________

Year 56 57 58 59 60 61 62 Flood (m3/s) 38.2 58.9 120.6 57.6 159.9 40.4 66.2 Year 63 64 65 66 67 68 69 Flood (m3/s) 73.6 66.5 206.8 84.8 97.1 142.1 82.1

[Q50 = 214 m3/s]

3. Calculate the peak runoff rate resulting from the probable maximum precipitation at Ardingly Reservoir from the following data:

Time (h) Rainfall (mm) Time (h) Rainfall (mm)

o 2 3 4 5 6 2 5 8 11 14 31

6 7 8 9 10 11 12 13 93 31 14 11 8 5 2

Percentage runoff = 68% (from catchment characteristics) Baseflow = 1 m3/s (from catchment characteristics) 10 mm, 1 hour unit hydro graph time to peak = 4 h Catchment area = 21.82km2

(Hint. Use a synthetic UH with Tp = 4 h)

4. Describe, in detail, what methods you would use to estimate the 50-year return period flood (both peak discharge and flood hydrograph) for the following two cases:

(a) an ungauged catchment; (b) a gauged catchment with stream flow records of 15 years. Suggest ways in which your estimate could be improved (presuming that your improved estimates are required within 1 year!).