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(a) A 1 m-high broad-crested weir controls flow in a river channel that is approximately rectangular in section with width 10 m (Figure Q1)

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(a) A 1 m-high broad-crested weir controls flow in a river channel that is approximately rectangular in section with width 10 m (Figure Q1). The bed slope is 1:1000 and the Manning coefficient is estimated to be 0.025 s/m'%. Given that the coefficient of discharge for the weir is 0.85, and assuming a 5% loss in flow energy over the weir, calculate the flow depth immediately upstream of the weir (section A in Figure

Q1) and immediately downstream of the weir (section C) for a discharge of 20 m/s. Neglect bed level differences between A and C for this calculation. [4 marks]

(b) For the situation described in part (a), a hydraulic jump occurs at some distance downstream from the weir (section D). If the flow depth on the downstream side of the jump (section E) is 0.9 m, classify the flow profile between C and D and calculate the profile with a minimum of 5 points. {10 marks]

(c) Calculate the specific energy at A, B, C, D and E and sketch the specific energy diagram for the flow, clearly indicating points on the diagram corresponding to sections A, B, C, D and E. (5 marks]

(d) With reference to part (b), how would you expect the jump location to change if the Manning coefficient between C and D was higher than the given value of 0.025 s/m'?? Briefly explain your answer. [3 marks]

(e) Classify the flow profile downstream of E and speculate as to what may be causing this profile. (3 marks]

A 8 C dD €F

Figure Q1

Q2.

(a) Find the volumetric and mass rates of bedload transport per unit width of channel in a rectangular irrigation canal 12 m wide with bed slope 1:1000 and dso=6 mm. The flow rate in the canal is 25 m*/s, particle and water densities are 2650 kg/m° and 1000 kg/m? Respectively, and the critical Shields’ parameter is assumed to be 0.05. Use the Meyer-Peter and Muller formula in your calculations [8 marks]

(b) A long irrigation channel with rectangular cross section is designed to convey water at a rate of 5 m°*/s. The channel bed slope is 1:500 and the bottom material is gravel with a representative size of 10 mm. Particle and water densities are 2650 kg/m? and 1000 kg/m°, respectively. The kinematic viscosity of water is 10* m/s.

What are the ranges of values of channel width B for which the bed particles are stable? Answering this question, you will need to:

1. Identify the overall procedure for solving this question. (5 marks]

2. Compute the hydraulic radius corresponding to the critical condition for the bed particles. (5 marks]

3. Select a procedure for calculating Manning's coefficient and obtain its value. (2 marks]

4. Find the ranges of values of channel width B for which the bed particles are stable. [5 marks]