Hydrological effects of the hydraulic structures constructed in the valley of the River Little Vistula in Poland from the mid-18^th century to the present

This study of the hydraulic structures constructed in the River Little Vistula (Mała Wisła) valley covers its western reach from the village of Strumień (Schwartzwasser) to the mouth of the River Przemsza. Its purpose was to assess the impact of these structures on changes in the conditions of runoff formation within the valley from the mid-18^th century to the present. Historical materials (maps, sketches and plans) collected in the State Archives in Opole and Katowice were used in the study. Analyses of Austrian plane-table maps from the years 1763–1764 and 1861–1862 (1:28 800 scale) and of Prussian maps from the years 1827–1828 and 1881–1883 (1:25 000 scale) were also conducted. As a result of the study, the type and rate of hydraulic works were determined along with the techniques and methods used when constructing these structures in the 18^th and 19^th centuries. It was found that during the last 260 years, the main channel of the River Little Vistula moved within the meandering zone. Within the area of the Zarzecze and Mała Wisła settlements, a “new” River Vistula channel was formed during the flood in 1736, which shifted ca. 0.5–1.0 km to the south. The hydraulic structures which were constructed, mainly levees, caused water levels to rise excessively in the area during high water stages and the swollen waters often causing the levees to cave in, or to breach them. The river engineering work which was conducted also affected the formation of runoff in the valley of the River Little Vistula. It has been found that both anastomosis processes and river meandering were inhibited. In some channel reaches, temporal activation of deep erosion processes as well as channel shallowing were observed. Deep erosion reached up to 2 metres and channel shallowing up to 1 metre. These processes took place during river engineering work and the River Vistula bed took around a dozen years to stabilise following the completion of the work.