thread162-365226 Looking for mos

[Sebast73]

thread162-365226

Looking for most efficient (faster) way to model a storm drainage system with 30 CB and structures around a closed loop pavement and parking area which eventually discharge into an existing Detetion Basin. There is also additional under ground ADS pipe storage capacity set aside for attenuation . the predeveloped lot is steep and wooded with post developement imperviousness = 58%. Its insane there is no where near enough storage i believe with my intermediate level of experience. The pond will store 86000 CF. It is a 7 acre lot.

I have been given the task to assure another engineers design is sufficient due to increase in impervious area. Do not have originsl calcs but seems as if original model was calculated incorrectly in yhe first place.


Hope some one appreciates this post ?

Sebast73

 

[Ekenny_G]

I would almost suggest using Hydrocad or StormCAD. What format was the original model?

 

[Sebast73]

That the Kicker, do not have access to original data, just final numbers which are significantly higher peak flows than what I am coming up with. Therefore it leads me to believe the previous engineer used the Rational Method ? Not certain thou.

I am currently using HydroCAD, and I am coming up with this concern. My pre dev. flows are lower for small storms say 2, 5 and 10 year, it is not until I run the 25 year storm when the Pre matches the Post / What would cause this ? I will upload the files if anyone feels like taking a look?

 

[psmart]

Pre/post differences can sometimes seem obscure, but are generally due to Tc and CN changes. If you want to post the pre and post (Preferably side-by-side in the same HydroCAD file) I'll be glad to have a look. Please post the simplest file which demonstrates the effect you're asking about.

Peter Smart
HydroCAD Software

http://www.hydrocad.net

 

[Sebast73]

I was not 100 percent certain how to bring both files PRE and POST into same HydroCAD file so I have uploaded the two separately.

Excuse my inexperience with the software, Eager to learn, although sort of green to me.

Thanks in advance for any input you may have.

 

[Sebast73]

Previous post had the PRE existing condition HydroCAD file. this Post will have the POST Condition file.
Again, excuse my inexperience with the software and the forum.

Looking forward to some advise.

 

[psmart]

I assumed you were just asking about pre/post runoff results. At what point are you comparing the pre/post results?

Peter Smart
HydroCAD Software

http://www.hydrocad.net

 

[Sebast73]

At the POC "B" the Outlet structure in the D-Pond. Although I would appreciate any input or and or opinions based on fact or experience. The final outcome must be reviewed by a municipality so if anything is unclear, great to know now. Thanks again for any input you may have. I could post the 155 page Stormwater management report which should explain the analysis better, but I do not expect you spending the majority of your time in a day on reading. I'm sure you would, if your were getting compensated but since your not I apprec. the simplistic approach..

 

[psmart]

I thought you were asking about a pre/post RUNOFF issue. Once you include a detention pond the results will depend on the exact design of the pond. Some events may higher and others lower. It all depends on the exact design of the pond.


Peter Smart
HydroCAD Software

http://www.hydrocad.net

 

[Sebast73]

Thank you for your response, I have been out of the office working in the field the past few days therefore it has taken me a few days to reply. The Detention pond is an existing fixture from a previous design which was to be sufficient for a 3 parcel plot which the lot of interest today is one of the three. Therefore another engineer designed the pond and my duty is to assure if is sufficient for the new development. Again, any input is greatly appreciated due to the fact that I am fairly new at using HydroCAD and hydrology in general. Lately it has become a more prevalent portion of my daily work.

 

[Ekenny_G]

From the original post, it looks like you have two component of the design. The first is the catch basins and pipe network. The second is the Detention basin.
I am guessing your are more concerned with the basin component? From the model, you can quickly determine the pre-Runoff volume and the Post-Runoff volumes. Then you can check how much storage is provided in the basin. The minimum required storage should be the difference between post runoff volume and pre-runoff volume. If the basin has an outlet structure, you can also check that the release rate is not greater than the pre-discharge rate for the design storm event.

 

[Sebast73]

Ekenedilichukwu, that makes complete sense. Thank you.