Modeling on naturalization of inflow and outflow nutrients sources of Blue Nile River at the Lake Tana in Basaltic Plate
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ORIGINAL ARTICLE
Modeling on naturalization of inflow and outflow nutrients sources of Blue Nile River at the Lake Tana in Basaltic Plateau of Ethiopia Asimamaw Nigusie Asitatikie1 · Endalkachew Diress Nigussie2 Received: 20 March 2020 / Accepted: 5 September 2020 © The Author(s) 2020
Abstract Lake Tana is the largest natural reservoir in Ethiopia and the head water of Abbay basin. However, after building of an irrigation weir and further lying Tunnel to Tana Belles, Lake Tana maximum amplitude of water level canges from 2.18 to 3.56 m that differ substantially in 1.38 m from amplitude of natural water level fluctuation. Understanding the natural characteristics of the Lake is important to know its water balance and for sustainable development. But it is difficult to study the natural characteristics of the Lake and its water balance using the regulated water level and outflow data sets. Thus it is evident that the regulated water level and outflow data sets have to be first naturalized before they are used for any analysis and modeling. Lake level and outflow data that have been collected since 1976 were considered to assess the regulation effect and then for naturalization. Inflows to the Lake from the main tributaries have also been collected to find if there are any correlations with either the Lake Level and/or the outflow. Regression analyses were used to develop the naturalization models. The regression analyses of flows from Gilgel Abay and Gummar with Lake Level shows that there is a very good correlation between them in different seasons. Besides, same has also been observed between Lake Level and out flow. These relationships can be used to naturalize the regulated outflow and water level. Keywords Naturalization · Lake Tana · Regulated lake level · Regulated outflow
Introduction Lakes are one of humanity’s most important resources; often viewed as highly productive biological systems (Sewunet 2011). Anybody who has lived near a Lake can observe the phenomenon of Lake level fluctuation which is characterized by higher water Level during the spring and the last summer season and lower water levels during the autumn season. Such fluctuations are the results of several natural factors but also human activities. The primary the natural factors affecting Lake Levels are amounts of water inflow by rainfall, river inflow, ground water discharge to Lake, the surface and * Asimamaw Nigusie Asitatikie [email protected] Endalkachew Diress Nigussie [email protected] 1
Department of Hydraulic and Water Resources Engineering, Debre Tabor University, Debre Tabor, Ethiopia
Department of Engineering Hydrology, Amhara Design and Supervision Works Enterprise, Bahir Dar, Ethiopia
2
sub-surface runoff, etc., and outflow by evaporation, river outflow. Major influential human factors which affects the Lake level are diversion of water into and out of the basin for the irrigation and other purposes, regulation of outflow and dredging of outlet Tunnels for generation of hydropower. For this purpose the
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