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Natural hydromorphology refers to the hydrological, morphological and river continuity conditions of rivers, lakes, estuaries and coastal waters in undisturbed state. Natural hydromorphology is crucial for the good functioning of the aquatic environment. The restoration of aquatic ecosystems largely depends on restoring hydromorphological conditions to a more natural state.

For decades, humans have altered the physical character of water ecosystems, changing the shape of water bodies and the flow of river courses to farm the land, allow navigation, generate energy and protect settlements and agricultural land against flooding. For these purposes, rivers were straightened, channelised and disconnected from their floodplains; land has been drained, dams and weirs have been built, river banks have been reinforced and groundwater levels have changed. These activities have resulted in altered habitats, changed flows, interruptions in river continuity, and loss of floodplain connectivity.

Did you know?

34% of European surface waters are under significant hydromorphological pressures

Agriculture, flood protection, energy generation and navigation are main human drivers of hydromorphological pressures

Degraded hydromorphology can be restored by removal of river barriers, ecological flow measures or physical habitat improvements

All this has caused damage to the hydromorphological quality of water bodies, which plays a key role in sustaining aquatic ecosystems. Water flow and substrate provide physical habitats 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.

The hydromorphological characteristics of water bodies play an important role under the Water Framework Directive (WFD). The analysis of hydromorphological pressures, the assessment of hydromorphological status of the water bodies as a supporting element for ecological status, and determination of impacts resulting from hydromorphological pressures are some of the steps in which hydromorphology is considered in the WFD. For a water body to be in good ecological status, its hydromorphological conditions must be such that they can support communities of biological quality elements such as fish and other aquatic life that differ only slightly from an undisturbed natural state.

Drivers and impacts

There are several anthropogenic activities that cause hydromorphological pressures, e.g. construction of dikes or dams, straightening of rivers. Hydromorphological pressures are the most widespread significant pressures on surface water bodies reported under WFD for 34 % of surface water bodies, with the highest share reported for rivers (38%) and transitional waters (31%).

Pressures on hydromorphology serve various important human activities such as energy generation, farming, transport in waterways and protecting land that is under human use from flooding (Figure 1). In European rivers, the main human drivers of hydromorphological pressures are agriculture, flood protection and hydropower. Hydropower and flood protection are key drivers for these pressures in particular on large rivers and rivers at mid-altitude, while agriculture is a key driver in lowland rivers. For lakes, the main driver behind hydromorphological pressures is hydropower, while Mediterranean lakes are also affected by water storage for agricultural irrigation needs. In estuaries and coastal waters, the main human drivers are flood and coastal protection and navigation.

Figure 1
Pressures from hydromorphology serve different human uses


Coastal protection

Energy generation

Water transport

Hydromorphological pressures alter aquatic habitats and ecosystems due to impacts of habitat fragmentation and habitat loss, changes in the flow regime and disturbance of natural dynamics of sediment transport. Altered habitats due to morphological changes are the 2nd most common impact on European surface water bodies reported under WFD, after chemical pollution.

Surface water bodies with significant hydromorphological pressures (34 % of total) are at a risk of failing to achieve the objective of good ecological status of the Water Framework Directive. For the large majority of those water bodies with significant hydromorphological pressures, surface water monitoring confirms that they do not reach good ecological status (see Figure 2). Some water bodies with significant hydromorphological pressures are currently in good status but these pressures may present a risk of deterioration of their good status in the near future.

Figure 2
Percentage of surface water bodies that do not reach good ecological status out of total water bodies which are at risk due to significant hydromorphological pressures (based on data reported in 2nd RBMPs)

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The restoration of hydromorphological conditions, i.e. of the hydrology, morphology and river continuity, is important for restoring aquatic and floodplain habitats and ecosystems to a more natural state. Hydromorphological restoration can take place using a wide range of measures, such as the removal of river barriers, re-meandering of rivers, dike relocation, ecological flow measures, sediment management measures, improving habitats on river banks, river beds and on the floodplains, and natural water retention measures (see Figure 3). Such measures are typically planned as part of the programmes of measures to reach good ecological status under the Water Framework Directive. Also the EU Biodiversity Strategy 2030 includes a target to restore 25,000 km of free-flowing rivers in the EU by 2030, by removing river barriers and restoring floodplains and wetlands. The target of free-flowing rivers addresses restoration of both longitudinal river connectivity (along the river) and lateral river connectivity (between the river and its floodplains).

In several European river basins, there are already strategies in place to restore river continuity by taking measures to remove barriers or make barriers passable for fish and sediments. Also the restoration of bank structures, reconnection of backwaters or floodplains and restoration of wetlands are among the most common measures applied to achieve hydromorphological improvements.

Figure 3
Examples of hydromorphological restoration measures on rivers and their floodplains

Source: Floodplains: a natural system to preserve and restore. EEA Report No 24/2019

Free-flowing rivers, thematic page

Rivers and their floodplains, thematic page