Hydraulics, Water Supply, and Sanitary Systems
Core concepts
Understand fluid properties, continuity, Bernoulli and energy equations, friction losses (Darcy-Weisbach, Hazen-Williams), minor losses, and open-channel flow (Manning's equation). Know water supply design (demand, pressure, storage), pipe sizing, and sanitary drainage (fixture units, slope, venting).
Common traps
- Bernoulli vs. energy equation: include head losses and pump head in the energy equation; Bernoulli alone assumes no losses.
- Friction factor: depends on Reynolds number and relative roughness; laminar vs. turbulent regimes differ.
- Manning's equation: hydraulic radius = area / wetted perimeter, not diameter.
- Drainage slope: too flat causes solids to settle; too steep causes water to outrun solids.
Worked rule of thumb
For pipe flow, continuity gives Q = A·V. Energy equation: P1/γ + V1²/2g + z1 = P2/γ + V2²/2g + z2 + hL − hpump. For open channels, Manning: V = (1/n)·R^(2/3)·S^(1/2). A quick check - doubling diameter at the same slope greatly increases capacity because both area and hydraulic radius grow.
Always confirm units: head in meters, flow in cubic meters per second, and slope dimensionless.