Seepage calculation for flow net

Homework Statement

In the 3rd pictures , it's stated that q ( flow rate) = vA = kiA , so , i = hydraulic gradiene = difference in head between 2 points/ length . But , i am not sure why A ( area) is given by $$l_1$$ , $$l_2$$ and $$l_3$$ only ?

Homework Equations

The Attempt at a Solution

I think the author is wrong . It should be ($$l_1$$^ 2 ) ... instead , because it's forming the square elements( in 2nd picture) . Correct me if i am wrong .[/B]

 

Or the area is considered as length here ? So, only $$l1$$ , $$l2$$ and $$l3$$ are considered ??

 

[Chestermiller]

The other length forming the area is not the other side of the square. The area A is oriented perpendicular to the direction of seepage, and the other length is "into the page." They are getting the seepage flow per unit width into the page.

 

They are getting the seepage flow per unit width into the page.

Thanks !