Select the option that is appropriate regarding the following two statements labelled Assertion and Reason.
Assertion: In urban areas, roofing on built-up areas, concrete and asphalts surfaces are major factors that inhibit infiltration and surface retention.
Reason: The presence of pervious surface areas decreases infiltration and initial losses and leads to consequent increase in the effective rainfall.
🏙️ Understanding Urban Hydrology: Infiltration and Runoff
In hydrology, we study how water moves through the environment. Two key concepts are crucial for understanding the effect of urbanization on the water cycle:
Pervious Surfaces: These are surfaces that allow water to pass through them into the soil. Examples include grass, forests, and gardens. They promote infiltration (water soaking into the ground).
Impervious Surfaces: These are surfaces that do not allow water to pass through. Examples include roofs, concrete pavements, and asphalt roads. They prevent infiltration and lead to high surface runoff (water flowing over the land).
⚖️ Detailed Analysis of the Statements
Let's break down why the Assertion is correct and the Reason is incorrect.
Assertion: True
"In urban areas, roofing on built-up areas, concrete and asphalts surfaces are major factors that inhibit infiltration and surface retention."
This statement is absolutely correct. Roofs, concrete, and asphalt are all impervious surfaces. They act like a seal on the ground, preventing rainwater from soaking in. This blockage of infiltration is a defining characteristic of urban environments.
Reason: False
"The presence of pervious surface areas decreases infiltration and initial losses and leads to consequent increase in the effective rainfall."
This statement is incorrect. It describes the exact opposite of what happens. Pervious surfaces (like parks and soil) INCREASE infiltration and initial losses (water caught on leaves, in puddles). By soaking up water, they DECREASE the effective rainfall (which is the same as surface runoff).
💡 Key Takeaways for Hydrology
- Urbanization = More Runoff: Replacing natural, pervious land with impervious surfaces is the primary reason for increased flooding and runoff in cities.
- Pervious is Good for Infiltration: Natural surfaces like soil and vegetation are essential for replenishing groundwater and reducing surface runoff.
- Impervious is Bad for Infiltration: Man-made surfaces like roofs and roads prevent water from soaking into the ground, leading to higher volumes of runoff.