Beko-Abo Multipurpose Project Pre-Feasibility Study: Hydrology, Floods and Sediment Transport
Executive Summary
This report presents the hydrological investigations for the Beko-Abo Multipurpose Project on the Abay River (Blue Nile) in Ethiopia. The study covers hydrology, flood analysis, and sediment transport to support project design and evaluation.
Key Findings:
- Catchment Area: 93,490 km² at dam site (elevation 790m)
- Mean Annual Rainfall: 1,295 mm (catchment), 1,000 mm (site)
- Mean Annual Inflow: 753 m³/s (range: 459-1,132 m³/s)
- Design Floods:
- 20-year: 12,030 m³/s
- 100-year: 15,720 m³/s
- 1,000-year: 20,950 m³/s
- PMF: 31,000 m³/s
- Sediment Transport: 2,250 Ton/km²-year, leading to 10,950 Mm³ storage loss after 50 years
Main Report Sections
1. Introduction
Outlines the objectives and scope of hydrological investigations for the project, which will influence both upstream and downstream areas including Sudan and Egypt.
2. Project Area Description
Details the Blue Nile basin characteristics, including:
- 14 sub-basins covering 177,000 km²
- Elevation range from 500m to 4,230m
- Climate zones and rainfall patterns
3. Hydrometeorological Database
Compiles data from:
- 57 rainfall stations
- 12 meteorological stations
- 35 streamflow stations
- 12 sediment monitoring stations
4. Field Work and Measurement Program
Describes field activities including:
- Station inspections and installations
- Meteorological station setup
- Hydrometric station completion
- Cableway installation plans
5. Rainfall and Streamflow Analysis
Analyzes 50-year data series (1954-2003) showing:
- Mean annual runoff of 254 mm
- 80% of flow occurs July-October
- Identified wet/dry periods and trends
6. Hydrometeorological Parameters
Derives key design parameters including:
- Net reservoir evaporation losses (740-760 mm/year)
- Inflow series adjusted for Tana-Beles scheme impacts
7. Flood Study
Comprehensive flood analysis including:
- Frequency analysis of maximum daily floods
- Regional flood relationships
- Peak flood hydrograph analysis
- Probable Maximum Flood (PMF) estimation
- Design flood hydrographs for various return periods
8. Sediment Transport and Reservoir Sedimentation
Analysis of sediment data showing:
- High sediment concentrations (up to 25,632 mg/l)
- Specific sediment yield of 2,250 Ton/km²-year
- Reservoir sedimentation projections for different dam heights
- 14.9-56.4% active storage loss after 50 years depending on configuration
Conclusions and Recommendations
- The study provides comprehensive hydrological data for pre-feasibility design
- Higher dams show better long-term sustainability due to greater sediment retention capacity
- Continued monitoring and data collection recommended, especially for sediment transport
- Field measurement programs should be completed as planned