Oral Presentation Australasian Groundwater Conference 2017

Quantifying surface water – groundwater exchanges in the Campaspe Catchment (MDB) from geochemical tracers (391)

Camille Bouchez 1 , Peter Cook 1 , Daniel Partington 1 , Yueqing Xie 1 , Craig Simmons 1
  1. NCGRT, Adelaide, SA, Australia

Quantifying the magnitude of surface water – groundwater exchanges is crucial and is the very first step towards a coordinated management of water resources. Focused on the Campaspe catchment, a sub-catchment of the Murray Darling Basin, this works aims at investigating the temporal and spatial variability of SW-GW exchanges from the geochemical signature of the river. Radon-222 activities and water stable isotopic compositions were measured in April 2016 (18 samples), December 2016 (20 samples) and May 2017 (22 samples) and used to calibrate groundwater discharge along the stream. An overall similar pattern of groundwater discharges between sampling periods is apparent and shows that the river is losing in the upstream part and gaining downstream. Discrepancies between sampling periods could be related to variable water allocations in the catchment with weirs and irrigation activities impacting local hydraulic gradients. This study also exploits hourly EC and water level data recorded since April-2016 at seven points of the river, in order to provide insights into SW-GW exchanges at a finer time scale. Indeed, while temporal river EC and flow data should reflect temporal patterns in surface water – groundwater interactions, field data have rarely been used as quantitative proxies of SW-GW exchanges. Here, we measure characteristic time of water level and EC signals as a response to perturbations created by flood events. The results are analysed in terms of flood intensity and river characteristics. In the context of allocation-dominated river flows, geochemical tracers should provide relevant insights into water dynamics of the river – aquifer continuum. This approach strongly benefits from complementary groundwater modelling studies within the Campaspe Catchment.

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