Abstract
Dam reservoir construction is one of the most important factors shaping river-valley morphology in the Anthropocene. While a large number (>58,000) of these constructions are in operation all over the world, we remain quite ignorant of what happens upstream of them (in so called backwater zone), especially for the case of gravel-bed rivers. Existing studies have shown that adjustments of the gravel-bed river in the backwater zone differ between the initial and long-term adjustments. The initial adjustments (occurring ≈ <20 years following dam construction) are controlled by large floods and in-channel deposition which trigger bi-directional bar↔bank interactions (bank erosion causing bar growth and vice versa) resulting in channel-widening. The long-term adjustments (≈ >20 years following dam construction) are characterized by river sinuosity increa sing and channel planform stabilization resulted from deposition of fine sediment and associated vegetation expansion. The long-term adjustments are controlled by the initial river morphology, which creates accommodation space for the deposition of fine sediment and for the associated expansion of vegetation on channel bars. The multi-thread river in backwater zone is significantly narrowed, its sinuosity increase (phase 1) and the planform is stabilized (phase 2). Whereas, in the case of initially single-thread river only planform stabilization occur (phase 2). This article summarizes recent findings on the backwater effects on gravel-bed channel morphodynamics, suggesting that backwater zones may be treated as hot-spots of human-induced changes in river geomorphology and biogeomorphology.
Highlights
Definicja strefy cofkiStrefa cofki zbiornika zaporowego definiowana jest jako fragment doliny rzecznej powyżej zbiornika zaporowego, który jest zatapiany wodami podczas wyższego niż normalny/średni poziom jego piętrzenia (ryc. 1) (Liro, 2019)
This article summarizes recent findings on the backwater effects on gravel-bed channel morphodynamics, suggesting that backwater zones may be treated as hot-spots of human-induced changes in river geomorphology and biogeomorphology
While a large number (>58,000) of these constructions are in operation all over the world, we remain quite ignorant of what happens upstream of them, especially for the case of gravel-bed rivers
Summary
Strefa cofki zbiornika zaporowego definiowana jest jako fragment doliny rzecznej powyżej zbiornika zaporowego, który jest zatapiany wodami podczas wyższego niż normalny/średni poziom jego piętrzenia (ryc. 1) (Liro, 2019). Dotychczasowe prace sugerują, że przebieg ewolucji koryta żwirodennego w cofce zbiornika zaporowego zależy zarówno od czasu oddziaływania cofki na procesy fluwialne, jak i inicjalnej struktury koryta i doliny rzecznej (Liro, 2015, 2016, 2017). Kręte koryto potoku Smolnik w strefie cofki Zbiornika Rożnowskiego, funkcjonującego od 1942 r., rozwinęło się na skutek depozycji drobnoziarnistych osadów i rozwoju roślinności na wcześniej istniejących łachach żwirowych Liro) The sinuous channel of the Smolnik Stream in the backwater fluctuation zone of the Rożnów Reservoir (built in 1942) This morphology was developed as the a results of fine fine-sediments deposition and the expansion of vegetation expansion on the previously -existing gravel bars. Model długookresowych zmian koryta żwirodennego w cofce zbiornika zaporowego Model of long-term changes to a gravel-bed channel planform in a dam-reservoir backwater zone Źródło: Liro (2017); nieznacznie zmienione / Source: Liro (2017); slightly modified
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