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Slides for John Quinn... Here are the author’s details...

Slides for John Quinn... Here are the author’s details. C. J. Walsh, A. W. Leonard CRC for Freshwater Ecology T. D. Fletcher, A. R. Ladson CRC for Catchment Hydrology and Institute for Sustainable Water Resources. What’s wrong with this picture?. The guy washing his car?

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Slides for John Quinn... Here are the author’s details...

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  1. Slides for John Quinn...Here are the author’s details... C. J. Walsh, A. W. Leonard CRC for Freshwater Ecology T. D. Fletcher, A. R. Ladson CRC for Catchment Hydrology and Institute for Sustainable Water Resources

  2. What’s wrong with this picture? • The guy washing his car? • The design of a drainage system that allows this to be possible? • What is its effect: • on the car washer? • on the drainage engineer?

  3. Streams in dry weather

  4. Minimum requirementfor drainage connection <1 No runoff to drains in dry weather

  5. Overland flow from the catchment

  6. Streams after small-moderate storms

  7. Streams after large storms

  8. Drainage connection index Limits • Completely connected if dry weather spills go down the pipes • Completely unconnected if zero runoff to the pipes in storms up to the size that would produce overland flow in the pre-urban catchment

  9. Drainage connection index • Calculated for blocks of catchment land not crossing a drainage line • 1 if all effective rainfall piped to stream • 0 if no rainfall up to ‘the overland flow’ storm is retained • Scaled by frequency of rainfall events.

  10. Calculating connection: The Dandenongs

  11. Assessing development scenarios for effective imperviousness • Conventionally drained block • Property area = 600m2 • TIA = 300m2 • TI = 300/600 = 0.50 • 27 m2 paving draining to garden • (connection = 0) • EIA = 180 + 93 + (27x0) = 273m2 • EI = 273/600 = 0.45

  12. Assessing development scenarios for effective imperviousness • Some stormwater treatment • as for (a), but withtank receiving180m2 roof runoff on avg retains 8mm/d event (conn=0.23) • 93m2 permeable paving on avg retains 5mm/d event (conn = 0.42) • EIA = (180x0.23) + (93x0.42) + (27x0) = 273m2 • EI = 80.5/600 = 0.13

  13. Assessing development scenarios for effective imperviousness Rain garden • Stormwater treatment train • as for (b), but withall roof and paving runoff draining to rain garden that retains 15mm/d event (conn = 0) • EIA = 80.5 x 0 = 0m2 • EI = 0/600 = 0

  14. Assessing development scenarios for effective imperviousness: scaling up to the streetscape EIA houseblocks 1630 m2, EIA Road = TI Road = 1600 m2 Total EIA pre-treatment = 3230 m2 Biofiltration system along road retains 10mm event from this EIA: connection of street = 0.15 EIA street = 3230 x 0.15 = 485m2 Total area = 12800m2 EI street = 485/12800 = 0.04

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