Numerical methods

for seepage

through earthen

dams analysis

Roland YONABA, Research Assistant

Presented at Cape Coast University

August, July the 19th, 2013

PRESENTATION OUTLINE

• Dams ?

• Earthen-made dams (& facts)

• Overview of the seepage phenomenon

• The research problem

• Perspectives for further research

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DAMS ?

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EARTHEN MADE DAMS

Dams made with heavily compactedearthen materials (sand, clay, silt,…)

Convenient to retain a low water height(<= 10 m)

Cheap ()

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EARTHEN DAMS FACTS (IN B.F.)

• Since 1920. Common uses

– irrigation

– water supply

– cattle watering

• Almost 2000 dams in Burkina Faso nowadays

• Quite all of them are earthen-made

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THE SEEPAGE PROBLEM

• Wet areas downstream ARE NOT naturalsprings. Usually.

• Water always follows the path of leastresistance.

–Carry material throughout the dam

–Erosion → Collapse

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EVALUATING SEEPAGE (ACTUAL METHODS)

• The hydraulic method : 𝑞 = 𝑘𝐻𝑖

• Kozeny’s parabola

𝑦0 = 𝑑2 + ℎ2 − 𝑑 𝑡ℎ𝑒𝑛 𝑞 = 𝑘𝑦0

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HOW CAN WE ACCURATELY EVALUATE SEEPAGE ?

• Numerical models solve propagative motions

• Types of numerical methods

• Finite Volumes (3D space)

• Finite Elements and Finite Differences (2Dspace)

• Why Finite Differences ?

– Fast setup for modelling

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HOW CAN WE ACCURATELY EVALUATE SEEPAGE ? (Cont’d)

• General objective

– Build a general purpose model that can predictheadline, pressure, flow distribution and evaluateseepage quantities through an earthen dam.

• Assumptions

– Soil is uncompressible and isotropic

– Flow is steady and laminar : Darcy’s Lawapplies

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ENGINEERING EXAMPLE

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ENGINEERING EXAMPLE (Cont’d)

PERSPECTIVES FOR FURTHER RESEARCH

• Benchmark (efficiency, accuracy)against FE, FV methods

• Investigate anisotropic damstructure models

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