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? The design of a drainage system that allows this to be possible? What is its effect: on the car washer? on the drainage engineer? John, Thought I’d throw this one in for you. This is a poster from the NSW EPA’s stormwater awareness advertising campaign. It annoys the hell out of me, because I reckon it is giving exactly the wrong message to the drainage engineer (i.e. it’s not your fault: it’s the dills up in the catchment who don’t know how to respect your perfectly valid drainage design!)

Streams in dry weather

Minimum requirement for drainage connection <1 No runoff to drains in dry weather

Overland flow from the catchment

Streams after small-moderate storms

Streams after large storms

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

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.

Calculating connection: The Dandenongs

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

Assessing development scenarios for effective imperviousness Some stormwater treatment as for (a), but with tank receiving 180m2 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

Assessing development scenarios for effective imperviousness Rain garden Stormwater treatment train as for (b), but with all 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

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