Arjo Dedessa Irrigation Project Feasibility Study Summary
Project: Arjo Dedessa Irrigation Project
Location: Ethiopia
Report Date: May 2007
Prepared by: Water Works Design & Supervision Enterprise in association with Intercontinental Consultants and Technocrats India Pvt. Ltd.
Report Structure
The feasibility study report is organized into five main volumes:
- Volume I: Survey and Investigation (including geological and geotechnical studies)
- Volume II: Natural Resources (forestry, energy, catchment development)
- Volume III: Water Resources (hydrological studies, dam design, irrigation systems)
- Volume IV: Agriculture (soil survey, land evaluation, agricultural planning)
- Volume V: Environmental and Socio-Economic Aspects
Key Geological and Geotechnical Findings
The document focuses primarily on the geological and geotechnical investigations conducted for the project.
Borehole Investigations
Multiple boreholes were drilled at key locations including:
- Dam axis (AD1-AD7)
- Original spillway (ADSP)
- Saddle dam axis (ADS-1, ADS-2)
- Quarry site (ADQ-1)
Field Tests Conducted
| Test Type | Purpose | Key Findings |
|---|---|---|
| Lugeon Tests | Measure rock permeability | Variable permeability values ranging from 0-42 Lugeons depending on location and depth |
| Variable Head Permeability Tests | Measure soil permeability | Permeability coefficients ranging from 1.47×10⁻⁴ to 5.53×10⁻⁴ cm/sec |
Discontinuity Analysis
The report includes detailed discontinuity analysis of rock cores, documenting:
- Joint types (incipient joints, bedding plane joints, etc.)
- Angles with core axis
- Surface characteristics (roughness, staining, weathering)
Core Box Photographs
The report contains extensive photographic documentation of core samples from all boreholes, with:
- Depth intervals clearly marked
- Samples taken for laboratory testing identified (yellow blocks)
- Core loss areas marked (red blocks)
Conclusions
The geological and geotechnical investigations provide comprehensive data for:
- Dam foundation design
- Slope stability analysis
- Seepage control measures
- Construction material selection
The permeability tests indicate generally favorable conditions for the proposed irrigation infrastructure.