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Geoscientific Model Development An interactive open-access journal of the European Geosciences Union
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Volume 11, issue 4 | Copyright
Geosci. Model Dev., 11, 1627-1639, 2018
https://doi.org/10.5194/gmd-11-1627-2018
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.

Model description paper 25 Apr 2018

Model description paper | 25 Apr 2018

tran-SAS v1.0: a numerical model to compute catchment-scale hydrologic transport using StorAge Selection functions

Paolo Benettin1 and Enrico Bertuzzo2 Paolo Benettin and Enrico Bertuzzo
  • 1Laboratory of Ecohydrology ENAC/IIE/ECHO, École Polytechinque Fédérale de Lausanne (EPFL), Lausanne, Switzerland
  • 2Department of Environmental Sciences, Informatics and Statistics, Ca' Foscari University of Venice, Venice, Italy

Abstract. This paper presents the tran-SAS package, which includes a set of codes to model solute transport and water residence times through a hydrological system. The model is based on a catchment-scale approach that aims at reproducing the integrated response of the system at one of its outlets. The codes are implemented in MATLAB and are meant to be easy to edit, so that users with minimal programming knowledge can adapt them to the desired application. The problem of large-scale solute transport has both theoretical and practical implications. On the one side, the ability to represent the ensemble of water flow trajectories through a heterogeneous system helps unraveling streamflow generation processes and allows us to make inferences on plant–water interactions. On the other side, transport models are a practical tool that can be used to estimate the persistence of solutes in the environment. The core of the package is based on the implementation of an age master equation (ME), which is solved using general StorAge Selection (SAS) functions. The age ME is first converted into a set of ordinary differential equations, each addressing the transport of an individual precipitation input through the catchment, and then it is discretized using an explicit numerical scheme. Results show that the implementation is efficient and allows the model to run in short times. The numerical accuracy is critically evaluated and it is shown to be satisfactory in most cases of hydrologic interest. Additionally, a higher-order implementation is provided within the package to evaluate and, if necessary, to improve the numerical accuracy of the results. The codes can be used to model streamflow age and solute concentration, but a number of additional outputs can be obtained by editing the codes to further advance the ability to understand and model catchment transport processes.

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Solutes introduced in the environment are transported by water to streams and lakes. The tran-SAS package includes a set of codes to model this process for entire watersheds by using the concept of water residence times, i.e. the time that water takes to move through the landscape. Results show that the model is implemented efficiently and it can be used to simulate solute transport in a number of different conditions.
Solutes introduced in the environment are transported by water to streams and lakes. The...
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