Environmental Analysis of the Areal Expansion and Lake Level Rise of Lake Beseka, Main Ethiopian Rift
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Date
2007-03-02
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Addis Ababa University
Abstract
Lake Beseka has been drastically expanding from its original size of about 3Km2 (in the year 1964) to its current size of 41 km2 (in the year 2006) in the last four decades. Equally, the lake level has been rising at an average annual increment rate of 0.28m.
The expansion of the lake has imposed several impacts on the social and natural environment of the surrounding area. The continuing rise of the lake level resulted in inundation of valuable grazing and farmland and watering points. Further rise could result in a complete inundation of the road and railway line passing nearby and substantial amount of the farm and grazing land in the vicinity. The ultimate increase in size of the lake may lead to the spillover of lake water into the river Awash, which due to the highly alkaline and saline nature of the former may affect the hydrochemistry of the river and the ecosystems down stream.
This work addresses the areal expansion and lake level rise of Lake Beseka using an environmental analysis approach where water balance modeling and land use/land cover classifications and change detection analysis were employed.
The water balance modeling revealed that surface water sources are not significant contributors to the lake level rise; rather sub-surface inflow, which includes spring discharges and deep groundwater sources are significantly affecting the lake level.
Land use/land cover (LU/LC) change detection between the years 1973 and 1986 and between 1986 and 2003 were conducted, with the objective of creation of historical and current LU/LC maps and LU/LC change map of 1973, 1986 and 2003. The maps were derived utilizing standardized digital remote sensing classification techniques using three multi temporal Land sat scenes acquired on January 12, 1973 (MSS), January 28, 1986 (TM), and January 27, 2003 (ETM+).
The change detection analysis revealed that the lake body has increased by 21.82 km2 (301.301%) between 1973 and 1986, and by 9.86 km2 (33.938%) between 1986 and 2003. Between 1973 and 2003, the lake has expanded by about 31.68 km2 (335%).
The land use/land cover of the area significantly changed in the last three decades. This change has a direct effect on the expansion of the lake. Vegetation cover (shrub land) had been reduced by 65.41 km2 (30%). This in turn affects the runoff yielded from the catchment entering in to the lake. Unlike vegetation cover, degraded land had increased by 33.28 km2 (89.575%), which increases runoff entering in to the lake. Irrigation farmland which increased by about 13.63 km2 (5 7.411%). Water for irrigation is brought from Awash River that in turn is an input to the inflow of the lake; this has a great effect on areal expansion of the lake. The above result indicated that the land use/land cover change of the area has an additive effect on the lake’s areal expansion.
LU/LC changes in the area are still intensified due to areal expansion of the Lake, population pressure, and unwise intervention of man with the environment (including unsatisfactory Irrigation Practices). Conservation of the natural resource, rehabilitation and management of the environment through land terracing and vegetating with productive plants are the envisage possible strategies that have to be taken to combat the existing and future adverse LU/LC changes that are associated with areal expansion of the Lake.
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Keywords
Environmental, Analysis of the Areal Expansion, Lake Level Rise, Lake Beseka, Main Ethiopian Rift