22-27 September 2019
Trade Fairs and Congress Center (FYCMA)
Europe/Madrid timezone

Integrating Fiber-optics distributed temperature sensing and electromagnetic geophysics data for multiscale characterization of GW-SW interactions in heterogeneous streambeds.

23 Sep 2019, 12:00
15m
Conference room 1.A ()

Conference room 1.A

Oral Topic 5 - Tools, methods and models to study groundwater Parallel

Speaker

Mr Jaime Gaona (Free University Berlin / Leibniz Institute of Freshwater Ecology / University of Trento)

Description

Groundwater-surface water interactions play a key role in determining accurate estimation of groundwater resources. However, the quantification of water exchanges occurring along and across multiple scales of streambeds still represents a big technical challenge. Given the difficulties to directly measure the seepage and/or infiltration volumes, indirect observation of water exchanges becomes an interesting alternative approach. Temperature profiles together with vertical hydraulic gradients of the sediment allow the calculation of vertical flux exchanges, but the values calculated from such few locations may not be representative of the spatial and temporal variability of exchanges. Conversely, distributed techniques such as fibre-optics distributed temperature sensing provide the opportunity to infer groundwater discharge and surface water infiltration based on the distinct thermal footprints they leave in the sediment-water interface. Moreover, the technique can capture not only the spatial heterogeneity of these patterns attributable to groundwater but also the areas of surface water infiltration during transient events. Electromagnetic induction geophysics can complete the exploration of heterogeneity by identifying the regions of preferential groundwater-surface water interaction based on the distribution of hydraulic conductivity values derived from electrical conductivity observations. Furthermore, the integration of the traditional point data with the high-resolution data from distributed techniques improves the performance of flow and heat transport models used for modelling groundwater-surface water interactions. The study builds a MODFLOW-MT3DMS model to simulate groundwater-surface water interactions in the same study site in East Germany where point and distributed data was collected. The FloPy python suite helps to incorporate the high-resolution data of distributed techniques into the 3D model. The study evidences how models based on distributed geophysics data outperform those defined on sediment cores. Secondly, the model validates the reliability of fibre-optics to identify groundwater-surface water exchanges based only on the spatial and temporal evolution of temperature anomalies in the sediment-water interface. Additionally, 3D flux estimates from the 3D flow and heat transport model cast doubt on the accuracy of the 1D vertical estimates of groundwater-surface water interaction obtained from point techniques. Altogether, the study enables discussing the advantages of using distributed techniques for the investigation of groundwater-surface water interactions with a multi-scale approach while showing the potential of 3D flow and heat transport models fed with this data for upscaling of local groundwater-surface water measurements.

Primary author

Mr Jaime Gaona (Free University Berlin / Leibniz Institute of Freshwater Ecology / University of Trento)

Co-authors

Prof. Alberto Bellin (University of Trento) Dr Jörg Lewandowski (Leibniz Institute of Freshwater Ecology / Humboldt University Berlin)

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