Seite - 1148 - in Book of Full Papers - Symposium Hydro Engineering

capacity of the lower part of the basin, to ensure lower water levels and velocities in the most critical sections. Fig. 10: Velocity field in the case of active 100-m outflow openings in the levees: (a) with backfilled diversion channel (left) or (b) still open diversion channel at the construction pit (right). Here only some findings from the extensive set of calculations are presented, which show the diversity of the response of the water current to the developments in the floodplains. In the calculations the design engineer could evaluate the different ideas, concepts, scenarios, and thus appropriately designed the excavation of the construction pit and the diversion channel, the sequence of construction phases of embankments and levees and other planned works, and thus tried to minimise the impact on flood and erosion hazard. Despite trying to find the best possible construction sequence, analyses revealed that in the individual construction phases poorer runoff conditions in some areas are to be expected than those prior to the Brežice HPP construction or those upon the completion, as suggested by the calculations. As these areas are populated, and infrastructure facilities of national significance are at stake, the calculation results underlined the need for priority construction of flood levees and additional temporary measures to protect the areas and infrastructure that would be, during the construction, exposed to increased flood and erosion hazards (e.g. of a motorway section). 5. CONCLUSIONS The appropriate siting of structures and planned developments, which have a significant impact on the runoff regime and can increase flood and erosion hazard for other users in space, needs to take into account both the impact of (stage-wise) construction on the aquatic environment and the impact of action of water on the structures and other works. When determining the acceptability of interventions, the emphasis is usually given to establishing the differences between the existing situation and the planned situation, i.e. the situation after the completion. As shown, during prolonged construction it is necessary to consider the impact of temporary structures, disposal sites, and the individual construction phases, i.e. in a situation when the planned intervention is still not operating as a functional unit. 1148