7.     Morphological alterations

7.1.        Introduction

This chapter should describe different morphological alterations of European water bodies including

• Channelized streams
• Disconnecting floodplains and rivers
• Land reclamation

<this introduction has to be improved>

In the past it wasn't unusual to channelize or straighten the streams meandering through agricultural lands. By straightening a stream, landowners increased the speed of water flowing downstream and the discharge at which water drained away from their land. Straightening the channel also made their fields more farmable because they could farm along a straight waterway (Figure 8.1).

Figure 8.1: Straightened and regulated shape streams flowing through agricultural fields

  No photos included 

Source: Eider RBMP p. 30

However, channelization often makes things worse in the long run. By increasing the velocity of water moving in the channel, the flowing water scours the stream bed and deepens the channel (Figure 8.1b). The banks get higher and often more unstable. 

Channelization increases stream bank erosion, more sediment enters and clogs the stream. In addition, channelization reduces the amount of vegetation along the stream bank, which means less food and cover for wildlife. Increased sedimentation makes it difficult for some fish to feed and spawn, and the increased velocity of the stream drives out fish that cannot tolerate fast-moving water.

River channels are fundamentally conduits for water and sediment, but the specific processes of water and sediment movement vary widely among channels. These processes create unique habitats and patterns of nutrient exchange to which the local in-channel and floodplain communities of plants and animals are adapted.

The morphology of transitional and coastal waters is influenced, inter alia, by the following anthropogenic interventions:

• Land reclamation and polders;
• Dredging; sand and gravel extraction; and sand replenishment and similar coastal protection measures;
• Flood barriers in estuaries, and dams and diversion structures;
• Marine structures incl. offshore wind farms, transformer substations etc.; shipyards and harbors; and
• Bottom-trawling.

 Many coastal and transitional waters are impacted as a result of the expansion of the navigable channels.  The position of channels is fixed by dredging and the construction of stream deflectors and groins, preventing the previous dynamic shifts. In addition to these larger measures, various local encroachments have occurred and are still occurring in the coastal waters, such as beach replenishment or the reinforcement of smaller harbors.

7.2.        European overview

Historical bends were lost to channel straightening projects, as it is well documented on many rivers and streams in Europe (Brookes 1987, Goldi 1991, Iversen et al. 1993).  Moreover, hundreds of kilometres of small streams and ditches have been replaced by under-drainage systems both in Denmark and other parts of Europe (Brookes, 1987; Wingfield & Wade, 1988; Iversen et al., 1993).

Many lowland rivers in Western Europe have been substantially modified to aid land drainage and support the intensification of agriculture (Harrison et al., 2004).   Low-gradient rivers flowing through the agricultural and urban landscapes of north-west Europe have long been subjected to intensive management (Purseglove 1988; Moss 1998; Rackham 2000). Probably more than 95% of lowland river channels in south-east England and Denmark have been modified to enhance land drainage, river navigation and flood prevention (Iversen et al.,1993; Brookes 1995). As a result, many have highly simplified and uniform channels, unnaturally steep banks and little dynamic connectivity with their flood plains.

River modification accelerated in the twentieth century, largely associated with the intensification of agriculture, when many rivers were straightened, deepened and widened to facilitate catchment drainage and to prevent local flooding (McCarthy 1985; Brookes 1988). Instream gravel deposits and most instream woody debris were often dredged from such rivers, further reducing their physical heterogeneity (Swales 1989; Brookes 1988). The characteristic longitudinal and lateral sediment deposition pattern of actively meandering channels was then replaced by a more uniform and diffuse deposition of finer material in constrained channels. The physical complexity of natural marginal and riparian habitats was also usually greatly simplified. Water quality changed to reflect a greater input of nutrients and organic material from more-intensively managed catchments (Sweeting 1996; Riis & Sand-Jensen 2001).

Medium-sized and large mountain rivers are among the most degraded river types in Europe and numerous river restoration projects are currently carried out to achieve ‘good ecological status’ (Jähnig et al., (2009).

The WFD required river basin management plans report on hydromorphological pressures on water bodies. Five groups of hydromorphological pressures on surface waters (rivers and lakes) were included in the analysis, namely (1) Water abstractions; (2) Water flow regulations and morphological alterations of surface water; (3) River management; (4) Other morphological alterations; (5) Other pressures. Each of the five groups of hydromorphological pressures comprised of several subcategories of pressures, such as (1) Water abstractions include pressures from Agriculture, Public Water Supply, Manufacturing, Electricity cooling, Fish farms, Hydro-energy, Quarries, Navigation, Water transfer, and Other;  (2) Water flow regulations and morphological alterations of surface water include pressures from Groundwater recharge, Hydroelectric dam, Water supply reservoir, Flood defence dams, Water Flow Regulation, Diversions, Locks, and Weirs;  (3) River management include  pressures from Physical alterations of channels, Engineering activities and Dredging;  (4) Other morphological alterations include pressures from Barriers and Land sealing, while (5) Other Pressures group includes pressures from Sludge disposal to sea, Exploitation/removal of animals/plants, Introduced species and Other subcategories.   The data reported on significant pressures and stored in WISE-WFD database are not fully suited for illustrating channelized streams and issues on disconnecting the flood plains. As data are not supporting a comprehensive analysis, thus an European overview can be given through case studies.

Assessment below to be updated and improved

• Six out of 15 Member States had more than 40 % of their river water bodies being subject to impact by altered habitats  (Figure 8.2) and two countries. Hungary and Germany had more than 60 % of river water bodies being subject to impact from altered habitats.
• In the Czech Republic, United Kingdom and Hungary more than 60 % of lake water bodies has altered habitats as a significant impact.  

Figure 7,2 Percentage of river WBs and lake WBs with habitat alteration being an impact

7.3 Case studies

We hope that Member States and relevant stakeholders will comment on the current case studies and contribute with updates and new case studies. The current case studies are partly copy and paste from RBMPs or other relevant documents.

7.3.1.      Country examples of altered river habitats

In Europe many rivers and streams were channelized and straightened, total stream length was shortened, many connected side-arms got lost, and the number of oxbow lakes reduced. There are many national examples illustrating that a large proportion of waters have been significantly modified.  On the following pages is listed a number of country assessments of the state of river habitats.

England and Wales

Source: Environment Agency 2011

Denmark

A survey of Danish stream channels indicates that 97.8 % of Danish watercourses have been artificially straightened and that only 2.2 % (880 km) have natural morphological characteristics. The density of channel works is 300 times greater than in the U.S.A. and 15 times greater than in England and Wales (Brookes et al. 1987).

Finland

Source: Laitinen and Jormola 2008

Almost every ditch and stream in Finland has been altered: Many natural streams have been widened to increase drainage, deepened and straightened for agriculture. Drainage of agricultural areas is a prerequisite for cultivation in the Finnish climate and lowland conditions. Almost all brooks and ditches in farming lands have been widened, deepened and straightened to allow sufficient drainage depth and prevent local flooding. Regular dredging has weakened the ecological condition of brooks and increased erosion, sedimentation and invasion by aquatic plants of the downstream sections. Decreased water flow and poor water quality also cause problems. In addition, biodiversity suffers and the form of the streambed becomes monotonous. Only few species can live in straightened and deepened streams.

Text box: Channelized rivers for timber floating in Finland and Sweden

Austria

Source: Poppe et al. 2008

Up to 80% of the large rivers in Austria (n=53) are moderate to heavily impacted. The main pressure types are channelisation, continuum disruption, impoundment, water abstraction, hydro peaking and land use. Data of near natural as well as anthropogenically altered catchments in Austria were compiled. The main pressures were identified through pressure-specific indices.

Up to 80% of the large rivers in Austria are moderately to heavily impacted (Muhar et al., 2000). As water pollution is not the main problem anymore, the main impacts on Austrian running waters concern hydromorphological alterations.

In Austria only about one third of the total length of the main rivers remains free flowing. The remainder has been impounded or otherwise modified for hydroelectricity generation or flood protection and erosion control (Lebensministerium, 2010).

International Danube River Basin Management Plan

80% of the former flood plains/wetlands in the Danube river basin district have been lost during the last 150 years.

Switzerland

In Switzerland below elevations of 600 m 46 % of watercourses are heavily impacted in terms of structural diversity and there are about 101 000 artificial barriers with a height difference of more than 0.5 m (FOEN, 2010).

Germany

Source: UBA 2010

Floodplains along the large German rivers

Source

The large German rivers have generally been technically modified with weirs and locks for the benefit of navigation and hydropower use. Furthermore, large parts of their floodplains have been separated off from the river and restricted by dykes. Installations and interventions for the purpose of flood alleviation may cause significant pressures on hydromorphology. Today nearly all sections of the major rivers have dykes. The building of dykes resulted in the loss of floodplains as retention spaces for flood water. For example, the development of the Upper Rhine resulted in a river bed up to 12 km wide giving way to a channel between 200 and 250 m in width; the Rhine floodplains between Basel and Karlsruhe decreased by 87 %. Overall, the natural floodplain area of the Upper Rhine was reduced by 60 % or 130 km2, which in turn entailed considerable expenditure for the associated increased risk of flooding in downstream areas.

Only 10-20 % of the former floodplains on major rivers are now available to retain flooding. Only 10 % of the floodplains analysed in river basins > 1000 km2 can be described as slightly or moderately changed (Figure 25). Most of the rivers covered by floodplain mapping are Federal waterways. The usage pressure on the major rivers is also reflected in their structural quality. Over 90 % of Federal waterways have had their natural structure “distinctly” to “completely changed” (structure classes 4-7, Figure 25).

The Netherlands – Vecht River

Source:  http://edepot.wur.nl/176364

Canalisation of the river Vecht went along with changes in land-use and took place during three major time-intervals: ±1895-1905, 1925-1935, and 1955-1965. The area of heather and moorland peat decreased dramatically as the agricultural, urban and other human uses increased. The percentage of forest remained the same over the whole period. In general, the morphological features of the streams in the Vecht catchment show degradation over the last one hundred years.

The total stream length was shortened by about 20% while the valley length remained about the same. Forty percent of the connected side-arms got lost and the number of oxbows increased in the thirties due to straightening of the major streams but decreased until today with about 38%. In general, most streams were meandering around 1900, in the thirties and sixties some were still slightly meandering, and currently most are straight.

Gravel extraction from rivers

Rivers in north-eastern Italy, as other Italian rivers and some rivers of the Carpathians, have experienced widespread channel adjustments in the last 100 years, in particular incision and narrowing (Rinaldi et al. 2005 ; Surian, 2006; Surian et al., 2008). Channel width has been reduced by 50-70 % and bed-level has been lowered of 2-3 m on average, but locally up to 8.5 m. Gravel mining and channelization works have been the main causes of channel changes and it have altered fluvial processes, in particular sediment fluxes. Gravel mining was very intense between the 1950s and the 1980s. During the 20-30 years large volumes of sediments were removed from the channels.

Urban areas

Source: Binder 2008

During the last 150 years rivers in urban areas of Europe were sealed in concrete, habitats got lost, the hydro morphological processes within such system are even today often strongly interrupted. Better sewage treatment during the last 30 years and the improvement of the water quality, was the basic for urban river restoration projects. There are many good examples of river restoration in urban areas. Urban streams have become increasingly important in the planning of urban ecology and green areas in European towns and cities in recent years. Today river restoration, in connection with other projects for city development and urban planning are offering win-win situations: to improve flood control and the ecological functions, to keep people in town, to offer recreational value and to raise the quality of living in urban areas.

 Text box: Urban development and river regulation

Source: Based on Goldschmid and Schmid 2006 pdf

Status of channel water bodies in Hungary

Hungary is one of the few countries in Europe with a geography that is completely landlocked, meaning it has no coast. A great proportion of the geographical land of Hungary is taken up by the Great Plains located in central and eastern Hungary, where the lie of the land is generally low and flat.    Hydrographically Hungary can be divided into two roughly equal parts: one part belongs to the Danube and the other one is in the Tisza Basin.   In the late nineteenth century, during the large-scale river regulation works on the Tisza River and in smaller extend on the Danube River, canal systems were also created partly as artificial waterways, partly to help the agricultural landuse, and partly to draine inland excess water away. The most important canal of  theTransdanubia part of the countryis the 100 km long Sió Channel connecting Lake Balaton and the Danube River. 

As a consequence of large scale river regulation works and construction more than 4500 km long flood protection levee system nowadays roughly one forth of the territory of the country is under 100 year probability flood level (Figure 8.5).

 There are about 43 000 km long inland excess water drainage channels in Hungary dominantly on the areas at inland excess water risk. This is one of the reasons that while Hungary designated 869 river water bodies, out of them 255 water bodies are called channel.

In the WISE-WFD database there is no code to distinguish channel type river water bodies.  However, 255 river water bodies could be identified by their name as channel type water bodies.  Figure 8.6 illustrates examples of the channel types. 

Figure 8.5: Regulated channels and streams

Out of the total 869 RWBs 350 were classified as HMWBs from which 101 are channel type, while from the 146 AWBs 87.7% is also channel type (Figure 8.6).  26 WBs called channel were classified as natural type, which fact raises question that either the name of the water body does not fit tto the reality or the classification is wrong.  There are 819 RWBs with at least one identified hydromorphological pressure.  Out of  them there are 235 water bodies with channel name.

Figure 8.6  Ratios of channel and river water body types in Hungary

There are only 50 river water bodies which have no hydromorphological pressure. Out of the 819 RWBs with at least one hydromorphological pressure 235 were channel type. 

References

Binder 2008: River restoration: an European overview on rivers in urban areas. In proceedings from  4th ECRR Conference on River Restoration Italy, Venice S. Servolo Island 16-21 June 2008. Avaiable at http://ecrr.org/archive/conf08/pdf/proceed_all.pdf

Brookes A 1987: “The distribution and management of channelized streams in Denmark”, Regulated Rivers: Research & Management 1, no. 1 (1987): 3-16.

Brookes, A. (1995): River channel restoration: theory and practice. In: Changing River Channels (eds A.M.Gurnell & G.E.Petts), pp. 369–388. Wiley & Sons, Chichester, UK.

Engström, Johanna, Christer Nilsson and Roland Jansson (2009): Effects of stream restoration on dispersal of plant propagules. Journal of Applied Ecology 46, no. 2 (2009): 397-405.

Environment Agency 2011: The state of river habitats in England, Wales and the Isle of Man. Available at http://www.environment-agency.gov.uk/static/documents/Leisure/GEHO0310BRTM-E-E.PDF

Goldi, C. (1989): Resuscitation programme for flowing waters in the Canton of Zurich. Anthos 2:1-5.

Goldschmid and Schmid 2006 pdf

Harrison, S. S. C., J. L. Pretty, D. Shepherd, A. G. Hildrew, C. Smith and R. D. Hey (2004): The effect of instream rehabilitation structures on macroinvertebrates in lowland rivers. Journal of Applied Ecology 41, no. 6 (2004): 1140-1154.

Iversen, T. M., B. Kronvang, B. L. Madsen, P. Markmann, and M. B. Nielsen (1993): Re-establishment of Danish streams: restoration and maintenance measures. Aquatic Conservations: Marine and Freshwater Ecosystems 3:73-92.

Jähnig, Sonja C., Stefan Brunzel, Sebastian Gacek, et al., “Effects of re-braiding measures on hydromorphology, floodplain vegetation, ground beetles and benthic invertebrates in mountain rivers”, Journal of Applied Ecology 46, no. 2 (2009): 406-416.

Kondolf, G. M. (1995) Geomorphological stream channel classification in aquatic habitat restoration: uses and limitations. Aquatic Conservation 5:127-141.

Kondolf, G. M. (2006): River restoration and meanders.

Ecology and Society 11(2): 42.   URL: http://www.ecologyandsociety.org/vol11/iss2/art42/

Laitinen and Jormola 2008: Drainage and fishery needs in the restoration of agricultural brooks In proceedings from  4th ECRR Conference on River Restoration Italy, Venice S. Servolo Island 16-21 June 2008. Avaiable at http://www.ecrr.org/archive/conf08/pdf/proceed8.pdf

Muhar S., Schwarz M., Schmutz S., Jungwirth M. (2000) - Identification of rivers with high and good habitat quality: methodological approach and applications in Austria. Hydrobiologia, 422/423, 343-358.

Muotka, Timo and Jukka Syrjänen (2007): Changes in habitat structure, benthic invertebrate diversity, trout populations and ecosystem processes in restored forest streams: a boreal perspective.  Freshwater Biology 52, no. 4 (2007): 724-737.

Naturvårdsverket http://www.naturvardsverket.se/ImageVault/Images/conversionFormatType_WebSafe/id_5081/scope_0/ImageVaultHandler.aspx

Poppe et al. 2008: The prioritisation of restoration measures in multiple-affected rivers.  An Austrian approach. In proceedings from  4th ECRR Conference on River Restoration Italy, Venice S. Servolo Island 16-21 June 2008. Available at http://ecrr.org/archive/conf08/pdf/proceed_all.pdf

Riis T. and Sand-Jensen K. 2001: Historical changes in species composition and richness accompanying perturbation and eutrophication of Danish lowland streams over 100 years. Freshwater Biology 46, no. 2 (2001): 269-280

Rinaldi M., B. Wyżga, og N. Surian, «Sediment mining in alluvial channels: physical effects and management perspectives», River Research and Applications 21, nr. 7 (September 2005): 805-828.

Surian 2008: Channel adjustments and sediment fluxes in gravel-bed rivers of north-eastern Italy: implications for river restoration. In proceedings from  4th ECRR Conference on River Restoration Italy, Venice S. Servolo Island 16-21 June 2008. Avaiable at http://ecrr.org/archive/conf08/pdf/proceed_all.pdf

UBA 2010: Water resource management in Germany, part 1 fundamentals p. 55-56