Amibara Drainage Project Phase-II Summary
Project Overview
The Amibara Drainage Project Phase-II is a major infrastructure initiative by the Government of Ethiopia's Ministry of Water Resources, designed to address drainage problems in the region. The project involves detailed designs for various structures including outfall systems, pumping stations, cross-drainage structures, and road bridges.
International consultants Water and Power Consultancy Services (India) Ltd. prepared the technical documentation, following Indian Standard Codes with references to American and British engineering standards.
Key Structures
1. Outfall Structure
The primary drainage outlet for Main Drain MD2, designed to discharge into the Awash River. Two alternatives were considered:
- Gravity outfall at Ch. 21300m - Preferred option as it's more technically sound and economically viable
- Pumping station at Ch. 9550m - More expensive to construct and maintain
| Design Parameter | Value |
|---|---|
| Normal discharge | 3.55 m³/sec |
| 20-year flood discharge | 24.0 m³/sec |
| Bed level of drain | 716.20 m |
| High flood level (50-year) | 721.017 m |
2. Pumping Station (Alternative Design)
A study was conducted for a pumping station as an alternative to gravity drainage, but it was determined to be less favorable due to:
- High construction and operational costs
- Need for trained personnel and reliable electricity
- Complex maintenance requirements
The cost analysis showed the pumping scheme would be significantly more expensive (151 million Birr) compared to the gravity system (97.79 million Birr).
3. Cross-Drainage Structures
Key crossings designed in the project:
- MD1 and MD2 crossing - RCC box structure to carry MD2 below MD1
- MD2 and Angolele Pasture Irrigation Pump Canal - RCC conduit with wing walls
4. Road Bridges
Seven new bridges proposed over MD2 at various chainages to maintain village connectivity. Designed as single-lane RCC structures with masonry substructures.
Design Features
- Use of reinforced concrete boxes instead of pipes for larger structures
- Consideration of local materials (boulders, earth) where possible
- Hydraulic designs following Khosla's theory for pressure calculations
- Structural designs per Indian Standard codes (IS:456-1978, IRC:6-1966)
- Load considerations for vehicular traffic (IRC Class A)
Conclusion
The gravity outfall structure at Ch. 21300m was recommended as the optimal solution due to its:
- Lower construction and maintenance costs
- Reliable operation without need for external power
- Minimal operational requirements
- Long-term trouble-free service
The project emphasizes using locally available materials and designs that accommodate future development while solving current drainage issues in the Amibara region.