River Channel Position
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Feedback mechanisms
New Channel Course Regime
River sediment-gradient-current Feedback (Local, well-established): Three key elements for a river channel position regime shift are the sediment, the current and the gradient of the river. As already mentioned above, a river will only change its course if the new channel provides better conditions in terms of gravity and resistance. When sediment deposits on the ground of the riverbed the gradient declines and slows down the current. This in turn leads to more deposition of sediments with the consequence that the gradient even more declines. Finally, the river is blocked by sediments and the water spills to the side, looking for a better way.
Economic Opportunities Feedback (Regional, contested): A river serves as transport way for the local industry and is therefore important for regional and global trade. To decrease travel time and transportation costs the industry is interested in channelization and meander cutoffs because it makes the transportation route shorter. This in turn makes the location along the river more attractive for the industry.
Superlobe Feedback (Local, contested): The superlobe feedback mechanism seems to be responsible for the wandering of river deltas. The reason why river deltas wander is that channel cutoffs lead to formation of so-called lobes which in turn can form so-called superlobes. They in turn are responsible for further cutoffs.
Balancing feedbacks
The balancing feedbacks in the causal loop diagram involve the elements "need for protection" and "defense infrastructure". That implies, that only human activities can keep the system in its state and prevent a shift from one channel to another or at least retard it, otherwise the river will switch to a new course due to natural processes.
Drivers
Several drivers exist that are responsible for the river channel position regime shift.
Shift from Regime 1 to Regime 2
Important shocks that contribute to the regime shift include:
Strong rainfall events (regional, well established): Important shocks for the system are strong rainfall events. They cause floodings which often actually cause the river to shift its course because they have enough power to provide the impetus for a crevasse splay or a levee/dyke break. Furthermore they have the potential to breach defense infrastructure such as a spillway that tries to control the riverflow.
Key thresholds
Shift from the old channel course to the new channel course
Sediment blocking Threshold: Threshold at which too much sediment has build up to make the river change its course.
Levee/Dyke break Threshold: threshold at which a levee or dyke breaks in case of a strong flooding
Sinuosity Threshold: Threshold at which the channel shifts because of a too high sinuosity of the meandering river channel.
Scouring Threshold: Threshold at which too much scouring leads to a channel shift or the break of a levee.
Leverage points
Defense Infrastructure (local, well-established): Defense infrastructure can be build up to protect the area which is threatened by the negative impacts of a river channel position. However, this is only a temporarily solution, because as mentioned above the shifts is typically unlikely to prevent. Another solution would be to use floodplain areas for controlled inundation in case of a strong flooding (so-called flood polders) which would then decrease the current of the river and therefore the probability of a river channel shift (see Tisza River case study).
Need for protection (local, well-established): The need for protecting the area in which a regime shift is likely to occur could be reduced. Housing and infrastructure could be build up more stable or even moved to areas which are less threatened by negative impacts from channel shifts. Agricultural cultivation methods could be changed, for example by cultivating crops that are more robust in case of a strong flooding.
Channelization/meander cutoffs (local, well-established): Artificial meander cutoffs or channelization in order to get economic benefits could be stopped to avoid abrupt channel shifts.
