2.2. Application of Manning's Formula

Try these first

1. 1.

   What does the letter 'n' represent in Manning's formula?

   Hint

   Think about what affects flow in a channel.

2. 2.

   Define what a wetted perimeter is.

   Hint

   Consider where the water touches the channel.

3. 3.

   What is the primary purpose of Manning's formula?

   • To calculate water temperature
   • To estimate discharge in open channels
   • To measure channel width

   Hint

   Think about what you need to know for water flow.

4. 4.

   True or False: The wetted perimeter is the same as the total perimeter of the channel.

   • True
   • False

   Hint

   Consider where water flows in the channel.

5. 5.

   A trapezoidal channel has a bottom width of 6 m, a slope of 2:1, and an n value of 0.025. What slope must the channel have to carry a discharge of 150 cubic meters per second at a depth of 4 m?

   Hint

   Don’t forget to check your area and perimeter calculations.

6. 6.

   In a circular pipe with an diameter of 1.2 m flowing full, estimate the maximum discharge coefficient if its n value is 0.015 and it is inclined at 1 in 800.

   Hint

   You may need to find the hydraulic radius prior to plugging values into the equation.