Bernard’s distribution (mass) graph Bernard’s distribution graph is plotted with time on the X-axis and which quantity on the Y-axis for a given storm-runoff event?

Introduction / Context:
Bernard’s distribution graph is a dimensionless way of representing how total surface runoff is distributed through time during a storm. It is useful for estimating peak discharge blocks.

Given Data / Assumptions:

• Time is divided into equal intervals (e.g., 5 or 10 minutes).
• Each interval’s contribution is expressed as a percentage of the event’s total surface runoff volume.

Concept / Approach:
Unlike a cumulative mass curve, Bernard’s distribution graph presents the percentage per interval (non-cumulative) so designers can identify the fraction that occurs in the peak block (e.g., “10-minute peak percentage”).

Step-by-Step Solution:

Verification / Alternative check:
This interpretation is consistent with how “10-minute peak percentage” is used to derive peak-rate estimates from total volume.

Why Other Options Are Wrong:

• (a) instantaneous discharge is a hydrograph, not Bernard’s distribution.
• (b) total volume is a single scalar, not a per-interval percentage.
• (c) cumulative percentage vs time is a mass curve, not Bernard’s distribution.

Common Pitfalls:
Confusing Bernard’s interval distribution with cumulative mass curves; ensure you use the correct graph for peak-rate calculations.

Final Answer:
Percentage of total surface runoff during uniform time intervals on the Y-axis