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COMMISSION INTERNATIONALE DES GRANDS BARRAGES ------- VINGT-SIXIÈME CONGRÈS DES GRANDS BARRAGES Autriche, juillet 2018 ------- A CHANGING FLOW REGIME IN CENTRAL GERMANY: MAGNITUDES, CAUSES AND EFFECTS ON RESERVOIR MANAGEMENT*1 Markus MÖLLER Chief Hydrologist, THÜRINGER FERNWASSERVERSORGUNG, ERFURT GERMANY 1. INTRODUCTION The Harz (10.2 – 11.5 degr. East and 51.5 – 52.0 degr. North) is the main water tower in central Germany. Because of its freshwater endowment, the Harz mountains water resources of have been developed since the 16th century to support the mining industry and since the late 19th century for public water supply. Today, nine multi-purpose dams located in the Harz are providing high quality raw water for public water supply. Based on these reservoirs, water treatment and long- distance water transfer schemes have been developed in the 20th century, comprising a total of 1250 km of mains pipe serving more than 3 million people and numerous industries in the five states of Lower-Saxony, Saxony-Anhalt, Saxony, Thuringia and the City State of Bremen. Neustadt dam – a stone masonry dam (H = 33.4 m; L = 127.0 m) – is the Southernmost and smallest of these nine dams and is fulfilling its water supply function since 1905. At present, all safely available water (1.3 MCM) from the dams reservoir is committed in a raw water supply contract and the buyer – the local water company WVN – has requested * CHANGEMENT DU REGIME HYDROLOGIQUE EN ALLEMAGNE CENTRALE: MAGNITUDE, CAUSES ET EFFETS SUR L’EXPLOTATION DU RESERVOIR 252