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For decades, humans have altered the shape of water bodies and the flow of river courses to farm the land, facilitate navigation, construct hydropower plants and protect settlements and agricultural land against flooding. For these purposes, rivers have been straightened, channelised and disconnected from their floodplains; land has been reclaimed, dams and weirs have been built, embankments have been reinforced, and groundwater levels have changed. These activities have resulted in altered habitats, changed flows, interruptions in river continuity, loss of floodplain connectivity and severe impacts on the status of the aquatic environment. These changes have caused damage to the morphology and hydrology of the water bodies, i.e. to their hydromorphology (EEA, 2018; EEA, 2019).

Hydromorphology plays a key role for aquatic ecosystems. For example, water flow and substrate provide physical habitat for plants and animals, such as fish and benthic invertebrates. Good hydromorphological functioning is an essential element of ecosystem health and underpins the delivery of many ecosystem services and benefits for society (EPA Catchments Unit, 2016; Houlden, 2018).[1] 

[1] https://www.catchments.ie/hydromorphology-what-is-it/ and http://www.hrwallingford.com/news/Hydromorphology-the_forgotten_facet_of_the_WFD

In the second RBMPs, hydromorphological pressures are the most commonly occurring pressure on surface waters, affecting 34 % of all such water bodies (EEA, 2018). The most reported hydromorphological pressures are physical alterations related to flood protection, urbanisation, agricultural development and navigation as well as barriers including dams and weirs built for different purposes (hydropower, flood protection, irrigation, or navigation). In addition, several thousands of water bodies are affected by hydrological alterations driven by water abstractions (for public water supply, agriculture, or industry) and reservoirs used mainly for hydropower and irrigation. However, in the second RBMPs of most Member States, the identified hydro-morphological pressures are not clearly apportioned to specific drivers (EC, 2019).

Further, 16 % of European water bodies have been designated as heavily modified (13 %) or artificial (3 %) water bodies.

Key hydromorphological pressures are described in the following sections of this report elaborating on the role of hydropower, navigation, flood protection and agricultural drainage as major drivers of impacts on hydromorphology in Europe. Also, separate sections address the role barriers to illustrate their very dense distribution and far-reaching impacts on the European river network and key issues related to the loss of lateral connectivity to floodplains.

Certain aspects of hydromorphological pressures and impacts are less well-known so far in terms of their extent and implications on European scale. One of these aspects is the issue of changed sediment dynamics due to hydromorphological pressures which is gaining more and more attention and will require targeted management interventions in the near future (see Box 22). In the meantime, the issue should remain in focus of further data collection and research to identify the main underlying processes, impacts on water bodies and appropriate management approaches.

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