The depth of the impounded water in a 72 m long earthen dam is 6.2 m, while the tail water is 2.2 m deep. The hydraulic conductivity of the isotropic and homogeneous soil-fill of the dam is 0.53 m day⁻¹. Flow net method is used to estimate seepage wherein the number of flow channels is 6 and the number of potential drops is 21. The seepage rate through the dam in m³ day⁻¹ is _____.
Official Answer Key:
43.50 to 43.70
Step-by-Step Solution & Explanation
Head causing seepage, H = 6.2 − 2.2 = 4.0 m. Flow-net seepage formula (per unit length of dam) is q′ = K·H·(Nƒ/NƉ), where Nƒ = number of flow channels, NƉ = number of potential drops.
q′ = 0.53 × 4.0 × (6/21) = 0.53 × 4.0 × 0.2857 = 0.6057 m³/day per metre length.
Total seepage over the 72 m dam length: Q = q′ × L = 0.6057 × 72 = 43.61 m³/day. This lies within the accepted range 43.50–43.70.
Section 5 — Irrigation and Drainage Engineering
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