Predicting Flood Inundation and Risk Using Geographic Information System and Hydrodynamic Model

Foreword High flows of water is a common problem in most rivers. Earlier generations were more aware of the risks to build close to the rivers and the highest water level was locally known. Nowadays, building permits are more and more frequent below that level. Furthermore, forestry methods with clear cuts and drainage of wetlands result in a more rapid effect of heavy rain fall on the water flow in the rivers. The Swedish Meteorological and Hydrological Institute (SMHI) measures the amount of rainfall in the catchment area and calculates the flow in the streams and rivers. When the flow become high a warning is given. The problem dealt with in this study is to model the water overflow and estimate the economical and environmental risks when areas along the rivers are flooded. To cope with this and similar problems the four governmental agencies Lantmäteriet (National Land Survey), Swedish Geological Survey (SGU), SMHI and the National Ship Administration jointly created the project KRIS-GISπ. This study is a feasibility study, where the Digital Landscape Model has been created by using topographic data from Lantmäteriet. SMHI has submitted values for the water flow and Lantmäteriet data on property and building values from the Land Information System. With these data as input the hydrological model MIKE21 has been used to simulate the water flow and inundation. Many thanks to the data providers and the company DHI, who provided a license for MIKE21 free of charge. Special thanks to the authors of this report and especially to Dr Xihua Yang, who managed to produce this work during his three months stay in Gävle.