pond outlet culvert vs. pipe reach question
pond outlet culvert vs. pipe reach question
(OP)
Hi. I know, this topic has been beaten badly, but i still have a question.
I have a simple driveway culvert that I have modeled as a reach, and also as a catchbasin pipe outlet.
The pond outlet model indicates the culvert is undersized, and the flood elevation is breached. (I set the flood elevation as the centerline of the road.)
The reach model indicates the culvert has excessive capacity, based on the expected peak flow, and the culverts' manning capacity.
So I set the auto-resize to on, performed the calculation, and both culverts are resized, to the top of pipe crown.
However, the pond still overtops the road. Why doesn't the pipe get resized to NOT allow overtopping?
Second question: (Theory) why does the "pond" method produce such a different capacity of the culvert? The manning capacity of the pipe is far greater than the peak flow, and the inlet condition setting in the pond outlet screen effects the pipe very little. So I would expect my "no storage" pond would pass all the flow into the culvert, and no headwater at all would occur. However, in my parralell analysis my "no storage" pond is overtopping the road.
Very curious.
Thank you very much.
I have a simple driveway culvert that I have modeled as a reach, and also as a catchbasin pipe outlet.
The pond outlet model indicates the culvert is undersized, and the flood elevation is breached. (I set the flood elevation as the centerline of the road.)
The reach model indicates the culvert has excessive capacity, based on the expected peak flow, and the culverts' manning capacity.
So I set the auto-resize to on, performed the calculation, and both culverts are resized, to the top of pipe crown.
However, the pond still overtops the road. Why doesn't the pipe get resized to NOT allow overtopping?
Second question: (Theory) why does the "pond" method produce such a different capacity of the culvert? The manning capacity of the pipe is far greater than the peak flow, and the inlet condition setting in the pond outlet screen effects the pipe very little. So I would expect my "no storage" pond would pass all the flow into the culvert, and no headwater at all would occur. However, in my parralell analysis my "no storage" pond is overtopping the road.
Very curious.
Thank you very much.
___
Craig T. Bailey, PE
www.bailey-associates.com
Talk To Other Members
RE: pond outlet culvert vs. pipe reach question
2)The inlet energy loss will frequently restrict the flow to less than the Manning's capacity. If you set a very low Ke value the culvert capacity will approach the Manning's capacity of the pipe.
RE: pond outlet culvert vs. pipe reach question
RE: pond outlet culvert vs. pipe reach question
In the resize tab, you can choose to have the program automattically resize all, or certain nodes. Everytime you change rainfall, and "calculate," those items will get resized. Or - "if your feeling lucky, punk," you can select "ongoing resize." That will certainly keep you on your toes.
Good luck,
Craig Bailey
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Craig T. Bailey, PE
www.bailey-associates.com
RE: pond outlet culvert vs. pipe reach question
Do I estimate the basing size and elevation data, also the culvert sizes and slopes?
Thx,
RE: pond outlet culvert vs. pipe reach question
What are you trying to detain? The entire cities' 500 year storm? :)
The approach I would take would be to determine the storage required at the basin first, manually. Hydrocad does not have pond sizing capabilities, other than the estiamted graph feature on the reports window.
Then set up your assumed culvert outlet parameters, (using 2 as your multiplier.
set the auto-resize settings, and 'let er rip!
You won't be able to auto-resize the channels.
good luck, and I'm curious as to what you are analyzingto give such big numbers.
ctbailey
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Craig T. Bailey, PE
www.bailey-associates.com
RE: pond outlet culvert vs. pipe reach question
to develop these lands without a rigorous analyses of the site. The site in question is in a floodway. The only way to develop such a site is to re-direct the flows via a channel and relese the flows such that the 2 current natural outlet locations (split flows) are maintained.
A detention basin can capture the volume and reduce the peaks if properly sized and outlets are also sized to handle the releases.