We need water to survive, but not too much of it.
How much is too much? It’s a fine line.
Flooding enriches the land, recharges ground water, and turns desert into fertile farmland. It also destroys property, infrastructure, and worst of all, human life.
In practical terms, the best guideline is to watch out when water is on the move over normally dry land.
Flood causes and effects
Areal flooding happens when the amount of rain exceeds the capability of the land to channel it away.
The ground may already be saturated, for example, or frozen. The rain may fall on impermeable surfaces like bedrock or asphalt.
Riverine flooding happens, of course, when there’s too much water to fit into the channel. The excess water may come from storm runoff or snow melt.
The ocean can also flood over land. We looked at some videos of storm surge last week.
Coastal flooding – another type of surge event – happens when storm winds push vast amounts of water onto coastal land. Low atmospheric pressure and storm waves also contribute to the flooding. This can be particularly devastating when it happens at high tide.
Catastrophic flooding is potentially the most lethal, because vast amounts of water are released with little or no warning. A dam may fail, for example, or a powerful earthquake cause huge tsunami waves.
The deadliest flood in modern times was a riverine flood in 1931. It happened in China along the Yangtze, Haui, and Yellow rivers after heavier than normal snowfall during winter, followed by strong monsoon rains that summer and an unusually high number of landfalling tropical cyclones.
In the month of July alone, four weather stations along the Yangtze reported over 2 feet of rainfall.
Chinese authorities claimed the death toll was 145,000. Western authorities put the number of dead between 3 and 4 million.
Almost 29 million people were displaced by the flood waters.
Water from areal flooding often mixes with surface material to cause landslides and debris flows, especially if the ground is steep. California is notorious for such events.
In late 1933, for example, forest fires denuded the San Gabriel Mountains above La Crescenta, Montrose, and La Canada in Southern Califiornia. Then came weeks of heavy rain in December, followed by a cloudburst on New Year’s Eve.
At one minute after midnight, at least three landslides dropped millions of tons of thick muddy water and debris onto the communities below. Forty-five people died in this, the Great Flood of 1934.
Afterwards, the US Army Corps of Engineers and Los Angeles County built a flood control drainage system to prevent another such flood.
Today’s technology and training give everybody an advantage these days when the water starts to rise.
Bangladesh is a good example.
It sits on the Ganges River floodplain. Over the last two weeks, as of this writing, heavy monsoon rains and Himalayan melt water have caused flooding there that has affected two million people.
However, only 17 have died, compared to thousands in recent similar floods.
The government of Bangladesh has modernized its weather forecasting system, giving people a warning time of five days. People also now can visit an information website or call an information number.
In the West, floods are forecast and monitored by many public and private agencies, with state-of-the art technology and the most advanced techniques. There is plenty of information available to the public.
The problem is getting people to use it.
Some people are always going to ignore evacuation orders.
During Superstorm Sandy in 2012, for instance, 20 people drowned in their New York City homes, according to the Centers for Disease Control. All of them lived in or near an evacuation zone.
They didn’t leave because they were afraid of looters, couldn’t find transportation, and most tragically, thought an earlier hurricane (Irene) had been mild.
Know if you’re in a storm surge zone.
Don’t hang around – for whatever reason – if an evacuation is called. There are shelters now that will take pets. Public transportation can be arranged ahead of time. Your life is more important than anything else. Preserve it.
Awareness is another concern.
Schools have always taught that water recedes from the coast during a tsunami. However, in 2004, a surprisingly large number of people, among them many Westerners, just stood there wondering why the sea had just receded from the shore after the Sumatra earthquake.
Maybe they thought that school lessons weren’t needed here – they were on vacation?
On video, it also appears that many also didn’t realize a tsunami was coming in until it was too late to flee.
Flooding deaths don’t have to be catastrophic. Every year quite a few people die because they believe drowning is something that happens to other people.
They don’t realize that just a few inches of water can float their car or that a flash flood can overwhelm them when there isn’t a cloud in the sky where they’re camping or picnicking.
Or that the neighborhood volcano (Eyjafjallajökull, in this April 14, 2010, video) might wake up under a glacier, causing an outburst flood:
Icelanders are aware of these jokulhaups. Bangladeshis are very aware of flooding risks.
Those of us who live in easier circumstances need to do a little investigating. There’s plenty of information.
There you go. Get started, and then follow through, 24/7/365, no matter where you live, work, and travel.
Next week, we’ll take a look at flood control, how it works, and what its strengths and weaknesses are.
- The New Year’s Flood of 1934 – Survivor’s Stories (PDF). Historical Society of the Crescenta Valley Ledger
- Bangladesh floods test disaster response improvements. iRIN Humanitarian News and Analysis
- Flood. Wikipedia
- The 1931 China floods. Wikipedia