Question

Recession limb of hydrograph is controlled by ____________.

• A. Basin characteristics only
• B. Storm characteristics only
• C. Basin and storm characteristics
• D. Initial and infiltration losses

Hint:

Remember the hydrograph controls:
- Rising limb: Controlled by both storm and basin characteristics.
- Recession limb: Controlled only by basin characteristics (since the storm has already ended).

Answer 1

The Correct Option is A

Step 1: Understanding the Concept:
A storm hydrograph consists of three main parts: the rising limb, the crest segment (peak), and the falling (recession) limb.
The recession limb represents the withdrawal of water from storage within the watershed after the rainfall has ceased.

Step 2: Detailed Explanation:
The recession limb begins from the point of inflection on the falling side of the hydrograph and continues until baseflow conditions are restored.
At this stage of the hydrograph:
- Active rainfall has ceased, meaning storm characteristics (such as rainfall intensity, duration, and movement) no longer influence the flow.
- The discharge is supplied entirely by the depletion of water stored in the channel network, surface depressions, and groundwater aquifers (baseflow).
- The rate of this depletion depends on the physical properties of the watershed, such as basin shape, channel slope, drainage density, soil permeability, and geological formations.
Because the recession is a natural depletion process independent of the storm event itself, its mathematical representation (usually an exponential decay model like \(Q_t = Q_0 \cdot e^{-kt}\)) depends solely on the physical basin characteristics.
Therefore, the recession limb is controlled by basin characteristics only.

Step 3: Final Answer:
The correct option is (A).