Hydrology in Los Angeles?
Hydrology in Los Angeles?
(OP)
I have seen this done a few different ways and was curious for those working in the Los Angeles area. What software do you use to figure out the Stormwater Flowrate/Q on site?
I was always told to use the LA County Hydrology manual and input the numbers from the 50-year 24 hour Isohyet maps into the TC calculator to find the Peak Flow rate.
Now my partner does it a different way and uses an older 1990 LA County Hydrology manual that has K values on a map for different areas that you plug into an equation using a Capitol Flood Q's by Rainfall Zone table.
My partner who has 20 years more experience than I do, says that the way everyone taught me to use the TC Calculator is wrong and gives wrong numbers.
So what does everyone else do for finding a site's Peak Flow Rate to size the storm drain pipes? Especially for those that have only seen the current LA County Hydrology Manual.
I was always told to use the LA County Hydrology manual and input the numbers from the 50-year 24 hour Isohyet maps into the TC calculator to find the Peak Flow rate.
Now my partner does it a different way and uses an older 1990 LA County Hydrology manual that has K values on a map for different areas that you plug into an equation using a Capitol Flood Q's by Rainfall Zone table.
My partner who has 20 years more experience than I do, says that the way everyone taught me to use the TC Calculator is wrong and gives wrong numbers.
So what does everyone else do for finding a site's Peak Flow Rate to size the storm drain pipes? Especially for those that have only seen the current LA County Hydrology Manual.
Civil Development Group, LLC
Los Angeles Civil Engineering specializing in Hillside Grading
http://www.civildevelopmentgroup.com
http://www.civildevelopmentgroup.com/blog





RE: Hydrology in Los Angeles?
For small sites (only a few acres/hectares)you could probably get away with using a rational method to calculate flows and further be able to size pipes. There is a number of ways to calculate time of concentration, you would need to select a method that is most appropirate for your site. The HEC-22 manual provides a few different ways of establishing a TC.
If you need to design any kind of attenuation facility or the siet is over a few acres, the rational method should not be used but rather using software like HydroCad or SWMM. These two pieces of software (as an exmaple) allow you to produce hydrographs for your site which therefore allows you to produce accurate attenuation calculations for required storage.
For the LA region, I would assume (haven't done work there)that you would use a 24-hour SCS Type I storm distribution and local rainfall data as a starting point for developing your flows. Again, you local engineering standards should provide this information.
Hope this helps.
RE: Hydrology in Los Angeles?
Also, I am looking for info for sites less than an acre. Like 20,000-40,000 sq. ft.
I am curious if there is an easier software to use? Something better? Just more information from others.
Civil Development Group, LLC
Los Angeles Civil Engineering specializing in Hillside Grading
http://www.civildevelopmentgroup.com
http://www.civildevelopmentgroup.com/blog
RE: Hydrology in Los Angeles?
thread162-201630: Hydrology Software
RE: Hydrology in Los Angeles?
Yes my partner is super old school, and can convince a lot of city engineers he is right basically in any situation. I love him for that, as that to me is a true engineer!
Civil Development Group, LLC
Los Angeles Civil Engineering specializing in Hillside Grading
http://www.civildevelopmentgroup.com
http://www.civildevelopmentgroup.com/blog
RE: Hydrology in Los Angeles?