×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Jobs

Modeling a Vegetated Underdrained Soil Filter

Modeling a Vegetated Underdrained Soil Filter

Modeling a Vegetated Underdrained Soil Filter

(OP)
I have come across some results recently that seem a bit odd when modeling an underdrained soil filter in HydroCAD 10. I have always modeled my primary outlet as exfiltration only above the invert elevation with a velocity input depending on the soil media. My secondary outlet is the grate on top of my emergency overflow structure which also collects the underdrain before discharging offsite. I can see two problems with my latest models:

1) My outflow volume does not match my inflow volume (roughly 50% of the inflow) even though I have the exfiltration specified as a primary outlet. Theoretically, shouldn't the two volumes match assuming no loss to the surrounding soils?

2) My Outflow rate exceeds my Inflow rate. In one case I am showing an inflow of 4.05 cfs and an outflow of 6.55 cfs. What am I missing?

Any help would be appreciated.
Chip

RE: Modeling a Vegetated Underdrained Soil Filter

Without seeing your actual data, it could be hard to say. That being said:

1. the most common reason for an outflow volume to be half of the inflow would be that the modeling time has not extended until flow is complete.

2. the most common reason I have found for outflow greater than inflow is that modeled water surface elevations have exceeded those I have defined. This can create a erroneously high head condition which produces an erroneously high outflow.

RE: Modeling a Vegetated Underdrained Soil Filter

This looks like the same question sent to HydroCAD support today.

You'll get an answer either way, but if you use both channels we have to spend extra time responding to both inquiries.

Please post only in one place.

Peter Smart
HydroCAD Software
www.hydrocad.net

RE: Modeling a Vegetated Underdrained Soil Filter

(OP)
My apologies, I was not aware that this forum was monitored by HydroCAD support as well. I appreciate the timely responses though and will check into my model when I get a chance.
Thanks,

RE: Modeling a Vegetated Underdrained Soil Filter

The great thing about posting here is that everyone gets the benefit of seeing solutions to what may be common problems.

Also, if one searches this forum, one may find the solution and save Peter support time, allowing him to keep improving this great product!

RE: Modeling a Vegetated Underdrained Soil Filter

Echo Terry's comments above.

First thing I'd do, is add some dummy storage above the crown of all your detention ponds, to make sure you're not pegging them out, and see what the head in those ponds actually comes to. If that fixes the inflow/outflow problem, then your ponds are too small.

Hydrology, Drainage Analysis, Flood Studies, and Complex Stormwater Litigation for Atlanta and the South East - http://www.campbellcivil.com

RE: Modeling a Vegetated Underdrained Soil Filter

Have you reviewed all the warning messages?

I assume you're getting a Qout>Qin warning - click the message for complete details and solutions.

If you're getting an "overfilled storage" message also see www.hydrocad.net/overfilled.htm

Peter Smart
HydroCAD Software
www.hydrocad.net

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Resources