Effective Dispersion in Temporally Fluctuating Flow in Heterogeneous Media
Abstract
We report on the effective dispersion of a solute in the temporally fluctuating random flow through a heterogeneous medium. Flow in natural formations is subject to temporal fluctuations on a range of time scales, including hyperannual climatic fluctuations, seasonal and irrigation cycles, daily barometric variations and earth tides. The interaction of spatial heterogeneity with temporal fluctuations and local dispersion enhances both longitudinal and transverse solute dispersion. Within a stochastic modeling framework we systematically quantify the impact of spatio-temporal flow fluctuations on effective dispersion coefficients, which measure solute spreading in response to longitudinal and transverse fluctuations of the hydraulic gradient, spatial heterogeneity and local dispersion. One observes three contributions that originate from (i) local dispersion, (ii) the interaction between local dispersion and spatial heterogeneity, and (iii) the interaction of local dispersion, spatial heterogeneity and temporal fluctuations. Longitudinal and transverse temporal fluctuations of the hydraulic gradient cause macroscopic (i.e., independent of local dispersion) contributions to the longitudinal as well as the transverse effective dispersion coefficients. An application to a field scale tracer experiment indicates that temporal fluctuations are a possible cause of observed macroscopic transverse solute spreading. Furthermore, the enhancement of solute dispersion due to temporal fluctuations shows that aquifer remediation techniques that rely on the mixing of injected reactants with resident contaminants can benefit form forcing flow fluctuations. This study provides a quantitative basis for the design of such hydraulic manipulation techniques.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2005
- Bibcode:
- 2005AGUFM.H52D..05C
- Keywords:
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- 1829 Groundwater hydrology;
- 1832 Groundwater transport;
- 1869 Stochastic hydrology