Investigation of tidal asymmetry in the Shatt Al-Arab river estuary, Northwest of Arabian Gulf

Abstract

Approximately one-year water level records were utilized for examining the tidal dynamics and tidal asymmetry at the Shatt Al-Arab river estuary. The harmonic and the tidal skewness, two traditional methods in quantifying tidal asymmetry in tidal systems, were used. The water level measurements revealed a presence of a tidal wave attenuation when propagating further towards the inland direction, with notable reductions in the tidal range. The results of the harmonic analysis indicated that the diurnal and semi-diurnal constituents experience considerable damping towards the upstream direction. The largest constituent was M2, followed by K1, O1, and S2. The largest shallow water constituent was MK3, followed by M4, MS4, MN4, and M6. The tidal form number ranged from 0.68 to 0.7 along the estuary; then, mixed, mainly semi-diurnal tidal nature was observed. However, six possible combinations of tidal constituents were used to quantify the tidal asymmetry, involving the interactions between astronomical constituents alone as well as with the higher harmonics. According to the harmonic method, the relative phase difference of M2 and M4 constituents was in the range of 63 to 87.06, suggesting a flood dominance behavior of tidal wave along the estuary. Positive values of the tidal skewness were observed at all stations, with a pronounced increase towards the inland direction. The M2 and M4 interaction was the main contributor to tidal asymmetry, followed by M2-K1-O1, M2-S2-MS4, M2-M4-M6, K1-M2-MK3, and M2-N2-MN4 interactions.