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 = 3.5 my = 2.4 mn = 0.03

Water flows uniformly 2.4 m deep in a rectangular grass-lined earth channel 3.5 m wide (Manning n = 0.03). The bed drops 0.8 m per kilometre. Use Manning’s equation in SI units to find the mean velocity V.

b = 3.5 my = 2.4 mn = 0.03drop = 0.8 m/km
V = m/s
2.Easy
b = 1 my = 1.2 mn = 0.012

Water flows uniformly 1.2 m deep in a rectangular finished concrete channel 1 m wide (Manning n = 0.012). The bed slope is S = 0.005. Use Manning’s equation in SI units to find the mean velocity V.

b = 1 my = 1.2 mn = 0.012S = 0.005
V = m/s
3.Medium
b = 6 my = 0.7 mn = 0.012, S = 0.003

A rectangular finished concrete channel is 6 m wide. Water flows uniformly 0.7 m deep. Manning n = 0.012 and the bed slope is S = 0.003. Find the flow rate Q in m³/s.

b = 6 my = 0.7 mn = 0.012S = 0.003
Q = m³/s
4.Medium
b = 5.5 my = 1.4 m2 : 1n = 0.03, S = 0.003

A trapezoidal grass-lined earth channel has a bottom width of 5.5 m and side slopes of 2:1 (horizontal:vertical). Water flows uniformly 1.4 m deep. Manning n = 0.03 and the bed slope is S = 0.003. Find the flow rate Q in m³/s.

b = 5.5 my = 1.4 mz = 2n = 0.03S = 0.003
Q = m³/s
5.Hard
D = 375 mmn = 0.013, V = 1.2 m/s

A concrete sewer with an inside diameter of 375 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 = 375 mmn = 0.013V = 1.2 m/s
S = m/m
6.Hard
D = 300 mmn = 0.013, V = 1 m/s

A concrete sewer with an inside diameter of 300 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 = 300 mmn = 0.013V = 1 m/s
S = m/m

Answer key

  1. 1. V = 0.9504 m/s
  2. 2. V = 2.943 m/s
  3. 3. Q = 13.14 m³/s
  4. 4. Q = 21.05 m³/s
  5. 5. S = 0.005714 m/m
  6. 6. S = 0.005343 m/m

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