Page - 1146 - in Book of Full Papers - Symposium Hydro Engineering

Fig. 9: Basic division of construction phases of building HPP Brežice embankments In the first phase the embankments at both Sava River banks are built from the HPP weir upstream, with an opening on the right bank at the construction pit due to the inflow into the diversion channel and the upstream outflow opening, which allows for outflow into the right inundation, to preserve the processes as in the existing situation when floods flow from the channel to the retention. The construction of embankments, in fact, obstructs the outflow of water from the channel to floodplains, which would increase the discharge between the already built embankments toward the cross-section at the construction pit. In high-water situations the discharge at the retention, and thus water levels (and flood risk), would decrease, while higher discharge toward the construction pit would require the construction of higher levees along the pit. Based on these analyses, the second stage involved the building of embankments from NPP Krško dam downstream, including the relief system for retention of peak discharges in the left inundation. After the completion, the latter is fitted with hydromechanical equipment, which is during the construction stage, of course, neither installed nor in operation. In this way, flood water from the channel could flow into the inundation only in the right bank, upstream the NPP Krško dam, and at the section where the embankments are not built yet. Analyses have shown that during high discharges the left retention would partially fill up also through the relief system being constructed as higher discharges would overflow the levee of the construction pit. As the construction of 2nd phase structures additionally reduced the spilling of water from the channel to the retention, at 100- year return period events the water levels of the Sava River in the area between the already built embankments would rise relative to the previous condition (up to 70 cm), while in a major part of the retention areas the water levels would decrease (up to 35 cm). Due to the influence of the construction pit and the disposal site with 1146