Modeling Ril Road Track in HydroCAD

[DCMP]

I am trying to model railroad track which will be placed in the existing grassed area. There will be an inlet every 180' which will direct water into parallel SD system and ultimately into the natural stream. Tracks are confined between two retaining walls and the stone ballast under the track is 27' wide and 2' thick. Top of the ballst is relatively flt but the bottom is sloping at the rate of about 7%. There will be 3' wide and 3' deep under drain trench filled with stones and perforated under drain. The bottom of stone ballast is impermeable and sloping at 40:1 towards under drain trench which is in the middle of the track.
The under drain follows bottom slope which is 7%.

The elevations are as follows:

Top of the track - upper end el. - 378 and lower end 365.5
Bottom of the UD Trench Upper end - 372 and lowe end 359.5

I am trying to model that the storm water will initially percolate through stone ballast, then into under drain trench and then into under drain pipe via perforation. I am not sure if I have modeled under drain and perforation correctly. I have attached PDF for your review. Could you look at the attached pdf and let me know if there is anything I need to change? Since the perforation are on the UD, which is on a sloping ground what elevation should I use? Which elevation should I use for exfilteration since the upper end 12.5' higher than lower end? Notice that the outflow is greater than inflow - how is this possible?

 

[psmart]

1) Your results suggest the presence of warning messages that have been suppressed from the printed report. These messages will identify possible problems (such as excess discharge) and suggest solutions. To give a complete picture of your situation, I suggest that you post or send the HydroCAD .HCP file rather than the printed report.

2) For the perf pipe, if you select vertical orifice orientation you can set a row spacing that can be used to approximate the effect of the pipe slope. However, the pipe itself is usually the controlling factor, rather than the perforations. (See the capacity for each device at the bottom of the pond summary.)

3) Is there any above-grade storage present? You've only included the stone voids in the model. This is usually accompanied by additional storage definitions for the above-grade ponding.

4) Exfiltration is normally used to model the flow of water from a pond into the surrounding soil. In your case, the water flows directly from the stone voids into the perf pipe, so I don't think the exfiltration outlet is needed.




Peter Smart
HydroCAD Software

http://www.hydrocad.net

 

[DCMP]

Peter,

1) I made changes as you suggested and have attached file for your review.

2) change as you suggested

3) No there is no above grade storage what I am trying to determine is if there is any peak shaving due to stone and perforated pipe. In other words is there going to be increase in time of concentration? Because water will not travel as it would in normal channel. It is going to percolate through stone ballast and then into UD trench. I used DRIP calcs (pavement drainage through crack - in our case it is 100%) and figure that the time of concentration for remotest point to enter into the pipe would be approximately 24 minutes but there is no standard method to determine time of concentration in such case. Also the perforation bound to be blocked to certain degree with stones so water will not enter into perforation quickly.

4) I have uploaded rough typical section to give you an idea. I can not load more than one file so I will send you HCAD file in the next posting

 

[DCMP]

Hydrocad file

 

[psmart]

DCMP: Your HydroCAD file was empty. It may have been locked by HydroCAD when you uploaded the file.

When you model the stone voids as a pond, you are simulating the storage and discharge effects of a level pool. This approach does not account for the travel time through the stone. If the travel time is significant, it might be incorporated by including it as an additional Tc flow segment within the subcatchment. This would allow the pond node to represent strictly the storage and discharge effects.



Peter Smart
HydroCAD Software

http://www.hydrocad.net

 

[TerryScan]

Peter,

DCMP's example indicates what might be a very helpful "wish-list" feature for HydroCad. You already have the "Horizontal Cylinder" storage entity. How about the ability to define this as a box rather than cylinder? (a box with a slope).

The Storage in DCMPs initial pdf printout is not starting at the true bottom of storage (359.50) and...because of the slope...is not an accurate depiction of the storage. Typically I would calculate the true horizontal storage for something like this and enter a "custom storage" into Hydrocad.

 

[psmart]

TerryScan: In the next release, "horizontal cylinder storage" will be renamed as "pipe storage" and generalized to handle additional shapes including pipe-arch, elliptical, and box. Since a slope can be used with any geometry, a sloped trench could be modeled with the sloped box capability.

The ability to slope other storage otions (such as a prismatoid) is also on the wish-list. Thanks!


Peter Smart
HydroCAD Software

http://www.hydrocad.net

 

[DCMP]

Thanks TerryScan and Peter.

I agree with you guys that the volume needs to be done by custom storage. And TerryScan, you came up with bright suggestion of having different shapes on a sloping ground. I was wondering Why I can not enter slope in the prismatoid or horizontal cylinder since most ground are sloping. And nowadays we do more LID than standard ponds, typically dry swales with some slope.

Anyways, Peter stated that in the next release it will be incorporated. I am glad to see that our suggestions are being considered sincerely. I am first time user of HydroCAD and very please with the performance. Also Peter when do you think the new release will be available?

Once again thank you Peter and TerryScan.

DCMP

 

[psmart]

DCMP - The next release is still under development, and the date has not been finalized. Until we're certain, I'm not going to make any guesstimates.

Peter Smart
HydroCAD Software

http://www.hydrocad.net