Dabus Irrigation Development Project Feasibility Study
Project Overview
The Dabus Irrigation Development Project is located in Benishangul Gumz National Regional State, Ethiopia, about 725 km from Addis Ababa. The project aims to develop an efficient irrigation system covering approximately 10,580 hectares (gravity option) or 10,235 hectares (pump option) using water from the Dabus River.
Key Components
1. Water Abstraction Options
| Option | Description | Key Features |
|---|---|---|
| Diversion Weir (Option 1) | Weir at Site 2 with 12km idle canal | Requires siphon across river, multiple cross-drainage structures |
| Diversion Weir (Option 2) | Weir at Site 3 without idle canal | More direct connection to command area |
| Pumping (Option 3) | 12 pumping stations along river | 102 pumps (63 left bank, 39 right bank), no main canals |
2. Irrigation System Design
The project proposes a surface irrigation (furrow) system with the following components:
- Gravity System:
- Main canals (left and right bank)
- 20 Secondary canals (8 right, 12 left)
- 84 Tertiary canals
- 931 Quaternary canals
- Pump System:
- 12 pumping stations (7 left, 5 right)
- 27 Tertiary canals
- 586 Quaternary canals
3. Technical Specifications
Furrow Irrigation Parameters
- Depth: 0.3m
- Width: 0.15m
- Average length: 100m
- Spacing: 1m
- Slope: 0.005m/m
- Stream size: 5 l/s
Water Requirements
- Gross duty: 2.80 l/s/ha (12hr irrigation)
- Peak irrigation requirement: 15.4m³/sec
- River has 20% excess flow during dry season
4. Drainage System
The project includes comprehensive drainage with:
- 22 Interceptor Drains (12 left, 10 right)
- 16 Cross-drainage structures (culverts and siphons)
- Designed for 1 in 5 year rainfall events
- Drainage duty: 2.97 l/s/ha
5. Night Storage Ponds (NSP)
17 NSPs are proposed to store water during nighttime with:
- Capacities ranging from 2,635m³ to 45,860m³
- 1.2mm thick Geo membrane lining
- 0.5m freeboard above maximum water level
Cost Comparison
| Option | Irrigation System Cost (ETB) | Headwork Cost (ETB) | Total Cost (ETB) | Cost per ha (ETB/ha) |
|---|---|---|---|---|
| Site II Diversion + Gravity | 3,371,188,460 | 1,257,743,084 | 4,628,931,544 | 437,517 |
| Site III Rock & Shell Fill Dam + Gravity | 3,371,188,460 | 1,178,261,597 | 4,549,450,057 | 430,005 |
| Pump Option | 1,813,946,042 | 3,714,944,711 | 5,528,890,753 | 540,195 |
Recommended Option
The study recommends the Rock & Shell Fill Dam with Chute Spillway (clay central core) combined with Gravity Irrigation as the most cost-effective solution at 430,005 ETB/ha, with a total project cost of 4,549,450,057 ETB.
Project Benefits
- Development of 10,580 hectares of irrigable land
- Improved agricultural productivity in the region
- Water resource utilization from the Dabus River
- Employment opportunities during construction and operation