Solute dynamics across the stream-to-riparian continuum under different flood waves

초록

To enhance the understanding of solute dynamics within the stream-to-riparian continuum during flood event-driven water fluctuation (i.e., flood wave), a variable saturated groundwater flow and solute transport model were developed and calibrated against in situ measurements of the Inbuk stream, Korea, where seasonal flooding prevails. The solute dynamics were further investigated for flood waves (varying by amplitude [A], duration [T], roundness [r], and skewness [t(p)]) that were parameterised by real-time stream stage fluctuations. We found that the solute transferred faster and farther in the riparian zone, especially within the phreatic zone, above which in the variable saturated zone the concentration required a significantly longer time, particularly at higher altitudes, to return to the initial state. By comparison, solute transferred shallowly in the streambed where the solute plume exhibited an exponential growth trend from the centre to the bank. The dynamic changes of solute flux and mass along the stream-aquifer interface and stream concentration were linked to the shape of flood wave. As the flood wave became higher (A NE arrow), wider (T NE arrow), rounder (r SE arrow), and less skewed (t(p)NE arrow), the maximum solute storage in aquifer increased. Maximum stream concentration (C-str_max) not only presented a positive linear relationship with A or t(p) but also showed a negative logarithmic trend with increasing T or r. The sensitivity of C-str_max to A was approximately two times that of t(p), and between these values, the r was slightly more sensitive than T. C-strmax linearly increased as hydraulic conductivity increased and logarithmically increased as longitudinal dispersivity increased. The former relationship was more sensitive than the latter.

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