Unit 1 - Essays - Causes of River Floods SIMPLE ENGLISH UPDATED Flashcards
With the aid of an example, assess the relative importance of the factors that caused a recent river flood event.
- Too Much Rain and Melting Snow (Natural Causes, Short-Term Effect)
What Happened?
The 1998 monsoon season was much wetter than normal. Bangladesh had 60% more rain than usual.
In Cherrapunji, India (which is near Bangladesh), it rained 2,245 mm in just one month (July).
The three big rivers (Ganges, Brahmaputra, and Meghna) were already full. This extra rain made them overflow.
Himalayan snow melted in summer, adding even more water to the rivers.
How Did This Cause the Flood?
Bangladesh is at the bottom of these rivers, so all the extra water flowed into it.
The rivers could not hold so much water, so they overflowed.
The flood lasted a long time (almost three months) because more rain kept coming.
Was This a Very Important Cause?
Yes, this was the main reason why the flood happened.
Without the extra rain and melted snow, there would not have been a flood this big. - Bangladesh’s Flat Land and Large Rivers (Why the Flood Was So Big and Lasted So Long)
What Happened?
Bangladesh is a very flat country. Most of the land is only 1-10 meters above sea level.
80% of the country is a floodplain (land next to a river that can flood easily).
In 1998, 1,000,000 km² of land was underwater.
How Did This Cause the Flood?
Because the land is so flat, the floodwater spread very quickly across the country.
The water could not drain away fast because there are no hills or slopes to move it.
Cities like Dhaka had even worse flooding because they have poor drainage systems (bad ways to remove water).
Was This a Very Important Cause?
Yes, this made the flood worse and last longer.
Even when the rain stopped, the water had nowhere to go, so the country stayed flooded for months. - Human Mistakes: Cutting Down Trees and Bad City Planning (Made the Flood Worse)
What Happened?
Deforestation (cutting down trees) happened in Nepal and northern India.
In Dhaka, the city grew too fast (from 3.5 million people in 1980 to 10 million in 1998).
70% of Dhaka was in a flood-prone area, but people still built houses and roads there.
How Did This Cause the Flood?
Trees normally soak up rainwater, slowing it down before it reaches the rivers.
With fewer trees, the rainwater rushed into the rivers very quickly, making them overflow faster.
In cities, people built on land that used to absorb water, blocking natural drainage.
As a result, some areas stayed flooded for over two months.
Was This a Very Important Cause?
Yes, this made the flood much worse.
Without cutting down trees or bad city planning, the floodwaters might have gone away faster. - Weak Flood Defenses and Poor Government Response (Made the Disaster Worse)
What Happened?
The government had built embankments (walls to stop floods), but many broke when the rivers got too full.
The Flood Action Plan (FAP) focused on building walls instead of finding better solutions.
There was no early warning system, so people did not know the flood was coming.
How Did This Cause the Flood?
When the embankments broke, floodwater spread even faster into villages and cities.
30 million people lost their homes, and the government did not help them fast enough.
The flood caused $2.8 billion in damage and over 1,000 people died.
Was This a Very Important Cause?
This did not cause the flood, but it made the damage much worse.
If the government had stronger flood defenses, fewer people would have suffered.
Conclusion: Which Causes Were the Most Important?
The biggest cause of the flood was heavy rainfall and melting Himalayan snow. This was the main trigger that caused the rivers to overflow.
Bangladesh’s flat land made the flood spread quickly and last for a long time.
Human mistakes (cutting down trees and bad city planning) made the flood much worse by stopping water from draining away.
The government’s poor flood defenses made it harder for people to recover.
Final Decision:
Nature started the flood, but human actions made it worse.
If Bangladesh had better flood defenses and better city planning, the damage would not have been so bad.
“Assess the view that rainfall intensity is the most important factor in causing a river to flood.”
- Rainfall Intensity – How Heavy Rain Causes Floods
Main Idea: If rain falls too fast, the ground and rivers cannot absorb it, so water runs off quickly and causes flooding.
Example 1: Bangladesh (1998 flood)
Monsoon rain was heavier than normal, with some places getting over 300mm of rain in one day.
Total rainfall in July-September was 30% higher than usual, causing rivers to rise.
The flood lasted over three months, covering two-thirds of Bangladesh.
Example 2: Boscastle (2004 flood)
75mm of rain fell in just two hours, and at the worst point, it rained 300mm per hour.
The small rivers Valency and Jordan could not handle the water, causing a flash flood.
The flood happened in only 30 minutes, leaving no time to prepare.
Why This Matters:
When rain is very heavy, water cannot soak into the ground, so it quickly flows into rivers.
If the rain is too intense, even a short storm can cause serious flooding.
- The Shape and Type of Land Affects Flooding
Main Idea: Some landscapes make flooding worse because they do not absorb water well or they drain water too fast into rivers.
Example 1: Boscastle (2004 flood)
Steep valley sides meant rainwater ran straight into the river instead of soaking into the ground.
The ground was made of hard rock (slate) that does not absorb water, so rainwater became runoff.
The river flooded very quickly, in just 30 minutes.
Example 2: Bangladesh (1998 flood)
The country is very flat, so when rivers overflow, water spreads out and stays for a long time.
Bangladesh has three huge rivers (Ganges, Brahmaputra, Meghna) that bring water from upstream areas, increasing flood risk.
The Brahmaputra’s drainage basin is 580,000 km², meaning rain from far away also contributes to flooding.
Why This Matters:
Boscastle flooded quickly because the valley shape forced water straight into the river.
Bangladesh flooded for a long time because its low, flat land kept water trapped.
The land’s shape affects whether a flood is short and fast (Boscastle) or long and widespread (Bangladesh).
- Human Activities That Make Flooding Worse
Main Idea: People’s actions, like cutting down trees and building on floodplains, can increase flooding by stopping the land from soaking up water.
Example 1: Bangladesh (1998 flood)
Deforestation in the Himalayas meant less trees to absorb water, so more water flowed into rivers.
Since 1950, forest cover in the Himalayas has decreased by 50%, increasing flood risks.
Dhaka (Bangladesh’s capital) is covered in concrete (70% of the land), stopping rain from soaking in.
Example 2: Boscastle (2004 flood)
The old stone bridge in the village had a narrow arch that got blocked with trees and debris, stopping water from flowing.
When the blockage broke, it released a surge of water, making the flood worse.
More buildings had been built on floodplains, meaning there was more property damage than in the past.
Why This Matters:
Deforestation means there are fewer trees to slow water down, increasing the amount of water entering rivers.
Urbanization (building roads, bridges, and houses) reduces how much water the land can absorb.
Human actions make natural floods worse and more damaging.
- Long-Term Weather Patterns and Seasons Also Affect Flooding
Main Idea: Some places flood often because they have wet seasons, snowmelt, or already full rivers before heavy rain arrives.
Example 1: Bangladesh (1998 flood)
Monsoon season (June-October) brings 80% of the country’s annual rain, so rivers are always high in these months.
Himalayan snowmelt in spring increases river levels before the monsoon even starts, making floods worse.
Because the ground and rivers were already full, any extra rain caused severe, long-lasting flooding.
Example 2: Boscastle (2004 flood)
The flood happened in August, after weeks of heavy rain had already made the ground very wet.
Before the flood, the soil was 60% saturated, meaning it could not soak up much more water.
This made the intense rainfall even more dangerous, as all the extra rainwater went straight into the river.
Why This Matters:
Some places are naturally prone to flooding because they get a lot of rain every year.
If the ground is already wet, heavy rain causes flooding faster than usual.
In Bangladesh, the flood lasted months because of the seasonal monsoon and snowmelt.
In Boscastle, the flood lasted only a few hours, but the wet ground made it worse.
Conclusion
Rainfall intensity is important, as seen in Boscastle (flash flood in 30 minutes) and Bangladesh (300mm of rain in one day).
However, the landscape (drainage basin shape and rock type) controls how quickly or how long the flood lasts.
Human activities (deforestation, urbanization, blocked rivers) make floods worse, even if the rainfall is not extreme.
Long-term weather patterns (monsoon, snowmelt, previous rain) make flooding more likely, even before an extreme rainfall event happens.
Final Judgement: Rainfall intensity is the trigger, but landscape, human actions, and seasonal weather patterns are more important in deciding how bad a flood will be.
