Abstract
Abstract. While both surface water and groundwater hydrological systems exhibit structural, hydraulic, and chemical heterogeneity and signatures of self-organization, modelling approaches between these two “water world” communities generally remain separate and distinct. To begin to unify these water worlds, we recognize that preferential flows, in a general sense, are a manifestation of self-organization; they hinder perfect mixing within a system, due to a more “energy-efficient” and hence faster throughput of water and matter. We develop this general notion by detailing the role of preferential flow for residence times and chemical transport, as well as for energy conversions and energy dissipation associated with flows of water and mass. Our principal focus is on the role of heterogeneity and preferential flow and transport of water and chemical species. We propose, essentially, that related conceptualizations and quantitative characterizations can be unified in terms of a theory that connects these two water worlds in a dynamic framework. We discuss key features of fluid flow and chemical transport dynamics in these two systems – surface water and groundwater – and then focus on chemical transport, merging treatment of many of these dynamics in a proposed quantitative framework. We then discuss aspects of a unified treatment of surface water and groundwater systems in terms of energy and mass flows, and close with a reflection on complementary manifestations of self-organization in spatial patterns and temporal dynamic behaviour.
Highlights
While surface and subsurface flow and transport of water and chemicals are strongly interrelated, the catchment hydrology (“surface water”) and groundwater communities are split into two “water worlds”
The key is to acknowledge that organization manifests through organized dynamic behaviour in time, which occurs through non-Fickian travel time distributions of water and chemical species
We propose that the degree of organization in dynamic behaviour in time manifests through the deviation of the breakthrough curve from the case of a well-mixed Gaussian system, which is quantified within the CTRW framework based on the power law exponent
Summary
While surface and subsurface flow and transport of water and chemicals are strongly interrelated, the catchment hydrology (“surface water”) and groundwater communities are split into two “water worlds”. We argue that similar conceptualizations and methods of quantification – whether related to preferential flow paths, dynamics and patterning of chemical transport and reactivity, or characterization in terms of energy dissipation and entropy production, for example – can and should be applied to both catchment and groundwater systems, to the benefit of both research communities. We show that preferential flow causes deviations from the maximum-entropy state, though these deviations have different manifestations depending on whether we observe solute transport in space or in time Based on this insight, we propose, essentially, that related conceptualizations and quantitative characterizations can be unified in terms of a theory that is applicable in catchment and groundwater systems and connects these two water worlds. Note that a 10 % faster fluid velocity implies 30 % more power as the latter grows with the cube of the fluid velocity
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