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Practical Modeling of Solute Transport in River Corridors

While less than 1% of the Earth’s surface is occupied by rivers, a large fraction of its biodiversity is supported by them. Transport of carbon and nitrogen, as well as contaminants from watersheds, is controlled by transport in river corridors, which include the river and exchange with groundwater. A well-known sentiment in hydrology is that all state-of-the-art models for transport in such river corridors are incapable of capturing fundamental aspects observed in river tracer test data. I think I know why: all practical models assume instant mixing of inflowing groundwater in the river. Using high-performance computing and detailed 3-D models of the river-groundwater exchange is possible but impractical for hydrologists. We need a way to account for limited mixing in the river that is simpler, and we propose to use residence time in the river, i.e., age, in computer models of transport. This can be done using an “aging” term similar to the one used in population dynamics and materials modeling. I will formulate such a residence time-based model and test it against many datasets from river tracer tests worldwide. Our group has built a massive database of over 200 tracer tests in ~50 different rivers, including a wide range of measured river hydrologic properties. First, I will determine if the new model can be configured to adequately simulate the tracer tests, to see if this model works. Second, I will search for correlations between the parameter values of the new model and the measured river properties to figure out how we can calibrate the model independently. These help to have a model capable of capturing fundamental aspects observed in river tracer test data, which is essential for better managing the water quality of rivers and biodiversity depended on that.