Modelling Behaviour of the Salt Wedge in the Fraser River and Its Relationship with Climate and Man-Made Changes

Albert Tsz Yeung Leung,Jordan Matthieu,Jim Stronach

doi:10.3390/jmse6040130

Albert Tsz Yeung Leung, Jordan Matthieu + Show 1 more

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https://doi.org/10.3390/jmse6040130

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Abstract

Agriculture is an important industry in the Province of British Columbia, especially in the Lower Mainland where fertile land in the Fraser River Delta combined with the enormous water resources of the Fraser River Estuary support extensive commercial agriculture, notably berry farming. However, where freshwater from inland meets saltwater from the Strait of Georgia, natural and man-made changes in conditions such as mean sea level, river discharge, and river geometry in the Fraser River Estuary could disrupt the existing balance and pose potential challenges to maintenance of the health of the farming industry. One of these challenges is the anticipated decrease in availability of sufficient freshwater from the river for irrigation purposes. The main driver for this challenge is climate change, which leads to sea level rise and to reductions in river flow at key times of the year. Dredging the navigational channel to allow bigger and deeper vessels in the river may also affect the availability of fresh water for irrigation. In this study, the salinity in the river was simulated using H3D, a proprietary three-dimensional hydrodynamic numerical model which computes the three components of velocity (u,v,w) in three dimensions (x,y,z) on a curvilinear grid developed specially for Fraser River, as well as scalar fields such as salinity and temperature. The results indicate various levels of impact to the salinity in the river and adaptive measures must be established to maintain the long-term viability of the industry. This study found that sea level rise and changes in river discharge would have a larger impact on the availability of fresh water than would channel deepening at the present sea water level. In a low river discharge regime, the impact from sea level change is more significant than in the high river discharge regime. On the other hand, the influence from changes in river discharge on withdrawal appears to increase when water level is lowered. Dredging the channel to accommodate larger vessels with deeper draft would further affect the salinity and shorten the withdrawal window; the effect of channel deepening becomes more pronounced in the lower flow period.

Highlights

Many of the largest economies in the world are located near or in a river estuary where saline water from the ocean meets the freshwater draining from inland: The Hudson River in New York, the Mississippi River in New Orleans, the Buffalo Bayou in Houston, the Yellow River in Shanghai, and the Pearl River in Hong Kong, just to name a few
It is difficult to draw definitive conclusions regarding which factor dominates the salt wedge dynamics from this set of model results because, as presented in Section 3.4.1 and in Figure 10, each of the sea level rise cases incorporates different flow rates associated with the projected normal year, dry year, and wet year as predicted by MIROC for its own time horizon; speaking, these model runs have two varying factors, the flow rate and sea level, and it is not immediately obvious which factor is more important in governing the salinity in the river
Some conclusions can be drawn regarding the evolution of salinity in the Fraser River resulting from environmental changes and direct man-made changes

Summary

Introduction

Many of the largest economies in the world are located near or in a river estuary where saline water from the ocean meets the freshwater draining from inland: The Hudson River in New York, the Mississippi River in New Orleans, the Buffalo Bayou in Houston, the Yellow River in Shanghai, and the Pearl River in Hong Kong, just to name a few These are not coincident, because an estuary often is of critical commercial value to nearby areas; and altogether, estuaries serve to contribute to human welfare and value to the world’s economy, and provide essential ecosystem services such as food production and recycling of nutrients [1]. Understanding the complicated interaction between changes in sea level and runoff as well as bathymetry of the river and their impacts on the salinity in the river is essential for developing proper and timely strategies to ensure resiliency of coastal areas against natural and anthropogenic changes in the future

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