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CHANGES IN THE MAGNITUDE AND TRANSFORMATION OF FLOOD WAVES SUBSEQUENT TO THE CHANNELIZATION OF THE RABA RIVER, POLISH CARPATHIANS
Author(s) -
WYZGA BARTLOMIEJ
Publication year - 1996
Publication title -
earth surface processes and landforms
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.294
H-Index - 127
eISSN - 1096-9837
pISSN - 0197-9337
DOI - 10.1002/(sici)1096-9837(199608)21:8<749::aid-esp675>3.0.co;2-5
Subject(s) - overbank , channelized , sinuosity , flood myth , geology , floodplain , hydrology (agriculture) , outflow , channel (broadcasting) , inflow , geomorphology , fluvial , geography , geotechnical engineering , structural basin , oceanography , cartography , engineering , electrical engineering , telecommunications , archaeology , computer science
Alterations in flood flows of the Raba River are examined to determine the influence exerted on flood waves by changing morphological conditions. With stable vertical channel position, the river increased its sinuosity during the 1920s to 1940s, and the change was accompanied by a growing tendency to flood‐wave attenuation. The temporal change in flood‐wave transformation is typical of a developing low‐flow system. Subsequently, streambed degradation has been induced due to channnelization works which straightened and narrowed the river. Flood waves became progressively more flashy as channel incision progressed. The increase in magnitude of flood waves passing the deepened reach was greatest for bankfull flows and diminished for lower in‐bank flows and higher overbank flows. The tendency to magnification of peak discharges has been also found in other Carpathian rivers which were considerably degraded in the 20th century in response to channelization. Introducing an empirically found correcting factor into the analysis of the ratio of outflow to inflow peak discharges shows how the conditions of peak‐flow transformation in a reach have changed since the beginning of the study period. A marked coincidence between changes in vertical channel location and variations in the ‘corrected’ peak‐discharge ratio proves channel changes to be a very important reason for the growing flood hazard in southern Poland. Gradient oversteepening and channel narrowing, caused by channelization, lead to formation of a river system having a steep, straight, narrow and deep channel. Such a morphology distinguishes the system from natural low‐flow and high‐flow systems. Reduced floodplain water storage and self‐acceleration of flow concentrated in a channel zone make flood waves progressively more flashy on their way down the channelization‐formed system.