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| Titel |
Spectral decomposition of time-scales in hyporheic exchange |
| VerfasserIn |
Anders Wörman, Joakim Riml |
| Konferenz |
EGU General Assembly 2015
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 17 (2015) |
| Datensatznummer |
250111963
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| Publikation (Nr.) |
 EGU/EGU2015-12117.pdf |
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| Zusammenfassung |
| Hyporheic exchange of heat and solute mass in streams is manifested both in form of
different exchange mechanisms and their associated distributions of residence times as well
as the range of time-scales characterizing the forcing boundary conditions. A recently
developed analytical technique separates the spectrum of time-scales and relates the forcing
boundary fluctuations of heat and solute mass through a physical model of the hydrological
transport to the response of heat and solute mass. This spectral decomposition can be done
both for local (point-scale) observations in the hyporhiec zone itself as well as for transport
processes on the watershed scale that can be considered ”well-behaved” in terms of
knowledge of the forcing (input) quantities. This paper presents closed-form solutions in
spectral form for the point-, reach- and watershed-scale and discusses their applicability
to selected data of heat and solute concentration. We quantify the reliability and
highlight the benefits of the spectral approach to different scenarios and, peculiarly, the
importance for linking the periods in the spectral decomposition of the solute response
to the distribution of transport times that arise due to the multitude of exchange
mechanisms existing in a watershed. In a point-scale example the power spectra of
in-stream temperature is related to the power spectrum of the temperature at a specific
sediment depth by means of exact solutions of a physically based formulation of the
vertical heat transport. It is shown that any frequency (Ï) of in-stream temperature
fluctuation scales with the effective thermal diffusivity (κe) and the vertical separation
distance between the pairs of temperature (É) data as Ï / κe/(2É2), which implies a
decreasing weight to higher frequencies (shorter periods) with depth. Similarly
on the watershed-scale one can link the watershed dispersion to the damping of
the concentration fluctuations in selected frequency intervals reflecting various
environments responsible for the damping. The frequency-dependent parameters indicate
that different environments dominate the response at different temporal scales. |
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