What is the depth of flow

Question

Problem:

Water is flowing in a trapezoidal channel with 10 ft bottom width and 2H/1V side slopes. The channel is running on a slope of 0.00778 ft/ft and the flow exerts a shear stress of 1.5 lb/ft² on the channel bed.

Required:

Question: What is the depth of flow?

Note: Please explain comprehensively and give step by step solution.