Water Resources and Hydraulic Engineering
Water Resources and Hydraulic Engineering tests open-channel flow, hydrology, irrigation, dams and hydraulic machines.
Core rules
- Manning: Q = (1/n) A R^(2/3) S^(1/2), where R = A/P. For a wide rectangular channel R ≈ y.
- Specific energy E = y + V²/(2g); critical flow occurs at minimum E and Fr = 1.
- A sharp-crested rectangular weir: Q = (2/3)Cd√(2g) L H^(3/2).
- Irrigation: delta in metres = 8.64B/D, where B is base period in days and D is duty in ha/cumec.
- Unit hydrograph: direct runoff volume equals 1 cm over the catchment; S-curve converts one duration to another.
- Turbine choice: Pelton for high head, Francis for medium head, Kaplan for low head and large discharge.
Worked example
A rectangular channel is 4 m wide, carries 1.5 m depth, n = 0.015 and bed slope 0.001. Find Q. A = 4×1.5 = 6 m²; P = 4 + 2×1.5 = 7 m; R = 6/7 = 0.857 m. R^(2/3) = 0.857^0.667 ≈ 0.902; S^(1/2) = 0.0316. Q = (1/0.015)(6)(0.902)(0.0316) ≈ 11.4 m³/s.
Traps
Using flow depth instead of hydraulic radius; entering slope as a percentage; adding the wrong side slopes to wetted perimeter; confusing duty with delta; taking unit hydrograph volume as more than 1 cm.