Beko-Abo Multipurpose Project Pre-Feasibility Study
Hydrology, Floods and Sediment Transport Summary
Project Location: Abay (Blue Nile) River, Ethiopia
Dam Site Elevation: 790 m.a.s.l.
Catchment Area: 93,490 km²
Report Date: May 2013
Prepared by: NORPLAN, NORCONSULT, EDF, SCOTT WILSON JV in association with Shebelle Consult and Tropics Consulting Engineers
Dam Site Elevation: 790 m.a.s.l.
Catchment Area: 93,490 km²
Report Date: May 2013
Prepared by: NORPLAN, NORCONSULT, EDF, SCOTT WILSON JV in association with Shebelle Consult and Tropics Consulting Engineers
1. Key Hydrological Parameters
| Parameter | Value | Unit |
|---|---|---|
| Mean Annual Rainfall (catchment) | 1,295 | mm/year |
| Mean Annual Rainfall (site) | 1,000 | mm/year |
| Mean Annual Inflow (pre-Beles) | 753 | m³/s |
| Driest Year Flow (1972) | 459 | m³/s |
| Wettest Year Flow (1998) | 1,132 | m³/s |
| Mean Annual Runoff | 254 | mm/year |
2. Design Floods
| Return Period | Peak Discharge | Unit |
|---|---|---|
| 20-year | 12,030 | m³/s |
| 100-year | 15,720 | m³/s |
| 1,000-year | 20,950 | m³/s |
| Probable Maximum Flood (PMF) | 31,000 | m³/s |
3. Sedimentation
| Parameter | Value | Unit |
|---|---|---|
| Specific sediment yield | 2,250 | Ton/km²-year |
| Annual sediment inflow | 255 | MT/year |
| Reservoir storage loss after 50 years (high dam) | 10,950 (14.9% active storage) | Mm³ (%) |
4. Key Findings
Hydrology
- The Abay River exhibits a mono-modal flow pattern with about 80% of annual flow occurring July-October
- Base period analysis (1954-2003) shows mean annual flow at Kessie station of 517 m³/s
- Significant flow regulation occurs from Lake Tana (regulated outflow ~97 m³/s) and Tana-Beles scheme (diversion ~77 m³/s)
Flood Analysis
- Flood frequency analysis based on 48 years of maximum daily data at Kessie station
- Peak/day adjustment factor of 1.24 applied to convert daily to instantaneous peaks
- Design flood hydrographs developed for various return periods up to PMF
Sediment Transport
- Recent measurements (2009 campaign) show high sediment concentrations (up to 25,632 mg/l)
- Specific sediment yield estimated at 2,250 Ton/km²-year, higher than previous studies
- Higher dams show advantage for long-term sediment management (14.9% active storage loss vs 56.4% for lower alternatives after 50 years)
Field Measurements
- Key stations at Kessie Bridge and Bure Bridge (near dam site) established
- Measurement campaigns conducted in 2008-2010
- Plans for permanent meteorological and hydrometric stations at Bure Bridge site
5. Recommendations
- Continued sediment monitoring program needed for feasibility studies
- Higher dam alternatives recommended for better sediment management
- Completion of permanent hydrometric station at Bure Bridge
- Additional field measurements during various flow conditions