Mass flux estimation and mass transport mechanism in estuaries

Abstract

Hydrodynamic surveys were conducted in a partially stratified estuary. Longitudinal salt fluxes through a cross-section were measured and the optimal number of lateral and 'vertical points for observation and estimation of fluxes ofpollutants found. The hydrodynamic data were decomposed to investigate the mechanism of instantaneous and tidally averaged mass fluxes.The decomposition method developed showed that instantaneous salt flux arose principally from the combination of velocity fluctuation with the tidal mean salinity. The error analysis showed that the estimate of mass flux was sensitive to the error inherent in the velocity data and the error range was within + 10% of the total flux. Seven. depth and four width points gave acceptable estimates of the water flux, salt flux, and longitudinal dispersion.An important feature of estuarine flow systems is the great spatial and temporal (seasonal, semidiurnal, and diurnal) variation resulting from interaction between tidal oscillation and freshwater flow. Having field observations be representative in an estuary is thus highly dependent on the sampling design (sampling locations, sampling rate, and sampling durations) as well as a rational procedure of data analysis and synthesis (Kjerfve 1979). Cross-sectional variations in velocity and pollutant (dissolved or suspended) concentrations may have a significant effect on longitudinal mass flux. One must decide how many lateral and vertical measuring positions are required to estimate longitudinal mass fluxes through a cross-section within an acceptable error. The standard sampling rate is typically once every hour, but only a few studies have been conducted with sufficient spatial resolution to estimate longitudinal mass fluxes precisely.Velocity and concentration values have been decomposed to investigate the relative importance of transverse and vertical variations (e.g. Hansen 1965; Fischer 1972;Smith 1980;Lewis and Lewis 1983). These AcknowledgmentsWe thank R. E. Lewis for advice during this research and K. R. Dyer for supplying the data for Southampton Water.

Circulation and salt balance in the São Francisco river Estuary (NE/Brazil)

“…In general, the flood-ebb asymmetry in current was more significant during the spring tide, while stratification and shear intensification/relaxation were dependent on the tidal currents, leading to maximum stratification and shear during maximum flood currents, and not exceeding the maximum ebb currents (PARK; DAVES, 1990;MIRANDA et al, 2012). Potential explanations for the observed greater asymmetry during the sampled spring tidal condition were twofold.…”

“…To date, a significant number of studies determining hydrodynamic processes and salt balance within estuarine systems throughout the world have focused on systems with very low or very high rates of freshwater discharge (2.3 to 3750 m 3 /s) and varying water depths ranging from 3 to 24 m (e.g., CAVALCANTE et al, 2013;DAVID;HUNKINS, 1981;KJERFVE, 1986;LEWIS;LEWIS, 1983;PARK;DAVES, 1990;RESTREPO;KJERFVE, 2000). Similarly, the quantification of circulation patterns and salt transport of tropical estuaries along the northeastern Brazil is limited and has been concentrated in regional research (MIRANDA et al, 2004).…”

Quantification of Water, Salt and Nutrient Exchange Processes at the Mouth of A mediterranean Coastal Lagoon

“…Regulation of the above described fluxes can produce drastic changes in the balance of processes and alter the fluctuations of the physical and chemical characteristics of a coastal lagoon (Comin, 1982). Quantification of water, salt and nutrient exchanges between salt marshes, lagoons, estuaries and the coastal ocean has been conducted in several macro-tidal environments (Uncles and Jordan, 1979;Lewis and Lewis, 1983;Uncles et al, 1986;Dame et al, 1991;Park and James, 1990;Sylaios and Boxall, 1998;Uncles and Lewis, 2001;Mendoza-Salgado et al, 2005). Nevertheless, studies on the factors determining water quality and exchange dynamics with the coastal zone of a typical, Mediterranean, micro-tidal, fishery-exploited coastal lagoon are limited.…”

Caracterização Da Dinâmica Hídrica E Do Material Particulado Em Suspensão Na Baía De Paranaguá E Em Sua Bacia De Drenagem

“…Para contornar isto, os valores das propriedades (u, v, salinidade, temperatura e densidade) na superfície (Z = 0 ) foram extrapolados a partir dos 3 pontos imediatamente adjacentes, assumindo-se curvatura contínua, ou seja, que a segunda derivada calculada considerando-se os pontos Z iguais a 0,1, 0,2 e 0,3 era equivalente àquela entre os pontos em Z iguais a 0, 0,1 e 0,2. Assumiu-se velocidade nula (u = 0 e v = 0) junto ao íundo (Z = 1), aplicando-se o princípio de "aderência", segundo o qual, não existe movimento na camada de água de espessura ínfima em direto contato com o fundo (Miranda, 1996 foi calculada pela equação 2.1 (adaptada de Rattray & Dworski, 1980;Park & James, 1990): (/ = 2 ). A área total da seção A, a cada instante de tempo, Afa), foi calculada como:…”