Is history of rivers important in restoration projects? The example of human impact on a lowland river valley (the Obra River, Poland)

• The main goal: to reconstruct a trajectory of lowland river channel changes
• The trajectory differs from other planform transitions in the Polish Lowlands.
• If sediment transport conditions are altered, potential for restoration may be limited.
• Artificial canals can be replaced by drainage systems resembling past river styles.
• Restoration is not always synonymous with reconstructions of former channels.

Palaeoenvironmental and palaeohydrological reconstructions can provide important guidance for river restoration projects. This paper reconstructs the trajectory of river pattern changes of a lowland river (the Obra River, western Poland) as a basis to inform realistic restoration activities. The history of river changes is reconstructed for the last 12,700 radiocarbon years BP. The sequence and timing of change differ from widely recognized, conventional assessments of transitions from braided to meandering planforms in the Polish Lowlands. Traces of a laterally migrating anabranching system were found in the middle Obra valley. In its lower course, a transition from a braided to meandering planform took place later than in other rivers of the Polish Lowlands. Sediment delivery from parts of the catchment situated downstream of lakes in the river course could have been the main reason for maintenance of the braided pattern. Restoration scenarios that take into account the trajectory of river planform changes are hypothesized in relation to variations of sediment supply and degree of anthropogenic impact.