TABLE 1: Manning n for various channel types

Channel description	n
Clean, straight, no rapids or pools	0.035
Clean, winding, some pools and shoals	0.042
Sluggish reaches, weedy, deep pools	0.084
Very weedy, deep pools, encroaching shrubs	0.11

1. Table 2 shows the change in the area (A) and hydraulic radius (R) of a stream cross-section during and after a storm. Complete the Table by using the Manning Equation to calculate the flow velocity and discharge of the stream at the observation times. For your calculations, assume that the stream channel is clean and winding with some rapids and shoals, and that it has a gradient of 5 m/km (S = 0.005). (24 marks)

TABLE 2: Observations of area and hydraulic radius on a hypothetical stream

Time (hrs)	A (m2)	R	V (m/sec)	Q (m3/sec)
midnight	71	0.33
12:15	71	0.33
12:30	193	0.52
12:45	287	0.81
1:00	348	1.33
1:15	301	0.92
1:30	252	0.82
1:45	203	0.46
2:00	169	0.43
2:15	119	0.41
2:30	92	0.25
2:45	83	0.35

2. Plot the stream discharge values calculated in Table 2 above as a hydrograph on Fig. 1. Label the rising limb, falling limb, and peak of your hydrograph. Determine the total volume (in litres) of water which flowed through the cross-section between midnight and 3:00 A.M. Assume that your calculated discharges (Q) apply for the full 15 min after the time at which they were calculated. (Hint: 1 m³ = ? litres). (13 marks)