Patterns of Recent Changes in Channel Morphology and Flows in the Upper and Middle Odra River

Our research introduces the river regulation effects on three sections of the upper and middle Odra River (south-western Poland), with differently channelized parts. In the upper and lower reaches, the river was straightened, narrowed, and trained with groins, whereas in the middle section, it was also impounded by numerous barrages. The discharge duration (DD) and water stage duration (WSD) curves for water-gauge stations from these river sections were analyzed to recognize changes in river flows and channel morphology since the mid-20th century. This analysis is supplemented by an examination of repeated surveys of the gauge cross sections of the river, annual precipitation totals in its catchment, and their relationship to the variation of the North Atlantic Oscillation (NAO) index. Our findings provide new hydrological insights for the region. The three river sections exhibited different patterns of the adjustment of the channel morphology to the river channelization: upper section was typified by channel incision, middle section by channel stability, and lower section by channel incision in its upper part and vertical stability of the channel bed in the lower part. Barrages in the middle section stabilized water stages in a wide range of hydrological conditions. Annual precipitation totals and river run-off did not change systematically over the study period. The variation in precipitation totals was inversely related to annual values of the NAO index. The study confirms the usefulness of DD/WSD curves to analyze changes in river run-off and the vertical position of the channel bed.