Modelling the Impact of Climate Change on the Flow Regime and Channel Planform Evolution of the Lower Drava River

Abstract

Climate change is expected to have a significant impact on changing the flow regime of the lower Drava River. Four flume experiments were run to see how stabilized, increased and decreased flow and the occurrence of a series of floods affect channel planform evolution. Constant discharge produced alternate bars that subsequently merged into bigger bedforms, bedform migration, and a higher sinuosity of the channel. While merging and migration of bedforms may happen in the lower reaches of Drava, its sinuosity is unchanged due to river regulation. Reduced flow initiated transition from a braided to incised single-thread planform, with the formation of dormant channels. Drava already has a single-thread planform (because of dikes) and, in cases of flow reduction, will have the remnant of inactive channels. Increased discharge showed greater erosion and reworking of channel banks, a decrease of sinuosity ratio and active high bluff zones. On Drava sinuosity ratio is more difficult to change because of levees, but erosion, reworking of banks, and increased high bluff risks are possible. Floods simulation generated the construction of an anabranching planform alongside the incised main channel with terraces along banks (active during floods), bars, alluvial islands, and side channels (active during low flows). On the lower Drava River, this situation correlates with past floods.