Proceedings of the Thirty-second (2022) International Ocean and Polar Engineering Conference
Shanghai, China, June 5–10, 2022
Copyright © 2022 by the International Society of Offshore and Polar Engineers (ISOPE)
ISBN 978-1-880653-81-4; ISSN 1098-6189

www.isope.org

Experimental Study on the Motion Characteristics of Density Current Under the Impact of the Groin
Shuo Huang1, Wenrui Huang2

1 College of Civil Engineering, Tongji University, Shanghai, China

2 Department of Civil Engineering, Florida State University, Tallahassee, USAABSTRACT
Estuarine density currents often carry sediment into the navigationchannel. Groins are engineering structures often used to regulate the flow
and sediment transport in the channel. In our study, flume experiments
based on PIV had been conducted to investigate the influence of the groinon the density current. The velocity and turbulence characteristics wereanalyzed. The results show that the groin modifies the velocity field in
the channel, and the density current disperses after passing through thegroin, resulting in the decrease of the density current thickness and theincrease of average velocity in the channel area.

KEY WORDS: Density current; estuarine channel; groin; PIV;
turbulence characteristics.

INTRODUCTION
With the continuous development of marine resources, estuary, as atransitional area between rivers and oceans, is of great importance andstrategic significance. The economic development and personnel
prosperity in the estuary area have an important relationship with thechannel in the estuary area. As the main pathway of ships transport fromthe ocean to ports, the channel is an important means of materialtransport, information exchange and resource allocation. The economic
effects brought by channels every year make great contributions to theGDP of the region (Li, et al., 2020). Meanwhile, the expansion of theport means the need for deeper channel depths (van Kessel, et al., 1998).
Channel regulation projects, such as groins and jetties, have been carriedout in estuaries around the world to meet the needs of navigation (Jiao,et al., 2020). One of the largest is the Deep-water Navigational Channel(DNC) in the North Passage of Yangtze Estuary, which has been
implemented since 1998 and 19 groins and 2 jetties have been built inthree phases (Li, et al., 2014), as shown in Fig. 1(a). However,sedimentation increases dramatically as the channel deepens, and annual
siltation in 2002 (Phase I), 2005 (Phase II), 2008, and 2013 (Phase III)was 21, 36, 57, and 81 million m3, respectively (Wan, et al., 2018). The
annual amount of dredging required to maintain the DNC was far greaterthan the original estimation, and the subsequent demand for channel
maintenance put huge economic pressure on the government(Niroomandi, et al., 2018, Shen, et al., 2018, Shen, et al., 2020).

Fig. 1 (a) DNC in the North Passage of Yangtze Estuary; (b) schematic
diagram of gravity current in the channel.
Due to the difference in density at both ends of the channel in the estuary,
the lighter freshwater moves seaward in the upper layer, and the heavier
seawater moves landward along the bottom of the channel, forming thedensity-induced current, which also known as gravity current (Huang,2010, Liu, et al., 2011, Zhou, 1998), as shown in Fig. 1(b). Numerous
studies have shown that the gravity current is closely related to thechannel siltation (Gao, et al., 2004, Hsu, et al., 2006, Hudson, et al., 2017,Shi, et al., 2003, Uncles, et al., 1993). Brenon et al (1999). concluded
that the dynamic behavior of sediment in the estuary is affected bysalinity gradient. Burchard et al. (1998) considered that the formation of2855