Units of runoff measurement in hydrology When reporting stream runoff or basin outflow as a rate for hydrograph analysis and design, which unit is most commonly used in engineering practice?

Introduction / Context:
Discharge, or runoff rate, is fundamental for hydrographs, flood routing, and structure sizing. The SI base rate used in most hydrologic and hydraulic design is cubic metres per second, often abbreviated as cumecs.

Given Data / Assumptions:

• Standard SI engineering practice.
• Focus on discharge rates, not depth-runoff (mm over catchment).

Concept / Approach:

Discharge Q is volume per unit time. For rivers and design flows, m^3/s provides a consistent scale from baseflow to flood peaks and integrates easily with energy/power calculations.

Step-by-Step Solution:

Verification / Alternative check:

Design manuals and flood-frequency analyses universally present discharges in m^3/s (or cfs in US customary units).

Why Other Options Are Wrong:

• m^3: Volume, not rate.
• m^3/min, m^3/h: Usable but not the prevailing convention for hydrologic design hydrographs.
• L/s: Common for small-supply systems, not river basin flood work.

Common Pitfalls:

• Mixing instantaneous peak with mean daily discharge units.

Final Answer:

Cubic metres per second (m^3/s).