Question

Difference between observed total rainfall hyetograph and the excess rainfall hyetograph is termed as ____________.

• A. Base flow
• B. Subtraction
• C. Abstraction
• D. Overland flow

Hint:

Remember the water balance equation of a storm:
Total Rainfall = Excess Rainfall + Abstractions.
Therefore, any water "lost" to infiltration, depression storage, or interception is categorized under Abstractions.

Answer 1

The Correct Option is C

Step 1: Understanding the Concept:
When rainfall occurs over a watershed, not all of the precipitated water contributes to surface runoff.
A portion of the rainfall is lost or retained by various physical and biological processes before it can flow over the surface.
The difference between the total rainfall hyetograph and the effective (or excess) rainfall hyetograph represents these losses.

Step 2: Detailed Explanation:
In hydrology, the term "Abstraction" (or rainfall losses) refers to the collective loss of water that does not contribute to direct surface runoff.
Abstractions include several processes:
1. Interception: Rainfall caught by vegetation canopy and evaporated back into the atmosphere.
2. Depression Storage: Water trapped in small puddles and depressions on the ground surface.
3. Infiltration: Water that penetrates the soil surface and recharges soil moisture or groundwater.
4. Evapotranspiration: Evaporation from the soil and transpiration from plants during the storm.
The total rainfall hyetograph represents the time-distribution of total precipitation.
The excess (effective) rainfall hyetograph represents the time-distribution of the water that actually becomes surface runoff.
Mathematically, we can write:
\[ \text{Excess Rainfall} = \text{Total Rainfall} - \text{Abstractions} \]
Therefore, the difference between the observed total rainfall hyetograph and the excess rainfall hyetograph is termed as "Abstraction" (or loss).

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