|Storm frequency for eaves gutters as per Code||1 in 20 years (if you choose to use the location list)(10yrs NZ)|
|Time of concentration||5 minutes, as per code requirements for Aust. (10mins NZ)|
|Pipe class||PVC, for small diameters this is recommended.|
|Coefficient of runoff||1 , ie 100% runoff from a roof, as per Code requirement.|
|PIPE SIZE||MIN GRADE AUST||MIN GRADE NZ||PIPE SIZE||MIN GRADE AUST||MIN GRADE NZ|
There are also requirements for the depth of the pipe, generally known as soil cover requirements. This is normally dependent on the location of, the material of the pipe, and the likely vehicle loads. The heavier the vehicle the deeper the pipe must be. Cover requirements range from 100mm for single dwellings with no vehicle loads, to 500mm under roads. Please consult the plumbing code for greater clarification.
Pipes under public roads come under different codes and Council requirements. Please consult a Civil Engineer to design pipes in this location.
Storm Return Period, Time of Concentration and Coefficient of Runoff:
The time of concentration is the time it takes water to travel from the furthermost point in the catchment to the point under investigation. For building sites in Australia this is taken as 5 mins. (NZ 10 mins).
The coefficient of runoff is the percentage of storm water that actually runs off. eg a coefficient of runoff of 1, means 100% runoff, This program uses "1" ie 100% runoff as on a roof, or other impervious surface.
The program uses an average recurrence interval (ARI) of 1 in 20 year (5 min duration) storm for Australia, and (10mins 1:10 year NZ) for the towns on the drop down list.
However, you may use the program to determine the stormwater pipe size for any condition, if you know the rainfall intensity, and the coefficient of runoff. Multiply the catchment area by the coefficient of runoff before entering it in the program. eg 50% runoff, is the same as 50% catchment area with 100% runoff.
If using your own intensity, you must select the location choice to:- "I prefer to enter a known intensity"
Intensity for towns not listed
These are two great sites. Look for the Intensity, Duration, frequency curves (IDF) or words to that effect.
For Australia Time of concentration (TOC) 5mins ARI 20 years.
New Zealand Time of concentration (TOC) 10mins ARI 10 years.
Intensity, Frequency, Duration curves.. For Australian towns.
and for New Zealand from here Also, your local Authority, Consulting Engineer, or Hydraulic Consultant may be able to advise.
Learn much much more
B.Tech MIEAust CPEng RPEQ
DISCLAIMER: It is the users responsibility to ensure input data is calculated
and entered correctly, and that the program is suitable for the roof
OTHER HYDRAULIC CALCULATORS