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Francois Clemens

Bio: Francois Clemens is an academic researcher from Delft University of Technology. The author has contributed to research in topics: Sanitary sewer & Combined sewer. The author has an hindex of 23, co-authored 170 publications receiving 2032 citations. Previous affiliations of Francois Clemens include Norwegian University of Science and Technology & City University of New York.


Papers
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Book ChapterDOI
23 Sep 2018
TL;DR: In this paper, the DEST method is proposed to detect and quantify exfiltration from sewer systems under variable flow conditions; the method is based on the principle of setting up a mass balance of a tracer substance.
Abstract: Due to the ageing of our underground wastewater infrastructure, leakage of sewers and pressure mains and subsequent infiltration or exfiltration are becoming an increasingly important issue. Herein, we present a novel method to detect and potentially quantify exfiltration from sewer systems under variable flow conditions; the DEST method. The DEST method is based on the principle of setting up a mass balance of a tracer substance. At an upstream point a tracer is injected in a sewer with a constant rate for a certain period, subsequently downstream high frequent time discrete grab samples are combined with discharge measurements to complete the mass balance. The method is applied on a sewer section in Loenen (NL) to investigate its feasibility. Two different tracers are used; Lithium chloride and Deuterium. Preliminary results indicate that both tracers show similar behaviour at the downstream measurement point. Final lab results are expected at the end of March, allowing in depth analysis of the experimental results with a focus on the measurement uncertainty.

2 citations

11 Nov 2009
TL;DR: In this article, data from call centres at two municipalities were analyzed in order to quantify flooding frequencies and associated flood risks for three main failure mechanisms causing urban flooding, and the results showed that quantified flood risk for the two cases is well above the standard which is defined in sewer management plans.
Abstract: Data from call centres at two municipalities were analysed in order to quantify flooding frequencies and associated flood risks for three main failure mechanisms causing urban flooding. The aim was to find out whether current operational strategies are efficient for flood prevention and if directions for improvement could be found. The results show that quantified flood risk for the two cases is well above the standard which is defined in sewer management plans. The analysis pointed out that gully pot blockages are the main cause of flooding and handling gully pot blockages should therefore be a priority for sewer operators. Reactive handling of calls, as is currently applied, is inefficient if all calls are reacted upon since a small portion of all calls report serious consequences like flooding in buildings or wastewater flooding. Preventive cleaning of sewer pipes proves to be an efficient strategy to reduce flooding due to sewer blockages as flood risk associated with sewer blockages is lower in case of higher cleaning sewer frequencies. Sewer blockages often have serious consequences, thus preventive handling is to be preferred to reactive cleaning. According to the results of this analysis, reduction of flooding sewer overloading is not of primary concern, because serious consequences for this failure mechanism are rare compared to other failure mechanisms.

2 citations

31 Dec 2013
TL;DR: In this paper, the authors studied the extent to which rainfall data can be used to explain variations in insurance claim data and addressed the issue of time lag between claim date and time of the damaging rainfall event, which may lead to underestimation of correlations between rainfall and damage variables.
Abstract: Sewer flooding due to extreme rainfall may result in considerable damage. Damage data to quantify costs of cleaning, drying, and replacing materials and goods are rare in literature. In this study, insurance claim data related to property damages were analysed for the municipality of Aarhus, Denmark. The aim of this paper was to study the extent to which rainfall data can be used to explain variations in insurance claim data. In particular, the paper addresses the issue of time-lag between claim date and time of the damaging rainfall event, which may, if not taken into account, lead to underestimations of correlations between rainfall and damage variables. Rainfall data from two rain gauges were used to extract rainfall characteristics. From cross correlations between time series of rainfall and claim data, it can be concluded that rainfall events induce claims mostly on the same day, but also on the three days after. A linear model that takes into account rainfall data from previous days slightly improves correlations between rainfall and damage variables compared to a simple linear model. Best correlation coefficients were found between maximum hourly rainfall intensity and daily number of claims (0.47-0.57) and daily total damage (0.43-0.53).

2 citations

Journal ArticleDOI
TL;DR: In this paper, experiments were conducted in a O600mm tank to analyze the 3D motion of buoyant particles in the free-surface vortex flow and revealed two stages in the particle motion.
Abstract: Experiments are conducted in a O600 mm tank to analyse the 3D motion of buoyant particles in the free-surface vortex flow. The experiments revealed two stages in the particle motion: stage 1 is the...

2 citations


Cited by
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Journal ArticleDOI

6,278 citations

Journal Article
TL;DR: In this article, the authors present a document, redatto, voted and pubblicato by the Ipcc -Comitato intergovernativo sui cambiamenti climatici - illustra la sintesi delle ricerche svolte su questo tema rilevante.
Abstract: Cause, conseguenze e strategie di mitigazione Proponiamo il primo di una serie di articoli in cui affronteremo l’attuale problema dei mutamenti climatici. Presentiamo il documento redatto, votato e pubblicato dall’Ipcc - Comitato intergovernativo sui cambiamenti climatici - che illustra la sintesi delle ricerche svolte su questo tema rilevante.

4,187 citations

Book
01 Jun 1976

2,728 citations

Book ChapterDOI
01 Jan 1997
TL;DR: The boundary layer equations for plane, incompressible, and steady flow are described in this paper, where the boundary layer equation for plane incompressibility is defined in terms of boundary layers.
Abstract: The boundary layer equations for plane, incompressible, and steady flow are $$\matrix{ {u{{\partial u} \over {\partial x}} + v{{\partial u} \over {\partial y}} = - {1 \over \varrho }{{\partial p} \over {\partial x}} + v{{{\partial ^2}u} \over {\partial {y^2}}},} \cr {0 = {{\partial p} \over {\partial y}},} \cr {{{\partial u} \over {\partial x}} + {{\partial v} \over {\partial y}} = 0.} \cr }$$

2,598 citations