Formulation of transport in a catchment-scale conceptual model

Abstract

Standard conceptual hydrological models can rarely accommodate stream tracer dynamics at the catchmentscale. They rely on the generation of runoff through the propagation of a pressure wave and do not accountfor the actual advective movement of particles. Over the last years different model frameworks have beendeveloped to account for this shortcoming. The difference between the frameworks lies in whether they arebased on mixing coefficients or storage age selection functions. Both methods have shown their ability tocapture the stream chemistry response. It is however not clear how these distinct approaches compare toeach other and to reality.To provide more clarification in this matter, this research applied both frameworks separately to model thehydrological and stream water chemistry response for a specific catchment. The results are analysed usingthe concept of transit times, where information on the fluxes and states in all model components is used togenerate distributions that describe the age structure of water. By comparing the distributions generated byboth methods and by evaluating the overall model performances, more insight is gained on the two frame-works and on their ability to capture subsurface mixing dynamics.From the results of this research it is concluded that both frameworks show similar performance. They arehowever conceptually different, which might have implications for their ability to capture specific dynamics.These implications depend on the characteristics of the catchment of interest. It is still concluded howeverthat performance for each frameworks is likely to be similar. Because the model description of the MixingCoefficient framework is less complex, it is recommended to continue research with this framework.