Discharge is commonly measured in which unit?

• A. cubic meters per second (m3/s)
• B. liters per second (L/s)
• C. cubic kilometers per year (km3/yr)
• D. gallons per minute (gal/min)

Answer: (A)

Discharge is a volumetric flow rate—the amount of water passing a cross-section per unit time. In hydrology, the standard SI unit for this is cubic meters per second, because velocity (meters per second) times cross-sectional area (square meters) gives a flow rate in cubic meters per second. This unit is convenient for rivers and streams of all sizes and directly expresses how much water moves past a point each second.

Liters per second is simply a smaller, scale-down version (1 L/s = 0.001 m^3/s), so it’s used for smaller channels or lab measurements rather than typical river discharge. Cubic kilometers per year would describe a volume over a year, not a rate at a moment in time, and gallons per minute uses US customary units and is not standard for hydrological discharge. Therefore, cubic meters per second is the most appropriate and widely used unit.