Data obtained from Trebon State District Archives clearly show that the South-Bohemian National Agricultural Association (hereinafter the SBNAA) succeeded in attracting the attention of people from the local and state administration to the needs of South-Bohemian water management and to plans for new water works during the years the association existed, 1925-1941. SBNAA actively participated in organising water management events. They initiated the cooperation of interest organisations, government bodies responsible for water-management services and consultancy boards. The paper follows the work of the SBNAA which concentrated on the Vltava mostly and describes the process of preparation of plans for the construction of a dam lake in Vltava near Zelnava and subsequent plans for the construction of water works near Frymburk and Lipno. The economic crisis in 1929-1933 and subsequent economic recession resulting from the preparation of Czechoslovakia and the whole national economy for the construction of a fortification system prevented the commencement of the construction which had been prepared in plans. Drawings of the dam and all the expected parameters of the planned lake on the Vltava near Zelnava, including plans for the modification of the confluence of both the Vltavas in a scale of 1 : 5760 has been recently discovered in the Fund of the SBNAA. The lake was supposed to have the dam made of soil with a sealing clay core; on the flooded side the dam was supposed to be 12.6 m above the riverbed. The spot height of the dam crest was supposed to be 735 metres, and its crest width 7 metres; the spot height of the riverbed in the axis of the dam was 722.4 metres, maximum width of the dam at its foundations was approximately 80 metres. This enables us to calculate the size of the area which was supposed to be flooded partly or completely: Frymburk, Dolni Vltavice, Cerna v Posumavi with its graphite mines and many other villages, secluded residences or settlements. The map of the lake itself has a Czech key. No wonder that all individuals affected by the construction of the dam (such as the Schwarzenberk's and their graphite mines) as well as villages actively protested against the project and were successful eventually. Financial problems were the greatest impediment to the implementation of the project, its overall cost, lack of money and unwillingness of the government to fulfil all its promises and obligations.
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