AquiferWatch

is a tool that water users can use to predict aquifer levels a month in advance for managing abstraction relative to cutoff levels. It depicts current groundwater levels monitored by the Marlborough District Council (MDC) and model predictions for near-future groundwater levels. Model predictions are computed for the case that no further rainfall is received in the Wairau catchment and for current levels of groundwater abstraction. They are scenario simulations for dry-weather conditions with the aim to estimate lead-times to critically low levels. Predictions are reset to observed levels for the purpose of forecasting. Computations are based on historic Wairau River recession time series and not based on weather forecasts. Rainfall in the Wairau catchment can lead to a rise of groundwater levels in the prediction period.

Included in the plots are critical groundwater levels that signify thresholds below which abstraction might have to be restricted by the MDC. For comparison with historic groundwater levels, median groundwater levels and percentile ranges are depicted. The median is a measure for long-term average groundwater levels. The historic range of groundwater levels is depicted by the 90% percentile band.

Aquifer Storage:

The Rapaura Formation of the Wairau Aquifer is up to 30 m thick and contains ca. 330 million m³ of groundwater. Only about 10% of that groundwater is sustainable storage that is subject to seasonal fluctuations. The majority is reserved for maintaining spring flows and for preventing seawater intrusion. Groundwater storage is estimated from groundwater levels. The annual fluctuations of sustainable storage is caused by higher river flows and aquifer recharge during the winter months and lower flows and recharge during summer (Wöhling et al. 2018). The summer lows in aquifer storage typically coincide with a higher abstraction demand.

Further Information:

Wöhling & Burbery (2020): Eigenmodels to forecast groundwater levels in unconfined river-fed aquifers during flow recession

Wöhling et al. (2020): Detecting the cause of change using uncertain data: Natural and anthropogenic factors contributing to declining groundwater levels and flows of the Wairau Plain Aquifer, New Zealand

Wöhling et al. (2018): Quantifying River-Groundwater Interactions of New Zealand's Gravel-Bed Rivers: The Wairau Plain

Wairau Aquifer Project

AquiferWatch is a joint research effort between the Marlborough District Council, Lincoln Agritech Ltd, and the Technische Universität Dresden, Germany. It was funded under the MBIE Envirolink Scheme and co-funding from TU Dresden.