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

2. Purpose of Exfiltration • Encourage return of storm runoff to the groundwater • Reduce the hydraulic load on the minor (e.g. piped) system • Improve quality of runoff by removal of some particulate matter • Reduce thermal impact on the runoff • Split inflow hydrograph into two components of Outflow and Groundwater recharge

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

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

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

6. Define Trench parameters

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

8. Main storm sewer is solid 450 mm pipe with invert =100.85 Press [Compute] to update volume table 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. Defining the Trench Pipes

9. Results of Routing

10. The Etobicoke Trench