trapezoidal channel

[alejo12]

The problem states a trapezoidal channel: The sidewalls rise 2 feet for every 1 foot of horizaontal and T=12 feet. Q-854 cfs at critical flow.

The problem says the channel is carrying Q at the critical flow. CERM 11 edition , pg. 19-18 says:

(Q^2/g = A^3/T ) for non rectangular channels.

The problem asked for the channel bottom width. So, I solve for Area (A).

My question is , how can I solve for Area if I don't have the critical depth nor the channel width ???

A=db+mb ???

will appreciate any help.

 

[Chucktown PE]

A also equals 12d - 0.5d2 where d = depth. I got that A was equal to 64.8 square feet. So b = 3.8.

 

[alejo12]

yes, I also got the same area, A.

Thanks a lot, I was driving myself crazy !