Abstract
Abstract. The longitudinal variation of salinity and the maximum salinity intrusion length in an alluvial estuary are important environmental concerns for policy makers and managers since they influence water quality, water utilization and agricultural development in estuarine environments and the potential use of water resources in general. The supermoon total lunar eclipse is a rare event. According to NASA, they have only occurred 5 times in the 1900s – in 1910, 1928, 1946, 1964 and 1982. After the 28 September 2015 total lunar eclipse, a Super Blood Moon eclipse will not recur before 8 October 2033. In this paper, for the first time, the impact of the combination of a supermoon and a total lunar eclipse on the salinity intrusion along an estuary is studied. The 28 September 2015 supermoon total lunar eclipse is the focus of this study and the Sebou river estuary (Morocco) is used as an application area. The Sebou estuary is an area with high agricultural potential, is becoming one of the most important industrial zones in Morocco and it is experiencing a salt intrusion problem. Hydrodynamic equations for tidal wave propagation coupled with the Savenije theory and a numerical salinity transport model (HEC-RAS software "Hydrologic Engineering Center River Analysis System") are applied to study the impact of the supermoon total lunar eclipse on the salinity intrusion. Intensive salinity measurements during this extreme event were recorded along the Sebou estuary. Measurements showed a modification of the shape of axial salinity profiles and a notable water elevation rise, compared with normal situations. The two optimization parameters (Van der Burgh's and dispersion coefficients) of the analytical model are estimated based on the Levenberg–Marquardt's algorithm (i.e., solving nonlinear least-squares problems). The salinity transport model was calibrated and validated using field data. The results show that the two models described very well the salt intrusion during the supermoon total lunar eclipse day. A good fit between computed salinity and measurements is obtained, as verified by statistical performance tests. These two models can give a rapid assessment of salinity distribution and consequently help to ensure the safety of the water supply, even during such infrequent astronomical phenomenon.
Highlights
A supermoon total lunar eclipse is one of nature’s loveliest celestial events (Espenak, 2000)
Calculations during the supermoon total lunar eclipse using the coupled analytical hydrodynamic–salt intrusion model required the recalculation of the geometric parameters of the estuary i.e., cross-sectional area A0 and convergence length a
The analytical and numerical models introduced in the previous sections are applied to the Sebou estuary to evaluate the supermoon total lunar eclipse effect on salinity distribution
Summary
A supermoon total lunar eclipse is one of nature’s loveliest celestial events (Espenak, 2000). During this event, three things will occur at once. The moon will be both full and at its closest point to Earth (356 877 km); this is known as a supermoon or perigee Moon (NASA, 2015). This will occur at the same time as a total lunar eclipse; that means the Moon, Sun and Earth will be aligned. Tidal motions are controlled by changes in the position and alignment of the Moon and Sun relative to Earth (Stronach, 1989) (Fig. 2).
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