Question

Ruggedness number of a watershed is given as

• A. Basin relief \(\times\) Drainage density
• B. Basin relief Drainage density
• C. Drainage density/ Basin relief
• D. Basin relief - Drainage density

Hint:

Ruggedness Number $R_n = \text{Relief } (H) \times \text{Drainage Density } (D_d)$. Indicates terrain roughness and erosion susceptibility.

Answer 1

The Correct Option is A

Step 1: Understanding the Concept:
The ruggedness number is a dimensionless geomorphic index combining watershed elevation steepness with dissection intensity.
Key Formula or Approach:
\[ R_n = H_b \times D_d \]
where \(H_b\) is total basin relief (m), and \(D_d\) is drainage density (\(\text{km/km}^2\) or \(\text{m}^{-1}\)).

Step 2: Detailed Explanation:
Strahler (1957) defined the Ruggedness Number (\(R_n\)) of a watershed as the product of maximum basin relief (\(H_b\), elevation difference between highest ridge point and basin outlet) and drainage density (\(D_d\), total stream length per unit basin area):
\[ R_n = H_b \times D_d \]
High ruggedness numbers occur in mountainous, deeply dissected regions subject to severe flash flooding and soil erosion.

Step 3: Final Answer:
Therefore, ruggedness number is given as Basin relief \(\times\) Drainage density, matching option (A).