Remove bank fixation

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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).

Figure 1: Removal of bank fixation with toe protection (modified after http://www.donau.bmvit.gv.at/projekt/massnahmen/uferrueckbau/).

Applicability

This kind of bank removal can especially be applied and will be very efficient in impounded large gravel bed rivers like the upper Danube, where gravel bars are drowned and shallow low-velocity habitats are virtually absent. In these impounded rivers, spawning and nursery habitats like shallow near-bank gravel bars, side channels, and backwaters are often the bottleneck for stream-type specific fish species. River banks have been heavily fixed and the potential for river restoration is limited due to uses like navigation, hydropower or flood protection and mitigation measures are restricted to the river banks..

Similar or complementary measures to enhance river bank habitat are to modify hydraulic structures like groynes (see fact sheet “Remove or modify in-channel hydraulic structures (e.g. groynes, deflectors)”) and the placement of large wood (e.g. rootwads).

Expected effect of measure on (including literature citations):

There are some empirical studies published as grey literature but no information on this measure in open scientific literature (see below). Therefore, the assessment of the effect of this measure is mainly based on expert judgement.

HYMO (general and specified per HYMO element)

  • Increase of shallow gravel bar habitat, low-velocity zones and backwaters, i.e. spawning and nursery habitats for fish (Zauner et al. 2001).
  • Increase of fine sediment deposition in backwater areas downstream from near-bank gravel bars (Zauner et al. 2001).

Physico-chemical parameters

  • No information available.

Biota (general and specified per Biological quality elements)

BQE Macroinvertebrates Fish Macrophytes Phytoplankton
Effect high high high no effect

Macroinvertebrates:

  • Increase in diversity and limnophilic species (Zauner et al. 2001).

Fish:

  • Increase in abundance and dominance of rheophilic fish species, for example common nase, barbel, and dace in the Danube river (Zauner et al. 2001, Zauner 2003).
  • Increase in abundance of juvenile fish (Zauner et al. 2001, Zauner 2003).

Macrophytes:

  • Most probably significant increase in number and abundance of macrophytes due to the increase in shallow low-velocity zones, which are virtually absent in impounded large, degraded rivers (e.g. waterways like the Danube river).

Phytoplankton:

  • Probably no effect on phytoplankton.

Temporal and spatial response

Pressures that can be addressed by this measure

Cost-efficiency

Case studies where this measure has been applied

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

Other relevant information

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