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

Optimization of pollutant discharge in artificial islands
Chong Pana,* Zekun Songa,b, Shuqiao Fanga,b, Zhijia Zhenga,b,Mei Xua

a. Key Laboratory of Nearshore Engineering Environment and Ecological Security, Second Institute of Oceanography, Ministry of Natural Resourcesb. Key Laboratory of Ocean Space Resource Management Technology, Ministry of Natural ResourcesHangzhou, Zhejiang Province, China

ABSTRACT
A two dimensional hydrodynamic-diffusion model based on MIKE21
software is established to predict the hydrodynamic environment and thewater exchange characteristics of Haihua island and its surrounding sea
area. The diffusion exchange process of pollutants is predicted underdifferent discharge modes. The results show that for the same amount ofpollution, when the water level is controled to be above 0m and the gatesof 1#~4#culvert bridges are opened the pollutants in the island will
oscillate between the artificial island and the shore under the action ofebb and flood tide and the exchange time is 25.5 days. After theoptimization of the opening mode of the gate the migration and diffusion
speed of pollutants is obviously accelerated and the exchange time isshortened to about 10.1 days.

KEY WORDS:

artificial island; hydrodynamic diffusion model;
pollutant discharge; water exchange.

INTRODUCTION
Haihua island is located in the southern shore of Yangpu Bay, Hainan(Fig. 1). It is composed of three artificial islands formed by reclamationfrom the sea. Between the artificial islands and between the artificial
islands and the shore there are four culvert Bridges with box culverts andgates. The water body inside the island can exchange with the water bodyoutside the island by opening the box culvert door, so that the pollutants
can be discharged outside the island so as to enhance the self-purification
capacity of the water body inside the island. The main functions of
Haihua island are living, tourism and recreation. With the increase of
population density on the island especially the intensification of humanactivities in tourist season, the pollutants produced will increase
accordingly. The efficiency of water exchange will directly affect thewater quality of the sea and the main function of Haihua island.
Therefore, the study on the water exchange capacity of Haihua island sea
area and the optimization of pollutant discharge are of positive
significance for improving the self-purification capacity of the sea areaand protecting the Marine environment.

Fig.1 The location of Haihua artificial islands
Many scholars have studied the water exchange capacity of sea areas.
The research methods of water exchange capacity mainly include thecalculation method of measured indicator concentration （Parker, 1972;
Davies, 1982; Graebel, 2007; Wang, 1990）、 box model （Gao, 1991;Dong, 1999）、Lagrange particle tracking （Signell, 1992; Zhao, 2002）
and convection-diffusion model （Luff, 1996; Dong, 1999）etc. The
calculation method of measured indicator substance concentration isoften not applicable due to the lack of measured data. The box model
assumes that the pure seawater is immediately mixed and diluted withthe polluted seawater, which tends to overestimate the water exchange
capacity of the bay. The Lagrange particle tracking method considers thenon-uniformity of the flow field and the migration and transport
operation, but it cannot reflect the real material diffusion process. It is a
widely accepted and adopted method to study mass transport anddiffusion using convection-diffusion model and to quantitatively analyze
ocean water exchange capacity. Cao（2020）used FVCOM Marine
numerical model coupled with convection-diffusion model on the basis967