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Published byEvan Marshall Modified over 9 years ago
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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
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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
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Project OutlineCatchment Introduction River Poddle 225 ∅ 450 ∅ 225 ∅ Stormwater sampling
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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 = 1200µm 10% < 200µm Washoff
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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 =1000µm 13% < 200µm Gully
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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% < 200µm
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ComparisonRunoffWashoffGully Sediment yield
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Conclusions Gullies ineffective in trapping < 200 µm 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
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