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 = 1 mn = 0.025

Water flows uniformly 1 m deep in a rectangular gravel channel 1.5 m wide (Manning n = 0.025). 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 = 1 mn = 0.025drop = 0.5 m/km
V = m/s
2.Easy
b = 4.5 my = 1.9 mn = 0.012

Water flows uniformly 1.9 m deep in a rectangular finished concrete channel 4.5 m wide (Manning n = 0.012). The bed drops 0.8 m per kilometre. Use Manning’s equation in SI units to find the mean velocity V.

b = 4.5 my = 1.9 mn = 0.012drop = 0.8 m/km
V = m/s
3.Medium
b = 3 my = 1.4 mn = 0.025, S = 0.0008

A rectangular gravel channel is 3 m wide. Water flows uniformly 1.4 m deep. Manning n = 0.025 and the bed slope is S = 0.0008. Find the flow rate Q in m³/s.

b = 3 my = 1.4 mn = 0.025S = 0.0008
Q = m³/s
4.Medium
b = 2.5 my = 1.2 m1.5 : 1n = 0.022, S = 0.0015

A trapezoidal clean earth channel has a bottom width of 2.5 m and side slopes of 1.5:1 (horizontal:vertical). Water flows uniformly 1.2 m deep. Manning n = 0.022 and the bed slope is S = 0.0015. Find the flow rate Q in m³/s.

b = 2.5 my = 1.2 mz = 1.5n = 0.022S = 0.0015
Q = m³/s
5.Hard
b = 1 my = 1.2 mn = 0.015, Q = 2.2 m³/s

A rectangular brickwork channel 1 m wide must carry 2.2 m³/s in uniform flow at a depth of 1.2 m. Manning n = 0.015. Find the required bed slope S (in m/m).

Q = 2.2 m³/sb = 1 my = 1.2 mn = 0.015
S = m/m
6.Hard
b = 6 my = 2.4 m3 : 1n = 0.03, Q = 87 m³/s

A trapezoidal grass-lined earth channel with a bottom width of 6 m and side slopes of 3:1 (horizontal:vertical) must carry 87 m³/s in uniform flow at a depth of 2.4 m. Manning n = 0.03. Find the required bed slope S (in m/m).

Q = 87 m³/sb = 6 my = 2.4 mz = 3n = 0.03
S = m/m

Answer key

  1. 1. V = 0.5084 m/s
  2. 2. V = 2.404 m/s
  3. 3. Q = 3.832 m³/s
  4. 4. Q = 7.538 m³/s
  5. 5. S = 0.003032 m/m
  6. 6. S = 0.003968 m/m

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