design criteria for pipes

Dear SWMMers,

Is anyone aware of design standards for pipes that allow minor street flooding? We are designing drainage improvements for Ho Chi Minh City, and have been told that we can use the national standard of allowing surcharging within 0.25 m of street level, or use a design standard that has been adopted elsewhere.

Since we're using EXTRAN, we can obtain results with duration and volume of flooding, and are looking for guidelines that others have used. We expect this would look something like allowing x minutes of flooding to a depth of y for the n year storm.

Thank you very much for your assistance.
Regards,
Mitch Heineman, P.E.
Camp Dresser & McKee

Dear Mitch:

Since your project relates to the drainage systems of Ho Chi Minh city, I would point out the following for your considerations:

1. The national standard (i.e. allowing surcharging within 0.25 m of street level) may not applicable for this City since most of its streets are much higher than "first floor levels" of houses. By accepting the standard you may end up flood more than half of that City.

2. The service connections of the City are simply a mess.Please ensure that you have proper info. re: the ex. networks. Otherwise, you may not be able to model the systems correctly.

3. Flooding problems associated w/ Hochiminh City are usually due blockages of overland flow routes. Therefore, you may want to investigate into this type of problem.

Wish you have a sucessful project.
Cheer,
Tai D. Bui, P.Eng.