Drainage study using CALTRANS information

[GVCivilGuy]

I'm trying to do a drainage study near Lakespur, CA. They rely upon DOT design rainfall intensities. From a map called "I" am to look up my area and take from that a number. In my case the number is 1.4. From this number I'm to determine the 10 year and 100 year event. The problem is that I'm not sure how to calculte the 10 year and 100 year event.

 

[cvg]

Are you using rational method? For rational method calculation you will need to calculate time of concentration and rainfall intensity in order to determine what the peak discharge is (in cfs).

You can get the rainfall intensities from the NOAA 14 atlas. See the following website:

http://dipper.nws.noaa.gov/hdsc/pfds/

 

[Hoagie]

Do you mean Larkspur, CA? If so, you may want to check out Marin County drainage instructions for additional information.