Water & environment
Hydrology & Irrigation
5 self-contained study topics — notes, diagrams, formulas, and worked examples for exams and GATE.
Topics
- Hydrologic Cycle and PrecipitationCompute mean areal rainfall by the arithmetic, Thiessen-polygon or isohyetal method depending on gauge distribution and terrain, and use the IDF relation for design-storm intensity.
- Runoff EstimationFor a small catchment use the rational formula Q = CiA/360 with the rainfall intensity at the time of concentration; for larger design-storm estimates use the SCS curve-number method.
- Hydrograph AnalysisSeparate base flow from the total hydrograph to get direct runoff, derive the unit hydrograph (response to 1 cm of excess rainfall in duration D), then convolve it with the excess rainfall to predict a flood hydrograph.
- Flood Frequency AnalysisFit a probability distribution (commonly Gumbel or Log-Pearson III) to the annual maximum flood series, then read the flood magnitude for the required return period T where T = 1/(1 − F).
- Canal Irrigation BasicsUse Manning’s equation Q = (1/n)AR^(2/3)S^(1/2) to find the normal depth of uniform flow, and classify the flow as subcritical or supercritical by comparing depth with the critical depth (Froude number relative to 1).