I don’t get how houses/buildings can go under water?
In: 8
I have three quick experiments for you:
1) Grab a bowl. Fill it with water. Congratulations, you just have a “flooded” bowl.
2) Grab a bottle of soft drink (the plastic ones) and fill it with water. Then try to empty it. It doesn’t flow all the way out at once, because the hole doesn’t allow for that much water movement, thus it is a slow flow. You have a “flooded” bottle.
3) Grab a strainer/colander, and try to put the water from the bowl in #1 (to save water, I’m not an environmental monster) into it. You’ll see that even if the water doesn’t flow through the strainer in one swift motion, it definitely doesn’t pool up significantly.
With those experiments, it should become pretty obvious that floods happen when water flows in faster than it can flow out.
Usually city floods happen because concrete and asphalt are a lot more waterproof than a park or forest’s soil. That is because soil and sand act as a natural colander for the water to pour down through them. But even they have a limit, which is why you can have swamps, bogs and other water-logged soils and sands. This would be the difference between #1 and #3 up there.
Now cities do have sewers, which should take care of the excess water, except that if the downpours/water coming into the city come in faster than it can be moved out, you have a situation like the soft drink bottle, where it will get out, but it will take time. It will take even more time if the place where the sewers are draining the water to are also being flooded, and you must then wait for it to drain, before the water can drain properly. (This one can be simulated by putting the tip of the soft drink bottle underwater as it drains: If it keeps going, you’ll see it go much, ***much*** slower.)
So, in short, while the water should (and will) technically flow all the way out at some point, the speed at which it comes in, versus the speed at which it goes out are what cause the flooding.
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