Water Channel

A city is considering building a water channel which ends in a free waterfall in a park. A hydraulic engineer is asked to determine the water surface profile for a discharge flow rate of 750 ft³/s. The channel has a trapezoidal shape with a base width of 25 ft, and the angles on both sides are 30^o as shown in the figure. The slope of the channel is 0.0015.

Determine the critical and normal depths, and identify the surface profile type. Then compute the water surface profile using the direct step method.

• Assume the flow is gradually varied flow.
• Assume the Manning coefficient is 0.025 for gravelly excavated earth channel*.

* For practices, students are encouraged to repeat this problem using the Manning coefficient for concrete (shown in the picture).