text: Find the depth of rainfall from a storm of duration 6 hours and return period 10 years on a catchment of 5 km in Sheffield.
  #From the FSR maps, the M5-60 minutes rainfall is 20.5mm, and "r" = 0.4.
  #Divide 20.5mm by 0.4 to get 51.3mm, which is the M5-2 days rainfall depth.
  #Factor Z1 = 0.64, so multiply 51.3mm by 0.64 to get 32.8mm.
  #Factor Z2 = 1.16, so multiply 32.8mm by 1.16 to get 38.1mm.
  #The ARF is 0.96, so multiply 38.1mm by 0.96 to get 36.6mm.
  Therefore the expected depth of rainfall from the storm is 36.6mm. The mean intensity of rainfall is given by 36.6mm divided by 6 hours, which is 6.1mm/hour.