Slide 1

Characterisation of surface water runoff from an urban residential sewer separation scheme Dave Morgan, Paul Johnston and Laurence Gill Trinity College Dublin Phil Collins HRD Technologies Ltd Kwabena Osei Hydro International morgandt@tcd.ie Department of Civil, Structural & Environmental Engineering Trinity College Dublin

Slide 2

MotivationCatchment Introduction Considerable research conducted on source-area or end of pipe solids characterisation and modelling..... but SS prediction still a challenging proposition Can the consideration of a system mass balance: -Improve prediction of suspended solids and associated pollutants in the runoff -Inform SuDS retrofit MbMb M sew MgMg M hs M out M wo M wo = M g + M sew + M hs + M out Methodology -Field monitoring of small urban residential catchment (18 months) -Characterisation of sediment (loadings / PSD / TP / Cu / Pb / Zn) -Modelling of the suspended solids RG HDVS Separate Pipe and Gully System

Slide 3

Project OutlineCatchment Introduction River Poddle 225 450 225 Stormwater sampling

Slide 4

ComparisonRunoffGully Sediment yield Build-up rates 0.5 10.5 g/m 2 /day (bitmac road) ~ 0.05 g/m 2 /day (concrete footpath) Particle size D 50 = 1200m 10% < 200m Washoff

Slide 5

ComparisonRunoffWashoff Sediment yield 1 3 5 7 9 6 8 10 4 2 Gully sediment characteristics Annual accumulation of 36kg (10 gullies, 30% of imp. area) D 50 =1000m 13% < 200m Gully

Slide 6

ComparisonRunoffWashoffGully Sediment yield SSC -19 events/231 discrete samples - 30% of annual runoff volume -Site median EMC = 29mg/l -Total mass: 40kg PSD -D 50 = 34 microns -90% < 200m

Slide 7

ComparisonRunoffWashoffGully Sediment yield

Slide 8

Conclusions Gullies ineffective in trapping < 200 m particles 2 4 times higher annual pollutant load in SS compared to gully sediments High uncertainty in source loading rates modelling of SS washoff required to determine mass balance Thanks for listening.... Current work Modelling of suspended solids at the outlet Partitioning of easily eroded and stable solids fractions