Reservoirs of the Słupia river as morphogenetic agents

Abstract

Przy wykorzystaniu map dawnych, a także badań i obserwacji terenowych autorzy dokonali oceny stopnia przekształcenia rzeźby dna doliny Słupi w jej środkowym biegu, na odcinku, na którym w latach 20. XX w. wybudowano szereg urządzeń hydrotechnicznych, w tym dwie elektrownie wodne i towarzyszące im zbiorniki dolinne. Badania wykazały, że dno doliny Słupi w ciągu ponad 80 lat przekształciło się w zróżnicowanym stopniu, a tempo i zasięg współczesnych procesów formo- i osadotwórczych są niewielkie, z wyjątkiem górnych części zbiorników i odcinka koryta Słupi położonego poniżej elektrowni Krzynia.The subject of the study is the channel and valley floor of the Słupia river along its >10 km length reach south of Słupsk. In the early 20th century this reach of the valley was heavily altered through channelization and drainage, followed by extensive hydro-engineering works in the 1920s. The aim of this study is to recognize the magnitude of geomorphic change in the channel and the valley floor consequent to these human-induced perturbations. In 2001–2007 monitoring of selected processes and sites was carried out and involved mapping and repeated surveying of shorelines of reservoirs, bathymetric measurements, assessment of shoreline landforms, and repeated photography. Shoreline erosion, delta progradation and wave behaviour were among the monitored processes. Hydropower stations have been working continuously since their opening, whereas the reservoirs have never been flushed or dredged. The most important consequence is the dominant role of sedimentation in re-shaping of the Słupia valley floor, whose pattern is the following: – in the shallowest part of the reservoirs (10–30 cm) an older floodplain has been quickly and completely covered by deposits and vegetation succession proceeds, – in the middle sections, where reservoirs widen out, delta progradation takes place, – fine material is deposited in near-dam widening and in local coves, most intensively if water depth is less than 1 m, with the contributing role of aquatic plants. The course of fluvial processes below the Krzynia power station is different. The channel is modelled by scour and lateral erosion, which develop because of local scouring. In the effect of scour, the floodplain has been extensively drained over many kilometers, resulting in drying-up of oxbows cut off during the early 20th century straightening, desiccation of pool floors. At the same time, meanders migrate at the rate of 0.4–0.8 m per year