Question

For a concrete or paved surface, curve number will tend to be almost equal to

• A. 0
• B. 100
• C. 50
• D. 80

Hint:

CN Scale: $CN = 100 \implies$ Impervious concrete/asphalt (100% runoff). $CN \approx 30-50 \implies$ Dense forest with deep sandy soil.

Answer 1

The Correct Option is B

Step 1: Understanding the Concept:
The SCS Runoff Curve Number (CN) is a dimensionless index ranging from 0 to 100 reflecting the runoff potential of a land-use hydrologic soil group complex.
Key Formula or Approach:
\[ S = \frac{25400}{\text{CN}} - 254 \text{ (mm)} \]
\[ \text{For } S = 0 \text{ (Zero Infiltration Retention)} \implies \text{CN} = 100 \]

Step 2: Detailed Explanation:
The curve number \(CN\) scales from 0 (infinitely absorbent, 100% infiltration, zero runoff) to 100 (completely impervious, zero infiltration, 100% runoff).
Concrete, asphalt, rooftops, and paved surfaces have zero potential maximum retention (\(S = 0\)), meaning virtually every drop of precipitation is converted directly into surface runoff (\(Q = P\)).
Therefore, the curve number for paved and concrete surfaces approaches 100.

Step 3: Final Answer:
Thus, for a concrete or paved surface, the curve number is almost equal to 100, corresponding to option (B).