Baro-Akobo River Basin Hydrology Summary
Document: Final Report, Annex 1 (Water Resources), Part 2 - Hydrology
Prepared by: TAMS (New York) and ULG Consultants Ltd (UK)
Date: May 1997
For: Federal Democratic Republic of Ethiopia, Ministry of Water Resources
1. Basin Overview
- Location: Southwest Ethiopia (5Ā°31'-16Ā°54'N, 33Ā°-36Ā°17'E)
- Size: 76,000 kmĀ² (4th largest basin in Ethiopia)
- Climate: Single monsoon wet season (May/June-September/October)
- Rainfall: 900-2,400 mm/year (higher at elevations >2000 masl)
- Major Rivers: Baro, Akobo, Alwero, Gilo, Birbir, Geba, Sor
- Mean Annual Flow: ~23 billion mĀ³ at border with Sudan
- Contribution to Nile: 8% of total yield at Aswan High Dam
2. Key Hydrological Findings
River Flow Characteristics
- Peak flows typically in August-September
- Minimum flows December-April
- Most rivers perennial (some smaller courses dry seasonally)
Hydrometric Network
| Station | Catchment Area (kmĀ²) | Mean Annual Runoff (MCM) |
|---|---|---|
| Baro at Gambela | 23,461 | 11,718 |
| Baro at Itang | 24,636 | 12,296 |
| Gilo near Pugnido | 10,137 | 2,338 |
| Alwero at Abobo | 2,800 | 557 |
| Birbir near Yubdo | 1,563 | 1,825 |
Data Challenges and Methodology
- Data gaps in hydrometric records (only 54% of expected data available)
- Used statistical methods to infill missing data:
- Linear regression
- Patching Model (Pegram, 1985)
- Zucchini-Hiemstra Stochastic Model
- Rainfall-runoff relationships established (1-month lag at Gambela)
3. Comparison with Previous Studies
The study found that previous Russian studies tended to overestimate Mean Annual Runoff (MAR), while ARDCO-GEOSERV studies underestimated MAR. This study provides revised estimates based on more comprehensive data analysis.
4. Key Tables and Appendices
The report contains detailed tables and appendices including:
- Hydrometric station details and statistics
- Correlation coefficients between stations
- Observed and infilled flow data
- Monthly and yearly flow analyses
- Stochastic model results
- Flow duration curves
5. Significance
This hydrology study forms a crucial component of the Baro-Akobo River Basin Integrated Development Master Plan, providing the water resources foundation for future development projects including irrigation, hydropower, and water supply infrastructure.