And the waterfall is flat because its just a river going in a straight line and falling over edge which is exactly perpendicular to river's flow. Rivers are never like that.
Terrible pseudo-graphic incoming:
That's your river.
|\/.\/.\/.\/.\/|
|\/.\/.\/.\/.\/|
|\/.\/.\/.\/.\/|
|\/.\/.\/.\/.\/|
|\/.\/.\/.\/.\/|
==========
|\/.\/.\/.\/.\/|
|\/.\/.\/.\/.\/|
|\/.\/.\/.\/.\/|
|\/.\/.\/.\/.\/|
|\/.\/.\/.\/.\/|
That's how it's supposed to be:
||].\/.\/.\/.\/|\\
\.\/.\/.\/.\/.\/.\|
/.\/.\/.\/.\/.\/./|
|\/.\/.[].\/.\/|//
|\/.====.\/.|/
==//.fog.\\==
|=.lotsoffog=|
|].\/.\/.\/.\/[|\\
|\/.[].\/.\/.\/.\/|
|\/.\/.\/.[].\/.\/|
\\.\/.\/.\/.\/.\/|/
Where === is edge of waterfall, and .\/. is river flow, and || \\ // are river banks, and [] are stones sticking out.
Well, it's not very clear, but do you get an idea? If not, look at the other pictures of waterfalls.
http://fc02.deviantart.net/fs26/i/2008/136/a/f/Waterfall_by_SusieStock.jpg
http://fc09.deviantart.net/fs6/i/2005/034/b/7/Waterfall_by_PainIsBeautiful.jpg