3.3 Structural changes

3.3.1        Key impacts of physical modifications

On top of increasing demand for water and increased water pollution, rapid urbanisation and industrial growth have introduced additional types of stress to urban rivers, in the form of modifications to their morphology and hydrology.

In the last 150 years, riverside areas have been subject to structural changes such as channelization and straightening. These have taken space away from the river to serve flood protection and the creation of living space for growing towns. As a consequence they led to the deterioration of water quality and loss of recreation and amenity uses.

In many towns and cities, rivers and streams have been covered with concrete and rerouted into sewers, drains and culverts as urban areas have grown. In some European capitals, several man-made canals were added to the river network, for example in Berlin whose landscape is shaped by several important canals (Teltow, Landwehr, Berlin-Spandau shipping canal, and Hohenzollern canal).

Due to physical modifications, urban river spaces suffer from a lack of several functions, as illustrated in the table below.

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Table 3 Impacts of physical modifications on functions of urban rivers

Functions of urban river spaces

Impacts of physical modifications

Ecological functions  

Lack of habitat and biotope network function

Lack of permeability/passability

Lack of retention areas

Pollution and contamination

Social functions

Lack of accessibility of rivers and streams

Lack of attractive open spaces next to water

Inadequate perception of rivers by the public

Spatial functions

Separation of urban spaces and rivers due to technical infrastructure

Neglected areas along rivers

Based on Bender et al. (2012)

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Lakes within cities have also been physically modified as their natural shores were replaced by concrete structures and/or their hydrology modified to serve human uses.

The next sections describe the responses of cities and towns to impacts of physical modifications on their rivers, streams and lakes in recent decades. This report distinguishes between activities that aim at a) hydromorphological restoration mainly of rivers and streams of medium/small size, b) activities of de-culverting covered streams and rivers and c) restoration of urban water bodies with strong links to flood risk management. In practice, all these types of activities are strongly interconnected and often take place simultaneously in the context of the same restoration scheme.

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