This pilot study used remote sensing (multispectral and thermal infra-red) by UAV (unmanned aerial vehicle) to improve local rainfall recharge understanding and models at two unconfined aquifer locations, in the North Island, New Zealand. Long-term rainfall recharge lysimeter monitoring sites were existing at both pilot study locations, within these sub-regional aquifer systems. While lysimeters provide accurate information on rainfall recharge to groundwater the data is only accurate at the location of the measurement - the spatial distribution of recharge away from the lysimeter site has uncertainty and is largely informed by soil mapping and water budgets, often at coarse scale (i.e. >100’s m).
Improved characterisation of physical soil properties and rainfall recharge distribution to groundwater is important for both source protection of water supply at the local scale and provision of appropriate groundwater allocation limits at larger scales. Of interest and relevance to this study is the acquisition of high definition soil moisture information via the UAV sensors, and incorporation of this data into existing numerical rainfall recharge and groundwater flow models of these sub-regional aquifers.
The UAV remote sensing provided soil moisture information at centimetre (cm) scale. This high-resolution soil moisture data allowed rainfall recharge (measured at the lysimeter sites) to be extrapolated spatially over the sensed area; and was used to inform the uncertainty of modelled rainfall recharge over the unconfined areas of the aquifer systems. Similar satellite based remote sensing approaches for modelling rainfall recharge to groundwater provide for much wider coverage (i.e. national) but with significantly coarser spatial resolution (i.e. 10’s m).
Of relevance to this study is concurrent work on how the detailed characterisation of rainfall recharge via AUV sensing at the local scale can be used to inform source protection approaches for drinking water supplies with respect to potential pathogen contamination.