The Influence of Drainage Devices and Post-Bog Soil Changes on Water Retention in Drained Lower Supraśl River

Water shortages occurring in the natural environment are the result of progressing climate changes, including the decreasing amount of atmospheric precipitation. In Poland, during the vegetation periods, droughts occur every 4-5 years, which causes losses in the field production and in forest communities. Reducing the negative effects of drought is possible by retention of water within a catchment. This method of improving the water balance has been included in the provisions of the Water Framework Directive and Water Law. On the meliorated valley objects, there are melioration devices that enable regulation of the moisture content, including irrigation during periods of drought. Drainage ditches can also retain water in the early spring periods with high flows in rivers. The studies carried out on the Lower Supraśl river site showed that about 40% of drainage devices used for water damming (dams and ramps), as well as for water distribution (feeders and detailed ditches) are not technically efficient and do not fulfil the function of moisture content regulation. Fibrous-muck soils occurring on this object, due to the lack of rainfall and irrigation, reduced the water retention capacity by approximately 30%. Modernization and reconstruction of drainage devices on valley objects will enable increasing the retention within individual catchments.