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Lumped and distributed modelling of suspended solids in a combined sewer catchment in Santiago de Compostela (Spain)

R. Hermida, JOSE ANTA, M. Bermúdez, L. Cea, J. Suárez & J. Puertas

GEAMA Research TeamUniversidade da Coruña

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INTRODUCTION

• Flow and Pollution Modelling in Urban Systems

dust and dirt buildup

washoff

gully-pot processes

sewer erosion - transport

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OBJETIVES

• Comparison of a lumped and distributed model for TSS in “El Ensanche” combined sewer catchment

• Model developed with Infoworks CS 9.x– Ackers-White equation– KUL model

• 10 rain event were used for model calibration. More details presented yesterday:“Mobilized pollution indicators in a combined sewer system during rain events” del Río et al.

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DESCRIPTION OF THE URBAN CATCHMENT

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MODEL DEVELOPMENT

• Distributed model (del Río, 2011)– 316 subcathments:

183 streets, 128 roofs, 5 pervious areas

– 7 km of pipes (150 – 1200 mm)

• Lumped model (Hermida, 2012)

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BUILDUP

Model parameters : Ps, K1

Model parameters : C1, C2, C3

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1 NJ KsPM eK

WHASOFF

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SEWER TRANSPORT MODELSAckers & White (1996)

Model parameter are fixed. Model variables: s, d50

KUL (Boutelegier and Berlamont, 2002)

Too many model parameters (6 parameters). Model variables: s, d50

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SEWER TRANSPORT MODELSKUL : Shields approach (Shizari and Berlamont, 2010)

Shields number has to be re-evaluated in each time – step (not allowed in IF)

Ota and Nalluri equation (2003)

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0.0361.67

24 e

e

e

e s egd s

KUL equation as function of s, d50

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SENSITIVITY ANALYSIS: POLLUTION MODEL

• InfoWorks doesn’t allow an easy implementation of formal MC inference

• Sensitivity analysis of the different Infworks quality subroutines with Matlab.

• Methodology proposed by Kleidorfer (2009):– Local sensitivity analysis– Global sensitivity analysis

• Graphical methods• Hornberger – Spear – Young

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SENSITIVITY ANALYSIS RESULTS

BUILDUPBuildup factor is more sensitivity than the decay factor

Model is sensitivity to both parameters

WHASOFFModel is almost insensitivity to C3 coefficient and can be neglected

C2 is more sensitivity than C1

Model is sensitivity to both parameters

SEDIMENT TRANSPORT MODELd50 is more sensitivity than the specific density s

Model is sensitivity to both parameters

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MODEL CALIBRATIONHydraulic model calibration• 11 rainy days: NS=0.85

Pollution model calibration• Visual calibration: 3 events• Model validation: 7 events• Distributed model

– Ackers – White – KUL (Ota & Nalluri)

• Lumped model– Ackers – White – KUL (Ota & Nalluri)

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MODEL CALIBRATION

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• Successful application of sensitivity analysis to determine the most relevant parameters for pollution modelling in InfoWorks CS

• All the sensitivity tests shows similar results

• Lumped model works better in terms of NS and EMC

• Distributed model works better in terms of Cmax

• KUL – Ota & Nalluri approach avoids the determination of a large number of model parameters

• Ackers – White is more accurate than KUL approach for lumped model and viceversa.

CONCLUSIONS

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THANKS FOR YOUR ATTENTION

www.geama.org/hidraulica

jose.anta@udc.es

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SENSITIVITY ANALYSISHornberger – Spear – Young Method (Kleidorfer, 2009)

– MC framework– Comparison of model outputs with a synthetic run with NS– Analysis of the distance of behavioral (NS>0) and non

behavioral (NS<0) empirical cumulative pdf

Nash-Sutcliffe

Synthetic run

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BUILDUPHSY: Ps HSY: K1