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 = 1.5 my = 0.6 mn = 0.014

Water flows uniformly 0.6 m deep in a rectangular unfinished concrete channel 1.5 m wide (Manning n = 0.014). The bed drops 0.5 m per kilometre. Use Manning’s equation in SI units to find the mean velocity V.

b = 1.5 my = 0.6 mn = 0.014drop = 0.5 m/km
V = m/s
2.Easy
b = 4.5 my = 1.6 mn = 0.012

Water flows uniformly 1.6 m deep in a rectangular finished concrete channel 4.5 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 = 4.5 my = 1.6 mn = 0.012drop = 3 m/km
V = m/s
3.Medium
D = 600 mmn = 0.013, S = 0.002

A concrete storm sewer with an inside diameter of 600 mm flows just full (as an open channel, not under pressure). Manning n = 0.013 and the slope is S = 0.002. Find the flow rate Q in m³/s.

D = 600 mmn = 0.013S = 0.002
Q = m³/s
4.Medium
D = 1200 mmn = 0.013, S = 0.0005

A concrete storm sewer with an inside diameter of 1200 mm flows half full. Manning n = 0.013 and the slope is S = 0.0005. Find the flow rate Q in m³/s.

D = 1200 mmn = 0.013S = 0.0005
Q = m³/s
5.Hard
b = 4.5 my = 0.5 m3 : 1n = 0.022, Q = 4 m³/s

A trapezoidal clean earth channel with a bottom width of 4.5 m and side slopes of 3:1 (horizontal:vertical) must carry 4 m³/s in uniform flow at a depth of 0.5 m. Manning n = 0.022. Find the required bed slope S (in m/m).

Q = 4 m³/sb = 4.5 my = 0.5 mz = 3n = 0.022
S = m/m
6.Hard
b = 3 my = 1 m3 : 1n = 0.022, Q = 4.5 m³/s

A trapezoidal clean earth channel with a bottom width of 3 m and side slopes of 3:1 (horizontal:vertical) must carry 4.5 m³/s in uniform flow at a depth of 1 m. Manning n = 0.022. Find the required bed slope S (in m/m).

Q = 4.5 m³/sb = 3 my = 1 mz = 3n = 0.022
S = m/m

Answer key

  1. 1. V = 0.7678 m/s
  2. 2. V = 4.365 m/s
  3. 3. Q = 0.2746 m³/s
  4. 4. Q = 0.4359 m³/s
  5. 5. S = 0.003004 m/m
  6. 6. S = 0.0004901 m/m

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