Modeling Athletic Field / Synthetic Surface - Subdrain

[pjhealy]

How to model an athletic (football/soccer) field with sub-drains, pre- and post-development conditions?

The existing field is 8" loam/sand mix over 8" gravel base over 4" perforated PVC pipe sub-drains spaced 25' apart (slope=0.025) within gravel, running to 6" solid PVC collector pipes (headers) to daylight. The underlying soils are C-series (fine sandy loam).

The proposed field will be synthetic surface (FieldTurf or Sportexe) which has a 2" or 2.5" thick silica sand/rubber mix infill over a 2 or 4-layer synthetic mat with punched or formed holes to drain. The mat has the fiber blades of 'grass' woven within. One manufacturer (Sportexe) claims their mat will handle 15" per hour min. The mat will be placed over a 2" top layer of 'final grade aggregate' crushed stone (0.5" minus) over a 6" base layer of crushed stone (2" minus). The whole field is surrounded by a concrete curb to which the mat is affixed. This will create a 'pond' situation. A network of composite sub-drains will be spaced 15' apart. The drains will lie within the base stone layer over a geotextile fabric over the underlying soil. The field surface has a minimum pitch (s=0.005), crowned at the center, longitudinally. The sub-drains may be pitched up to s=0.020 (stone base layer thickness will vary). The sub-drains will collect on the edges into 12" headers, thence to a detention pond.

Thanks,

Ken Strom / Patrick Healy

 

[psmart]

If the water formed a level-pool, you could model the field as a detention pond with the perforated pipe as the outlet control. But I suspect that the travel time through the various layers will create a longer detention time (and hence a lower peak) than the level-pool model would suggest.

This suggests that you could use an additional pond routing (or even a reach routing) to simulate the upper layers, but I don't have any specifics. Given the unknowns, I would look at your overall modeling objectives and see how accurate an outflow hydrograph you really need from the playing field. Modeling as a level-pool with a perforated pipe outlet would tend to give you a worst-case (maximum) discharge.

There have also been several previous threads on this subject, For example see

http://www.eng-tips.com/viewthread.cfm?qid=176635

Peter Smart
HydroCAD Software

http://www.hydrocad.net