Pond Pack and Rationale Method 1

[mbherlihy]

I am working in Georgia and trying to run Pond Pack using the Rational Method. I'm having trouble with the Q/Qp (ratio)'Template data'. I don't have this catalogue listing.

Can anyone assist, or is anyone using Pond Pack and the Rational Method (*note not SCS Method) on small sites (less than 25 acres)?

Thanks in advance.

 

[francesca]

Q/Qp is used to derive a unit hydrograph. The Rational Method is a simple linear equation (Q=CiA) and doesn't result in/require a hydrograph. Do you mean you're using the Modified Rational method?

 

[mbherlihy]

Yes, you are correct. I am using a Pond Pack training manual and Lesson #3 states Rational Watershed analysis, but in the text body states Modified Rational Method.

So any experience with successfully using Modified Rational Method and Pond Pack? If yes, how can I obtain Q/Qp template data for this software?

 

[francesca]

Have you tried the Georgia DOT's drainage manual?

 

[mbherlihy]

Francesca, thanks for the replies. No, I have not tried the GDOT drainage manual, I'll look there. It sounds as if I'll find this in table format. Which is somewhat helpful..

But more specifically,

Has anyone had a successful experience using the Rational Method in Pond Pack, and if yes, how did they obtain this Q/Qp template data in digital format to be used by Pond Pack.

Thanks again for all the input. I'm getting closer.

 

[ychenut]

Hi there,

I was using PondPack, but with SCS unit hydrograph method. I remember the included tutorial was based on Rational method. I would use modified rational method rather than the one you were trying. The former is simpler to use, I guess. Their purpose are both transforming a single number, ie, peak runoff, into a hydrograph. Q/Qp might be more flexible coz you could input as many points as you want.

then with this inflow hydrograph and outlet hydrograph (determined by OCD), the size of pond could be esitmated by the difference intergrated against time. The methodology is simple, but the input, operation of pondpack is tedious. Personally, I believe Haestad sucks! I've found 2 bugs in the past 3 months for their 2 products, ie, pondpack and civilstorm.

Take look at the POndpack user manual, page 4-175, I copied it here, pay attention to the last sentence.

"Use the Q/Qp Template dialog box to create or edit a template. The template is a
way of translating a single Rational peak to a full runoff hydrograph over time.
The template data is usually acquired from the local regulatory agency."

 

[mbherlihy]

Ychenut, thanks for your input. I'm not crazy about Pondpack and this process either. I seem to recall coming across the same 'last sentence' as well.

I've contated the Bentley / Haestad technical support, to show me how to input this Q/Qp data. They have not responded to my specific question of Q/Qp input. All I've learned is that it is Modified Rational is the prefered method for reasons you and Francesca mention.

I think I'm drilling down to the realization that Q/Qp input is the issue. After retrival of tabular data (which I never found in the GDOT drainage manual), how do I input this into Pondpack?

Anyhow the quest continues and thanks to all for the input.

 

[francesca]

Do you have the Lindeburg Civil Engineering Reference Manual? If so, go to page 20-11 (10th Edition). There you will find the NRCS Dimensionless Unit Hydrograph, which is of course overkill for the Modified Rational Method (page 20-20).

The ModRat method uses a trapezoidal hydrograph with ordinates (0,0), (time of concentration, Qp), (storm duration, Qp), (time of concentration + storm duration, 0). To translate this into the Q/Qp graph, you'd have:

  T  | Q/Qp
-----------
 0   |  0
 Tc  |  1
 Td  |  1
 Tc+d|  0

You could flesh it out with intermediate points.

I have never used the ModRat method and don't intend to. I find the TR-55/SCS Curve Number method to be quick and easy to use and it is much less controversial.