Hydrological modelling of Lake Tana to establish a water budget and to optimise water allocation

An increasing number of water resource development projects (mainly hydropower and irrigation) take place near Lake Tana and in its catchment (Northern Ethiopian highlands). These interventions certainly impact on the lake water balance. In addition, previous studies indicate that the hydrology of Lake Tana is not fully defined. Outflows at the Chara Chara outlet are known, inflows from rainfall and contributing rivers and evaporation rates are not accurately known. Moreover, comprehensive studies that consider the available water, the different abstractions and losses in the system and simulate the impacts on the lake and point out optimal water allocations are not validated. To fill these gaps, this research aims at developing a hydrological model to better understand hydrological processes, determine the water budgets of the lake and eventually launch a decision support system for the optimal water allocation. In addition to the existing rainfall and discharge monitoring stations in the catchment, additional stations will be established. Using these data and remote sensing means (satellite imagery, TRMM data), areal rainfall, evapotranspiration and evaporation elements of the water balance terms will be determined; for the hydrologic model developed, model parameters will be calibrated automatically and validated. Knowing the different water abstractions and results of the hydrologic model, simulations of the lake level fluctuations and accompanying impacts will be investigated under different scenarios. Using the river/reservoir system model, optimal water allocation and supply reliability under selected appropriate water uses will be defined. Preliminary results of this research will be presented at the Water2011 conference