Modelling Natural and Man-Induced Hydrological Changes on Sebkhet Kelbia, Tunisia

The 120 km2 ephemeral lake at Sebkhet Kelbia, which is unique in the Maghreb by virtue of its lack of a salt crust when dry, is internationally important for wintering waterfowl. It is threatened by dams for flood control and water-supply and its volume has been reduced by 63 per cent since 1933 by a combination of sedimentation and erosion. A deterministic digital model of the monthly water and salt balance of the whole 15 000 km2 catchment for 1900 to 1975 is fitted to the limited lake level and lake salinity data, as well as other disparate observations. The lake is shown to have cycles of long periodicity which make short runs of data very unreliable. The 1930-55 historic record shows that Kelbia is dry for 31-4 per cent of the time whereas the 76 years of synthetic data generated by the model show that it is dry for only 10-2 per cent of the period. The historical records for the period of World War II are shown to be suspect. The effects of sedimentation and erosion of the sill are so great that the actual records of lake level and salinity are not an adequate reflection of conditions today. The analysis shows that the dams will exacerbate some of the effects of reduced lake volume. Future desiccation will be 2-5 times more frequent than in the past. The lake will have more spells of freshwater conditions but in aggregate they will last for 8 per cent less time. The frequency of damaging overflows from Kelbia will double. An embankment at the outflow would keep the lake in existence for as long and as fresh as before the dams were constructed. Kelbia's conservation will benefit wintering waterfowl, the fishery, flood protection for communications and tourists from nearby hotels

Archaeology · Geography · Geotechnical engineering · Hydrology (agriculture · Natural (archaeology · Physical geography · Water resource management · Environmental Science · Flood Risk Assessment and Management · Geology · Hydrology and Drought Analysis · Soil erosion and sediment transport