Hydrogeological conceptual model of andesitic watersheds revealed by high-resolution heliborne geophysics
<p>We conducted a multidisciplinary study at the watershed scale of an andesitic-type volcanic island in order to better characterize the hydrogeological functioning of aquifers and to better evaluate groundwater resources. A heliborne Time Domain ElectroMagnetic (TDEM) survey was conducted ov...
| Main Authors: | , , , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2019-05-01
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| Series: | Hydrology and Earth System Sciences |
| Online Access: | https://www.hydrol-earth-syst-sci.net/23/2321/2019/hess-23-2321-2019.pdf |
| Summary: | <p>We conducted a multidisciplinary study at the watershed scale of an
andesitic-type volcanic island in order to better characterize the
hydrogeological functioning of aquifers and to better evaluate groundwater
resources. A heliborne Time Domain ElectroMagnetic
(TDEM) survey was conducted over Martinique in order to investigate
underground volcanic structures and lithology, characterized by high lateral
and vertical geological variability and resulting in a very high
heterogeneity of their hydrogeological characteristics. Correlations were
made on three adjacent watersheds between resistivity data along flight lines
and geological and hydrogeological data from 51 boreholes and 24 springs,
showing that the younger the formations, the higher their resistivity.
Correlation between resistivity, geology and transmissivity data of three
aquifers is attested: within the interval 10–100 ohm m and within a range
of 1 to 5.5 Ma, the older the formation, the lower its resistivity, and the
older the formation, the higher its transmissivity. Moreover, we demonstrate
that the main geological structures lead to preferential flow circulations
and that hydrogeological watersheds can differ from topographical watersheds.
The consequence is that, even if the topographical watershed is small,
underground flows from an adjacent watershed can add significant amounts of
water to such a catchment. This effect is amplified when lava domes and their
roots are situated upstream, as they present very high hydraulic conductivity
leading to deep preferential groundwater flow circulations. We also reveal,
unlike basaltic-type volcanic islands, that hydraulic conductivity increases
with age in this andesitic-type volcanic island. This trend is interpreted as
the consequence of tectonic fracturing associated with earthquakes in this
subduction zone, related to andesitic volcanic islands. Finally, our approach
allows characterization in detail of the hydrogeological functioning and
identification of the properties of the main aquifer and aquitard units,
leading to the proposition of a hydrogeological conceptual model at the
watershed scale. This working scale seems particularly suitable due to the
complexity of edifices, with heterogeneous geological formations presenting
high lateral and vertical variability. Moreover, our study offers new
guidelines for accurate correlations between resistivity, geology and
hydraulic conductivity for volcanic islands. Finally, our results will also
help stakeholders toward a better management of water resources.</p> |
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| ISSN: | 1027-5606 1607-7938 |