Luca Locatelli

Backfilling of a Scour Hole around a Pile in Waves and Current

This paper presents the results of an experimental investigation of the backfilling of scour holes around circular piles. Scour holes arounda pile aregenerated either by a current or a wave.Subsequently, the flow climate is changed from current to wave, combined waves and current, or wave to a smaller wave, leading to the backfilling of the scour hole. The investigation has shed light onto the mechanism behind the backfillingprocess.Theresultsshowthatthescourdepthcorrespondingtotheequilibriumstateofbackfillingisthesameasthatcorrespondingto the equilibrium state of scour aroundthepilefor thesame wave (or combined waves and current) climate. The time scale of backfilling hasbeen determinedasafunctionofthreeparameters,namely,(1)theKeulegan-Carpenternumberoftheinitialwaveorcurrent(whichgeneratestheinitial scourhole);(2)thatofthesubsequentwave,whichbackfillsthescourhole;and(3)theShieldsparameterassociatedwiththelatterwave,forlive- bedconditions.Inthecaseofthecombinedwavesandcurrent,thecurrent-to-wave-velocityratioisalsoinvolved.Thetimescaleofthebackfilling process is completely different from that of scour. The time scale of backfilling is much larger than that of scour when the Keulegan-Carpenter numberassociatedwiththebackfillingisKCf ,Oð10Þ(typicalwindfarmapplication),whilethetimescaleofbackfillingcanbesmallerthanthat of scour when KCf ..Oð10Þ. DOI: 10.1061/(ASCE)WW.1943-5460.0000161.

Modelling the impact of retention–detention units on sewer surcharge and peak and annual runoff reduction

Stormwater management using water sensitive urban design is expected to be part of future drainage systems. This paper aims to model the combination of local retention units, such as soakaways, with subsurface detention units. Soakaways are employed to reduce (by storage and infiltration) peak and volume stormwater runoff; however, large retention volumes are required for a significant peak reduction. Peak runoff can therefore be handled by combining detention units with soakaways. This paper models the impact of retrofitting retention-detention units for an existing urbanized catchment in Denmark. The impact of retrofitting a retention-detention unit of 3.3 m³/100 m² (volume/impervious area) was simulated for a small catchment in Copenhagen using MIKE URBAN. The retention-detention unit was shown to prevent flooding from the sewer for a 10-year rainfall event. Statistical analysis of continuous simulations covering 22 years showed that annual stormwater runoff was reduced by 68-87%, and that the retention volume was on average 53% full at the beginning of rain events. The effect of different retention-detention volume combinations was simulated, and results showed that allocating 20-40% of a soakaway volume to detention would significantly increase peak runoff reduction with a small reduction in the annual runoff.

Factors affecting the hydraulic performance of infiltration based SUDS in clay

The influence of small scale soil heterogeneity on the hydraulic performance of infiltration based sustainable urban drainage systems (SUDS) was studied using field data from a clayey glacial till and groundwater simulations with the integrated surface water and groundwater model HydroGeoSphere. Simulations of homogeneous soil blocks with hydraulic properties ranging from sand to clay showed that infiltration capacities vary greatly for the different soil types observed in glacial till. The inclusion of heterogeneities dramatically increased infiltration volume by a factor of 22 for a soil with structural changes above and below the CaCO3 boundary. Infiltration increased further by 8% if tectonic fractures were included and by another 61% if earthworm burrows were added. Comparison of HydroGeoSphere infiltration hydrographs with a simple soakaway model (Roldin et al., 2012) showed similar results for homogeneous soils but indicated that exclusion of small scale soil physical features may greatly underestimate hydraulic performance of infiltration based SUDS.

A systematic model identification method for chemical transformation pathways – the case of heroin biomarkers in wastewater

This study presents a novel statistical approach for identifying sequenced chemical transformation pathways in combination with reaction kinetics models. The proposed method relies on sound uncertainty propagation by considering parameter ranges and associated probability distribution obtained at any given transformation pathway levels as priors for parameter estimation at any subsequent transformation levels. The method was applied to calibrate a model predicting the transformation in untreated wastewater of six biomarkers, excreted following human metabolism of heroin and codeine. The method developed was compared to parameter estimation methods commonly encountered in literature (i.e., estimation of all parameters at the same time and parameter estimation with fix values for upstream parameters) by assessing the model prediction accuracy, parameter identifiability and uncertainty analysis. Results obtained suggest that the method developed has the potential to outperform conventional approaches in terms of prediction accuracy, transformation pathway identification and parameter identifiability. This method can be used in conjunction with optimal experimental designs to effectively identify model structures and parameters. This method can also offer a platform to promote a closer interaction between analytical chemists and modellers to identify models for biochemical transformation pathways, being a prominent example for the emerging field of wastewater-based epidemiology.