WATERSHED RUNOFFAND RIVER FLOOD MODELING IN LAND USE PLANNING

Abstract

In land use planning along river paths it may be useful to consider the statistics of the flooding process of the river. The set of rules regulating land use planning in Italy results in the return period required being very long and, as a result, there are very high river discharge peaks which are taken into consideration and not much possibility of making experimental observations. Correct planning of land use should include some description of river flooding in these critical conditions. To do this a basin scale hydrological model and a robust numerical scheme of the 2D complete SWE have to be integrated. Knowing that experimental validation is very difficult we showed the reliability of the numerical schemes used to get consistent solutions. A watershed runoff forecast model was used to obtain the river hydrograph to apply as a boundary condition in the study of river flood inundation on the flat plain near the Olbia airport (Sardinia, Italy). A threshold of 1 cm was used as a condition to consider whether or not to include the cell in the computational field in the description of the wetting-drying process. And this seems to fit well in the model. The numerical model is conservative, ensuring preservation of water volumes with a precision of 10-4. The great surface water gradient in some sections is evident proof of the importance of the SWE inertial terms in wave front propagation. The flow peak loss during the alluvial plane flooding resulted in a reduction of about 10% of the discharge peak at the river mouth. This numerical method, which has been validated in previous similar applications, describes sufficiently well flooding in a complex area with river morphology limited by airport and road infrastructures.