Reducing flood hazard by effective polder operation: A case study of the Golina polder

The aim of the study was to determine an effective variant of operation of the Golina polder to reduce flood hazard in the Warta River valley. We implemented a trial-and-error method for the development of computational variants. Our approach was based on staged analyses of alternatives, which took into account different locations and parameters of the inlet and outlet-controlling structures. Various control scenarios for flooding and draining the polder were also considered. A hybrid hydrodynamic model consisting of a 1D part for the main river area and a 2D part for the polder area was used for calculations. The model was built based on a digital elevation model (1 m resolution) and channel sections of the Warta River. The calibration was based on data collected during the flood in 2010 from the water gauge Sławsk (located directly at the Warta River) and water surface elevation measurements carried out in the polder area. Alternatives in subsequent stages were determined based on the results of previous stages, as well as experiences from the 2010 flood and consultations with the Regional Water Management Board in Poznań. The performance of the alternatives was evaluated according to six criteria that described the effectiveness of the polder operation in terms of its practical use and effectiveness in reducing flood hazard. The results showed that our approach made it possible to identify an effective variant of polder operation. Additional calculations were also performed to determine the magnitude of flows for which flooding of the polder should be considered to reduce downstream flooding.