The math of hurricane rita

1. Oct 24, 2005

Plastic Photon

The story: when hurricane Rita came by, my dad and I were putting up boards when I decided to start making a formula to estimate the additional water that will be spewed into the streets due to people and the city cutting their grass before the storm.

What I thought, cutting grass would reduce the amount of water capable of being held by the grass.

So my inetial formula was - S = g1w - g2w where S is the extra amount of spewed water into the street due to less water held by cut grass. But I thought this was too simple and too obvious, so...

S = (g1w1 + g1a1) - (g2w2 - g1a2) In this case g1=lwh the volume of the uncut grass over a sqaure yard and g2 the volume of the cut grass, w will stand for inches of rain received and a1 and a2 are absorption rates of the water into the ground per square yard for uncut and cut grass. I chose to leave out evaporation due to the sun because this was a hurricane and I didn't expect the sun to shine, maybe UV rays will get by but is this significant?

My problem was I knew the formula was incorrect (I did not calculate run off or slope), and I asked my dad for advice. He said I should add in the the amount of water poured over a 50 mile radius. This is my problem, I am not too sure how to express this so here it is...
We will let (g1w1 + g1a1)=r1 and (g2w2 - g1a2)=r2

S = (r1d1 - r2d2)a In this case d1 and d2 are the run off rates (drainage) of water into the street done by liters per second and a is the area of the 50 mile radius.

Essentially what I was trying to understand is is it better to cut your grass before a hurricane because the water retained by your yard and the medians and sides of roads (city funded) might not be as much as if it were not cut. Will this cause massive flooding at a faster rate as to where the flood drains cannot keep up? There were other factors I did not put in such as wind, flying objects, absorption of water into the grass, animals, etc.

When all was said and done my dad laughed at the idea and said for a hurricane in this area it wouldn't matter because none of this could prevent the 15ft storm surge the news was hyping.

I am not too sure how accurate if at all the formula is but I thought you might enjoy the idea. If there is anything you'd like to add, correct or discuss, feel free to do so.

2. Oct 25, 2005

masudr

Surely your relation could well be a first-order approximation for something more complicated. In general, it is easier to model real-life problems with a differential equation, since we often find that it's derivatives which are related to other things; the solution of that diff. eqn. usually gives a good relationship between the variables involved.

3. Oct 25, 2005

Plastic Photon

Well that is one problem so far I am not equipt in handling are differential equations, we have not yet gotten to these in my math class at school. I'll keep that in mind.