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.

Intuïtie en informatie in besluitvorming voor rioleringsbeheer

Abstract: Passend rioleringsbeheer is nodig om voldoende dienstlevering te balanceren met investeringskosten. Besluitvorming binnen rioleringsbeheer kan echter bemoeilijkt worden door gebrek aan data en interacties met verschillende actoren. Deze beperkingen zorgen veelal voor niet heldere en niet reproduceerbare besluitvormingsprocessen, die voornamelijk gebaseerd zijn op intuitie, ofwel het onder riolisten bekende ‘gezond boerenverstand’. Het is onduidelijk hoe en welke informatiebronnen gebruikt worden in vervangingsbeslissingen, en in hoeverre deze besluiten beinvloed worden door intuitie. Het doel van deze studie is dan ook het analyseren van de beschikbaarheid en het gebruik van informatie en intuitie in besluitvorming voor rioolvervanging. Daarnaast wordt ook het succes van intuitieve besluitvorming onder de loep genomen. Achttien interviews zijn afgenomen in zeven Nederlandse gemeenten, samen met een analyse van de betreffende GRP’s. Sommerende inhoudsanalyse is toegepast als voornaamste analysetechniek. Eenentwintig informatiebronnen zijn aangeduid, die gebruikt worden in intuitieve risicoanalyses betreffende de volgende aspecten: buisinstorting, onvoldoende hydraulische prestatie, overlast voor bewoners en gerelateerd reputatie van de organisatie, kosten voor graafwerkzaamheden en bovengrondreconstructie en overlast voor verkeer. Het is aannemelijk dat intuitieve besluitvorming verkozen wordt boven rationeel redeneren, vanwege de complexe context van rioleringsbeheer en gelimiteerde databeschikbaarheid en –kwaliteit. Een conclusie is dat aan de voorwaarden die gelden voor vakkundige intuitie (regelmaat en kansen om te leren) niet wordt voldaan. Het is daarom moeilijk om besluiten te reproduceren in vergelijkbare omstandigheden, te rechtvaardigen of te evalueren.

The Impact of Lateral House Connections on the Serviceability of Sewer Systems

Abstract: It remains unknown how lateral house connections affect the performance of the sewer system, since the assessment of serviceability is mainly based on the state of the main sewer system. Further insight into the contribution of lateral house connections to the overall level of service provided can aid to target investments to parts of the system where it is most effective. To this end, techniques from the reliability theory were applied to a commercial sewer maintenance database to quantify the impact of lateral house connections on the serviceability of sewer systems. Analysis of the data showed that the failures follow a Poisson distribution. A comparison of the derived failure rate with values obtained from a different study revealed that the blockage rate of lateral house connections is an order of magnitude greater than the failure rate of the dominant mechanism of main sewer systems, thereby making the impact of lateral house connections on the serviceability of sewer systems substantial.

Applicability of CFD Modelling in Determining Accurate Weir Discharge: Water Level Relationships

Abstract: Being able to accurately determine weir discharges is of key importance in urban water management. The most common method is performing a level measurement and calculating the discharge using the standard weir equation. Since this equation is only valid in certain conditions, this can lead to large deviations from the actual discharge. In this paper, lab measurements and CFD calculations are applied to determine a new method for the derivation of accurate Q(h) relationships. Detailed scale model experiments have been performed for the internal weir of a SST. The scale model is precisely reproduced in a CFD model, with which corresponding calculations have been performed. It is shown that the water levels from the scale model can be reproduced by the CFD model without parameter tuning. Q(h) relationships have been derived from both the scale model experiments and the CFD calculations. They have been mutually compared with the relationship from the standard equation as well. It is shown that the derived relationships are very similar indicating the applicability of CFD for this purpose. All derived relationships form a much better description of the actual weir discharge than the standard equation.

Decision Tree Analysis Of Processes Generating Water-Related Building Damage : A Case Study In Rotterdam, The Netherlands

Abstract: The objective of this study was to identify the main failure mechanisms behind water-related building damage and to investigate to what extent these processes are related to characteristics of buildings and rainfall events. Results are based on the mining of property level insurance damage data, for a case study in Rotterdam, the Netherlands. This study has found that most frequent causes of water-related damage relate to roof leakages (28%), bursts of household water supply pipes (19%) and blocked household wastewater systems (18%). Cases of sewer flooding or depression filling were less present (2.4% and 0.6%), but showed stronger correlations with heavy rainfall events than any other failure mechanism. Classification tree analysis revealed that water discharges from neighbours is the main damage cause for high-rise buildings on days with no or minor rainfall (< 7.5 mm/h). Moreover, damage due to blocked household wastewater systems is associated with low-rise buildings younger than 50 years.

The mismatch between long-term monitoring data and modelling of solids wash-off to gully pots

Abstract: Urban runoff remobilises solids and their associated pollutants from urban-built environments and transports them to drainage systems via gully pots. This study presents an extensive monitoring cam...

Climate Change 2007: The Physical Science Basis.

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.

Boundary Layer Theory

Abstract: The boundary layer equations for plane, incompressible, and steady flow are $$\matrix{ {u{{\partial u} \over {\partial x}} + v{{\partial u} \over {\partial y}} = - {1 \over \varrho }{{\partial p} \over {\partial x}} + v{{{\partial ^2}u} \over {\partial {y^2}}},} \cr {0 = {{\partial p} \over {\partial y}},} \cr {{{\partial u} \over {\partial x}} + {{\partial v} \over {\partial y}} = 0.} \cr }$$