Hydraulics Discussion

[urbanresource]

This thread has started to discuss the basics of hydraulics. It is always nice to revisit the fundamentals from time to time, to make sure we're all headed in the right direction.

Anyhow, I am officially opening the Hydraulics thread for discussion. This could include anything from using software to understanding the HGL. I have listed a few items below to get this thread going. Also, I have included my input on each item as well, as I like sharing my knowledge, in hopes of learning something I did not know, or have not thought of before. Thank you for viewing and I look forward to all feedback!

1. Hydraulic analysis software

I use WSPGW and it has served me pretty well when I need to run an analysis to determine adequacy of pipe sizing, and the overall system. Has anyone encountered anything with this software which has been negative?

2. Downstream HGL control

I typically go off of existing as-built plans to find the HGL, when connecting to an existing storm main. Same goes for any outlet into a channel. Although, this could be way off (particularly for older as-built plans), it is the best guess, and in some cases, all we have to use. We have to remember that hydrology and hydraulics is not an exact science. Its best guess some times, and could vary from one engineer to the next. When outletting into a natural stream, I use soffit as the downstream HGL control.

3. Hydraulic analysis at junction structure, catch basins, transition structures, etc.

When using WSPGW, I typically add a Wall Entrance at catch basins, and JX for junction structure connection.

4. HGL minimum depth

I maintain a minimum of 2’ below finish surface or finish grade when analyzing the HGL relative to finish surface or finish grade.

5. Tricks to manipulate and improve HGL depth.

I typically increase pipe size and/or increase pipe grade to help improve this. In some cases, you may just be stuck with a high HGL, so you just have to use the appropriate pipe size to make sure the HGL does not jump above ground. Larger radiuses also do not help. Manning’s friction factor can also have an impact if you are going from RCP (n=0.013) to HDPE (n=0.012), although not common, especially if you have a large system.

6. Please feel free to add any additional items that would be useful for discussion.

 

[gbam]

1. StormCad or Inroads is what we use for software. I have also written a spreadsheet that automates HEC22. I have never used WSPGW so I cannot comment on it. I like my spreadsheet the best because I have set it up the way I want to display results unlike the "canned" software.

2. DS control I also use As-builts and previous studies. I also like to set my control aabove the DS control if vertical clearance is available. IE, I will set my sofit of SD above the DS HGL that way I can start at my sofit.

3. I use the HEC22 method for analyziong structure losses. Same method is used in the two software packagesI use.

4. Minimum HGL Depth - Typically set to 6"-1' below inlet and/or manhole rim.

5. I usually use benching to improve hydraulics to structures as well as pipe diameter. It depends on the situation, of course.

6. A good gut check is always important. Check out volume of storm against deten volumes etc...

 

[cvg]

WSPG is typically only used in Southern California and is not prevalent around the country. StormCad is generally more user friendly, however it doesn't handle open channels. I have never used the windows version.

 

[urbanresource]

Thank you GBam. Please see my questions/comments to your responses below.

2. I think this can only be done when the existing HGL is relatively low. How would this be possible if you have an existing pipe already under pressure, and the DS HGL is high?

5. I am not familiar with the term benching. Can you please elaborate? Thanks!

 

[gbam]

UR,
Regarding #2. If there is available elevation difference one can use a drop manhole or structure to provide a "higher" tie-in elevation. When this is possible the losses from the existing system to the new system can be reduced. Note, that this is only possible provided the available evelations.

Regarding #5. Benching is the shaping of a manhole or box structure to provide a "smooth" transition through the structure. There is discussion in HEC-22 regarding losses and the extent of benching. For instance if you have a 4'x4' square access hole with a 24" entering and 36" exiting, the bench will provide a "rounded" bottom and width transition through the structure.

 

[angelab]

cvg, the latest version of StormCAD handles open channels of any shape