My little girl is 7 and just isn’t wrapping her head around this and I need to find a better way to explain this.
She is so so smart because she saw the coverage of Helene, and heard 17″ and hot confused.
I told her the water runs from the high places to the low places, but then she asked why the water doesn’t leave the low places and why is it still flooded.
I’m bad at dumbing things down.
In: Planetary Science
[Water falls on hill, water runs down hill and gathers in river, water in river rises, and flooding results.](https://thefloodhub.co.uk/wp-content/uploads/2020/09/Image5.jpg)
17” is a lot of rain. Keep in mind that the ground is rarely flat, and water flows downhill. The area of ground that flows towards a creek or river is called the “catchment area,” and all of the flowing water in the entire catchment area will eventually make it to the river. So that 17” times the entire catchment area can result in a very large volume of water, more than the river actually can handle within its banks.
I don’t know why it isn’t showing under my post, but my daughter is just very confused as to why the water doesn’t just wash away or drain away.
I’m very proud of her for asking the smart question but I feel like every way I explain it makes it too complicated
17″ of rain is 17″ *everywhere*.
It has to go somewhere.
If you have 50% of the land at 50 feet above sea level, and the remaining land is 75 feet above sea level, then the parts that are 50 feet above sea level are going to have three feet of water on them.
Say 17” (about 1.5 feet to simplify the number) of rain fall across an area that is 1 square mile. That’s an area of 27 million square feet. Times 1.5 feet of water gives you a total water volume of about 40 million cubic feet of water.
If all that land was perfectly flat, then yes you’re right, everywhere would just have 1.5 feet of water sitting on it. But that’s not have water works, land isn’t perfectly flat, it’s sloped, and water drains down into creeks and streams and rivers.
So if all that water drains down into river going through a valley that’s only 1,000 feet wide, that is 40 Million cubic feet of water (about 300 million gallons of water) flowing down all these streams and creeks into the valley. Causing the river in that valley to overflow its banks and flood the surrounding towns.
If you live near a river with a dam, go out to see the dam after a few days of moderate steady rainfall, and take a look at how different the water flow is from a regular day. Of course, it also helps if its a dam you see often to observe what regular waterflow looks like.
17″ spread across the entire region is concentrated to many feet of water when it all collects at the bottom in the rivers.
Take a baking pan full of water and then pour it into a glass. Let her experiment with it in the tub. Try different cups, plates and glass sizes. If you cover a plate in dirt and then wash it away with the Baking pan it should help her visualize the process.
Maybe make the comparison that 17″ of water filling a volume of a small area like a square foot isn’t much water overall, but if you took the water from an area of say 1,000 miles filled up to a volume of 17″ it is an enormous amount of water.
Land is not flat. There are valleys that are low ground and the water that falls on higher ground rushes downhill and settles in those low spots. Think of a puddle in a parking lot x 1 million.
Another way of thinking about it… let’s say the lowest 20% of an area floods, while the 17″ from the other 80% drained down to the low point. That means they have 5x 17″ of water that settled in that low spot. That’s over 7 feet.
Latest Answers