Engineering geological evaluation of Bowa Dayole dam site, North Shewa Zone, Oromia, Ethiopia

Area of Science:

• Geotechnical Engineering
• Engineering Geology
• Hydrogeology

Background:

• Developing nations like Ethiopia face food and water scarcity due to climate variability.
• The Bowa Dayole dam project aims to improve agricultural irrigation and alleviate water shortages.
• Complex geological conditions at the dam site pose significant engineering challenges.

Purpose of the Study:

• To conduct a comprehensive engineering geological evaluation of the Bowa Dayole dam site and reservoir area.
• To assess the suitability of foundation and abutment rocks for the proposed masonry gravity dam.
• To identify and propose mitigation measures for geological challenges impacting dam stability and performance.

Main Methods:

• Geological mapping and discontinuity surveying to characterize site geology.
• Core drilling and laboratory testing (e.g., Point Load Index Test) for rock strength assessment.
• In-situ permeability (packer) tests and bearing capacity analysis to evaluate foundation conditions.

Main Results:

• The dam foundation comprises fractured aphanitic basaltic rock and weak tuff, exhibiting a wide range of unconfined compressive strengths (0.16–146.88 MPa).
• Rock mass quality varied from poor to excellent (Rock Quality Designation), with low hydraulic conductivity (<1 Lu) suggesting minimal leakage risk.
• Allowable bearing capacities varied significantly, with tuff rock (0.037–0.11 MPa) posing lower capacity than basaltic rock (0.1–18.86 MPa).

Conclusions:

• The dam site presents complex geological conditions requiring careful engineering considerations.
• While the tuff unit has poor bearing capacity, uniform settlement can be managed through even load distribution by basaltic rock and robust foundation design.
• The Bowa Dayole dam project is feasible with appropriate engineering geological mitigation strategies to ensure long-term stability and functionality.