2 Sustainable Urban Drainage Evolution: the Way Forward
2.1 The Floodability Concept
2.2 Identification of Floodability Opportunities
If possible, reverse the urbanization process: such solutions usually entail high costs, the occupation of large urban areas, a prepared population, cultural changes and societal willingness-to-pay for past unsustainability (i.e., integrated cities – nature is not common in ancient city centres).
If transformation is not feasible, improve the area’s recovery ability: the aim of this approach is not to reduce hazards but to reduce damage and accelerate recovery while progressing towards a resilient system. This approach usually entails lower costs than does the reversion option, is feasible in dense urban areas, is assisted by technologies and strengthens society by attaining its new ability to survive floods (i.e., it reduces fear of catastrophic events).
If flooding events are frequent, adapt and learn to live with the floods; such floodability measures have similar costs to those of adaptation. This approach is feasible in dense urban areas, but results cannot be achieved if societal behaviour does not change (especially considering that floodability measures may increase local risk). Urban planning must take the presence of flood risk into account; thus, the urban materials used must be different than typical materials. Technology can help with this approach, but the measures used must be robust (i.e., must require low maintenance and maintain efficiency even if electricity or information technology resources are not available), and the population must be prepared for an event because proper behaviour is the first mitigation measure against the damage caused by an event (floodable society).
The “live with flood” and “reverse urbanization” approaches are implemented for areas with frequent flooding (up to return period values of 10–20 years);
The “transform the urban area” approach is used for areas experiencing infrequent events (up to 50 years) to protect the society and economy from relevant damages through the relocation of unique and strategic assets from affected areas;
The “speed up recovery” approach is implemented in areas experiencing rare events (less frequently than 50 years) to safeguard future urban development of the area and to avoid its abandonment due to large flooding events.
2.2.1 Risk Treatment - Reverse the Urbanization Process
2.2.2 Risk Treatment – Improved Recovery
2.2.3 Risk Treatment - Adaptation
2.3.1 Venice (Italy): When the Resistance Approach Fails
2.3.2 Jinhua City (China): Recovering Abandoned Areas and Connecting People
3 Conclusions and Directions for the Future
Floodability is an evolution of flood resilience in the sense that, even during flooding, a floodable urban area still retains a sufficient level of liveability and is able to recover its full level of liveability soon after the event.
The design of floodable urban areas requires that economic and societal activities are mapped to define the areas, paths, activities and services to be defended, relocated, strengthened or dismissed; this process aims to shift the utilized flooding strategies from the preservative approach to the “live with” philosophy.
The learning-by-doing cycle is the centre of the paradigm, as technical solutions must be implemented with the help of the population who learn from events to better cope with flooding; they first adapt to reduce damage and then change to seek growth. Thus, people’s experiences are used to modify the applied strategies, and some actions are abandoned while new actions are implemented.