Definition of basin yield and runoff terms Pick the correct statement about “yield” of a drainage basin and how runoff is expressed.

Introduction / Context:
Hydrologists distinguish between instantaneous discharge, event runoff, and long-term yield. Correct terminology prevents confusion in water-resources planning.

Given Data / Assumptions:

• “Yield” refers to a long-term average or accumulated runoff from the basin.
• Runoff can be expressed as depth, volume, or discharge depending on context.

Concept / Approach:
Yield typically means the dependable or average quantity of water produced by a basin over a specified period (e.g., annual yield). Instantaneous measures (hydrograph ordinates) do not represent yield.

Step-by-Step Solution:

Verification / Alternative check:
Textbooks define yield as long-term runoff availability; project reports quote annual yield or firm yield based on storage–yield analysis.

Why Other Options Are Wrong:

• (a) confuses yield with instantaneous discharge.
• (c) overly restricts yield to surface runoff only; baseflow contributes too.
• (d) imposes a single unit/time scale on runoff, which varies by application.

Common Pitfalls:
Using peak discharge to represent basin yield; they are different metrics for different design questions.

Final Answer:
Yield of a drainage basin is the runoff evaluated over long periods (e.g., annual or multi-year totals)