Integrating 1D and 2D hydrodynamic models for flood simulation

Abstract

The one-dimensional (1D) hydrodynamic model ISIS has been extensively used for designing river engineering and irrigation schemes and mapping flood risks. This paper presents the integration of a two-dimensional (2D) model with ISIS to enhance its capability for simulating floodplain flows. The 2D model is based on the DIVAST model, a research model widely used for predicting flows and water quality indicators in estuarine and coastal waters. One of the main advantages of using DIVAST is that the model has a very robust subroutine for simulating flooding and drying processes. In this study DIVAST is dynamically linked to the ISIS model and the linked model is used to predict overland flood flows. In order to increase the flexibility of the DIVAST model for dealing with complex flow situations while minimising the computational time, several modelling options were considered. These options include the so-called hydrodynamic approach, gravity wave approach and flood wave approach. A series of numerical tests were undertaken to assess the accuracy and efficacy of these approaches for simulating flows over initially dried land and dam-break flows. The model was then used to predict the flood flow in an urban area for an assumed extreme flood flow condition.