Author(s): Petr Sklenar; Karel Mares; Ivana Maresova
Linked Author(s):
Keywords: Uncertainty in flood evaluation; Inflow-outflow balance in reservoir; High water mark assessment; Peak flow estimation
Abstract: During the flood in 2002, the peak discharges reached values at 15 dam reservoirs that significantly exceeded the design discharge values. Water passed through the bottom outlets and mainly over the safety spillways, after reaching a level in the dam reservoir that had not been allowed for in the project parameters. The dams and their outlets and safety spillways, however, have represented and will probably continue to represent the main monitoring profiles where the value of peak discharges can be most reliably estimated, both in real time during a flood event and during subsequent evaluation of the flood. During the extreme flood in 2002, the gauging stations on the tributaries flowing into the dam reservoirs were destroyed or were put out of operation (instruments malfunctioned or were destroyed, power supply failed, stations were inaccessible). The total inflow therefore formed a major basis for determining the discharges into the dam reservoirs during the course of the flood. This inflow is evaluated from the increase (decrease) in the volume of water in the reservoir in a given time unit – most frequently one hour – and thus expresses the total average inflow into the reservoir within this time unit. The values of the runoffs from the dam reservoirs and the total inflows into the reservoirs are then compared with the results from other methods, in particular with discharges estimated by the “slope - area” method. These results mostly came from determining the course of the peak discharge water level obtained from the after-flood traces. The main sources of uncertainty in evaluating of peak discharge of flood are emphasized. Some findings are evidenced by actual cases from the August 2002 flood situation.
Year: 2005