The description of the reconstruction of the fragment of the hydrotechnical system Łączany was introduced in this work. This system has the essential influence on the threat flood the of the locality Zarzecze. The executed surveys and hydraulic calculations of the appointed cross-sections of the section of the main channel R, this hydrotechnical system made possible the qualification of the cause of the flood threat of the terrains of the locality Zarzecze, located in the zone of the influence of the water barrage Łączany. The decrease the conveyance of studied section of the channel R was affirmed, i.e. from the km 4+050 to the km 4+113, from the value 3.19 m³ ∙ s^–1 (acc. to Reclamation design… [1957]), to the value 1.06 m³ ∙ s^–1. The lower conveyance was caused become decrease of the surface of the cross-section and decrease of the slope of the bottom, in the result of the reconstruction of this part of channel during the execution of the passage with the culvert. Water discharges about larger intensity than 1.06 m³ ∙ s^–1, stepping out from the channel R, flowing in to the pumping station channel burden pumping station Zarzecze. In the case of water discharge with larger intensity the water store in the pumping station channel, and after crossing of his capacity follows submergence of the terrains of the locality Zarzecze.

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