Exfiltration Trench Idealized diagram of exfiltration trench Perforated distribution pipe Outflow Control Device Exfiltration X Water table Outflow Q Inflow I

Purpose of Exfiltration zEncourage return of storm runoff to the groundwater zReduce the hydraulic load on the minor (e.g. piped) system zImprove quality of runoff by removal of some particulate matter zReduce thermal impact on the runoff zSplit inflow hydrograph into two components of Outflow and Groundwater recharge

Basic Theory Inflow = Outflow + Exfiltration + Change of storage I Q X V

Trench Cross-section For laminar flow: where K = hydraulic conductivity Water table elevation G Topwidth T Height H Invert elevation IL Filter Clear stone Depth y P + y/2 P=IL-G B y eff

Define Trench parameters Data window is opened by using Geometry/Trench menu command from Trench Design form.

Define Trench parameters

Define outflow control [Compute] Plot V,Q=f(H)

Defining the Trench Pipes Main storm sewer is solid 450 mm pipe with invert = Two 200 mm diam. perforated pipes are plugged at down stream end to distribute inflow along trench Pipes positioned graphically with clearance shown. Position refined by editing table. Press [Compute] to update volume table

Results of Routing

The Etobicoke Trench