Rainfall-Runoff Modeling

1
Rainfall-Runoff Modeling
2
Modeling Considerations

• Development of a rainfall-runoff model depends on
  
• (1) Time scale
• (2) Basin scale
• For larger time scale (month, year, or longer)
• Runoff f(Rainfall) VQ g(VRain)
• For shorter time scale (eg. Storm events)
• Runoff Hydrograph f( Rainfall Hyetograph)
• Q(t) f I(1), I(2), , I(t)

3
Rational Formula

• First proposed by Kuichling in 1889
• Qp k C i A
• where k unit conversion factor,
• 1.008 for English unit 0.278 for
  metric unit
• Qp peak discharge (ft3/s or m3/s)
• i rainfall intensity (in/hr or
  mm/hr)
• A drainage area (acres or km2)
• Note i average intensity of rainfall
  corresponding to the
• duration of time-to-concentration.

4
Time-of-Concentration

• Definition
• It is an elusive hydrologic variable and it is
  very difficult to measure.

5
Time-of-Concentration Methods (1)
6
Time-of-Concentration Methods (2)
7
Time-of-Concentration Methods (3)
8
Comparison of Time-of-Concentration Models
9
Time-Area Method

• Can be considered as an extension of the rational
  method in which rainfall intensity in not uniform
  over the storm duration

10
Time-Area Method (Eg. 1)
11
Time-Area Method (Eg. 2)
12
Time-Area Method (Eg. 3)
13
Time-Area Method (Eg. 4)