Erer Irrigation Project Feasibility Study - Summary
Project Overview
The document presents the feasibility study for the Erer Irrigation Project in Ethiopia, focusing on planning and design criteria for the dam, spillway, and irrigation system.
Key Components
1. Erer Dam Design
- Type: Zoned earthfill dam with central impervious core
- Height: Approximately 31m above river bed
- Crest Width: 9m
- Slope Protection: Dumped rock riprap upstream, hand-placed riprap downstream
- Seepage Control: Cutoff trench, chimney drain, horizontal filter, rock toe
- Stability Analysis: Considered for various loading conditions including seismic
2. Spillway Design
- Type: Chute spillway with Ogee crest (ungated)
- Location: Left bank of the river
- Design Flood: 10,000-year return period flood
- Components: Approach channel, Ogee weir, inclined chute, stilling basin
3. Irrigation System
- System Layout: Primary, secondary, tertiary, and quaternary canals
- Irrigation Methods: Border, check basin, and furrow irrigation
- Design Efficiency: 55% overall efficiency proposed
- Canal Design: Using Manning's formula, considering non-scouring/non-silting velocities
4. Agricultural Planning
- Cropping Seasons: Belg (February-June) and Meher (July-November)
- Proposed Crops: Maize, groundnut, rice, mango, onion, tomato, sweet potato, potato
- Minor Crops: Sorghum, haricot beans, sugarcane, fodder crops, papaya, guava, citrus
Key Tables
Permissible Velocities in Canals
| Channel Bed Materials | Permissible Velocity (m/s) |
|---|---|
| Very light loose sand | 0.30-0.60 |
| Sandy loam, black cotton soil | 0.60-0.90 |
| Firm loam, alluvial soil | 0.90-1.10 |
| Hard clay or grit | 1.0-1.20 |
Irrigation Efficiency Estimation
| Efficiency Component | Unlined Canals | Lined Canals |
|---|---|---|
| Water conveyance | 0.60-0.65 | 0.75-0.85 |
| Operational | 0.85 | 0.90 |
| Field application | 0.70-0.75 | 0.70-0.75 |
| Overall efficiency | 36-41% | 47-57% |
Conclusion
The feasibility study provides comprehensive design criteria for the Erer Irrigation Project, covering dam construction, spillway design, irrigation system layout, and agricultural planning. The proposed zoned earthfill dam with appropriate seepage control measures and the designed irrigation system aim to optimize water use efficiency while considering local climatic conditions and agricultural practices.