A Modeling Study on the Influence of Sea-Level Rise and Channel Deepening on Estuarine Circulation and Dissolved Oxygen Levels in the Tidal James River, Virginia, USA

Ya Wang,Jian Shen

doi:10.3390/jmse8110950

Abstract

The impact of channel deepening and sea-level rise on the environmental integrity of an estuary is investigated using a three-dimensional hydrodynamic-eutrophication model. The model results show that dissolved oxygen (DO) only experienced minor changes, even when the deep channel was deepened by 3 m in the mesohaline and polyhaline regions of the James River. We found that vertical stratification decreased DO aeration while the estuarine gravitational circulation increased bottom DO exchange. The interactions between these two processes play an important role in modulating DO. The minor change in DO due to channel deepening indicates that the James River is unique as compared with other estuaries. To understand the impact of the hydrodynamic changes on DO, both vertical and horizontal transport timescales represented by water age were used to quantify the changes in hydrodynamic conditions and DO variation, in addition to traditional measures of stratification and circulation. The model results showed that channel deepening led to an increase in both gravitational circulation strength and vertical stratification. Saltwater age decreased and vertical exchange time increased with increases in channel depth. However, these two physical processes can compensate each other, resulting in minor changes in DO. A comparison of the impact of a sea-level rise of 1.0 m with channel deepening scenarios was conducted. As the sea level rises, the vertical transport time decreases slightly while the strength of gravitational circulation weakens due to an increase in mean water depth. Consequently, DO in the estuary experiences a moderate decrease.

Highlights

IntroductionMore and more anthropogenic interventions, such as reclamation, harbor constructions, flood control measures, and channel dredging, have occurred in estuaries around the world
To accommodate economic development, more and more anthropogenic interventions, such as reclamation, harbor constructions, flood control measures, and channel dredging, have occurred in estuaries around the world
We found that the minor change could be explained by the competition of vertical and horizontal dissolved oxygen (DO) replenishments

Summary

Introduction

More and more anthropogenic interventions, such as reclamation, harbor constructions, flood control measures, and channel dredging, have occurred in estuaries around the world. Because of the need for port development, channel deepening is often needed to maintain and enhance navigation. It is critical that sustainable port development preserves ecological integrity. The impact of channel deepening and its impact on the environmental integrity of an estuary are concurrent concerns. Many studies have shown that channel deepening can affect tidal characteristics, resulting in as increase and a decrease in tidal range, estuarine stratification, and estuarine circulation [1,2,3,4,5,6]. Channel deepening often causes a decrease in dissolved oxygen (DO) [7,8,9,10].

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Conclusion