Table of contents
- Executive summary
- 1. Introduction
- 2. Fall and rise of urban rivers and lakes
- 3. Coping with key challenges for urban rivers and lakes
- 3.1 Water availability and supply
- 3.2 Water quality
- 3.3 Structural changes
- 3.3.2 Hydromorphological restoration of urban rivers and lakes
- 3.3.3 Uncovering Europe’s hidden rivers
- 3.3.4 Restoration to cope with urban flood risks
- 4 Lessons learned and way forward
- Acknowledgements
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.
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)
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.