GIS as a tool to aid pre- and post-processing of hydrodynamic models. Application to the Guadiana estuary

Abstract

The main objective of this work is to develop GIS based techniques to aid the setup of hydrodynamic models and to improve model results. This dissertation analyzes well-known GIS methods and proposes new ones to prepare and process estuarine model data. Estuarine hydrodynamic models require management of large quantities of georeferenced information. A Geographic Information System (GIS) can help to store, manage, analyze and display all these data during the input and the output phases. The hydrodynamics of the Guadiana Estuary was simulated using a 2D configuration in MOHID Water Modelling System, based on a boundary fitted curvilinear grid. GIS tools were used to pre-process the model grid and bathymetry. The water domain was extracted from the orthophoto using unsupervised classification of the image based on principal component analysis of the spectral bands. The large amount of bathymetric measurement points was decreased using a spatial regular pattern (hexagons). The missing bathymetry data in some very shallow parts of the estuary were estimated from the orthophoto using correlation between existing data and spectral band values. The bathymetry data were interpolated into curvilinear grids by several different methods, including an advanced method using river straightening (transformation to the along-channel coordinate system). The finite volume model MOHID was used to test these methods and evaluate the associated improvements. The model results were in good agreement with the observations under well-mixed conditions. Including the bathymetry estimated from orthophoto improved the accuracy of the simulations; and using advanced interpolation methods improved the results even more. The bathymetry interpolation in the channel-oriented coordinates significantly improved the direction of the water current. Good quality of the spatial input data was critical for obtaining good model results. The use of GIS tools to produce model inputs proved to be a valuable aid to coastal hydrodynamic modelling increasing substantially the model accuracy. This dissertation is useful in both theoretical and practical fields of science: in theoretical, by analyzing and developing GIS methods to prepare and process estuarine hydrodynamic model data, in practical, by creating an improved model setup for the Guadiana Estuary, using more accurate bathymetric data and a new curvilinear grid, thus obtaining more realistic results.