ABSTRACT

With the development of inland shipping traffic, the interaction between ship-induced hydrodynamics and revetments become more intense. It is essential to study the wave dissipation performance of waterway revetments. In this paper, field measurements were conducted in Changzhou segment of the Grand Canal, which has a vertical revetment structure. Water surface fluctuations caused by 220 groups of ships were recorded. The incident and reflected waves were separated from the recorded waves based on a proposed mathematical model. Then, the average reflection coefficients of the vertical revetment when cargo ships and yacht sailed through the measured segment were calculated for 0.84 and 0.86, respectively, which indicates that the wave dissipation performance of the vertical revetment is poor.

INTRODUCTION

Recently, with the development of inland waterborne transport systems, the ship scale and sailing speed of ships in inland waterway have rapidly increased in China, putting heavy pressure on the fluvial environment caused by ship-induced waves and currents (Roo and Troch, 2015). As one of the most developed inland waterborne transportation provinces in China, the southern segment of the Grand Canal in Jiangsu Province has become the largest water transport volume and highest shipping traffic density segment of the Grand Canal. Due to land use limit in Changzhou urban areas, Jiangsu Province, vertical revetments are mostly used. Waves near the waterway revetments are usually the superposition of incident and reflected waves as a result of narrow waterway width, resulting in worse navigation conditions. Therefore, it is an essential task to evaluate the wave dissipation performance of vertical revetments in inland waterway.

Generally, reflection coefficient is used to characterized the wave dissipation performance of revetment structure. The most important thing is to separate the incident waves and reflected waves before reflection coefficient calculation (Nallayarasu, Fatt, and Shankar, 1995; Medina, 2001; Gunaydin and Kabdasli, 2007; Lee and Shin, 2014). The simplest method is named single-point method proposed by Healy (1953), which cannot measure the high order wave. In order to obtain higher accuracy results, there are some other separation methods proposed. The wave process is measured at the same time with two or more separated wave gauges, then, these measured data are analyzed using Fourier series method to obtain the component of incident waves and reflected waves. These methods contain two-point (Goda and Suzuki, 1976), three-point (Mansard and Funke, 1980) and multi-point methods (Zelt and Skjelbreia, 1992). The two-point method is mostly aimed at the positive incidence of the wave direction perpendicular to the building. As an extension of the two-point method, the wave field characteristics of incident and reflected waves are analyzed after adding one more wave gauge, and least square method is introduced, improving the separation accuracy (Mansard and Funke, 1980). Based on the same principle as three-point method, the main idea of multi-point method is to introduce the error weight of each test point through the distance of any two wave gauges, so as to minimize the error and obtain the height of incident and reflected waves (Zelt and Skjelbreia, 1992). In this paper, multi-point method is used to separate the incident and reflected waves.

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