Using flushing rate to investigate spring-neap and spatial variations of gravitational circulation and tidal exchanges in an estuary

Abstract

Abstract. Spring-neap and spatial variations of gravitational circulation and tidal exchanges in the Sumjin River Estuary (SRE) were investigated using the flushing rate. The flushing rate was calculated between multiple estuarine segments and the adjacent bay to examine the spatial variation of two exchanges. The strength of gravitational circulation and tidal exchanges modulated significantly between spring and neap tides, where stratification alternated between well-mixed and highly-stratified conditions over the spring-neap cycle. Tidedriven dispersive flux of salt dominated over gravitational circulation exchange near the mouth during spring tide due to the larger tidal amplitude that caused well-mixed conditions and rapid exchange. In contrast, the central and inner regimes were found to be partially stratified during spring tide due to the reduction in tidal amplitude where both gravitational circulation and tidal exchanges were important in transporting salt. The combined contributions of two fluxes were also found during neap tide along the SRE due to the significant reduction in vertical mixing that accompanied strong stratification. Gravitational circulation exchange almost entirely dominated in transporting salt at the upstream end during spring and neap tides.

Determination of spatially varying Van der Burgh's coefficient from estuarine parameter to describe salt transport in an estuary

“…1 (Bell et al, 1999). The tidal amplitudes of the M 2 and S 2 constituents are found to decrease with 12 and 8 % within the estuary at HD, respectively (Shaha et al, 2010). The tidal cycle is semi-diurnal, with mean spring and neap ranges of 3.40 and 1.10 m, respectively.…”

“…Nunes Vaz et al (1989) suggested that the weaker turbulence during neap tide, when vertical mixing is suppressed, could lead to the acceleration of gravitational circulation (density-driven circulation). Such an influence of low mixing during neap tides was noted by Jay and Smith (1990) in the Columbia River Estuary, by Warner et al (2005) in the Hudson River Estuary and by Shaha et al (2010) in the Sumjin River Estuary.…”

“…The estuarine parameter v, proposed by Rattray (1965, 1966), has been widely accepted for describing the nature of salt transport in estuaries (Bowden and Gilligan, 1971;Fischer et al, 1979;Officer and Kester, 1991;Dyer, 1997;Savenije, 2005;Valle-Levinson, 2010;Shaha et al, 2010). This estuarine parameter v obviously illustrates which exchange process is responsible for transporting salt up-estuary (Fig.…”

“…No single mechanism is solely dominated along an estuary. Tide-driven mixing is dominant mostly downstream of an estuary, a combination of the two mechanisms in the central regimes and gravitational mixing in the inner most regimes (McCarthy, 1993;Savenije, 2006;Shaha et al, 2010).…”

Spatiotemporal variation of Van der Burgh's coefficient in a salt plug estuary

“…Tidal mixing and density-driven mixing vary along the axis of an estuary according to the tidal influence and the volume of river discharge. Tide-driven mixing usually dominates downstream; a combination of tidal and gravitational components influences the central regimes, and gravitational mixing tends to dominate upstream (Shaha et al, 2010). Therefore, a constant K value for an estuary, as suggested in earlier work (Gisen, 2015;Savenije, 1993Savenije, , 2005Zhang and Savenije, 2017), can not accurately represent the nature of salt transport in estuaries for high and low river discharge conditions.…”