Due to its topographical characteristics extensive flat floodplains present a retention area. This area has a significant impact on the transformation of flood waves, lengthening of the propagation time and consequently positive impact on flood safety of downstream areas. The impact of the retention area on the flood wave propagation over the studied area depends on the quantity of water mass spilled into the retention area and runoff regime over it. The conveyance and retention capacity of the area is significantly influenced by the land use. The thesis consists of a hydraulic analysis of the land use impact on the runoff regime in a retention area and consequently on flood wave propagation. The land use of the retention area
was presented by the hydraulic roughness. In the analysis, the impact of the land use on the runoff regime and flood hazard within the studied area was checked by indicators, such as water depth, velocity of the water current, extent of flooded areas, classes of flood hazard in accordance to the Slovenian regulation on flood hazard, etc. Moreover, using selected impact indicators such as propagation time, water surface elevation and peak of flood wave in outlet cross-section, it was possible to analyze the impact on downstream conditions that are relevant in terms of flood safety. The analysis was performed in two phases. The first phase consists of simulations of changing roughness in a theoretical modeling area with simplified geometry for selected flood waves. This modeling area was used to isolate the impact of topographical characteristics of riparian and retention areas on the communication of water
between the channel and retention area as well as on the formation of parallel streams in the area. On the other hand, the runoff regime of topographically more complex areas is more significantly influenced by the topography of the area than its land use. Conclusions based on the results of the first-phase simulations on the theoretical modeling area were tested on a practical case in the second phase, namely on the plain Krško-Brežiško polje.