# Recharge of shallow groundwater in weathered granitic agricultural catchments

Ophélie Fovet, Laurent Ruiz, Lise Andro, Mikael Faucheux, Yannick Fauvel, Zahra Thomas

► To cite this version:

Ophélie Fovet, Laurent Ruiz, Lise Andro, Mikael Faucheux, Yannick Fauvel, et al.. Recharge of shallow groundwater in weathered granitic agricultural catchments. 1st OZCAR-TERENO International Conference, Oct 2021, Strasbourg, France. hal-04701351

HAL Id: hal-04701351

https://hal.inrae.fr/hal-04701351v1

Submitted on 18 Sep 2024

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Distributed under a Creative Commons Attribution 4.0 International License
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RÉPUBLIQUE
FRANÇAISE

Liberté
Égalité
Fraternité

INRAO

l'institut Agro
agriculture • alimentation • environnement

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OYCAR

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# Recharge of shallow groundwater in weathered granitic agricultural catchments

Measuring water storage remains difficult, and mixing processes in the vadose zone are important but still poorly understood. Conceptual models have shown to be relevant for describing water flowpaths and transit times. We used a long-term high resolution monitoring set-up to develop a 1D conceptual approach of recharge based on the concepts of retention and drainage capacity to investigate the impact of unsaturated weathered granite on water residence times or solutes transfer/storage.

UMR SAS, Rennes, France

Ophelie FOVET, Laurent RUIZ,
Lise ANDRO, Mikael
FAUCHEUX, Yannick FAUVEL
and Zahra THOMAS

## In-situ long-term observation of the recharge

### Set-up

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### Data

* Cleaning saturation periods

* Need for recalibration

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In-situ calibration for soil but the weathered layer remains challenging

## 1D conceptual model

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$$dx = 0.10 \text{ m}$$
$$R_g(t, z) = \alpha_w [\text{WZMD}_{mx} - \text{WZSD}(t, z)]$$

$$\frac{dSS}{dt} = R(t, z_{end}) + \sum_{j=1}^{Z_{end}} R_g(t, j) - QS(t) = R(t, z_{end}) + \alpha_w \cdot UWZS(t) - \alpha_s \cdot SS(t)$$

<table><caption>Soil storage (0-50 cm)</caption><thead><tr><th>Parameters</th><th>unit</th><th>Calibrated value</th><th>Calibration data & criteria</th></tr></thead><tbody><tr><td>SMD<sub>mx</sub></td><td>mm</td><td>30.5 ± 5.4</td><td>RMSE_storage at 25cm&lt;0.20</td></tr><tr><td>k<sub>ET</sub></td><td>-</td><td>0.88 ± 0.06</td><td></td></tr><tr><td>WZD<sub>mx</sub></td><td>mm</td><td>3.6 ±1.7</td><td>DE(RMSE_storage at 55.85, 125, 165, 215 and 265 cm)&lt;0.50</td></tr><tr><td>α<sub>w</sub></td><td>day<sup>-1</sup></td><td>0.0086 ±0.001</td><td></td></tr><tr><td>α<sub>s</sub></td><td>day<sup>-1</sup></td><td>0.022 ±0.008</td><td></td></tr><tr><td>S<sub>y</sub></td><td>-</td><td>0.063 ± 0.021</td><td>RMSE-Level_J15&lt;0.50</td></tr><tr><td>SS<sub>mx</sub></td><td>mm</td><td>416 ±128</td><td></td></tr></tbody></table>

<figure><img src="image_14.png" /><figcaption>Weathered layers (50-270 cm)</figcaption></figure>

<figure><img src="image_15.png" /><figcaption>Groundwater dynamics</figcaption></figure>

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## Discussion and perspectives

### Annual recharge

* The timing of the autumnal GW rise seems better reproduced

* The gravity flux represents in average 30% of the total annual recharge

### Chloride simulation

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* Inter-annual trend requires a huge passive volume & annual cycles are not captured by the model

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Centre
Bretagne - Normandie

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65 Rue de Saint Brieuc,
35042 Rennes
France

ophelie.fovet@inrae.fr
https://www6.inrae.fr/ore_agrhys