BATHYMETRIC SURVEY AND ESTIMATION OF THE WATER BALANCE OF LAKE ARDIBO, NORTHERN ETHIOPIA

Abstract

Quantification of the water balance components and bathymetric survey is very crucial for sustainable management of lake waters. This paper focuses on the bathymetry and the water balance of the crater Lake Ardibo, recently utilized for irrigation. The bathymetric map of the lake is established at a contour interval of 10 meters based on depth measurements at 176 points. The depth-area relationship shows that only less than 25 percent of the area is greater than 50 meters deep. The maximum-recorded depth is 62.4 m. Input from direct rainfall and evaporation are the most important components of the water balance of the lake. The annual input from rainfall and inflow from surface runoff is 18.43 and 5.53 million cubic meters, respectively. The average annual open water evaporation, estimated from Colorado Class-A Pan records and Penman modified method is 23.49 million cubic meters. The net groundwater flux estimated as a residual of the other water balance components is -5.03 million cubic meters, indicating that groundwater outflow is greater than groundwater inflow. The recent abstraction for irrigation appears to affect the water balance and lead to grave environmental consequences on the fragile lacustrine ecosystem.