Notes

Slide Show

Outline

1	Design Construction & Performance of Exfiltration Trenches Alan A. Smith Alan A. Smith Inc.& Weslake Inc. and Tai D. Bui Weslake Inc.
2	Outline Basic concepts Analysis and Design Field observations Case Study - Brantford, Ontario Construction issues Conclusions
3	Conceptual sketch of exfiltration trench
4	The Etobicoke Trench (1993)
5	The Etobicoke Trench
6	Continuity equation
7	Reservoir Routing Equation
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11	Observations from Field Data Drawdown rate implies K @ 30 mm/h - much more than expected Trench base provides exfiltration capacity Water surface in voids shows a significant gradient 63 mm storm totally absorbed - much more than design storm.
12	Brantford Case Study Features of project location Pros and Cons of Trenches Design procedure Computer aided design Allowance for surface gradient Summary of results
13	Brantford, ON -Project Location
14	Trenches - Pros and Cons Rare habitat dependant on groundwater flow Conventional End-of-Pipe solution reduces groundwater flow. Native material has high hydraulic conductivity Ground water table well below ground level Cost of minor system is reduced No Pond = Reduced project cost Need to protect against spills Trench cost > Cost saving of minor system
15	Design Procedure
16	Typical trench parameter values
17	MIDUSS trench cross-section window
18	Suggested values for hydraulic conductivity (mm/h)
19	Water budget
20	Construction Issues Use both upstream as well as downstream plugs until surface is stabilized Ensure proper Erosion & Sediment Control Provide ‘sock’ on perforated pipes Surround clear stone fill with filter fabric.
21	Monitoring & Maintenance Measure groundwater table Sample groundwater quality Clean out perforated pipes (2-year intervals) Check draw-down rate in trench Monitor & control materials storage Ensure no hazardous materials
22	Conclusions & Recommendations