Pressure problem but without any given values. How?

[evilrain14]

Homework Statement

Both dams equally wide and equally high. The first dam holds back a very large lake, and the second dam holds back a narrow river.

Homework Equations

Which dam has to be built more strongly?
a.) the first dam
b.) the second dam
c.) both

The Attempt at a Solution

i know it would be the second dam that holds back a narrow river, but how can i prove it mathematically/algebraically?
how can i show the answer in ratio? -.-

i need your help please.

thanks!

 

[mishek]

Do you know what the hydrostatic pressure is?

 

[evilrain14]

yes. but my problem is, there is no any given values/numbers. i know what to answer but i can't prove it.. :(

 

[mishek]

Hello, do You know what a hydrostatic paradox is?