Articles | Volume 19, issue 11
Hydrol. Earth Syst. Sci., 19, 4411–4425, 2015
https://doi.org/10.5194/hess-19-4411-2015
Hydrol. Earth Syst. Sci., 19, 4411–4425, 2015
https://doi.org/10.5194/hess-19-4411-2015

Research article 02 Nov 2015

Research article | 02 Nov 2015

Impact of the Three Gorges Dam, the South–North Water Transfer Project and water abstractions on the duration and intensity of salt intrusions in the Yangtze River estuary

M. Webber1, M. T. Li2, J. Chen2, B. Finlayson1, D. Chen3, Z. Y. Chen2, M. Wang1, and J. Barnett1 M. Webber et al.
  • 1School of Geography, The University of Melbourne, Parkville, Victoria 3010, Australia
  • 2State Key Laboratory for Estuarine and Coastal Research, East China Normal University, Shanghai 200062, China
  • 3College of Water Conservancy and Hydropower Engineering, Hohai University, Nanjing 210098, China

Abstract. This paper assesses the impacts of the Three Gorges Dam, the South–North Water Transfer Project and other water abstractions on the probability of long-duration salt intrusions into the Yangtze River estuary. Studies of intrusions of saltwater into estuaries are typically constrained by both the short duration of discharge records and the paucity of observations of discharge and salinity. Thus, studies of intrusions of saltwater into estuaries typically seek to identify the conditions under which these intrusions occur, using detailed observations for periods of 20–60 days. The paper therefore first demonstrates a method by which to identify the conditions under which intense intrusions of long-duration occur and then applies that method to analyse the effect of the three projects. The paper constructs a model of the relationship between salinity and discharge and then employs Monte Carlo simulation methods to reconstruct the probability of observing intrusions of differing intensities and durations in relation to discharge. The model predicts that the duration of intrusions with chlorinity ≥ 250 mg L−1 (or ≥ 400 or 500 mg L−1) increases as the number of consecutive days with discharge ≤ 12 000 m3 s−1 (or ≤ 8000 m3 s−1 increases. The model predicts that in 1950–2014, the number of consecutive days with chlorinity ≥ 250 mg L−1 averaged 21.34 yr−1; if the three projects operate according to their normal rules, that average would rise to 41.20 yr−1. For a randomly selected year of discharge history from the period 1950–2014, under normal operating rules for these projects the probability of an intrusion rises from 0.25 (for 30-day intrusions) or 0.05 (for 60-day intrusions) to 0.57 or 0.28, respectively.

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Short summary
This paper demonstrates a method for calculating the probability of long-duration salt intrusions in the Yangtze Estuary and examines the impact of the Three Gorges Dam, the South-North Water Transfer Project and local abstractions on that probability. The relationship between river discharge and the intensity and duration of saline intrusions is shown to be probabilistic and continuous. That probability has more than doubled under the normal operating rules for those projects.