Do we need a more sophisticated multilayer artificial neural network to compute roughness coefficient?

Abstract

Artificial neural networks (ANNs) are one of the most rapidly growing fields of soft computing. Along with deep learning, they are currently the most widely used machine learning techniques. Artificial neural networks are especially suitable for problem-solving where a researcher deals with incomplete data sets and no algorithms or specific sets of rules to be followed.This article deals with a case of comparison of several modifications of neural networks that may be applied to compute Chézy’s roughness coefficient. Neural network modelling is often started with one hidden layer. Having even one hidden layer, a neural network presents a powerful computing system to give good results. If it is necessary, the number of hidden layers may increase. Usually, two or three hidden layers of neurons are used. Diverse activation functions may also apply. The article aims to explore the necessity of developing sophisticated multilayer artificial neural networks to compute Chézy’s roughness coefficient.Under the study, the following modifications of the neural network computing Chézy’s roughness coefficient were considered and analysed: (1) Application of two hidden layers of neurons; (2) Application of three hidden layers of neurons; (3) Use of a dropout algorithm for training neural networks by randomly dropping units during training to prevent their co-adaptation; (4) Apart from the sigmoid (logistic) activation function, the use of other artificial neuron transfer functions – hyperbolic tangent (tanh) and rectifying activation function (ReLU).The training and testing of the considered neural network options were carried out using the actual hydro-morphological and hydrological data related to the channel section on the Dnieper River (downstream of Kyiv), the Desna River section near Chernihiv, and the Pripyat River section near the town of Turiv. The Python object-oriented programming environment was applied to build and train the neural networks. The test results confirm the acceptability and sufficiency of computing the Chézy roughness coefficient using the ANN of direct propagation with one hidden layer and a sigmoid logistic activation function. The formation of a qualitative set of training data, as well as data arrangement and choosing a relevant computing model based on empirical knowledge, are, as concluded, among more actual issues than creating more sophisticated neural networks.