Page - 1141 - in Book of Full Papers - Symposium Hydro Engineering

immediate vicinity of the construction pit and the diversion channel used both for checking the velocity field and/or erosion risk during higher discharges than those enabled by the physical model. 3. ANALYSIS OF SCENARIOS OF GRADUAL INTRODUCTION OF SPATIAL DEVELOPMENTS During the construction of infrastructure systems many intermediate situations occur, as the individual work phases have different temporal dynamics. Therefore, many situations, i.e. scenarios, emerge, where it is necessary to check whether the individual combinations of (intermediate, temporary) measures do not excessively deteriorate the conditions in space. Such cases are, for example, the study of the impact of the construction pit with the diversion channel in combination with the impact of disposal sites with the material dredged from the construction pit or the determination of the optimal construction of levees along the reservoir. All intermediate conditions were compared in relation to the flow conditions at various discharges to those prior to construction, to remove the responsibility for anthropogenically enhanced flood risk. For high-discharge conditions the flood risk rate was checked, where the development of the construction pit and the diversion channel shape was taken into consideration, as determined using the physical model, which allows for a discharge capacity of approx. 1800 m3/s. The focus of the physical modelling was the conditions during the construction, e.g. the removal of abrupt changes in the riverbanks, which could lead to vortices that could reduce the throughput of the diversion channel [5]. The choice of locations of temporary disposal sites and the site for disposing of excess material was affected by spatial restrictions, optimisation of construction works, and particularly the requirement to not increase flood and erosion hazard. When determining the sequence of constructing the individual sections of the embankments along the reservoir, from Krško to Brežice, the main goal was to preserve, as long as possible, the communication between the main channel and floodplains, to preserve the inundation’s retention function. Therefore, the embankments were first constructed in the areas where at Q100 the communication of the Sava water flow with the inundation was smallest or only local. The calculations showed that the parallel (simultaneous) construction of embankments on the left and right banks preserved the flows on the left and right inundations, while the embankment built in one bank only would cause increased spilling and a rise in water levels in the inundation on the opposite bank. The calculations also confirmed that already the construction of the embankments in the lower part of the reservoir improved the flood safety of the Ljubljana–Zagreb motorway. These calculations took into account the implementation of other, accompanying interventions (e.g. replacement habitat), therefore the spatial situation changed gradually, while in some cases the impact of the individual spatial interventions was analysed. The calculation results for the individual 1141