Fuentes de acceso a ICP que se divulgó

Enhancement of urban rivers brings social responsibilities. It is the clean water in urban rivers that will attract people who would want to experience them. These beloved riverfronts have the aesthetic qualities of tranquillity, peace, a cooling effect as well as beauty. In turn through this demand, water also has an upgrading effect on real-estate value. Waterfront property has been reported to sell at a 50% higher price than units that are removed from the water, and units that have a water view but no frontage sell for 20 to 30 % higher, depending on proximity (Tourbier and Westmacott, 1992). Cities have recognised this and are marketing abandoned harbours and related derelict industrial sites for waterfront development.

A problem that needs to be addressed though are public health and safety concerns, particularly flood damage. Continuous increases in paved surfaces have led to more frequent flooding events throughout Europe. Cities that improve the attractiveness of rivers also must assume a responsibility not to place people in harms way. At the least, authorities must be held accountable for arranging the flood proofing of public infrastructure (sewer lines, oil-tanks and below ground garages) as well as organising adequate emergency and flood warning systems for residents. Sustainable strategies require mapping the extent of an “open floodway district” and “flood fringe areas”, as well as legislative passage of building codes for flood proofing. Possible measures are listed below:

Integrated Flood management

Contemporary flood risk management strategies for urban areas comprise following aspects:

• Basin-wide planning and management

• Inclusion of all scientific disciplines as technique, natural science, sociology, law, insurance and economy

• Collaboration of all actors and affected parties as authorities, privates, researchers and emergency staff

• Consideration of the residual risk, that is arising from events that overwhelm the protection structure’s design capacity. Accounting for uncertainties and temporal changes of governing influences

• Damage prevention, e.g. by zoning, flood proofing, reduction of exposure and vulnerability, raising private awareness, responsibility and preparedness

• Hazard reduction with soft and technical measures comprising mobile protection systems

• Forecasting, early warning and evacuation

• Consideration of interactions between rivers, urban drainage systems and groundwater

• Emergency planning and ex-post disaster relief

Following these guidelines, a partial re-naturalisation of flood flow-regimes can be maintained by ecologically oriented channel rehabilitation and by giving rivers more space for sea and flowing retention and sediment dynamics. Retention areas in urban and sub-urban sites can be utilized for recreation, as playgrounds, parks, sport-fields or wildlife areas. In the re- naturalized detention reservoirs of Wien River in Vienna, flows up to a 2-year flood of 30 m3/s pass the basins without artificial intervention. This ensures a dynamic creation and succession of natural habitats (Goldschmid, 2002). For larger discharges, flood protection is the governing aim. Flood detention schemes were also integrated along the urban Liesing brook in Vienna’s south. These areas are formerly used industry and commercial sites, adapted gardening and agricultural land, and green areas surrounding a highway junction. Controlled flood detention is maintained from bank-full discharge of 70 m3/s corresponding to a 100-year flood (Stadt Wien, 2001).

Flood proofing of structures

New buildings that have been permitted to be constructed on the floodplains should be built on stilts in order to avoid the reduction of flood area and storage capacities. Existing structures should be flood proofed to include provisions for intentional flooding of spaces below flood stages to balance internal and external pressure. Openings and doors should be reinforced. Structures should be equipped to be flood resistant hence having sufficient strength to withstand the pressure and the impacts of floating debris.

Flood proofing against water pollution

Below flood level oil tanks should be anchored to prevent flotation and leakage. Sewer lines should be equipped with flood proof lids and sewage treatment plants should be flood proofed. The storage of materials that are toxic, explosive when exposed to water, or buoyant (drift solids) should be prohibited.

Dikes, levees, floodwalls

Dikes and levees should not be built in the “open floodway” district. Wherever possible existing levees should be set back to give a river more space for flooding. Temporary floodwalls to divert floodwater flows can protect critical sites. In areas that are subject to tidal flooding, dikes need to be equipped with tidal gates or backwater valves.

Emergency access and flood warning

Structures should be accessible by elevated access ramps and catwalks. For structures with high intensity uses access ramps need to be suitable to be used by emergency vehicles. Flood warning systems for communities should be developed to be timely, accurate and neighbourhood specific.

Increasing interception losses

Interception is very efficient measure for runoff reduction. High trees with large canopy could reduce rainfall for 20-30 percentages even in very large thunderstorm.

For efficient flood damage and its control we should estimate the hazards, vulnerability and risk. Risk management can be carried out in several ways (strategies: to modify susceptibility to flood damage and disruption, modify flooding and modify the impact of flooding on individuals and community, (FEMA 1992, Casale 1997). Urban areas change hydrology and have high impact in terms of flood hazards; on the other hand, they are very vulnerable to flood damage. In terms of effects of urbanisation on flooding, it should be emphasised that the effects are shown especially in frequent yearly flooding, onto which the drainage systems are dimensioned and that as a rule do not cause significant damage. The influence on large, catastrophic events is in turn much smaller and calls for a special hydrological analysis. However, defence against flooding by way of constructions is a constituent part of a larger integrated water management plan of the whole river basin. Measures that are appropriate to one part may be ineffective (or worse) in another. In an urban environment the damage problems are solved, however, this is not the subject of the URBEM project. With small scale measures in river revitalisation very important details are solved, which influence flooding.