Changes in river channel pattern as a result of the construction, operation and decommissioning of watermills – the case of the middle reach of the River Liswarta near Krzepice, Poland

Changes in river channel pattern in the middle reach of the River Liswarta and in the lower reaches of its tributaries near Krzepice were analysed, and were related to the construction, operation and decommissioning of watermills. For this purpose, old maps which covered the period from the beginning of the 18^th century until the 20^th century were used alongside written historical sources. Maps from the first half of the 19^th century provided valuable source material. Traces of old mill water systems in the valley floor were analysed on the basis of a numerical terrain model and aerial photographs as well as on the basis of detailed geomorphological mapping. The research made it possible to determine the locations of former mills mentioned in written historical sources and also changes in the course of river channels related to mill construction. It was found that some reaches of the River Liswarta channel and the estuary reach of its tributary River Bieszcza were in fact old mill races. These mill races account for around 31% of the length of the river channel reaches analysed. Analysis of old maps indicated that in the 19^th century, the River Liswarta near Krzepice had multiple channels. This development of the River Liswarta channel was not only the result of natural geological, geomorphological and climate conditions, but also the product of watermill construction, since some channels within this network were artificial canals, including mill races. As a result of the construction of mill races, river channel reaches ranging from 1 to 2.5 km in length were shifted. Of the mills studied, as many as 80% ceased to exist in different parts of the period covered by the research. Traces of some of them can still be found in the form of ruins of foundations or of a water system with the remains of hydraulic structures, while some have only left their mark on the river channel pattern.