Predicting scour depth at seawalls using GP and ANNs Ali Pourzangbar, Aniseh Saber, Abbas Yeganeh-Bakhtiary and Lida Rasoul Ahari ABSTRACT Accurate prediction of maximum scour depth is important for the optimum design of seawall structure. Owing to the complex interaction of the incident waves, sediment bed, and seawalls, the prediction of the scour depth is not an easy task to accomplish. Undermining the recent experimental and numerical advancement, the available empirical equations have limited accuracy and applicability. The aim of this study is to investigate the application of robust data-mining methods including genetic programming (GP) and artificial neural networks (ANNs) for predicting the maximum scour depth at seawalls under the broken and breaking waves action. The performance of GP and ANNs models has been compared with the existing empirical formulas employing statistical measures. The results indicated that both the GP and ANNs models functioned significantly better than the existing empirical formulas. Furthermore, the capability of GP was used to produce meaningful mathematical rules, and an analytical formula for predicting the maximum scour depth at seawalls under breaking and broken waves’ attacks was developed by utilizing GP. Ali Pourzangbar (corresponding author) School of Civil Engineering, Iran University of Science & Technology, Tehran, Iran E-mail: a_pourzangbar@sut.ac.ir Aniseh Saber Architecture Department, School of Engineering, University College of Nabi Akram, Tabriz, Iran Abbas Yeganeh-Bakhtiary School of Civil Engineering, Iran University of Science & Technology, Tehran, Iran and Department of Mechanical Engineering, Institute Teknologi Brunei (ITB), Brunei, Darussalam Lida Rasoul Ahari School of Electrical, IT and Computer Sciences, Islamic Azad University of Qazvin, Iran Key words | artificial neural networks (ANNs), breaking wave, broken wave, genetic programming (GP), scour depth, seawalls INTRODUCTION Coastal protection structures such as seawalls and break- waters are constructed to protect harbors and coasts against attack from waves and to provide a self-sheltered area. The malfunction of coastal structures can result in major socio-economic and environmental problems such as coastal inundation and flooding. The design and construc- tion of coastal protection structures are very costly and time- consuming, and they require skilled labor, therefore, the optimum design of such structures is essential. Scour at sea- walls is one of the most important aspects of the stability of the structure. Oumeraci () and Lillycrop & Hughes () claim that scour can cause significant structural instability which can lead to structural failure. Hence, pre- dicting scour depth at seawalls is of great importance in the coastal engineering discipline. The incident wave climate, geomorphological properties of sediment bed, and structural configurations are key parameters in the predic- tion of the scour depth at seawalls. Several studies have been conducted on the non-break- ing wave-induced scour at coastal structures (e.g., De Best et al. ; Xie , ; Sumer & Fredsøe ; Sumer et al. ; Lee & Mizutani ); conversely, there are few studies available on the broken wave-induced scour. For the case of the non-breaking wave, it is shown that the scour and sediment deposition patterns in front of the coastal structures are governed by the action of standing waves. However, broken wave-induced scour patterns are different from those of non-breaking waves (Tsai et al. ). Fowler () conducted laboratory studies to investigate scour at the toe of a vertical seawall under the action of 349 © IWA Publishing 2017 Journal of Hydroinformatics | 19.3 | 2017 doi: 10.2166/hydro.2017.125 Downloaded from https://iwaponline.com/jh/article-pdf/19/3/349/391424/jh0190349.pdf by guest on 25 May 2020