Abstract
Rivers of the Polish Carpathians incised deeply during the twentieth century, but detailed information about the timing and amount of incision of their channels exists only for water-gauge cross sections. Applicability of photogrammetric extraction of digital elevation models (DEMs) from archival aerial photos for reconstructing changes in vertical river position was verified in the study of a 3-km reach of the Czarny Dunajec River. DEMs extracted from a few sets of archival aerial photos from the years 1964–1994 together with recent orthophotos and DEMs were used in the analysis. Measurements taken in river cross sections spaced at 100-m intervals indicated that on average the lowest point of the channel bed lowered between 1964 and 2009 by 1.74 ± 0.17 m, low-flow water surface by 1.57 ± 0.07 m, active river channel by 1.54 ± 0.12 m and the belt of river migration by 1.03 ± 0.15 m. However, the change in vertical river position during the years 1964–2009 varied greatly along the reach, with the elevation of low-flow water surface lowered by up to 3.61 ± 0.07 m in the upper part of the reach and increased by up to 1.34 ± 0.07 m in its lower part. Combining the information about changes in vertical river position and the width of river migration belt yielded data about the change in sediment volume in the reach, with an average annual loss of sediment amounting to 256 ± 37 m3 per 100-m channel segment. The study indicated that DEMs generated from archival aerial photos can be a useful tool in analysing recent vertical channel changes outside water-gauge stations.
Highlights
Rapid channel incision reflecting a loss of geomorphic dynamic equilibrium is a common phenomenon in contemporary fluvial systems affected by intense human disturbances (Florsheim et al 2013)
Cross-sectional flow area in each study cross section was calculated as a product of low-flow channel width and mean estimated water depth and averages of the cross-sectional flow area in all cross sections were computed for each date of the archival aerial photos
In the last few decades many rivers worldwide underwent dramatic changes to their vertical position, with the direction and the rate of these changes depending on the type of impacts on the rivers and their catchments (Kondolf et al 2002)
Summary
Rapid channel incision reflecting a loss of geomorphic dynamic equilibrium is a common phenomenon in contemporary fluvial systems affected by intense human disturbances (Florsheim et al 2013). River incision may result from a single causal factor, such as in-channel gravel mining (Peiry 1987; Collins and Dunne 1989), disruption of the continuity of bedload transport by a dam reservoir (Williams and Wolman 1984), channel regulation (Brookes 1987; Simon 1989) or land-use change in the catchment (Liébault and Piégay 2001; Keestra et al 2005), or from a combination of different factors Large-scale mining of gravel from channels (Rinaldi et al 2005; Wyżga et al 2010), an increase in river transport capacity resulting from channelization works (Wyżga 2001a; Korpak 2007; Zawiejska and Wyżga 2010), and a decrease in sediment supply from the catchments subjected to land-use changes (Lach and Wyżga 2002) were indicated as the causes of rapid incision of these rivers.
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