Juan G. R. Flood control in urban areas of Spain.
Water and Irrigation, Nº 1: 5-6, 2009, Alicante, Spain.
The flood control in urban areas, has each time more important, since every year product of heavy rains and high cumulative values reaching timely rainfall, causing human and economic losses, so it is necessary to protect adequate our cities and towns, so that internal and external drainage systems may be designed to reduce flood damage to a minimum.
In the period from September to May is the rainiest season in Spain and there is a high probability of timely flooding because appears the cold drop, which is a weather phenomenon that can cause heavy rain and we are not yet well protected to fight effects induced by it. Autumn is the season of heavy rainfall and thus has a high probability of occurrence of floods, human and material losses.
In many towns and cities in Spain, there are areas with poor sewage system that is unable to pass large volumes of water in a short time, have also built many homes and commercial areas in old channels of water that affect the natural movement of the water, but when there are heavy rains, the water tends to recover its old bed especially if it is relatively unprotected, which results in human casualties, property damage to: population, electric power, road and rail communications, bridge collapse.
Furthermore, the rapid urban development has not evaluated with sufficient guarantee the drainage plan and facility protection against internal and external flooding, too there are agricultural areas that are not adequately protected with efficient drainage systems, which results in that large areas being flooded and causing collateral losses in urban areas.
Spain has 3 different climatic regions, although recent studies have been more specific and consider that Spain has 6 climatic regions, which demonstrates the great variability of rainfall in the country in different regions, this element it is necessary to take in consideration to the design of drainage networks and protection again flood and avenues, where maximum rainfall recorded from 50 to 200 litres per m2 in an hour, although there are specific areas with intensities below 50 litres/m2 in an hour and maximum rainfall record of 800 litres/m2 in just over 2 hours, which are considered very high when to take into account that the average annual rainfall of Spain is 684 litres / m2.
There’s so much climate variability that is necessary to project the drainage systems from historical data of rainfall in each region, taking into consideration the mathematical probability of occurrence of the phenomenon and its intensity, climate change and urban development in the area. The inadequate urban planning, the no sufficient green areas in cities and the use of drainage networks of low discharge capacity, contribute to increased runoff of rainfall and hence increase the time of flooding. In the fight against external water that may affect urban areas is necessary to combat them with: belt channels, drainage channels, rectification of rivers, levees for protection, dams and as so the protection of watersheds upstream of populations with risk of flooding, with the aim of increasing rainfall infiltration and reduce superficial runoff.
The onset of flooding is more frequent in some autonomous communities than in others, the most affected: The Valenciana Community, Andalusia, Catalonia, Murcia, Aragon, Castilla La Mancha, Madrid, Extremadura, Ceuta and Melilla, on the other autonomous communities maximum rainfall may also occur but with lower probability of occurrence. There are urban and agricultural areas have been hit several times by floods, which indicate that demand immediate action by the State, the Communities and the municipalities to achieve more effective action plan, to avoid life unless and more protective to the people of the economic damage caused by floods.
As measures against flood have been carried out by different institutions in the country, but the number of works and the level of investment is still insufficient and therefore require a higher degree of carrying them. During the month of September 2009 in Spain have been affected by local flooding dozens of villages and cities, causing great economic losses, and three people swept away by heavy rains, which indicates the low efficiency of flood control by inadequate drainage.
The flood control in urban areas is not only a problem of Spain, but it also occurs with great intensity in different regions of Europe, America, Asia, Africa and Oceania, where flooding cause major damage and human losses, the problems to solve reflect a common factor that is necessary special hydraulic engineering projects that require huge investments and state aid to prioritize a plan of action to reduce flood damage to a minimum.