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| Titel |
Dense distributed temperature sensing to infer local seepage fluxes in coastal areas |
| VerfasserIn |
Koen Hilgersom, Nick van de Giesen |
| Konferenz |
EGU General Assembly 2014
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 16 (2014) |
| Datensatznummer |
250089484
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| Publikation (Nr.) |
 EGU/EGU2014-3689.pdf |
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| Zusammenfassung |
| In many deltas, land surfaces are largely below sea level, and consequently suffering from
saline groundwater seepage. This phenomenon affects the fresh water supply for, for
example, agriculture and drinking water production. In many of those deltas, sea level rise
and land subsidence enhance these problems.
Depending on the geology, the seepage fluxes can occur both distributed and locally.
Local seepage occurs through ancient channels that were filled with higher-conductive
material at later times, but also works its way up via small vents through the soil. The latter is
called boil seepage and usually is the most saline of the mentioned seepage types.
Boils commonly appear in ditches and canals, since the pressure gradient is most of
the time larger compared to the surrounding area. Although boils appear only as
local point inflows, their high discharge and consequent salt flux can make them
contribute for over 70% of the salt flux into lowland water systems (de Louw et al.,
2010).
Seepage measurement methods include the application of so-called seepage meters and
tracers like temperature. Conventional methods using temperature differences between
groundwater and surface water require drilling temperature sensors into the soil. Because the
locations of boils are sensitive to disturbances of the soil, we measure the seepage flux by
measuring a 3D temperature profile in the surface water above the boil instead. The seepage
flux is inferred from a numerical surface water model that includes salt and temperature
transport.
Laboratory and field results show the onset of stratification because of the denser
groundwater. In the winter situation, the temperature of the groundwater is relatively high,
and double diffusive processes may play a role, mainly because there is negligible
lateral flow most of the time, when the downstream pumping station is not active.
Therefore, a model is set up that is well able to represent these double diffusive
processes.
References
De Louw, P.G.B., Oude Essink, G.H.P., Stuyfzand, P.J., and van der Zee, S.E.A.T.M.: Upward
groundwater flow in boils as the dominant mechanism of salinization in deep polders, The
Netherlands, Journal of Hydrology, 394, 494-506, 2010. |
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