Characteristics of Point-Bar Development under the Influence of a Dam: Case Study on the Dráva River at Sigetec, Croatia

Abstract

Before the extensive engineering works the Dráva River had braided pattern. However in the 19-20 th centuries river regulation works became widespread, thus meanders were cut off, side-channels were blocked and hydroelectric power plants were completed. These human impacts significantly changed the hydro-morphology of the river. The aim of the present research is to analyse meander development and the formation of a point-bar from the point of view of indirect human impact. Series of maps and ortho-photos representing the period of 1870-2011 were used to quantify the longterm meander development, rate of bank erosion and point-bar aggradation. Besides, at-a-site erosion measurements and grain-size analysis were also carried out. As the result of reservoir constructions during the last 145 years floods almost totally disappeared, as their return period increased to 5-15 years and their duration decreased to 1-2 days. The channel pattern had changed from braided to sinuous and to meandering, thus the rate of bank erosion increased from 3.7 m/y to 32 m/y. On the upstream part of the point-bar the maximum grain size is 49.7-83.4 mm and the mean particle size is 7.6 mm, whilst on the downstream part the maximum grain size was only 39.7-39.9 mm and mean sediment size decreased to 6.1 mm. Due to the coarse sediment supply and the decreasing stream energy the point-bars develop quickly upstream and laterally too.

Morphological Investigation of a Critical Reach of the Upper Hungarian Danube

“…However, this kind of planform change caused by anthropogenic impacts is not a unique phenomenon, similar process could be recognized e.g. in River Dráva in the 19-20th centuries [27]. Based on these conclusions, reduction in the development of gravel bars and less diverse cross-sections, in terms of geometry, are expected.…”

Evolution of river planforms downstream of dams: Effect of dam construction or earlier human‐induced changes?

“…Scour near the dam has resulted in a relatively coarse bed with D 60 and D 10 values of 20.22 mm and 4.88 mm, respectively, 22 km downstream from the dam at Botovo. In this river section, channel bars appear and they are built of sediment characterised by mean grain size of 4.9–9.7 mm (Kiss and Balogh, ). At Barcs, 73.4 km downstream from the dam, the bed is finer with D 60 and D 10 values of 0.45 mm and 0.25 mm, respectively.…”

“…With continuing incision and sediment delivery from bed and banks, the lower island level was formed (Figure (d)) through lateral and vertical accretion on the island side, as well as via the attachment of unit bars to its downstream section. Owing to the limitation of sediment delivery by dam closure, the zone of sediment deficit reached at least 22 km downstream of the lowermost dam (see data shown by Bonacci and Oskoruš () and Kiss and Balogh () presented in ‘Results’ section). The sediment eroded from this zone could have contributed to the formation of the lower level of the islands.…”

Centurial Changes in the Depth Conditions of a Regulated River: Case Study of the Lower Tisza River, Hungary

“…These indirect impacts are characterized by spatial and temporal lags of varying intensities. The consequences of these human interventions have been well described on various rivers in the world (Rinaldi and Simon, 1998;Surian, 1999;Liébault and Piegay, 2001;Kondolf et al, 2002;Xu, 2002;Rinaldi, 2003;Yates et al, 2003;Antonelli et al, 2004;Harmar et al, 2005;Pinter and Heine, 2005;Chang, 2008;Kroes and Kraemer, 2013;Kiss and Balogh, 2015;Morais et al, 2016;Nagy and Kiss, 2016).…”