Showing papers by "Francois Clemens published in 2013"
TL;DR: In this article, the authors assess the quality of the analysis of visual sewer inspection data by analysing data reproducibility; three types of capabilities to subjectively assess data are distinguished: the recognition of defects, the description of defects according to a prescribed coding system and the interpretation of sewer inspection reports.
Abstract: In common with most infrastructure systems, sewers are often inspected visually. Currently, the results from these inspections inform decisions for significant investments regarding sewer rehabilitation or replacement. In practice, the quality of the data and its analysis are not questioned although psychological research indicates that, as a consequence of the use of subjective analysis of the collected images, errors are inevitable. This article assesses the quality of the analysis of visual sewer inspection data by analysing data reproducibility; three types of capabilities to subjectively assess data are distinguished: the recognition of defects, the description of defects according to a prescribed coding system and the interpretation of sewer inspection reports. The introduced uncertainty is studied using three types of data: inspector examination results of sewer inspection courses, data gathered in day-to-day practice, and the results of repetitive interpretation of the inspection results. After a thorough analysis of the data it can be concluded that for all cases visual sewer inspection data proved poorly reproducible. For the recognition of defects, it was found that the probability of a false positive is in the order of a few percent, the probability of a false negative is in the order of 25%.
120 citations
TL;DR: In this article, a database of water-related insurance damage claims related to private properties and content was analyzed, and the authors investigated whether the probability of occurrence of rainfall-related damage was associated with the intensity of rainfall.
Abstract: In this paper, a database of water-related insurance damage claims related to private properties and content was analysed. The aim was to investigate whether the probability of occurrence of rainfall-related damage was associated with the intensity of rainfall. Rainfall data were used for the period of 2003–2009 in the Netherlands based on a network of 33 automatic rain gauges operated by the Royal Netherlands Meteorological Institute. Insurance damage data were aggregated to areas within 10-km range of the rain gauges. Through a logistic regression model, high claim numbers were linked to maximum rainfall intensities, with rainfall intensity based on 10-min to 4-h time windows. Rainfall intensity proved to be a significant damage predictor; however, the explained variance, approximated by a pseudo-R2 statistic, was at most 34% for property damage and at most 30% for content damage. When directly comparing predicted and observed values, the model was able to predict 5–17% more cases correctly compared to a random prediction. No important differences were found between relations with property and content damage data. A considerable fraction of the variance is left unexplained, which emphasizes the need to study damage generating mechanisms and additional explanatory variables.
62 citations
TL;DR: Results show that both methods, visual inspection and core sampling, are associated with large uncertainties and that there is no obvious correlation between results ofVisual inspection and results of drill core analysis.
14 citations
TL;DR: In this article, the detection limits of the monitoring equipment itself are well-known, but there is little information available on detection limits for the discovery of illicit connections in mixing of sewers, and attenuation also plays an important role.
13 citations
TL;DR: A first trial application of the probabilistic evaluation framework for evaluation of sanitation options in the Nyalenda settlement in Kisumu, Kenya, showed how the range of values that an evaluation parameter may obtain in practice would influence the evaluation outcomes.
10 citations
TL;DR: In this article, the influence of surface tension on the air discharge in downward sloping pipe sections was investigated with clean water, surfactant-added water, and wastewater, and experiments have been performed with both clean water and wastewater.
Abstract: Stricter environmental regulations have led to new wastewater treatment plants and a centralization of existing wastewater treatment plants. Therefore, pressurized wastewater mains have become an indispensable link between the collection systems and the treatment plants. In urban areas in particular, these pipelines include many inverted siphons to cross other infrastructure, like railways, motorways, other pipelines, and buildings. Accumulation of air in downward sloping sections of these wastewater mains reduces the transport capacity significantly. A dominant air transport mechanism is the air-entraining hydraulic jump at the tail of an accumulated air pocket. The novelty of this paper is a systematic investigation of the influence of surface tension on the air discharge in downward sloping pipe sections. Experiments have been performed with clean water, surfactant-added water, and wastewater. The experiments with surfactant-added water confirm that the air discharge increases significantly at ...
7 citations
31 Dec 2013
TL;DR: In this article, 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).
5 citations
31 Dec 2013
TL;DR: In this article, the authors used C-band radar images to extract characteristics of rainfall events and linked these characteristics to various damage statistics at district level and per day, based on the 150 days with the largest damage amounts nationwide.
Abstract: Intense rainfall may locally cause considerable damage in cities, e.g. because of sewer floods. A better understanding of relationships between rainfall characteristics and rainfall-related damage can help insurers and flood authorities to respond more adequately to rainfall extremes. This paper aims to study to what extent weather radars can be helpful to predict damage locations and characteristics. For the Netherlands, damage data were analysed based on daily insurance records. A database of C-band radar images was used to extract characteristics of rainfall events. These characteristics were linked to various damage statistics at district level and per day. Results are based on the 150 days with largest damage amounts nationwide. Rainfall and damage locations clearly showed similar spatial patterns when visualized on maps, particularly for the case maximum hourly rainfall intensity and rainfall volume. Through linear regression with log-transformed damage variables, highest correlation was found between claim ratio and maximum hourly rainfall intensity (r=0.38). The average damage per claim does not show any significant correlation with rainfall variables, except a weak relationship with maximum hourly rainfall intensity (r=0.12). This means that more intense rainfall mainly affects the number of households claiming damage, while it hardly influences the amount of damage per individual household.
4 citations
31 Dec 2013
TL;DR: In this article, the applicability of surrogate sensors as robust sensors for water quality based RTC is demonstrated, based on 1.5 years of level, conductivity (EC) and turbidity (TU) measurements at 9 combined sewer overflow (CSO) locations.
Abstract: The objective of this paper is to demonstrate the applicability of, and need for, surrogate sensors as robust sensors for water quality based RTC. For this purpose 1.5 years of level, conductivity (EC) and turbidity (TU) measurements at 9 combined sewer overflow (CSO) locations have been performed and analysed to determine the most polluted CSO locations. The analysis is based on surrogate event mean concentrations (sEMC, defined as EC multiplied by TU) and surrogate pollution loads (sPL, defined as the sEMC multiplied by the overflow volume). It is shown that EC and TU measurements can serve as surrogate measurements to determine the relative pollution of a CSO location. Analysis of the EC and TU values with respect to the distance between the CSO location and the WWTP gave no indication that this is of importance. Comparison of the sEMC and sPL for the CSO locations, shows that water quality measurements will have a great impact on the application of RTC, leading to quality based RTC.
3 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
30 Jun 2013
TL;DR: In this paper, the authors assess the impact of different temporal and spatial rainfall resolutions on the hydrological response of a higly urbanized area, which is one of the pilot locations of RainGain Interreg IVB project, which aims at improving fine-scale measurement and prediction of rainfall to enhance urban pluvial flood prediction within cities.
Abstract: This study aims to assess the impact of different temporal and spatial rainfall resolutions on the hydrological response of a higly urbanized area. The catchment under study is one of the pilot locations of RainGain Interreg IVB project, which aims at improving fine-scale measurement and prediction of rainfall to enhance urban pluvial flood prediction within cities. Heavy rain precipitation can cause catastrophic flooding events over urbanized areas. Accurate information about rainfall is needed to be able to mitigate consequent damages. Due to the high percentage of imperviousness and low rate of vegetation interception, the reaction of urban drainage catchments to a storm event is short. Therefore, to describe fast runoff processes and short response times, urban hydrological modelling requires high resolution rainfall data. Here rainfall from dual polarimetric doppler X-band radar, belonging to the Dutch national meteorological observatory CESAR, is applied to an urban catchment of 3,7 km² that has a combined sewer system with 3062 nodes and 11 external weirs, which serve as outflow. The nodes are inter-connected by 3286 pipes. Among the latter, 4 are pressurized. There are also 2 external pumping stations transporting water to the WWTP and the river. The district belongs to a polder area, i.e. below sea level. For this reason, during heavy rainfall, excess storm water needs to be pumped out in the river system or temporally stored.
31 Dec 2013
TL;DR: In this paper, the authors analyse the impact of intuitie on the performance of rioleringsbeheer in a context of rioolvervanging, and find that intuitieve besluitvorming verkozen wordt boven rationeel redeneren in vergelijkbare omstandigheden, te rechtvaardigen of te evalueren.
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.
01 Jan 2013
TL;DR: The concept of bronscheiding is een van onderzochte mogelijkheden as mentioned in this paper, e.g., in the context of a vervanging van verouderde bestaande infrastructuur voor afvalwater bestaat echter voor het grootste deel uit ofwel gemengde systemen, of systemen waarin afval water and hemelwater worden gescheiden.
Abstract: In de afgelopen 15 tot 20 jaar zijn verschillende nieuwe concepten ontwikkeld voor de inzameling, het transport en de behandeling van afvalwater en op pilot-schaal toegepast en getest. Doelstelling hierbij is te komen tot een meer duurzaam afvalwatersysteem. De voordelen van de nieuwe concepten zijn onder meer de mogelijk om energie en grondstoffen uit afvalwater te winnen en de mogelijkheid om microverontreinigingen te verwijderen. Bronscheiding is een van onderzochte mogelijkheden. De bestaande infrastructuur voor afvalwater bestaat echter voor het grootste deel uit ofwel gemengde systemen of systemen waarin afvalwater en hemelwater worden gescheiden, waardoor het op grote schaal gescheiden inzamelen van bijvoorbeeld urine, zwart en grijs water geen eenvoudige zaak is. Echter, de vervanging van verouderde bestaande systemen of grootschalige renovatie van wijken biedt de mogelijkheid om over te gaan tot de invoering van bronscheiding in bestaande situaties. Iets dergelijks geldt bij renovatie van woningen voor de binnenhuisriolering. Het onderzoek naar nieuwe sanitatieconcepten heeft zich vooral gericht op de ontwikkeling van behandelingsconcepten en de uitgevoerde praktijktoepassingen betroffen betrekkelijk kleinschalige projecten in nieuwbouwsituaties. Dit artikel gaat in de mogelijkheden om te komen tot bronscheiding in bestaande situaties, hierbij is gekeken naar bestaande inzamel- en transportmethodes, maar er is ook een aantal niet direct voor de hand liggende mogelijkheden benoemd.
01 Jan 2013
TL;DR: In this paper, the applicability of surrogate sensors as robust sensors for water quality based RTC is demonstrated, based on 1.5 years of level, conductivity (EC) and turbidity (TU) measurements at 9 combined sewer overflow (CSO) locations.
Abstract: The objective of this paper is to demonstrate the applicability of, and need for, surrogate sensors as robust sensors for water quality based RTC. For this purpose 1.5 years of level, conductivity (EC) and turbidity (TU) measurements at 9 combined sewer overflow (CSO) locations have been performed and analysed to determine the most polluted CSO locations. The analysis is based on surrogate event mean concentrations (sEMC, defined as EC multiplied by TU) and surrogate pollution loads (sPL, defined as the sEMC multiplied by the overflow volume). It is shown that EC and TU measurements can serve as surrogate measurements to determine the relative pollution of a CSO location. Analysis of the EC and TU values with respect to the distance between the CSO location and the WWTP gave no indication that this is of importance. Comparison of the sEMC and sPL for the CSO locations, shows that water quality measurements will have a great impact on the application of RTC, leading to quality based RTC.
01 Jan 2013
10 Sep 2013
TL;DR: In this article, the authors studied the reproducibility of visual sewer inspection data and gave relevant suggestions to improve the quality by defining defects that are in the current standard defined ambiguously (i.e. can be understood in more than one way).
Abstract: Previous research learned that the reproducibility of visual sewer inspection data is poor (Dirksen et al.). Further research by Arjan et al. showed that the applied coding system has a major influence on the reproducibility. The aim of this study was to give relevant suggestions to improve the quality by defining defects that are in the current standard defined ambiguously (i.e. can be understood in more than one way). For this, the database of sewer examination data of graduated sewer inspectors in the Netherlands was studied.