Table 4 Morphologic indicators for channel changes and their meaning
Indicator | Description | Meaning |
|---|---|---|
Change in total river length | Total river length of the Rur River in a focus region compared to today’s river length, estimated from the DOP 2019 | Decrease in the river length is a sign for artificial straightening [87] |
Sinuosity | Total river length of the Rur River in a focus region divided by the thalweg [88,89,90,91,92], computed with the DEM 25 | Reduced sinuosity often is a sign for river straightening [54, 93], an increase is a sign for tending towards a new equilibrium [87] but can also occur when the flow velocity increases [55] |
Relative length of channel structures | Total length of channel structures in a focus region divided by the river length in the focus region | An increase in the channel structures is a reaction to changes in the sediment load and/or changes in the river slope [87], often due to straightening [94] |
Anastomosing channel | For anastomosing channels | Anabranching rivers are often caused by flood-dominated flow regimes [63, 83] |
Braided channel | For braided river structures in single channels | Sign for excess bedload, coarse bottom substrate and high valley bottom slope [57, 95], instable state [96] |
Side arm | For side arms | Occur at flood events as a reaction to hydraulic stress; today side arms are preserved as habitats [97] |
Relative of number oxbows | Number of oxbows in a focus region divided by the river length in km | Oxbows as channel cut-offs are a sign for river course shortening [55] |
Relative number of islands | Number of islands in a focus region divided by the river length in km | Changes in islands indicate recent flood events, island formation is a sign for coarse sediment input [55] |