An Analysis of the Influence of Floodplain Landuse on the Flood Propagation

Floods are among the most common natural disasters that cause most of damage and affect a large number of the population every year. Due to their favourable geographical features, lowland areas along streams present a great development potential. Therefore, there is an increasing demand for exploitation of these areas for various purposes (i. e. economic, sports and recreational activities, construction of residential neighborhoods, etc.) in the field of spatial development. To reduce the flood risk in these areas, infrastructure facilities, such as embankments, etc., are being planned as mitigation measures. Such measures can change the runoff regime and divert the hazard of flooding to other areas. Moreover, construction of levees changes the retention capacity of floodplains areas, which can have a significant impact on the peak attenuation and propagation time extension of flood waves and consequently on the flood safety of the downstream areas. Therefore, sustainable land-use planning in line with economic, environmental and social interests should – among other things – include the management of flood risk by preserving or improving retention capacity of existing flood plains. Extensive flat floodplains have, due to their retention capacity, a significant impact on the propagation and transformation of flood waves. The conveyance and retention capacity of an area is significantly influenced by land use. The paper presents results of a hydraulic analysis of the impact of land use on the runoff regime in a retention areas and consequently on flood wave propagation. The land use of the retention area was simulated by hydraulic roughness. The simulations were performed for flood waves with different values of peak discharge and lengths of duration. A spectrum of flood waves in which the retention areas have significant impact on the propagation was considered. The hydraulic analysis was carried out on the plain Krško-Brežiško polje. This plain is an important retention area next to the Sava River, between the town of Krško and the state border with the Republic of Croatia.