For the time being, the analysis is only based on a bibliographic study, as the MWO indicator has yet to be developed and specific metrics selected.
Wetlands play a major role in the regulation of water flow, attenuating both the number and the intensity (peak) of extreme events like floods and droughts. Using the natural capacity of wetlands to attenuate floods is another complementary, cost-effective way to reduce flooding risks. This is especially the case for wetlands located in floodplains as they provide ideal areas for retaining floods and for balancing the water regime, e.g. during low-flow conditions or during summer droughts.
Indeed most of the wetlands act like sponges: they store water during wet periods and often provide a reserve of water during dry periods. The storage role of wetlands is mainly due to their low topographic location (floodplains, depressions, etc.). Their vegetation serves as a buffer to decrease wave energy and allows the redistribution of water.
Wetlands also help prevent water logging in agricultural, industrial and urban lands. Finally, this regulatory service has proven efficient to limit the human and physical damages during flooding periods, and to be an inexpensive natural means of water regulation, compared to artificial protection and reconstruction structures that usually involve high costs.
There is increasing evidences that generalizations about the role of wetlands in flood and drought control are not applicable in all hydrological contexts. A specific, case-by-case approach is therefore required for understanding the local hydrological and ecological systems.
Example: partial restoration of Fetzara lake in Algeria
Fetzaralake in North-East Algeria consists of a shallow, seasonally flooded depression in the flood-plain of the Oued Seybouse. In the nineteenth century there was a large freshwater lake on the site, regarded as ‘one of the great freshwater lakes of the Maghreb’ and the site with the richest concentrations of breeding waterbirds anywhere in Algeria.
It was drained in 1937 for agricultural purposes although it was a key-element for water storage in the catchments. In the 1980s, heavy floods caused severe damage downstream. After this event, it was decided to recreate the functional role of the wetlands, by closing the sluice gate of the drainage canal in winter so as to retain rainwater. The stored water is then released progressively during spring and summer. This management also allows springtime irrigation and substantial grazing during the summer months, since the soil remains humid. The Fetzara lake is now listed as a wetland of international importance under the Ramsar Convention.
The current hydrological management is considered to be a good example of the wise use of wetlands with the potential to return the site to its former status as one of the most important wetlands in North Africa. But the value of the reinstated wetland for breeding birds is less clear. It might prove necessary to adapt the hydrological regime to stop the lake drying out completely in the summer months before Fetzara lake can once again become a regular breeding site for waterbirds.
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