enrichment levels in Auckland streams, where possible, a conservative maximum temperature criterion of 20°C is recommended for all streams where the protection of stream ecological value is a management concern.

A water sensitive pathway applicable to retrofit, new development, and re-development scenarios is proposed to address temperature effects: firstly, by reducing effective impervious areas to avoid thermal enrichment; secondly, by shading existing at risk areas to mitigate thermal effects; and thirdly, by integrating temperature moderating stormwater practices to prevent or mitigate discharge of thermally enriched water directly into Auckland freshwater streams.