the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 04 Aug 2023
Impacts of hydrofacies geometry designed from seismic refraction tomography on estimated hydrogeophysical variables
Abstract. Understanding the critical zone processes related to groundwater flows relies on subsurface structure knowledge and its associated parameters. We propose a methodology to draw the patterns of the subsurface critical zone at the catchment scale from seismic refraction data and show its interest for hydrological modelling. The designed patterns define the structure for a physically based distributed hydrological model applied to a mountainous catchment. In that goal, we acquired 10 seismic profiles covering the different geomorphology zones of the studied catchment. We develop a methodology to analyze the geostatistical characteristics of the seismic data and interpolate them over the whole catchment. The applied geostatistical model considers the scale variability of the subsurface structures observed from the seismic data analysis. We use compressional seismic wave velocity thresholds to identify the depth of the soil and saprolite bottom boundaries. Assuming that such porous compartments host the main part of the active aquifer, their patterns are embedded in a distributed hydrological model. We examine the sensitivity of classical hydrological data (piezometric heads) and geophysical data (magnetic resonance soundings) to the applied velocity thresholds used to define the soil and saprolite boundaries. Different sets of hydrogeological parameters are used in order to distinguish general trends or specificities related to the choice of the parameter values. The application of the methodology to an actual catchment illustrates the interest of seismic refraction to constrain the structure of the critical zone subsurface compartments. The sensitivity tests highlight the complementarity of the analyzed hydrogeophysical data sets.
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Notice on discussion status
The requested preprint has a corresponding peer-reviewed final revised paper. You are encouraged to refer to the final revised version.
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Preprint
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The requested preprint has a corresponding peer-reviewed final revised paper. You are encouraged to refer to the final revised version.
Journal article(s) based on this preprint
Interactive discussion
Status: closed
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RC1: 'Comment on egusphere-2023-903', Jacopo Boaga, 11 Oct 2023
The work is very well presented and of interest for HESS. The statistical approach is robust and the findings of big impact for the hydrological studies of mountain envrionment. The overall process and correlations of SRT with MRS and other hydrological measurements are well developed, and the case studies deserves publication. The main criticism I have is about the raw input of the seismic data. Authors present just a concise description of the field dataset colection, without showing seismograms or processing phase of the SRT (only some in supplementary material). Authors assert they collect up to 144 channels surveys with 24 channels seismograph (roll?), with 2m spacing (total length up to 286 m, see fig.5), adopting a not clear 8-10 m offset. They used a weak 5kg sledge hammer. The acquisition scheme is not better clarified (roll? Sources? Stacking? Source locations?). By our experience in SRT in mountain slopes, it seems very ambitious to pick first arrivals with such a source over 90-100 m distance. This obviously implies the errors of picking, and then of the inverted section. Authors should provide more information about the raw data collected, presenting clear picked seismograms to prove the timing errors adopted (in paper tab and figures, not in the supplementary materials).
Citation: https://doi.org/10.5194/egusphere-2023-903-RC1 - AC1: 'Reply on RC1', Nolwenn Lesparre, 13 Dec 2023
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RC2: 'Comment on egusphere-2023-903', Anonymous Referee #2, 27 Nov 2023
The authors propose a methodology to infer patterns of the subsurface critical zone at the catchment scale from seismic refraction data for hydrological modelling. The overall study appears to be a very good physically based distributed hydrological model applied to a mountainous catchment. As such, the study is highly relevant and fits within the scope of HESS.
The manuscript is well structured and well written. Nevertheless, I have some concerns regarding the thickness definition. In the NIHM model, transmissivity (\bar T) is obtained by integrating the hydraulic conductivity between zb and zw in the saturated zone and between zw and zs in the unsaturated zone - where zw is the hydraulic head with respect to the bottom zb. The water content (\bar θ) is determined by integrating θ in the unsaturated zone, while the storativity (\bar S) is determined by integrating S between zb and zw. Thus, by definition, \bar T, \bar θ and \bar S also depend on the state variable, i.e. the hydraulic head.
On the other hand, on page 16 (lines 425-430), the authors state: "The equations defining the groundwater flows show that key hydraulic variables such as the transmissivity \bar T and the water content \bar θ correspond to the integration over the porous media thickness of the hydraulic parameters K(h) and \theta(h), respectively as stated in (6). Thus, to solve the inverse problem seeking the hydrological model parameters, misestimating the thickness of the hydrological model underground compartments would inherently lead to a wrong assessment of the hydraulic parameters."
In my opinion, the term "thickness" is misleading here. It is not clear whether the author is referring to saprolite or soil thickness, or saturated or unsaturated thickness. In fact, if the former, it is only necessary to rewrite the text, but if they mean the saturated or unsaturated thickness, the dependence of hydraulic head and MRS on both hydraulic parameters and saturated thickness is not new. Please clarify this aspect in the manuscript before proceeding.Citation: https://doi.org/10.5194/egusphere-2023-903-RC2 - AC2: 'Reply on RC2', Nolwenn Lesparre, 13 Dec 2023
Interactive discussion
Status: closed
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RC1: 'Comment on egusphere-2023-903', Jacopo Boaga, 11 Oct 2023
The work is very well presented and of interest for HESS. The statistical approach is robust and the findings of big impact for the hydrological studies of mountain envrionment. The overall process and correlations of SRT with MRS and other hydrological measurements are well developed, and the case studies deserves publication. The main criticism I have is about the raw input of the seismic data. Authors present just a concise description of the field dataset colection, without showing seismograms or processing phase of the SRT (only some in supplementary material). Authors assert they collect up to 144 channels surveys with 24 channels seismograph (roll?), with 2m spacing (total length up to 286 m, see fig.5), adopting a not clear 8-10 m offset. They used a weak 5kg sledge hammer. The acquisition scheme is not better clarified (roll? Sources? Stacking? Source locations?). By our experience in SRT in mountain slopes, it seems very ambitious to pick first arrivals with such a source over 90-100 m distance. This obviously implies the errors of picking, and then of the inverted section. Authors should provide more information about the raw data collected, presenting clear picked seismograms to prove the timing errors adopted (in paper tab and figures, not in the supplementary materials).
Citation: https://doi.org/10.5194/egusphere-2023-903-RC1 - AC1: 'Reply on RC1', Nolwenn Lesparre, 13 Dec 2023
-
RC2: 'Comment on egusphere-2023-903', Anonymous Referee #2, 27 Nov 2023
The authors propose a methodology to infer patterns of the subsurface critical zone at the catchment scale from seismic refraction data for hydrological modelling. The overall study appears to be a very good physically based distributed hydrological model applied to a mountainous catchment. As such, the study is highly relevant and fits within the scope of HESS.
The manuscript is well structured and well written. Nevertheless, I have some concerns regarding the thickness definition. In the NIHM model, transmissivity (\bar T) is obtained by integrating the hydraulic conductivity between zb and zw in the saturated zone and between zw and zs in the unsaturated zone - where zw is the hydraulic head with respect to the bottom zb. The water content (\bar θ) is determined by integrating θ in the unsaturated zone, while the storativity (\bar S) is determined by integrating S between zb and zw. Thus, by definition, \bar T, \bar θ and \bar S also depend on the state variable, i.e. the hydraulic head.
On the other hand, on page 16 (lines 425-430), the authors state: "The equations defining the groundwater flows show that key hydraulic variables such as the transmissivity \bar T and the water content \bar θ correspond to the integration over the porous media thickness of the hydraulic parameters K(h) and \theta(h), respectively as stated in (6). Thus, to solve the inverse problem seeking the hydrological model parameters, misestimating the thickness of the hydrological model underground compartments would inherently lead to a wrong assessment of the hydraulic parameters."
In my opinion, the term "thickness" is misleading here. It is not clear whether the author is referring to saprolite or soil thickness, or saturated or unsaturated thickness. In fact, if the former, it is only necessary to rewrite the text, but if they mean the saturated or unsaturated thickness, the dependence of hydraulic head and MRS on both hydraulic parameters and saturated thickness is not new. Please clarify this aspect in the manuscript before proceeding.Citation: https://doi.org/10.5194/egusphere-2023-903-RC2 - AC2: 'Reply on RC2', Nolwenn Lesparre, 13 Dec 2023
Peer review completion
Journal article(s) based on this preprint
Data sets
Seismic profiles measured on the Strengbach catchment, France Sylvain Pasquet https://doi.org/10.26169/hplus.ohge_seismic_profiles
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Sylvain Pasquet
Philippe Ackerer
The requested preprint has a corresponding peer-reviewed final revised paper. You are encouraged to refer to the final revised version.