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3.2.1        Barriers

Overview

Humans have fragmented European water bodies with artificial barriers such as dams and weirs for centuries, as a means of ensuring water supplies, generating energy, facilitating navigation, and controlling flooding. Such human-made barriers reduce the ecological connectivity of a water body, impeding the flows of water, nutrients and sediment, create obstructions for species movement (particularly migratory species), often alter the quantity, quality and timing of river flows, both upstream and downstream, and can impact surrounding riparian zones and flood plains (Freshwater Information System, 2019).

There are different types of barriers, including dams, sluices, weirs, culverts, fords and ramp-bed sills and the extent differs to which these are recorded in the different national river assessment systems across Europe.

In the second RBMPs, barriers are a significant pressure for almost 30 000 surface water bodies (20 % of total) in WFD countries, with the highest numbers being reported in Sweden, Germany, Austria, France, Denmark, and Spain. Furthermore, barriers are the reason or one of the reasons for designating approximately 10 000 water bodies as heavily modified, which amounts to more than half of heavily modified water bodies in Europe.

A large number of barriers are reported in the RBMPs to be used for hydropower (dams for hydropower production), flood protection and irrigation (water storage reservoirs). However, for a large share of water bodies affected by barriers (ca. 40 %), the uses which the barriers serve are unclear, either being unknown or not explicitly reported or obsolete. Indeed, many barriers on European rivers originated in the 10th to 19th centuries to operate mills and a high proportion of these are by now redundant. It is estimated that alone in France, Spain, Poland and the UK, there are up to 30 000 mainly small dams which are now obsolete (Gough et al., 2018). In addition, there are many weirs without a practical use.

The most comprehensive overview of river fragmentation in Europe is provided by the recently published Pan-European Atlas of In-Stream Barriers.[1] The Atlas contains information on 630 000 barriers including not only large dams, but also hundreds of thousands of smaller weirs, ramps, fords and culverts. However, researchers have recently found that more than one third of barriers on European rivers are unrecorded, bringing the total to well over 1 million. This scale of river fragmentation is alarming and makes Europe the most fragmented river landscape in the world, with hardly any unfragmented, free-flowing rivers left (WWF, 2020). [2]

[1] Produced by the EU Horizon 2020 project Adaptive Management of Barriers in European Rivers (AMBER): https://amber.international/european-barrier-atlas/

[2] WWF, 2020, More than 1 million barriers destroying Europe’s rivers, new research shows, accessed 27^th July 2020, https://www.wwf.eu/wwf_news/media_centre/?uNewsID=364559

Figure 7             Man-made river barriers in Europe included in the AMBER Atlas

Notes: Insert notes here

Source: https://amber.international/european-barrier-atlas/