Abstract
Water supply from karst sources is a worldwide natural resource and the exploitation is tied to the knowledge of the positions of the hydrologic channels. We show that surface deformation induced by flood events in karst conduits is observable, and consists in uplift and outward movement from the hydraulic channel. Precipitation events produce the natural occurrence of subsurface hydraulic overpressure up to 1 MPa. Numerical modeling shows that the stresses are so strong to uplift and dislocate the surface by several mm and induce tilts in the order of microradians. The naturally induced deformation is compatible with a transient internal pressure loading of a channel. The results can be used to find new channels with dense GNSS networks. Sea water incursion and channels accessed for tourism could be monitored. Seismicity has been shown to have a seasonal variation in some areas, which could be explained by the subsurface stresses induced by the natural subsurface overpressure. The pressure induced deformation is expected to be observed in all karstic systems worldwide.
Highlights
The goal of our study is to detect underground hydrologic channels through geodetic observations
The location of channels is important for water provisioning, as in karstic environments there is not a diffuse water table, but localized water run offs
Being the cost of such devices much smaller than the one of classical dual frequency receiver it would be possible to have a set of 10 GNSS stations permanently observing deformation for a period of 1–2 years
Summary
The goal of our study is to detect underground hydrologic channels through geodetic observations. Our findings were triggered by the recent hydrologic models of the pressures building up during floods in the Karst system. This started off numerical finite element modeling of the deformation induced by the pressure buildup. Seasonal surface movements have been observed worldwide with GNSS and described with an annual and semiannual periodicity, on top of which shorter period and irregular transient movements are observed[1] These movements, with a strong vertical component, have been modeled by elastic response to seasonal surface water storage[2]. We find that the underground flood induces a soil uplift, tilting and lateral movement away from the over- pressured channel. The observations can be explained by an elastic half space model with a horizontal channel several km long on which a transient pressure pulse is applied
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