1. Irene Seco Manuel Gómez Alma Schellart Simon Tait Erosion resistance and behaviour of highly organic in-sewer sediment 7th International Conference on Sewer Processes & Networks Wednesday 28 - Friday 30 August 2013 The Edge Conference Centre, Sheffield

2. Wet weather pollution from combined sewer systems Release of in-sewer sediment deposits accumulated during dry-weather constitute a major source of pollutants that affect the water quality of receiving natural water bodies

3. Long dry-weather periods Intense precipitation events Long dry-weather periods Intense precipitation events Wet weather pollution from combined sewer systems Rain regime Particularities in the Mediterranean region in Spain: cumulative precipitation = 600 mm/year (concentrater 50 days/year) average dry-period between rain: 11 days ≈ 40% rainfall registered P(mm)>10mm cumulative precipitation = 600 mm/year (concentrater 50 days/year) average dry-period between rain: 11 days ≈ 40% rainfall registered P(mm)>10mm

4. Long dry-weather periods Intense precipitation events Long dry-weather periods Intense precipitation events Wet weather pollution from combined sewer systems Rain regime In-sewer sediment accummulation and consolidation Particularities in the Mediterranean region in Spain:

5. Wet weather pollution from combined sewer systems Low circulating flow (0.56 m 3 /s average Congost River. Vallès Oriental. Catalonia. Spain) Low circulating flow (0.56 m 3 /s average Congost River. Vallès Oriental. Catalonia. Spain) Low dilution capacity Particularities in the Mediterranean region in Spain: Flow regime in rivers Long dry-weather periods Intense precipitation events Long dry-weather periods Intense precipitation events Rain regime

6. Wet weather pollution from combined sewer systems Particularities in the Mediterranean region in Spain: Low circulating flow Low dilution capacity Low circulating flow Low dilution capacity Flow regime in rivers Long dry-weather periods Intense precipitation events Long dry-weather periods Intense precipitation events Rain regime High percentage of impervious surface in Urban areas Urban pattern

7. Wet weather pollution from combined sewer systems Particularities in the Mediterranean region in Spain: Low circulating flow Low dilution capacity Low circulating flow Low dilution capacity Flow regime in rivers Long dry-weather periods Intense precipitation events Long dry-weather periods Intense precipitation events Rain regime High percentage of impervious surface in Urban areas Urban pattern Sewer solids mainly from wastewaters Relevant Organic composition

8. Wet weather pollution from combined sewer systems Particularities in the Mediterranean region in Spain: Significant volumes discharged in a short time from sewer network (CSO) Significant organic Pollution in natural streams and sea Significant volumes discharged in a short time from sewer network (CSO) Significant organic Pollution in natural streams and sea Overflows during wet-weather Low circulating flow Low dilution capacity Low circulating flow Low dilution capacity Flow regime in rivers Long dry-weather periods Intense precipitation events Long dry-weather periods Intense precipitation events Rain regime High percentage of impervious surface in Urban areas Urban pattern

9. Objectives of this study Particular conditions of Build-up/Wash-off affects the initiation of sediment motion

10. Objectives of this study Consider potential incidence of the environmental conditions in-sewer on the transport loads and initiation of motion Analyse changes in transport potential for different lengths of antecedent dry-weather periods Investigate erosion behaviour of real in- sewer organic-rich sediment collected in Spain Particular conditions of Build-up/Wash-off affects the initiation of sediment motion

11. Long dry-weather period/Build-up Intense rainfall/Wash-off Suitable to be applied to the particular Mediterranean climate and urban pattern conditions Objectives of this study Improve prediction of in-sewer sediment transport loads Improve prediction of in-sewer sediment transport loads

12. Real in sewer sediment characteristics Sediment collected from a sewer system (residential and commercial area in Catalonia, Spain)

13. Real in sewer sediment characteristics relevant Organic content (O.M. around 80%) relevant Organic content (O.M. around 80%) organic nature of solid particles from domestic wastewaters, and the presence of greases Cohesive properties Sediment collected from a sewer system (residential and commercial area in Catalonia, Spain)

14. Real in sewer sediment characteristics relevant Organic content (O.M. around 80%) relevant Organic content (O.M. around 80%) Related with the organic nature of solid particles from domestic wastewaters, and the presence of greases Cohesive properties d50 = 0.31 mm (310 µm) Density = 1310 kg/m 3 Sediment collected from a sewer system (residential and commercial area in Catalonia, Spain)

15. Consolidation, microbiological degradation, chemical-biological interactions (bonding forces between particles ) Real in sewer sediment characteristics Effects on the transport of solids significant influence on the incipient motion Sediment with high organic content and cohesive properties

16. Laboratory erosion measurement Liem et al. (1997) investigation on erosional proecess of cohesive sediment using an in-situ measuring device. International Journal of Sediment Research, 12 (3), 139-147 Evaluation Erosion Rate Assessment critical threshold of motion at solid-fluid interface Evaluation Erosion Rate Assessment critical threshold of motion at solid-fluid interface Erosion meter devised (based on a design by Liem et al. 1997). Erosion meter devised (based on a design by Liem et al. 1997).

17. Laboratory erosion measurement A prepared sample is exposed to a consolidation period and subsequently subject to increased shear stress, to simulate increased flows through sewer pipes at the start of a storm event. Simulation of dry-weather periods Different lengths: 16, 64, 140 hours Environmental conditions: Anaerobic and Aerobic Constant low shear stress: 0.15 N/m 2 (dry-weather flows inside conduits) Simulation of dry-weather periods Different lengths: 16, 64, 140 hours Environmental conditions: Anaerobic and Aerobic Constant low shear stress: 0.15 N/m 2 (dry-weather flows inside conduits) Consolidation period Erosion phase Sampling and Analysis

18. Simulation of dry-weather periods Different lengths: 16, 64, 140 hours Environmental conditions: Anaerobic and Aerobic Constant low shear stress: 0.15 N/m 2 (dry-weather flows inside conduits) Simulation of dry-weather periods Different lengths: 16, 64, 140 hours Environmental conditions: Anaerobic and Aerobic Constant low shear stress: 0.15 N/m 2 (dry-weather flows inside conduits) Laboratory erosion measurement A prepared sample is exposed to a consolidation period and subsequently subject to increased shear stress, to simulate increased flows through sewer pipes at the start of a storm event. Consolidation period Simulation flows at start of storm event Increasing shear stress is applied in a stepwise way Simulation flows at start of storm event Increasing shear stress is applied in a stepwise way Erosion phase Sampling and Analysis

19. Simulation of dry-weather periods Different lengths: 16, 64, 140 hours Environmental conditions: Anaerobic and Aerobic Constant low shear stress: 0.15 N/m 2 (dry-weather flows inside conduits) Simulation of dry-weather periods Different lengths: 16, 64, 140 hours Environmental conditions: Anaerobic and Aerobic Constant low shear stress: 0.15 N/m 2 (dry-weather flows inside conduits) Laboratory erosion measurement A prepared sample is exposed to a consolidation period and subsequently subject to increased shear stress, to simulate increased flows through sewer pipes at the start of a storm event. Consolidation period Simulation flows at start of storm event Increasing shear stress is applied in a stepwise way Simulation flows at start of storm event Increasing shear stress is applied in a stepwise way Erosion phase Sediment samples collected during erosion tests at each shear stress interval Remaining sediment after tests collected Sediment samples collected during erosion tests at each shear stress interval Remaining sediment after tests collected Sampling and Analysis

20. Main Results Average erosion rate (q) linked to the applied shear stress (  b ) Aerobic Anaerobic T1 16h T3 140h T2 64h T4 16h T5 64h Erosion rate of sediments monitored in terms of Suspended Sediment concentration Erosion rate of sediments monitored in terms of Suspended Sediment concentration

21. Main Results Erosion Rate values Comparison between tests with increasing length of periods of consolidation. 16h (T1) 64h (T2) 140h (T3) 16h (T4) 64h (T5) Aerobic Anaerobic

22. Main Results Erosion Rate values Comparison between tests with increasing length of periods of consolidation. 16h (T1) 64h (T2) 140h (T3) 16h (T4) 64h (T5) Aerobic Anaerobic drop in overall values of Erosion Rates as length dry-period increase

23. Main Results Tests with the same consolidation period and different environmental ambience. (T1) Anaerobic (T4) Aerobic 64h consolidation period 16h consolidation period (T2) Anaerobic (T5) Aerobic

24. Main Results Tests with the same consolidation period and different environmental ambience. (T1) Anaerobic (T2) Anaerobic (T4) Aerobic (T5) Aerobic 64h consolidation period 16h consolidation period

25. Conclusions Laboratory tests to estimate erosional resistance from highly organic sediment beds under storm runoff conditions Improvements in prediction of in-sewer sediment transport loads (Mediterranean conditions) Laboratory tests to estimate erosional resistance from highly organic sediment beds under storm runoff conditions Improvements in prediction of in-sewer sediment transport loads (Mediterranean conditions)

26. Conclusions Environmental conditions influence over sediment-bed nature and structure

27. Conclusions Increase of erosional strength with depth Increment of resistance against erosion (as consolidation dry-period lengthen and oxygen is available) Environmental conditions influence over sediment-bed nature and structure

28. Conclusions comparing with results obtained with low-organic sediment and synthetic sediment (differences in sediment properties) Lesser magnitudes of Critical Shear Stresses Lesser magnitudes of Critical Shear Stresses Increase of erosional strength with depth Increment of resistance against erosion (as consolidation dry-period lengthen and oxygen is available) Environmental conditions influence over sediment-bed nature and structure

29. Conclusions Future investigations aimed to: -asses critical shear stress in highly organic sediment beds - analyse influence of temperature in dry-period Future investigations aimed to: -asses critical shear stress in highly organic sediment beds - analyse influence of temperature in dry-period

30. Concerned about pollution control Thank you for your attention

32. Long dry-weather periods Intense precipitaction events Long dry-weather periods Intense precipitaction events Wet weather pollution from combined sewer systems Particularities in the Mediterranean region climate in Spain: day-precipitation = 4 day/month cumulative precipitation = 600 mm/year (concentrater in spring and fall) average dry-period between rain: 11 days Max. dry-period: 70 days (2010-2012) Intense precipitation events following long dry- periods ≈ 40% rainfall registered P(mm)>10mm day-precipitation = 4 day/month cumulative precipitation = 600 mm/year (concentrater in spring and fall) average dry-period between rain: 11 days Max. dry-period: 70 days (2010-2012) Intense precipitation events following long dry- periods ≈ 40% rainfall registered P(mm)>10mm Rain regime

33. Main results Erosion of sediments from bed during tests were monitored in terms of Suspended Sediment concentration and related with Erosion Rate q : average Erosion Rate in a applied Shear Stress step (  b ) linked to Suspended Sediment Concentration (C SS ) V : water volume of the column over sediment sample A S : surface area bed subjected to erosion