The Impact of Retention Polders, Dyke-Shifts and Reservoirs on Discharge in the Elbe River - Hydrological Modelling Study in the Framework of the Action Plan for the Flood Protection in the Elbe River Basin of the International Commission for the Protection of the Elbe River (ICPER/IKSE/MKOL)

A hydrological model simulation study has been carried out in the Elbe basin using detailed data obtained from the relevant Czech and German institutes. The LISFLOOD model has been calibrated for the Elbe river basin using these data. Using this calibrated model setup, two studies have been carried out in the framework of the Action Plan for Flood Protection of the International Commission for the Protection of the Elbe River (ICPER/IKSE/MKOL). The 2002 flood without dyke-breaks: The first part of the simulation study was a simulation of the 2002 summer flood without dyke-breaks. It has been estimated here that without dyke-breaks, the discharge in the lower part of the Elbe river would have been 2.6 ¿ 9.1 % higher (117-384 m3/s). Waterlevels would have between 18 and 54 cm higher. Reservoir Study: The planned scenario for Saale reservoir steering investigated here does not have any significant influence on the discharge of the Elbe. The influence of changing the flood storage in the Bleiloch and Hohenwarte reservoirs in winter from 40 to 55 Mm3 and in summer from 25 to 35 Mm3 on river discharge has been assessed. The scenario results have shown that this planned scenario for reservoir steering in the Saale cascade does not have a significant influence on the discharge of the river Elbe, for the investigated flood events in 1994, 2002 und 2003 at gauging station Calbe-Griezehne (lower Saale). Also the influence on the discharge in the river Elbe is marginal: changes in peak discharge downstream the Saale-confluence are in the order of 0.2% (difference in discharge 4-8 m3/s). Furthermore, the influence of the Vltava reservoir cascade was investigated using two datasets provided by the Czech Hydro-Meteorological Institute (CHMI): one dataset with the actual situation and steering of the Vltava cascade, and a scenario without the Vltava cascade. For floods with a magnitude such as in August 2002, the difference between the scenario with and without the Vltava cascade is between 1.6 and 3.7% (84-171 m3/s) in the German part of the Elbe river. Polder and Dyke-shift Study: The potential effects of 5 polders and 20 dyke-shifts on discharge in the river Elbe have been estimated. The main outcomes are the following: The 20 planned dyke-shifts reduce the peak discharge of the 2002 summer flood with 1.3-4.6% (58-202 m3/s). Waterlevels would have been 10-31cm lower. For the 2006 flood the results are similar in character, but lower in magnitude. The measures reduce the peak discharge of the 2006 spring flood with 0.4-1.3% (10-48 m3/s). Waterlevels would have been 3-10cm lower. The 5 planned polders and 20 planned dyke-shifts simulated here, reduce the peak discharge of the 2002 summer flood with 3.9-10.8% (178-469 m3/s). Waterlevels would have been 23-74cm lower. For the 2006 flood, the results are again lower: the measures reduce the peak discharge of the 2006 spring flood with 1.2-3.3% (31-121 m3/s). Waterlevels would have been 8-21cm lower.JRC.H.7-Land management and natural hazard