Hybrid Gravimetry to Map Water Storage Dynamics in a Mountain Catchment

Quentin Chaffaut,Gilbert Ferhat,Jacques Hinderer,Nolwenn Lesparre,Solenn Cotel,Jean-Daniel Bernard,Frédéric Masson,Daniel Viville

doi:10.3389/frwa.2021.715298

Abstract

In mountain areas, both the ecosystem and the local population highly depend on water availability. However, water storage dynamics in mountains is challenging to assess because it is highly variable both in time and space. This calls for innovative observation methods that can tackle such measurement challenge. Among them, gravimetry is particularly well-suited as it is directly sensitive–in the sense it does not require any petrophysical relationship–to temporal changes in water content occurring at surface or underground at an intermediate spatial scale (i.e., in a radius of 100 m). To provide constrains on water storage changes in a small headwater catchment (Strengbach catchment, France), we implemented a hybrid gravity approach combining in-situ precise continuous gravity monitoring using a superconducting gravimeter, with relative time-lapse gravity made with a portable Scintrex CG5 gravimeter over a network of 16 stations. This paper presents the resulting spatio-temporal changes in gravity and discusses them in terms of spatial heterogeneities of water storage. We interpret the spatio-temporal changes in gravity by means of: (i) a topography model which assumes spatially homogeneous water storage changes within the catchment, (ii) the topographic wetness index, and (iii) for the first time to our knowledge in a mountain context, by means of a physically based distributed hydrological model. This study therefore demonstrates the ability of hybrid gravimetry to assess the water storage dynamics in a mountain hydrosystem and shows that it provides observations not presumed by the applied physically based distributed hydrological model.

Highlights

Mountain ecosystems provide important water resource locally and to populations established in the adjacent lowlands (Viviroli et al, 2007)
The main goal of this study is to show the pertinent contribution of hybrid gravimetry to evidence water storage spatio-temporal dynamics occurring in a small mountain catchment
We performed a hybrid gravity monitoring experiment to assess the spatio-temporal dynamics of water storage changes within the Strengbach mountain catchment

Summary

Introduction

Mountain ecosystems provide important water resource locally and to populations established in the adjacent lowlands (Viviroli et al, 2007). Mountains are recognized as sentinel for climatic changes as small changes in temperature or precipitation pattern can significantly impact water supply (e.g., Viviroli et al, 2011; Beniston and Stoffel, 2014) or forest ecosystems (Elkin et al, 2013; Beaulieu et al, 2016). This drives the need for new hydrological knowledge and understanding of mountain hydrosystems by integrating more in-situ measurements to complement satellite remote sensing (Bales et al, 2006). Distributed repeated measurements with relative and absolute field gravimeters provide access to water storage change (WSC)

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Conclusion