# Q1A · Discuss in detail types of Floods on basis of duration of onset of floods with releva…

Subject: Disaster Management

Exam: TEE

Reader: https://deep-learning-study-room.vercel.app/dm/#tee/papers/paper-2023-05-04/q1a

Canonical: https://deep-learning-study-room.vercel.app/read/dm/tee/papers/paper-2023-05-04--q1a/

Actual older TEE paper · 100 marks · Q1 compulsory; any four of Q2–Q7

### Q1A. Discuss in detail types of Floods on basis of duration of onset of floods with relevant examples. [5 marks]

#### Answer

**Definition.** A flood is the inundation of normally dry land by water. It may result from river overflow, intense rainfall, inadequate drainage, storm surge or sudden release of stored water.

## Two separate ways of classifying floods

| By onset | Meaning | Planning implication |
| --- | --- | --- |
| Slow-onset | Water rises gradually, often after prolonged rainfall. | There may be time for planned evacuation, but long duration disrupts livelihoods. |
| Rapid-onset | Water rises over a comparatively short period. | Warnings and prompt action become critical. |
| Flash flood | Very rapid rise, often within minutes to a few hours of the trigger. | Little lead time; fast flow and debris can be highly destructive. |

| By source | How it develops |
| --- | --- |
| River / fluvial | River discharge exceeds channel capacity and water spreads over its floodplain. |
| Urban / pluvial | Rainfall runoff exceeds drainage or infiltration capacity; a river need not overflow. |
| Dam-breach | Dam failure releases reservoir water suddenly downstream. |
| Coastal surge | Wind and low pressure raise sea level; high tide can compound flooding. |
| GLOF | Sudden release from a glacial lake, for example after its retaining barrier fails. |

“Flash” describes speed, whereas “dam-breach” describes the source. A dam-breach flood may therefore also be a flash flood. Onset speed and total flood duration are different; a rapidly starting event may leave some areas inundated for much longer. The PPT uses “rapid” and “flash” inconsistently, so describe the actual time-scale instead of forcing a rigid universal duration.

**Indian examples:** monsoon river floods in Assam illustrate river flooding; Mumbai in July 2005 illustrates severe urban flooding; Panshet in 1961 illustrates dam-failure flooding; coastal inundation during a cyclone illustrates coastal flooding. Uttarakhand in June 2013 included rapid mountain floods and debris flows. Source and speed of onset are different classification axes.

## Keep source and onset classifications separate

| Classification axis | Type | Indian example and explanation |
| --- | --- | --- |
| Source | River flood | Assam monsoon river flooding: rivers overflow or inundate adjacent low-lying land. |
| Source | Urban / surface-water flood | Mumbai, July 2005: exceptional rainfall combined with drainage and urban vulnerabilities. |
| Source | Dam-failure flood | Panshet, 1961: failure released stored water downstream. |
| Source | Coastal flood | The 1999 Odisha super cyclone produced destructive storm-surge inundation along the coast. |
| Onset / duration | Slow-onset or sustained flood | Seasonal Assam/Brahmaputra flood episodes can build and persist over days. The actual timing varies by event and location. |
| Onset / duration | Rapid-onset / flash flood | Uttarakhand, June 2013 included rapidly developing mountain floods and debris flows. A flash flood describes rapid onset, not a separate water source. |

One event can occupy both classifications: a sudden dam-break flood is a source-defined dam-failure flood and a rapid-onset flood. Do not treat “river” and “slow” as mutually exclusive categories or assume every river flood develops slowly.

Coastal-case source: [NDMA cyclone-management guidelines, hosted by NIDM](https://nidm.gov.in/pdf/guidelines/cyclones.pdf), discussion of storm surge and inland inundation during the October 1999 Odisha cyclone.

#### Real case and learning connection · Mumbai floods, 2005

The Mumbai flood case links intense rainfall with urban drainage and development conditions. For an answer on mitigation, explain how maintaining drainage and protecting water-storage spaces address specific pathways of flooding; do not claim that any single measure prevents every extreme event.

[Case reference ↗](https://nidm.gov.in/PDF/Newsletter/6_nov_2005.pdf)