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 = 3 my = 2.3 mn = 0.022

Water flows uniformly 2.3 m deep in a rectangular clean earth channel 3 m wide (Manning n = 0.022). The bed slope is S = 0.004. Use Manning’s equation in SI units to find the mean velocity V.

b = 3 my = 2.3 mn = 0.022S = 0.004
V = m/s
2.Easy
b = 3 my = 1.2 mn = 0.012

Water flows uniformly 1.2 m deep in a rectangular finished concrete channel 3 m wide (Manning n = 0.012). The bed drops 3 m per kilometre. Use Manning’s equation in SI units to find the mean velocity V.

b = 3 my = 1.2 mn = 0.012drop = 3 m/km
V = m/s
3.Medium
D = 1200 mmn = 0.013, S = 0.002

A concrete storm sewer with an inside diameter of 1200 mm flows half full. Manning n = 0.013 and the slope is S = 0.002. Find the flow rate Q in m³/s.

D = 1200 mmn = 0.013S = 0.002
Q = m³/s
4.Medium
b = 2.5 my = 2 m2 : 1n = 0.025, S = 0.003

A trapezoidal gravel channel has a bottom width of 2.5 m and side slopes of 2:1 (horizontal:vertical). Water flows uniformly 2 m deep. Manning n = 0.025 and the bed slope is S = 0.003. Find the flow rate Q in m³/s.

b = 2.5 my = 2 mz = 2n = 0.025S = 0.003
Q = m³/s
5.Hard
b = 3 my = 1.6 mn = 0.025, Q = 8.9 m³/s

A rectangular gravel channel 3 m wide must carry 8.9 m³/s in uniform flow at a depth of 1.6 m. Manning n = 0.025. Find the required bed slope S (in m/m).

Q = 8.9 m³/sb = 3 my = 1.6 mn = 0.025
S = m/m
6.Hard
b = 4 my = 2.2 mn = 0.022, Q = 13 m³/s

A rectangular clean earth channel 4 m wide must carry 13 m³/s in uniform flow at a depth of 2.2 m. Manning n = 0.022. Find the required bed slope S (in m/m).

Q = 13 m³/sb = 4 my = 2.2 mn = 0.022
S = m/m

Answer key

  1. 1. V = 2.695 m/s
  2. 2. V = 3.483 m/s
  3. 3. Q = 0.8718 m³/s
  4. 4. Q = 31.01 m³/s
  5. 5. S = 0.003023 m/m
  6. 6. S = 0.0009927 m/m

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