A balanced approach addressing the pressing issues in urban environment is not common in the water service sector, which has been traditionally based on a sectorial approach. Conventional urban water management focused mainly on protecting the urban human population against hydrological extremes (floods and droughts) and providing water services. The latter ones typically included water supply, urban drainage and flood protection, wastewater management and, more recently, some form of aquatic ecosystems protection. These however often did not address specific features of aquatic habitats, their needs and potentials. In many cases, to minimise drainage costs, urban streams and rivers were incorporated into major drainage systems and conveyed various types of municipal effluents, resulting in the ultimate habitats degradation.

Currently, the development of comprehensive knowledge generated by integration of various sectors of science as well as the recent developments in ecological engineering, increase opportunities to develop a more sustainable, economically viable urban environments. Newly emerging paradigms underline the need for water conservation, rational use, reuse, and sustainable integration of different components of urban river systems, including those of technical and natural character (Pinkham, 2004; Zalewski, 2006). This tendency creates opportunities for changing attitude to UAHs, and their use for concurrently improving efficiency of urban water management and the quality of human life in cities (Zalewski and Wagner, 2006).

Restoration, preservation, rehabilitation or remediation?

Among several approaches to urban aquatic habitats, the following are usually considered:

• Restoration - is a process which ideally brings a degraded river back to its original conditions. It includes restoring water quality, sediment and flow regime, channel morphology, communities of native aquatic plants and animals, and adjacent riparian lands. The goal of restoration is impossible to achieve in urban watercourses. Re-establishing the historical, original state would require replication of the original conditions, which no longer exist, and are not even well known.
• Preservation - preservation of aquatic habitats state and biodiversity is a realistic goal, when the urbanisation impact on ecosystems is not severe. This ideal situation generally occurs in peri-urban areas, where urbanisation has not yet fully invaded the surrounding landscapes and where industrial or agricultural activities are limited (Lafont et al. 2006).
• Rehabilitation - is a less ambitious but more realistic aim. It enhances or re-establishes lost or diminished biotic functions of ecosystems that can persist in it without attempts to restore pristine conditions. It improves the most important aspects of aquatic environment and creates habitats resembling its original conditions.
• Remediation - is an approach applied in those cases where environmental changes are irreversible and catchment conditions no longer support aquatic ecosystem functioning. The remediation goal is to improve ecological conditions of the aquatic ecosystem, which may not lead to a state resembling the original state of the stream. It means that after the remediation process we can obtain a new ecosystem, different from the original one (Lovett and Edgar, 2002).

Criteria for making a decision should balance potential increase of ecological benefits (and possibly of human well-being) and spatial, demographic, and economic limitations together with economic gains and losses.

Resources:

Breil, P., Marsalek, J., Wagner, I., Dogse, P. 2007. Introduction to Urban Aquatic Habitats Management. In Wagner, I. , Marshalek, J. and Breil, P. (eds). Aquatic Habitats in Sustainable Urban Water Management: Science, Policy and Practice. Taylor and Francis/Balkema: Leiden .

Pinkham, R., 2004. 21st Century Water Systems: Scenarios, Visions, and Drivers. http://www.rmi.org/images/other/Water/W99-21_21CentWaterSys.pdf. Rocky Mountain Institute, Snowmass, Colorado

Lafont, M., Vivier, A., Nogueira, S., Namour, P. & Breil, P. 2006. Surface and hyporheic Oligochaete assemblages in a French suburban stream. Hydrobiologia 564: 183-193.

Lovett, S. and Edgar, B. 2002. 'Planning for river restoration', Fact Sheet 9, Land & Water Australia, Canberra

Zalewski, M. 2006. Ecohydrology - an interdisciplinary tool for integrated protection and management of water bodies. Arch. Hydrobiol. Suppl. 158/4, p:613-622

Zalewski M. & Wagner I. 2006. Ecohydrology - the use of water and ecosystem processes for healthy urban environments. Aquatic Habitats in Integrated Urban Water Management. Ecohydrology & Hydrobiology. Vol. 5. No 4, 263-268