How Do I Calculate Annual Precipitation for a Watershed?

[remaan]

Hello every one, I wish if you could help with this problem :

b]1. Homework Statement [/b]

Given the following informaiton for a paritculart watershed, determine the amount of the annual precipitaion received

Homework Equations

water shed area : 4530 m^2
average flowrate : 39.6 m^3/second
Average infiltration 9.2 * 10 ^ -7 m/s
Evapo-transpirtaiton : 45 cm/year
change is storage -23.9 cm/year

The Attempt at a Solution

I am sure that the formula to solve this is : change in storage = input - output + prec. - Evaportaion .

However, I have some doubts :

First, I assumed that the Evapo-transpirtaiton is the same as : Evaportaion so I am going to substitute it in the formula .


Second, which is the major :
The units - do we need to convert the units ?
My idea is to convert all cm to m but then when prec.is found : how to know if m/year

or m/s ?


Hope hearing replying soon =)

 

[Lok]

Just transform all to a single unit. No matter what transformation you make if you have a single set of units the result will be right. And after you can transform the result in any unit system you want or anything that fits better, m/year maybe.

e.g.

m instead of any other length unit
year instead of second ...as at such a surface area the second seems small.

 

[remaan]

oh,
so, you're saying that I need to make all cm to m and all seconds to years.

But the numbers will be sooo big because there are a really huge amount of seconds in one year ..

So, is that ok ?

 

[Borek]

That's where the scientific notation (6.02x10²³) comes in handy.

 

[remaan]

Ok, thnx I 'll try this >

 

[Senjai]

Borek you made me laugh :)

 

[remaan]

But, what if I got powers with(-) sign ?

 

[Borek]

That's OK, that's part of the notation. Do you know what it means?

 

[remaan]

ya .. thnx alot