Investigation of changes observed in the statistical characteristics of Lake Tana’s water levels after damming the outflow, Ethiopia

Lake Tana is Ethiopia’s largest natural freshwater reservoir, located at the headwaters of the Blue Nile River. Since 1996, the outflow from the lake has been regulated, and the natural state of the lake including its water level dynamics has been modified. Understanding how this change affect the lake’s morphometry and its water level statistical characteristics is critically important for protecting aquatic ecosystems and determining the best use of freshwater resources. The results indicate that the regulation has changed the normality distribution nature of the lake water level and has increased the annual mean and annual maximum water levels by 0.25 m and 0.35 m, respectively. The range of the lake’s water level has been increased by 1.33 m. The regulation has significantly changed the statistical characteristics of the lake’s water levels. All these changes have potential impact on estimates of the lake’s water balance, its morphometric and ecosystem characteristics.