The Impact of Spontaneous and Induced Restoration on the Hydromorphological Conditions and Macrophytes, Example of Flinta River

Highly modified riverbeds are not able to spontaneously reproduce natural processes. The restoration of natural river systems is an important challenge to modern river engineering. Various procedures and solutions, both technical and non-technical, are applied in this process. This involves looking for simple solutions that are close to nature and that interfere with river ecosystems to a minimal extent. One of these solutions is deflectors, which constitute a type of simplified spur. This study presents the results of the research on the transformations of hydromorphology and macrophytes on selected sections of the Flinta River, which represents the most common type of river in the Central European Lowlands (a small river with a sandy substrate). Two neighbouring sections of the watercourse were selected. The first one has not been subject to any regulatory measures for over 30 years and is undergoing spontaneous restoration, while the second one was significantly altered (straightened, cleared of hydrophytes, and desilted) ten years ago. Three deflectors were introduced in this section in the years 2017–2018. Research conducted on both sections enabled the determination of the possibility of initiating renaturalisation processes by way of implementing simple solutions in the form of low-cost wooden deflectors. It also provided the basis for the assessment of the impact the measures taken had on the hydromorphological status of the watercourse and on macrophytes. Based on the studies conducted, it was possible to determine the size, dynamic, and scope of the changes taking place in the river under various conditions of its transformation, including those resulting from anthropopressure.