Set back embankments, levees or dikes

General description

In anthropogenically constrained rivers, typical restoration measures include the the set back of flood levees, allowing channel movements within a limited area and alleviating the effects of canalization, often referred to as "river widening". Within the new wider river bed the river can move, adjust and create the typical range of riparian habitats. Subsequently these projects create and maintain different floodplain features and increase the habitat diversity of a floodplain.

Photo : Setting back the embankement at the left riparian side to enlarge the active channel of the river Enns in Austria (source : BOKU, S.Muhar)

The setting back of embankements or flood levees provides the potential to restore some elements of riparian ecosystems. They promote instream habitat heterogeneity and the establishment of bare gravel bars as well as herbaceous pioneer vegetaion and shrubs (Rohde et al. 2005).

Applicability

Embankments can be removed on both or on one side of the river. After widening, groins or anchored tree fascines are sometimes installed for bank protection. Flood levees can be shifted back to enlarge the space for hydrogeomorphic processes (Rohde et al. 2005). The setting back of embankements must provide an adequate area to enhance hydrological and geomorphic processes to establish the whole range of riparian habitat types that can be found in near-natural reaches (Rohde et al. 2005). The extent of such measures is often limited by land constraints and thus many projects are a combination of full and partial levee removal (Roni et al. 2005).

Expected effect of measure on (including literature citations):

Category	Description	Source (citation)
HYMO	Promotion of instream habitat heterogeneity and establishment of riparian ecosystems	Rohde et al. 2005
Plankton	Biomass increased in reconnected habitats	Hein et al. 1999
Dragonflies	Benefit from improved lateral connectivity	Chovanec et al. 2002
Macroinvertebrats	Benefit from improved lateral connectivity	Chovanec et al. 2002
Fish	Benefit from improved lateral connectivity	Chovanec et al. 2002

Pressures that can be addressed by this measure

• Channelisation / cross section alteration
• Embankments, levees or dikes

Case studies where this measure has been applied

• Renaturierung Untere Havel
• Regge Velderberg
• Rijkelse Bemden - River bed widening
• Thur
• Bouxweerd - Artificial pool
• Low reach of River Cinca
• Töss
• Pastures Bridge Rehabilitation
• River Roding at Ray Lodge Park
• River Skerne EU-LIFE project
• Sella
• Haselünne
• Bakenhof - Dyke relocation
• Polder Ingelheim – Restoring former floodplains (INTERREG Sustainable Development of Floodplains)
• Hondsbroeksche Pleij – Restoring former floodplains (INTERREG Sustainable Development of Floodplains)
• Meuse - Overdiepse Polder
• Lower Traun
• Ruhr Binnerfeld

Useful references

• Chovanec, A., F. Schiemer, H. Waidbacher, and R. Spolwind (2002). Rehabilitation of a heavily modified river section of the Danube in Vienna (Austria): biological assessment of landscape linkages on different scales. International Review of Hydrobiology, 87, 2–3.
• Hein, T., G. Heiler, D. Pennetzdorfer, P. Riedler, M. Schagerl, and F. Schiemer (1999). The Danube restoration project: functional aspects and planktonic productivity in the floodplain system. Regulated Rivers: Research & Management, 15, 259-270.
• Rohde, S., M. Schutz, F. Kienast, and P. Englmaier (2005). River widening: an approach to restoring riparian habitats and plant species. River Research and Applications, 21, 1075–1094.
• Roni, P., K. Hanson, T. Beechie, G. Pess, M. Pollock, and D. M. Bartley (2005). Habitat rehabilitation for inland fisheries. Global review of effectiveness and guidance for rehabilitation of freshwater ecosystems. FAO Fisheries Technical Paper, 484.