Open Channel Flow (mannings equation) rectangular section

[Stacyg]

A rectangular concrete-lined channel is 2m wide with Manning's n 0.012 and a bed slope of 0.0025 m/m. Obtain the depth of flow when the discharge is 9m^3/s.

Q=V.A I have the discharge but how do I calculate the velocity without the area ?? Once I have the velocity I should be able to work it out.

Thanks

 

[dirk_mec1]

You've got two equations with two unknowns: eliminate v. Write the area A as b*h with b the width and h the height of the rectangular cross-section. Now solve for h.