Duty (\(\Delta\)) = area (hectares) irrigated by 1 cumec (1 m³/s) of water flowing continuously for base period \(B\) (days). Delta (\(D\)) = total depth of water (meters) required by the crop in base period. Relationship: \(D = \dfrac{8.64 \times B}{\Delta}\), derived from: 1 cumec flowing for \(B\) days delivers \(8.64B \times 10^4\) liters over \(\Delta\) hectares. This fundamental relationship governs canal design and water distribution in irrigation systems.