Scenario-based decision support for an integrated management of water resources

ABSTRACT

In this study, analyses of future scenarios of water demand and supply as well as an assessment of trade-offs for water allocation across the different water use sectors in the upper Blue Nile basin are made. Different periods of regulation of Lake Tana (Ethiopia) and subsequent impacts on the lake level hydrological regime are investigated. A decision support system is developed and available water supply for normal- and low-flow hydrological conditions are determined based on recorded flow data and a simple rainfall-runoff model. Different scenarios have been triggered and simulations are conducted to understand the implications of planned water resource developments in the area. We found that the annual inflows to Lake Tana under an average hydrological condition are about 5.7 × 10⁹ m³ and are estimated to reduce by about 27% when all planned water resources development projects are implemented in the catchment. These projects aim at the generation of 460 MW hydroelectric power and about a billion m³ per annum supply of water to the large-scale irrigation schemes. During low-flow conditions, supply will run short of demands and the lake water level can drop by 0.3 m from the natural outlet level (1785 m a.s.l). Lake water levels and long-term lake level fluctuations have been affected significantly due to regulation with subsequent impacts on the lake ecology. An upstream–downstream cooperation, transparency and participation in the decision making and establishment of an adequate data acquisition system are critically important elements in the management of water resources in the basin.

KEYWORDS:

• Scenario
• decision support
• Lake Tana
• water management

Acknowledgements

The authors acknowledge the efforts of the many field staff and data collectors for their help during the installation of monitoring stations and data recording. We thank the Wase-Tana project staff, particularly Deribew Fentie, Teshager Admasu and Birtukan Tamiru, and the MSc students for the logistic help and valuable field inputs. We are grateful to the Ministry of Water and Energy and National Meteorological Agency of Ethiopia for making various data available.

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

This research was supported by the Belgian Development Cooperation (VLIR-UOS).