Suspended Sediment & Turbidity Monitoring in NZ – a product of Extreme events

Evan Baddock - National Institute of Water and Atmospheric Research (NIWA), New Zealand , 29 June, 2020

During – measuring and sampling over extreme events.

This paper provides an overview of some of the important things to know about suspended sediment and turbidity monitoring in New Zealand Rivers.

In New Zealand it is common to use turbidity to derive suspended sediment concentrations. However, estimating suspended sediment loads from continuous turbidity measurements is complicated by numerous factors including stream flow changes, type and positioning of sensors, sediment flux, and biological fouling and debris causing false readings (to name a few). There is an increasing ‘confusion’ on how best to conduct the monitoring, instrument validation procedures, and in particular how to use the data for various purposes.

Continuous turbidity monitoring is becoming more frequently used in our networks around the country for a variety of purposes, ranging from use as a proxy variable to determine suspended sediment concentrations through to using it as an absolute value for environmental state assessment. While New Zealand has developed a ‘National Environmental Monitoring Standard’ (NEMS), for turbidity, this does not seem to cover or satisfy all use cases and challenges encountered when measuring.

Obtaining consistent and robust relationships between turbidity and suspended sediment are particularly challenging and this presentation will illustrate some of those challenges, what we have learnt from them, and possibly raise some questions for discussion.