Amibara Irrigation Project II - Drainage and Salinity Study
Document Summary
Basic Information
Project: Amibara Irrigation Project II
Report Title: Drainage and Salinity Study
Date: January 1982
Prepared by: Sir William Halcrow & Partners
Study Area: Melka Sadi Farm (4,200ha in Middle Awash valley)
Key Findings
- About 1/3 of Melka Sadi Farm area abandoned due to salinity and rising water tables
- Existing drainage system inadequate, leading to water table rise and soil salinization
- Excessive irrigation (minimum 60cm/year above crop needs) major contributor to problems
- Two aquifer systems identified: deep confined aquifers and shallow alluvial aquifers
- Banana (main crop) has low salt tolerance (EC >0.78 mmhos/cm becomes toxic)
Soil Characteristics
Soil Group | Description | Location |
---|---|---|
Saline alluvial/colluvial | Medium to coarse textures with weathering tuffs and clays | Southeast area |
Non-saline alluvium | Medium and fine textured with stratified profiles | Most of Melka Sadi Farm |
Vertisols | Fine textured, variable depth (few cm to >3m) | North and western portions |
Drainage Design Recommendations
- Proposed system to lower water table to 1.8m (1.5m where permeable layer is shallow)
- Five-phase construction plan covering approximately 1,018ha
- Different drain types/spacings based on hydraulic conductivity (0.4-2.5 m/day)
- Leaching trials recommended to reclaim saline soils
- Interceptor drains proposed near canals in problematic areas
Implementation Phases
Phase | Area (ha) | Saline Area (ha) | Relative Cost/ha |
---|---|---|---|
1 | 210 | 60 | 100 |
2 | 219 | 9 | 102 |
3 | 252 | 50 | 101 |
4 | 192 | 137 | 112 |
5 | 145 | 82 | 118 |
Key Recommendations
- Implement drainage system to control water table and reverse salinization
- Conduct leaching trials in saline areas during early phases
- Monitor water table after Phase 1 implementation
- Consider growing more salt-tolerant crops (e.g., cotton) in problem areas
- Improve irrigation efficiency to reduce excess water application