Question

Which of the following is not a technique for flood management and control in urban areas?

• A. Cleaning and widening of stormwater drains
• B. Creating more permeable, vegetated spaces
• C. Construction of retaining walls near settlements to avoid inflows
• D. Construction of retaining walls along water bodies

Hint:

Urban flood solutions focus on Source control (infiltration/permeable pavements), Conveyance control (widening drains), and Storage control (retention ponds). Building walls right next to buildings traps rainwater inside, making them a flood liability rather than an asset.

Answer 1

The Correct Option is C

Concept: Urban flooding differs significantly from rural flooding because urbanization alters hydrology by converting natural permeable surfaces into impervious concrete slabs and roofs. This dramatically increases surface runoff volume and speed, overwhelming conventional urban drainage infrastructure. Effective urban flood management relies on sustainable drainage engineering and hydrological design.

Step 1: Assessing Urban Flood Mitigation Strategies
To mitigate localized flooding, engineering responses should either increase hydraulic capacity, delay the peak discharge via storage, or assist infiltration:
• Widening and desilting infrastructure (Option A) directly restores and boosts the cross-sectional discharge capacity of stormwater pathways.
• Creating permeable surfaces (Option B) targets the root structural problem by promoting natural infiltration, lowering peak runoff volumes (Low Impact Development or Sponge Cities concept).
• Constructing retaining structures directly alongside rivers or drainage canals (Option D) prevents channelized water from breaching banks and spilling over into adjacent plains.

Step 2: Dissecting the Faulty Strategy
Now let us analyze Option (C): "Construction of retaining walls near settlements to avoid inflows". If concrete retaining walls are erected tightly around localized settlements or residential enclaves, they create a closed macro-basin barrier. While they might theoretically block structural outside inflows, they simultaneously trap all localized direct rainfall falling within that settlement. Because the water inside has no pathway to escape or discharge outwards, it pools rapidly inside the living zone, severely exacerbating the localized flooding effect. Therefore, constructing walls strictly around housing pockets instead of managing the primary drainage pathways is not a viable structural technique.