Floodplains and flooding risk prevention
Today, climate change manifests itself with an increase in extreme weather events such as floods. In May 2014, a low-pressure cyclone affected a large area of Southeast and Central Europe, causing floods and landslides (e.g., along the River Sava). Serbia and Bosnia and Herzegovina suffered the greatest damages. In Serbia alone, there were over 50 fatalities, roughly 32 000 people were evacuated, and over 1.5 million people were affected (Pavlović, 2014).
Since structural measures set up to protect property and goods from the effects of catastrophic floods are costly and not infallible, we have to think of other natural cost-effective defenses that offer more efficient and long-lasting sustainable solutions to flood hazards.
It is widely recognized that wetlands in general and floodplains in particular play an important role in the hydrological cycle, influencing groundwater recharge, low flows, evaporation and floods. This has led to policies being formulated worldwide to conserve and manage wetlands to deliver these key services, especially flood risk reduction.
The Parties to the Ramsar Convention, in its Resolution X.24 on Climate change and wetlands, ‘’RECOGNIZE that the wise use and restoration of wetlands contributes to building the resilience of human populations to climate change impacts and can attenuate natural disasters expected with climate change, such as the use of restored floodplain wetlands to reduce risks from flooding.’’
Ecological importance and services of floodplains
Floodplains have an important role in flood risk management by modifying the river discharge and protecting societies and economic activities from damage. Floodplains are also very heterogeneous habitats that create favourable conditions for many species and, thus, have a high environmental value.
When their natural habitats are preserved, floodplains play important flood control roles in different situations:
Slowing the flow
Wetlands close to the headwaters of streams and rivers can slow down rainwater runoff and spring snowmelt. This can help prevent sudden, damaging floods downstream.
Flood storage reservoirs
The floodplains of major rivers act as natural storage reservoirs, enabling excess water to spread out over large surfaces and thus reducing the velocity of flow. By draining floodplains and turning them into urban settlements or cultivated land, these surfaces of expansion of the surplus water are reduced, the velocity of surface flow increases and the damage caused by the floods become more and more important.
Floodplains under danger
Particularly during the past 100 years, huge areas of floodplain have been drained and cut off from their rivers by artificial embankments (termed bunds, dykes or levees in different countries). This means water that used to spread out slowly and relatively shallowly across broad floodplains is now concentrated into ever-smaller areas. Moreover, these areas have been developed especially for agriculture but above all for allowing the populations to settle there. As a result, floods are deeper and more likely to cause more damaging – sometimes catastrophic – impacts if and when artificial flood banks are breached.
Nowadays floodplain areas are reduced in size or no longer function as active floodplains, thereby impacting on the delivery of environmental services to local and regional communities and economies.
The preservation and restoration of wetlands are solutions that reduce the intensity of floods and the damage they cause. The protection or restoration of floodplains has proved to be more effective against flooding than dykes in many cases. These “natural infrastructures” may, in some cases, replace artificial infrastructures or be combined with them.
Floodplain management and restoration
Floodplain management and restoration are not only about reducing flood risk but also about promoting environmental, societal and economic benefits. Sustainable flood risk management combines elements to:
- reduce the exposure to flooding;
- lessen the vulnerability of people and property;
- execute a sensible management of land and the environment; and
- improve warning systems by setting up early warning systems with local populations.
Floodplain restoration is an important measure which gives more room to rivers, develops ecological beneficial hydrological regimes and enhances floodplain and wetland habitats.
Monitoring and observing environmental factors that signal the onset of a hazard are fundamental to early warning systems. Such systems generally include a mix of spatial remote sensing observations and in-situ monitoring.
Mapping hazard risk and exposure is another function of environmental monitoring. Most environmental management agencies carry the responsibility of providing some mapping services for risk management, as these bodies usually hold the necessary databases for the preparation and dissemination of such information.
A natural flood defense is an area in which a specific set of measures have been taken to reduce flood risk and at the same time support or enhance natural floodplain functioning. Natural flood risk reduction measures are non-technical measures that contribute to the restoration of the characteristic hydrological and geomorphological dynamics of floodplains and to ecological restoration. In general, these measures aim to enlarge the discharge and storage capacity of floodplains.
The protection of existing naturally functioning floodplain systems can also be regarded as an important natural flood risk reduction measure.