Chinese Rainfall
- Abraham Toribio II
For Chinese conduit design, the regulation recommends the rational method, so every city has a rainfall intensity formula with same form :
Keifer & Chu (1957) design rainfall (also called as Chicago Rainfall) describes how to generate a design rainfall using that intensity formula.
The fields specific to Chinese Rainfall generation are listed below:
Return Period
Period, in years, between events of the same intensity or of a greater intensity than this storm.
Calculation of A
Select method of specifying value of A:
- Calculated - A is calculated from a, C and return period values
- User - A is user defined
A (Calculated)
A is calculated as:
a(1 + Clog10P)
Where P is return period.
A (User)
User defined equation constant.
a
Equation constant, used in calculation of A when calculation of A is set to Calculated
C
Equation constant, used in calculation of A when calculation of A is set to Calculated
r
The portion of the duration of the event occurring before the peak
r Value Examples
place | r(times) | area | r(times) |
Chicago | 0.375(83) | Beijing | 0.355(57) |
Soviet | 0.35(—) | Shanghai | 0.367(80) |
Japan | 0.50(1050) | North china | 0.3-0.4(483) |
Most Chinese city | 0.3-0.4(—) | Wuhan | 0.3-0.4(—) |
b
User defined equation constant.
n
User defined equation constant.
Intensity and Rainfall Calculation
The duration for the design rainfall is 
Instantaneous intensity before peak is 
, corresponding duration is 
, and cumulative depth is 
.
Instantaneous Intensity after peak is 
, corresponding duration is 
, and cumulative depth is 
.
Total rainfall depth 
Set 
, the peak time ratio is r (which has a range of 0-1), then 
.
Assume the density formula is 
In China, A = a(1 + log10 P) where P is the return period and a is a constant.
the instantaneous intensity before 
and after peak 
are:
So and are calculated as follows:
From the above two equations, the cumulative rainfall depth is produced ad shown below:
The cumulative rainfall is calculated by following equations：
where
Reference on Chicago rainfall
C.J. Keifer, H.H. Chu, synthetic storm pattern for drainage design, proc paper 1332. ASCE. Aug. 1957.