engleski

Numerical modelling of estuary hydrodynamics

The aim of this work is the assessment of application of one- and two-dimensional numerical models in simulation of estuary hydrodynamics. The assessment is based on identification of the relative strength and limitations of two commercial numerical models ISIS Flow v2.3 (1-d) and MIKE21 (2-d). The estuary is analysed on meso- and macro-scale during several wave periods. In such spatial and temporal domain, the prevailing influence on the hydraulic-hydrological state is that of tidal waves and surface runoff, but also of the wind shear and atmospheric pressure. Numerical results in this domain have shown differences between 1-d and 2-d models, with regard to the difference in their basic assumptions. Numerical simulations were conducted on the River Clyde estuary in Scotland. The Clyde estuary has a meso tidal range (3 m) and long-term average river inflow of 110 m3/s. The spatial domain of 1-d model comprised the entire estuary, whilst the domain of 2-d model comprised the lower and middle estuary. In process of model calibration and numerical simulations recorded water levels were compared with model results for several historical events and on several locations along the estuary. In 2-d model sensitivity analysis was performed to the inflow rate, wind, and sensitivity to the spatial gradient of salinity. It was demonstrated that, in conditions without the strong influence of wind and atmospheric pressure, both 1-d and 2-d models give satisfactory assessment of the tidal hydrograph along the estuary. In conditions of stronger wind influence, however, 2-d model give a better assessment of extreme tidal levels. Further, direct dependence is shown of water levels on changes of atmospheric pressure. Inclusion of observed meteorological conditions has shown that the combined effect of wind and air pressure increased flood levels by 80 cm. As 1-d models still do not include air pressure effect and as they (ISIS-wind) give less satisfactory predictions than 2-d models (MIKE21) of wind shear effect, the utilisation of 2-d models is recommended for flood level predictions in estuaries with strong wind and air pressure influence.

Estuary hydrodynamics; ISIS Flow; River Clyde Estuary

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