Computationally Efficient Hybrid Downscaling of Surf Zone Hydrodynamics:
Methodology and Evaluation
Abstract
We present a hybrid surf-zone model that combines numerical simulations
and statistical/machine learning techniques, enabling accurate
calculations of nearshore wave and hydrodynamic parameters with high
computational efficiency. The approach involves defining representative
forcing conditions, carrying out numerical model (XBeach) simulations
for these cases, and using the results to train machine learning models
capable of predicting selected model output variables. Data
decomposition via Empirical Orthogonal Function analysis further
simplifies the process, reducing the output data dimensionality, with
minimal accuracy loss (with exception of certain wetting-drying
processes). Three machine learning approaches of increasing complexity
are compared: a multi-variate linear regression (LR), a Radial Basis
Functions (RBF) interpolator and a Deep Neural Network (DNN). The LR
model fails to account for the complex non-linearities in coastal wave
dynamics, which warrants the use of more complex machine learning
techniques. Both the RBF interpolator and the DNN models demonstrate
high levels of accuracy in the prediction of standard wave parameters,
including short and long (infragravity) wave heights, mean wavelength,
fraction of breaking waves, and depth-averaged currents. The proposed
surrogate model thus offers an efficient alternative to computationally
expensive numerical model simulations, enabling rapid and reliable
calculations of climatologies of nearshore hydrodynamic conditions and
modelling of specific event scenarios. We provide a comprehensive
description of the implementation details and assess the surrogate
model’s performance in representing various wave and hydrodynamic
parameters. We discuss potential use cases and limitations, noting that
this hybrid modelling technique can be adapted for use with other
numerical models in various settings.