Water Distribution Systems MCQ with answer and solution

Concept

Hazen-Williams equation in distribution networks

Formula

h_f = (10.67 × L × Q^1.852) / (C^1.852 × D^4.87)

Step-by-step solution

1. Hardy Cross iteratively balances head loss around loops using h_f = r × Qⁿ. 2. In water distribution engineering, the Hazen-Williams formula is universally used. 3. Its roughness coefficient C is independent of Reynolds number over typical municipal water velocities. 4. Therefore, the Hazen-Williams equation is the standard formulation used. Answer: A

Explanation

In municipal water distribution network design, the Hazen-Williams equation is the most widely adopted empirical formulation in the Hardy Cross method. Its roughness coefficient C remains practically constant across normal turbulent flow velocities in water mains, simplifying iterative loop flow corrections.

Why the other options are wrong

B) Bernoulli's equation is a broad energy conservation equation, not an empirical head loss equation for pipe loops. C) Euler's equation governs inviscid streamline motion. D) Stokes' law calculates particle settling velocity in viscous fluids.

Shortcut

Water supply Hardy Cross = Hazen-Williams equation (flow exponent n = 1.852).

Common mistake

Confusing pipe friction formulas with general energy equations (Bernoulli/Euler) or settling laws (Stokes).