M. Walaszek 1, P. Bois 1, J. Laurent 1, A. Wanko 1 1 Ecole Nationale du Génie de l’Eau et de l’Environnement de Strasbourg (ENGEES) Laboratoire des Sciences de l’Ingénieur, de l’Informatique et de l’Imagerie (Icube), 2 rue Boussingault, Strasbourg, France Ponding water ultrasonic measurements in urban stormwater constructed wetland for clogging monitoring

The Ostwaldergraben WETPOL The EU Water Framework Directive: good status before 2027 Ostwaldergraben: bad status - presence of pollutants (nutrients, organic matter, hydrocarbons, metals)  Necessity to improve the stream quality

2011 – Construction of 3 systems (sedimentation pond + constructed wetland) to compare their treatment efficacity To reduce pollution in stormwater before discharging into the stream The general project: the stream restauration WETPOL Watershed 3 Ostwaldergraben Watershed 2 Watershed 1

Objectives of the study WETPOL Stormwater constructed wetland (SCW): a specific functionning Variable input flow  Heterogeneous spatial and temporal water distribution inside the SCW, even if presence of a distribution system  Suspended solids in runoff and reeds litter: infiltration capacity reduce and physical clogging risk What are space and time dynamics of water ponding ? Observations Issues What can we deduce on clogging from water ponding ? Link rain event characteristics and SCW hydraulic response Describe the ponding behaviour after a rain event Study markers to prevent the clogging Objectives

The experimental site WETPOL Context and objectives Watershed 3 Ostwaldergraben Manhole Runoff Catchment area Total area (ha) 1.8 Active area (m²) 5,200 TypeResidential Artificial pondArea (m²)18 Hydraulic load (m 3 /m²/h) 10 Constructed wetland Area (m²) 100 Hydraulic conductivity (m/s) Hydraulic load (m 3 /m²/h) 0.5 to 1 % of active area (m²) 2%

WETPOL Context and objectives Link rain event characteristics and SCW hydraulic response Objective 1 Rain event Instrumenta tion Weather station (800m away) Information s provided Rain event duration Water height Intensity Dry period Return period Duration (h) Cumulated water height (mm) Average intensity (mm/h) Dry period (d) Return period 26/04/ to 6 months 27/04/ to 6 months 02/05/ weeks to 1 month 03/05/ to 2 weeks 04/05/ < 1 week 04/05/ weeks 07/05/ to 2 weeks 08/05/ < 1 week 10/05/ weeks 20/06/ months 03/07/ month 08/09/ to 2 weeks 10/09/ weeks to 1 month 11/09/ to 3 months 14/09/ to 2 weeks 14/09/ to 2 years 16/09/ weeks to 1 month 18/09/ weeks to 1 month 03/11/ to 3 months 08/11/ to 1.5 months 19/11/ to 3 months April to november rain events 21 studied Use of the Hierarchical Ascendent Clustering (HAC) analysis  To classify rain events and SCW parameters by similarity

WETPOL Context and objectives Describe the ponding behaviour during a rain event Objective 2 Peak ponding height Average ponding height Upward ponding time Downward ponding time Average ponding time Start ponding time End ponding time + upward and downward ponding velocity Ponding Instrumentation Ultrasoni c sensor (x9, Ijinus – M0111) Informations provided Ponding height Calculation of ponding parameters: + Statistical moments 9 X

WETPOL Context and objectives Study markers of clogging Objective 3 dh dt Clogging prevent by ponding and piezometric water levels comparison : Ponding Instrumentation Piezometric probes (2 pression probes) Informations provided Piezometric height Infiltration Capacity Unsaturated permeability Kns (using ponding water dynamic): Where : L the thickness of the SCW (0,3 m) ΔH the difference of ponding heights

WETPOL Context and objectives Correlate ponding water and Phragmites australis biomass Objective 4 Reed biomass Instrumentation / method Height and diameter measurements per 0.25m² Quadrat Informations provided Phragmites biomass for summer & winter 2013 To compute: And compare with heterogeneous ponding water distribution in the SCW But only 2 sampling campaigns not enough to conclude …

Rain event characteristics and SCW response link Cluster 1 e1, e2 Cluster 2 e6, e7, e8, e4, e12, e 3, e5, e11, e21 Cluster 1 e14, e15, e16, e19, e17, e13, e18, e20, e9, e10 WETPOL Context and objectives Cluster 1 e16 Cluster 2 e11, e17, e18, e3, e15, e9, e10, e14, e19, e13, e20, e6, e5, e4, e12, e7, e8 Cluster 3 e21 Cluster 4 e1, e2 SCW parameters classification Rain event classification Group 1 (e1&e2): ponding height & downward velocity  low infiltration velocity Group 2: big events & high ponding height variability Cluster 1Cluster 2Cluster 3Cluster 4 Duration (h) Water height (m) Intensity (m/h) Dry period (days) Cluster 1Cluster 2Cluster 3 Ponding height (m) Rise time (h) Descent time (h) Rise velocity (m/s) 4.0E-061.2E E-05 Descent velocity (m/s) 4.0E-061.0E E-05 Reduce variance Average ponding time SCW hydraulic response impacted by urban watershed hydrology

Spatial ponding water heterogeneity WETPOL Context and objectives Rain eventSensor detection (%) 26/04/ (4 sensors/9) 27/04/ /05/ /05/ /05/ /05/ /05/ /05/ /05/ /06/ /07/ /09/ /09/ /09/ /09/ /09/ /09/ /09/ /11/ /11/ /11/ to 6 months 3 months 6 months SensorDetected rain event (%)

Spatial ponding water heterogeneity WETPOL Context and objectives Average parameters for each ponding sensor from April to November 2013 Quartiles groups (quartiles 2 et 3 together) 4 & 7  High ponding heights 7 & 2  High descent velocity (high infiltration capacity) Heterogeneous ponding understanding  soil sampling location

WETPOL 2015 Markers of clogging: ponding and piezometric measures 13 Context and objectives dh dt Piezometric heights reduce + Ponding heights stability  Δh peaks increase Time of equilibrium increase  Clogging risk

Markers of clogging: unsaturated permeability Kns Kns  infiltration capacity of the SCW No significant Kns variation for this period (Max Kns= m/s, min Kns=0.064 m/s) Kns Intrinsic SCW property WETPOL Context and objectives

Conclusion and perspectives WETPOL Perspectives Pursuit of the study in the 1rst SCW (watershed 1) Extend the measurement period to 1 whole year Conclusion Impact of the variable incoming flow on SCW hydraulic characteristics  Highlight of ponding, infiltration capacity Monitoring possible with simple instrumentation and 2 water levels Ponding map  Help to choose soil and reed sampling locations

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