Impacts of Furrow Irrigation on Shesher and Welala Natural Reservoirs of Lake Tana Sub Basin, Ethiopia

Abstract

The survey was conducted from March 2012 to March 2013 based on field observations and samples. Shesher is natural reservoir of Lake Tana found at coordinates of 0350300 and 1322162 UTM and at altitudes 1805 a.s.l. Welala natural reservoir is found at UTM coordinates of 0348348 and 1326081 with altitude of 1804 a.s.l. The area of Shesher and Welala was estimated about 500 ha and 110 ha respectively, which are impounded by open water for extended period of a year and both with maximum depth of 3 m during rainy season. Both reservoirs filled their capacity during the rainy season through the inflow river of Ribb and the surrounding flood plain. But during pick dry season of March, 2012 and March 2013 the survey showed unexpected, amazing and sudden death of a home for many biodiversity that both Shesher and Welala natural reservoirs dried up totally. Birds fetch their food from remnants small shrink wet mud spot and it is not uncommon to see remnant dead fishes eaten by birds. This is due to several and unlimited human encroachments mainly for crop cultivation, with out any rules and regulations. Major crops cultivated by drained two reservoirs using gravitational force were Eragrastis teff, Cheak pea, Grass pea, Lentils and Safflower. During dry season no one could be able found drinking water even for their animals and humans, inhabitants started digging well to fetch water from the middle of Shesher and Welala reservoirs. The drainage system was carried out at every 50 m intervals by making large furrows in both sides of two reservoirs until their water totally vanished. These reservoirs should be properly and sustainably exploited by designing appropriate interventions with out land use change, for instance it could be serve for fisheries, ecotourism and livestock sectors. ObjectiveTo evaluate the current status of Shesher and Welala natural reservoirs with respect to anthropogenic activities and able to propose possible solutions Materials and Methods Study areaThe study was conducted in the north eastern part of Lake Tana (source of the Blue Nile). The lake is the largest one (3150 km 2 ) in Ethiopia, comprising 50 % of the total freshwater resources of the country. It is a shallow lake with a mean depth of 8 m and maximum depth of 14 m, situated 1800 m above sea level. Seven large, permanent rivers and about 40 small seasonal rivers feed the lake. The trophic status of Lake Tana is oligotrophic to mesotrophic [2,3]. Shesher and Welala natural reservoirs are found just at the boundary of the lake in fogera floodplains of Fogera woreda of South Gondar zone (Figure 1). These are breeding sites mainly for Clarias gariepinus fish species but not endemic Labeobarbus species of Lake Tana [4]. Fishing activities during the breeding seasons (rainy seasons) and post rainy seasons are immense than ever, fishermen used spears and seining as fishing gear during these seasons respectively.Two natural reservoirs were assessed from March 2012 to March 2013 based on field observations and samples. Interviews with the