Assessing the use of satellite derived bathymetry in estuarine storm surge models – study case: Tauranga Harbour

Abstract

Bathymetric data are fundamental in assessments of shallow-water hydrodynamic processes. In-situ surveys provide high data quality; however, they can be expensive due to the resources/personnel needed and accessibility in highly dynamic environments. To fill this gap, Satellite Derived Bathymetry (SDB) techniques have been developed such as empirical methods using multispectral images, e.g. the Stumpf method, which uses the ratio between colourbands. Despite of all the technical improvements related to SDB, its potential use in hydrodynamic models for predicting tides and surge in estuaries has been assessed only in a few studies. The present work aims to evaluate the potential use of empirical SDB techniques in estuarine surge modelling. The method that was applied in the present work consists of 2 parts. Firstly, we estimated the bathymetry in intertidal zones for Oruamatua sub-estuary in Tauranga Harbour using the Stumpf ratio technique. Secondly, using Delft3D FLOW model for simulating astronomical tide, we compared the output of 2 different simulation scenarios: (1) using the on-site surveyed bathymetry (compiled from multiple sources) and (2) using the Stumpf-derived SDB in intertidal zones. Models 1 and 2 were compared by calculating the root-mean-squared-error (RMSE), maximum absolute error (MAE) and Pearson correlation coefficient in relation to tide gauge observations collected at Oruamatua. Preliminary results showed that, despite restrictions of the Stumpf-ratio method implementation in intertidal zones, scenario 2 resulted in a similar level of accuracy (RMSE= 13cm; MAE=42 cm) to scenario 1 (RMSE= 13; MAE=41cm). Our results indicate that satellite-derived bathymetry techniques are accurate enough to use in hydrodynamic modelling, especially in remote areas, where the assessment of flooding risk is more difficult