Calibrate a Hydrograph to real flows

[kevinjackman]

I am using Civil 3D 2010, Hydraflow Hydograph Extension.

I have created a predevelopment hydrograph using the Type II distribution for a 24 hour, 100 yr event.  I get a Qpeak of 80 l/s.  Hand calculations verify this.

Regional stream analysis indicates a typical predevelopment Qpeak of 8 l/s/Ha which translates into 4 l/s for my site.

Is there a way to calibrate the computed hydrograph to get 4 l/s for the peak flow?

After that, how would I calibrate the Post development hydrograph?

Thanks a lot.

[kevinjackman]

Anyone?

[Matt.Anderson]

Calibration will require you to tweak your settings to achieve the results you need for response.  Since you indicated you are using SCS Type II rainfall - a very peaky method - and you have a peak result nearly 20 times the expected.

What is your goal? Volume of hydrograph?  Or just a hydrograph that proves that regional value?  Are you calculating stormwater detention from it? 

If the later is true - just use your peak regional value for the release rate if that is standard practice in your areas.

Matt

[kevinjackman]

Hi Matt,

I need to get the difference in pre and post volumes to size my detention pond, then size the outlet for the peak predevelopment flow.  Won't the extraordinary peaks affect the storage required?

It would be nice to show that my hydrographs are consistent with regional values.  I plan on attaching my hydrograph summarys as an appendix to my report.

Thanks a lot. 

[Matt.Anderson]

Here is the example that I would use:  http://www.civil3d.com/2010/10/stormwater-detention-estimates/

Your 4 lps value is the Target outflow.  

Check your local regulations for the storm distribution required - Is SCS Type II a valid for your area?  Are you expecting a 24-hour storm duration?  If so, try the Huff-3rd Quartile...

[kevinjackman]

Is there a way to 'scale' a peak flow?

8 l/s is a predetermined predevelopment flow rate for the area.

I want to scale the pre-dev peak flow so that I create a predevelopment hydrograph to match this 8l/s.

I am hoping that by doing so, I can use this scaled model to output a Post development hydrograph with a more resonable peak flow.

I am using Chicago Distribution.

Regulating Agency wants to see post development hydrograph.  Calculated peak is far to high (24hr, 100 yr).

C3d 2011, SSA.

[Matt.Anderson]

Scale - not within the program.  You can send you resulting hydrograph out to Excel, manipulate it and use those values for something. 

To mimic a peak flow values in the program, you will need to establish the subbasin parameters that dictate that flow. Ie, alter your time of concentration or runoff coefficients or rainfall amount to match.