The influence of changes in flow regime caused by dam closure on channel planform evolution: insights from flume experiments

Abstract

Constructions of dams influence river courses by cutting off sediment delivery and altering flow regime. We conducted flume experiments to study how sediment starvation, flow deficit and occurrence of series of floods with sediment load influence the evolution of channel planform. Results indicated that reduced flow caused a transition from a braided to incised single-thread planform with remains of inactive channels. The planform resembled rivers suffering from flow reduction caused by dams and constructions of irrigation canals (e.g., Central Platte River, USA). Simulation of series of floods with no sediment delivery caused the formation of an anabranching planform with incised main channel, alluvial islands, and side channels active at high flows. This evolution corresponds to river courses altered by sediment starvation and series of floods (e.g., the lower Drava River, Hungary). Floods with delivery of fines created a single-thread, incised channel with terraces along banks. Such channels are formed by rivers closed by dams, and compensating sediment deficit by sediment load from tributaries and/or floodplains (e.g., the Green River, USA). The flume tests demonstrated how flow and sediment deficit influence river channels and that the potential for restoration strongly depends on possibilities for the activation of sediment supply. However, restoration of pre-dam conditions is often impossible owing to other hydro technical works and land use changes. The highest restoration potential refers to the rivers compensating sediment delivery blocked by dams with tributary and floodplain resources.

A new braiding index to assess river regulation effects in multi‐thread channels: Insights from a highly regulated Himalayan river

“…Channel confinement near urban areas has stabilized river flow regimes, resulting in maintenance of near-constant channel widths while large-scale irrigation projects are responsible for channel narrowing (Wu et al, 2023). Such river regulation alters streamflow and hampers sediment supply downstream (Ghosh & Munoz-Arriola, 2023;Patil et al, 2022;Słowik et al, 2021), forcing multi-channel rivers to transform into single-thread channels or reduce their braiding intensity (Figure 5). In such conditions the braiding intensity becomes dependant on the number of low-stage active channels (Gao et al, 2022).…”

Interaction of surface water and groundwater in Nida valley, Poland

“…Human activities, such as the construction of dams, have been widely documented to have significant impacts on river water levels (Grant, 2012;Chang et al, 2016;Wang et al, 2018;Wei et al, 2020;Słowik et al, 2021;Bao, Ding and Han, 2022;Li et al, 2023). The variation in water level observed between the Smuga Umianowicka branch and the Nida River can be attributed to the water level regulation facilitated by the dam constructed on the Smuga Umianowicka branch.…”

Drivers of functional diversity in the hyporheic zone of a large river

“…1). This riverbed degradation resulted in the erosion of fine particles and the local pavement of the riverbed (Rollet et al, 2014;Słowik et al, 2021). From 2005 on, a restoration program progressively took place in this sector of the Ain River, with injection of medium-to-fine sediment, just upstream of gravel bar 5, to reduce the riverbed degradation (Lejot, 2008).…”