Remove bank fixation

Remove bank fixation

General description

In many rivers, habitat quality at the river banks is poor due to bank fixation (e.g. using riprap). Removal of bank fixation is a prerequisite for many other measures like re-meandering or widening as well as initiating later channel migration and dynamics.

In this fact-sheet, the removal of bank fixation and creation of habitats at the river bank (e.g. gravel bars) is described, which does not necessarily include other large scale measures to restore a natural planform or channel dynamics. Bank fixation is removed and shallow gravel banks are created using heavy machinery. In some cases, the toe of the bank is still fixed to prevent complete bank erosion and channel widening to ensure navigability (Figure 1).

Applicability

The applicability depends mostly on the socio-economic functions jeopardised by removing bank protection. It is mostly possible in rural, but hardly in urbanised areas. E.g. in the Netherlands buying buffer zones (15 m along small streams; 75 m along large rivers) from farmers is combined with this measure. When bank erode it does not affect agriculture.

Expected effect of measure on (including literature citations):

• HYMO (general and specified per HYMO element)

Bank removal may contribute to enlarge river depth and width variation and diversify the structure of the riparian zone as well as the structure and substrate of the river bed.

• physico-chemical parameters

This measure has little to no effect on the physical-chemical parameters.

• Biota (general and specified per Biological quality elements

The change in substrate on the bank from artificial to natural has significant effects on all biota. Vegetation - both aquatic and riparian - will develop, while benthic invertebrate and fish species composition will in due course adapt the new habitat conditions (from hard and bare to more soft and vegetated substrate). Eventhough this development is towards a more natural ecological state, indices may suggest otherwise because the artificial hard substrate used to protect bank are quite often populated by rheophilic and lithophilic communities.

Temporal and spatial response

The spatial response will mostly be restricted to the strecth where bank were removed. Erosion processes that are again possible will change sediment loads downstream. The magnitude of the process determines whether it is of any significant influence.

The temporal response (years to decades) depends on the magnitude of dynamic forces (e.g. stream power; flood events) and the erodibility of the banks until a dynamic equilibrium is reached.

The change in biotic communities depends on the change in habitat conditions and the colonisation potential in the catchment.

Pressures that can be addressed by this measure

• Channelisation / cross section alteration
• Embankments, levees or dikes
• Alteration of instream habitat

Case studies where this measure has been applied

• Asseltse Plassen - Bank erosion
• Lahn Cölbe
• Renaturierung Untere Havel
• Spree - Restoration and remeandering of the Müggelspree - downstream Mönchwinkel
• Lek bij Everdingen - Groyne shields
• Regge Velderberg
• Klebach - Side channel
• Thur
• Dommel Eindhoven
• Ems floodplain (LIFE project)
• Skjern - LIFE project
• River Quaggy, Chinbrook Meadows
• Vallacuera ravine. Removal of a dyke.
• Drava - Kleblach
• Bakenhof - Dyke relocation
• Enns - Aich
• Oberwerries - Optimisation of the pSCI “Lippe floodplain between Hamm and Hangfort” (LIFE05/NAT/D/000057)
• Soest - Optimisation of the pSCI “Lippe floodplain between Hamm and Hangfort” (LIFE05/NAT/D/000057)
• Lower Traun
• Lippeaue Klostermersch
• Ruhr Binnerfeld

Useful references

Surian, N, L Ziliani, F Comiti, MA Lenzi 2 & L Mao (2009) Channel adjustments and alteration of sediment fluxes in gravel-bed rivers of North-Eastern Italy: potentials and limitations for channel recovery. River Research & Applications 25: 551-567