engleski

Obtaining a representative bathymetry of a shallow estuary for numerical modelling : Maketu Estuary

Numerical modelling of estuarine hydrodynamics usually requires simplifying assumptions such as steady state or &#8220; a representative bathymetry&#8221; . A real estuary is never in a steady state and its coastline geometry and bottom topography are usually complicated, and numerical models are often needed. However, the accuracy and efficiency of numerical finite difference models in reproducing the tidal distribution and water movement in time and space depend partly on the quality of the bathymetry employed. Hydrographic surveys in the shallow Maketu Estuary (<3 m depths) were undertaken in October-November 1996 and February 1997. Many problems that are not encountered in deep sea surveys are present in shallow estuaries. A novel technique to survey from a jet ski with differential GPS and a high-resolution sounder with 1 cm vertical accuracy was developed. The data logging equipment was housed in a water-proof box containing a portable computer and power supply. The transects are generated using HYDRO 6 software. In this paper, data processing and computer-assisted map design techniques and the high-resolution bathymetric maps are presented. A comparison of these maps to aerial and ground photographs is undertaken to check the reproduction of bottom topography and errors are discussed. The bathymetry survey was also used to estimate the coefficients of the bottom friction on the shallow banks and in the channels, covered by different types of sediment.

Numerical modelling; bathymetry; shallow estuary

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