Question

3. a) A trapezoidal open channel is being designed to convey a discharge of 11.0 m3 /sec. The channel will be excavated into clay and will have the following properties: side slope with m = 1.5, bottom slope of So = 0.001, Manning’s n = 0.022, and bottom width b = 1.0 m. For these conditions is there a risk of channel erosion? b) The earth-works contractor that will carry out the excavation suggests that the side slope angle can be increased to 45o (i.e. m = 1). Comment on the impact that such a change would have on: 1) the required depth of excavation, and 2) the risk of erosion. c) Calculation of the normal depth using Manning’s equation does not consider freeboard. Define the term freeboard, and use equation (28), Chapter 4, to estimate the freeboard required for part a) of this question.

Answer 1