How Machine Learning Can Improve Predictions and Provide Insight Into Fluvial Sediment Transport In Minnesota

Understanding fluvial sediment transport is critical to addressing many environmental concerns such as exacerbated flooding, degradation of aquatic habitat, excess nutrients, and the economic challenges of restoring aquatic systems. Fluvial sediment samples are an integral part of developing solutions for these environmental concerns but cannot be collected at every river and time of interest. Therefore, to gain a better understanding for rivers where direct measurements have not been made, extreme gradient boosting machine learning (ML) models were developed and trained to predict suspended sediment and bedload from sampling data collected in Minnesota by the U.S. Geological Survey. Approximately 400 watershed (full upstream area), catchment (nearby landscape), near-channel, channel, and streamflow features were retrieved or developed from multiple sources, reduced to approximately 30 uncorrelated features, and used in the final ML models. The results indicate suspended sediment and bedload ML models explain approximately 70 percent of the variance in the datasets. Important features used in the models were interpreted with SHAP (Shapley additive explanation) plots, which provided insight into sediment transport processes. The most important features in the models were developed to normalize streamflow by the two-year recurrence interval and quantify the rate of change in streamflow, which helped account for sediment hysteresis. Generally, this study also showed a combination of mostly watershed and catchment geospatial features were important in ML models that predict sediment transport from physical samples. This study is a promising step forward in making fluvial sediment transport predictions using ML models trained by physically collected samples. The approach developed here can be used wherever similar datasets exists and will be useful for landscape and water management.