Estimating water levels and discharges in tidal rivers and estuaries: Review of machine learning approaches.

Understanding the dynamics of tidal rivers and estuaries is critical for reliable water management. Recently, the use of Machine Learning (ML) has increased in favor of hydrologic and hydraulic models. The advantages of ML over physically based models are most evident in modeling complex and nonlinear hydrologic processes and inverse problems. This study provides a critical review of ML approaches for forecasting, reconstruction, and establishment of stage-discharge relationships in tidal rivers and estuaries characterized by nonlinear interaction between the river and coastal processes. Gaps in this research area and the limited number of stage-discharge studies are identified and explained. The advantages and limitations of each approach are discussed from a critical perspective, and suggestions are made for future research directions. Advanced Recurrent Neural Networks (RNNs) and hybrid modeling systems combining physically based models with ML appear to be the most promising approaches for modeling complex physical processes in these environments. • A comprehensive review of machine learning techniques for predicting water level and discharge. • Focused on tidal rivers and estuaries characterized by nonlinear interactions. • Discussion on limitations and advantages of the machine learning approaches. • Presentation of hybrid approaches that performed better than just machine learning models. • Recommendations for future research directions. [ABSTRACT FROM AUTHOR]