Modeling a series of pipes as ponds?

[soates]

I have set up an exisiting pipe network system modeling each pipe as a pond (catch basin) with an outlet (culvert). I have an individual subcat contributing to each pond and then the ponds connected in series. The system is currently undersized and my goal is to delay my site's runoff until the existing system has capacity.

My question or problem is that my peak elevations for these catch basins modeled as ponds is anywhere from 40 feet (at the beginning of the network) to 5 feet (at the discharge end of the network) above the actual pipe invert(s). Is this the hydraulic grade line and therefore I can ignore the value or is there a way to "force" all the runoff into these pipes while maintaining the crown elevations?

 

[TerryScan]

If you are using pipes for underground storage (rather than just conveyance), you should model the system as a pond with the "Detention Pond (or other storage area)" option NOT as a catch basin. On the STORAGE tab, use the "Horizontal Cylinder" option to describe your pipe storage system.

 

[psmart]

These elevations are the HGL at each point in the system. This is the headwater required to force the existing flow throught the system without any storage.

If the elevation comes above grade, you are probably using above-ground storage (such as a parking lot). For accurate routing, you must include this storage volume as part of the appropriate pond(s). Once the storage is defined, this volume is likely to reduce the peak elevations considerably.

The "Horizontal Cylinder" storage option is intended for use with some type of outlet control (such as an orifice plate) at the lower end. Be cautious about using it with a standard pipe.