Open-channel flow (Manning) worksheet with answers

Free printable Open-channel flow (Manning) worksheet: 6 problems from easy to exam level, with an answer key. Print it or save it as a PDF.

New worksheetPractise online with hints

For teachers: free to print, copy and use in class. Every new worksheet has new values and its own answer key. A link to ExamProblems on your course page is appreciated.

Name: ____________________   Date: ____________

1.Easy
b = 1 my = 2.1 mn = 0.025

Water flows uniformly 2.1 m deep in a rectangular gravel channel 1 m wide (Manning n = 0.025). The bed slope is S = 0.0015. Use Manning’s equation in SI units to find the mean velocity V.

b = 1 my = 2.1 mn = 0.025S = 0.0015
V = m/s
2.Easy
b = 2.5 my = 2.1 mn = 0.014

Water flows uniformly 2.1 m deep in a rectangular unfinished concrete channel 2.5 m wide (Manning n = 0.014). The bed slope is S = 0.005. Use Manning’s equation in SI units to find the mean velocity V.

b = 2.5 my = 2.1 mn = 0.014S = 0.005
V = m/s
3.Medium
b = 1.5 my = 1.7 m1 : 1n = 0.025, S = 0.002

A trapezoidal gravel channel has a bottom width of 1.5 m and side slopes of 1:1 (horizontal:vertical). Water flows uniformly 1.7 m deep. Manning n = 0.025 and the bed slope is S = 0.002. Find the flow rate Q in m³/s.

b = 1.5 my = 1.7 mz = 1n = 0.025S = 0.002
Q = m³/s
4.Medium
b = 6 my = 2.5 m3 : 1n = 0.03, S = 0.0005

A trapezoidal grass-lined earth channel has a bottom width of 6 m and side slopes of 3:1 (horizontal:vertical). Water flows uniformly 2.5 m deep. Manning n = 0.03 and the bed slope is S = 0.0005. Find the flow rate Q in m³/s.

b = 6 my = 2.5 mz = 3n = 0.03S = 0.0005
Q = m³/s
5.Hard
D = 250 mmn = 0.013, V = 1 m/s

A concrete sewer with an inside diameter of 250 mm (Manning n = 0.013) must reach a self-cleansing velocity of 1 m/s when flowing just full. Find the minimum slope S (in m/m).

D = 250 mmn = 0.013V = 1 m/s
S = m/m
6.Hard
D = 250 mmn = 0.013, V = 1.2 m/s

A concrete sewer with an inside diameter of 250 mm (Manning n = 0.013) must reach a self-cleansing velocity of 1.2 m/s when flowing just full. Find the minimum slope S (in m/m).

D = 250 mmn = 0.013V = 1.2 m/s
S = m/m

Answer key

  1. 1. V = 0.8464 m/s
  2. 2. V = 4.293 m/s
  3. 3. Q = 8.817 m³/s
  4. 4. Q = 33.65 m³/s
  5. 5. S = 0.006814 m/m
  6. 6. S = 0.009812 m/m

Full step-by-step solutions: practise this topic on examproblems.com.