Pond Routing

[Loumenad]

I have seen the requirements for "Pond Routing" and have found nothing on what pong routing even is. By using various methods you are performing Hydrologic Analysis of an area, but not routing through ponds but rather to possibly a pond or basin. So is there a difference in methods, or does pond routing simply mean routing to an outlet (pond) or are you specifically routing into a pond.

I know HydroCAD has an option for pond routing, and you have the ability to add a pond to a system, so which/what is the pond routing then? What is needed to do pond routing?

 

[psmart]

Pond routing is the process of producing an outflow hydrograph, based on the stage-storage and stage-discharge characteristics of the pond.

By restricting the outlet and providing storage, a pond tends to reduce and delay the peak flow.

One of the most common pond routing procedures if the Storage-Indication Method, but most "level-pool" procedures produce comparable results.

http://www.google.com/#q=storage-indication+routing

Peter Smart
HydroCAD Software

http://www.hydrocad.net

 

[beej67]

"Pond Routing" means you take your storage characteristics and discharge characteristics of your pond, and the hydrograph coming in to the pond, and from those you use some iterative math to figure out the hydrograph going out of the pond.



Hydrology, Drainage Analysis, Flood Studies, and Complex Stormwater Litigation for Atlanta and the South East -

http://www.campbellcivil.com

 

[Loumenad]

I have a free version of HydroCAD and am unable to figure out which information I need to size a pond correctly. I used TR-55 to size the volume of storage needed for certain storms by hand, but am unable to use the software to then design a pond, which clearly this is able to do. What information is needed to use software to design a pond, the same to calculate peak flows from a site?

 

[psmart]

HydroCAD provides a pond sizing report, which will estimate the storage required to attenuate the pond inflow to any target level. For details please see

http://www.hydrocad.net/pondsizing.htm

Based on the estimated size you would do an initial pond design, and then refine the design until it meets your design objectives.


Peter Smart
HydroCAD Software

http://www.hydrocad.net

 

[Loumenad]

I have been using HydroCAD to compare hand calculations of TR-55 and have an issue with storage requirements. When using TR-55 a simple process for determining storage volume from runoff is by computing the ratio of peak pre-developed flow over peak post-developed flow and using an equation to find % storage. Doing this I find that only 61% of the runoff will need to be stored by this detention basin. So by designing the pond based on this storage I then use HydroCAD to verify the results but find a large discrepency in storage requirement, thus needed to redesign my pond considerably. Any advice on possible fixes?

 

[psmart]

Any storage estimate assumes that you have the appropriate outlet control(s) on the pond in order to maximize the storage effectiveness.

For example, if you use just a weir outlet, the pond is likely to fill to the spillway before the peak hits, leaving no available storage for peak reduction.

For this reason, most ponds will have more complex outlet structures that allow the lower flows to discharge early in the storm, leaving more volume available to mitigate the peak.

To make matters more complicated, many regulations require peak mitigation for multiple events, which usually results in a multi-stage outlet structure that is optimized for more than one event. When this is required, your stormwater regulations should have recommendations and standards for suitable outlet structures.

I'll let the more experienced pond designers on this forum pick up there...


Peter Smart
HydroCAD Software

http://www.hydrocad.net

 

[Loumenad]

The current city requirements are to store the 50 year storm while releasing at the pre-developed 5 year rate which creates a significant amount of storage. I see in the outflow table that the pre-developed peak flow is not achieved until much later in the storm event, requiring the need for a system to achieve the peak flowrate sooner in the rainfall event.

This appears that detention basins are a lot more complicated than originally thought!

 

[beej67]

This appears that detention basins are a lot more complicated than originally thought!

Yep.

Wait until there's water quality, min drawdown time, max recovery time, micropools, forebays, littoral shelves, 6 storms to attenuate, and a water balance calculation to show it stays wet during the dry season.

Hydrology, Drainage Analysis, Flood Studies, and Complex Stormwater Litigation for Atlanta and the South East -

http://www.campbellcivil.com

 

[TerryScan]

Lounenad,

It does appear you should get someone with expertise in Hydrology and Hydraulics. Aquiring rocket design software would not qualify me for designing a rocket.

From the TR-55 manual regarding it's storage volume calculations: "The procedure should not be used to perform final
design if an error in storage of 25 percent cannot
be tolerated."