The impact of sewer condition on the performance of sewer systems
Printed by: Gildeprint, Enschede Cover design by N. van den Heuvel An electronic version of this document is available free of charge in the Delft University Repository at http://repository.tudelft.nl/. Now I've reached the age I've tried to do all those things the best I can No matter how I try I find my way to the same old jam Led Zeppelin, Good times bad times (1969) Back to life, back to reality... Soul II Soul, Back to life (1989) vii Voorwoord Summary xii Nowadays, the maintenance
... maintenance activities to provide the required system performance are mainly based on the observed condition of individual assets and simulation results of calculations using as-built data. Assessing the actual sewer hydraulic performance for directing maintenance actions requires more information on the relation between the actual condition of an asset versus the influence it has on sewer network level. Therefore, the objective of this thesis is to develop methods to assess and quantify the effect of insewer defects on sewer performance. In order to meet this objective, the influence of sewer condition on hydraulic performance is studied and model calibration is applied to identify in-sewer defects affecting hydraulic performance. Furthermore, the impact of insewer defects on urban pluvial flooding and, subsequently, on infection probabilities for humans is addressed. The impact of in-sewer defects on urban pluvial flooding on network level is studied in two research catchments in the Netherlands ('Tuindorp' and 'Loenen'). Impacts are assessed using Monte Carlo simulations with a full hydrodynamic model of the sewer system. The studied defects include root intrusion, surface damage, attached deposits and settled deposits and sedimentation. These defects are based on the results of field observations and are translated to two model parameters (roughness and sedimentation). The calculation results demonstrate that the return period of flooding, number of flooded locations and flooded volumes are substantially affected by in-sewer defects. The impact of in-sewer defects is larger in the flat 'Tuindorp' area with the looped sewer system than in the mildly-sloping 'Loenen' area with the partly-branched sewer system. This mainly results from the flatness of the catchment. In the partly-branched sewer system, especially for sedimentation, the variance of all flooding characteristics is larger than in the looped system. The concept of 'hydraulic fingerprinting' based on model calibration is introduced to identify in-sewer defects which affect hydraulic performance. Model calibration enables detection of changes in hydraulic properties of the sewer system. Each model calibration results in a set of model parameter values, their uncertainties and residuals. The model parameter values also incorporate the antecedent condition of the catchment of the calibrated event and are therefore less suitable for the identification of in-sewer defects. The residuals on the other hand, and more specifically their absolute values, statistical properties and the correlation between residuals at different monitoring locations, are suitable as indicators of the occurrence of in-sewer defects. This allows the application of 'hydraulic fingerprinting' based on model calibration, where the 'fingerprint' is defined by the model parameters and the residuals. The concept of 'fingerprinting' is demonstrated for the combined sewer system 'Tuindorp'. The results show that 'hydraulic fingerprinting' can be a powerful tool for directing sewer asset management actions.