Showing papers in "Urban Water Journal in 2012"

Quantification of climate change effects on extreme precipitation used for high resolution hydrologic design

Abstract: Design of urban drainage structures should include the climatic changes anticipated over the technical lifetime of the system. In Northern Europe climate changes implies increasing occurrences of extreme rainfall. Three approaches to quantify the impact of climate changes on extreme rainfall are studied, all based on output from historical rain series of the present climate and output from Regional Climate Models. Two models are applied, one being based on an extreme value model, the Partial Duration Series Approach, and the other based on a stochastic rainfall generator model. Finally an approach is based on identification of areas, where the present climate resembles the anticipated future climate for the region in question. The results indicate that design intensities in Denmark are likely to be increased by 10–50% within the next 100 years. The increase in design intensities depend on the duration and the return period in question.

Three Points Approach (3PA) for urban flood risk management: a tool to support climate change adaptation through transdisciplinarity and multifunctionality.

Abstract: Urban flood risk is increasing as a consequence of climate change and growing impervious surfaces. Increasing complexity of the urban context, gradual loss of tacit knowledge and decreasing social awareness are at the same time leading to inadequate choices with respect to urban flood risk management (UFRM). The European Flood Risk Directive emphasises the need for non-structural measures aimed at urban resilience and social preparedness. The Three Points Approach (3PA) provides a structure facilitating the decision making processes dealing with UFRM. It helps to accept the complexity of the urban context and promotes transdisciplinarity and multifunctionality. The 3PA introduces three domains wherein water professionals may act and where aspects valued by different stakeholders come into play: (1) technical optimisation, dealing with standards and guidelines for urban drainage systems; (2) spatial planning, making the urban area more resilient to future changing conditions; and (3) day-to-day values, enh...

State-of-the-technology review on water pipe condition, deterioration and failure rate prediction models!

Abstract: This paper presents a state-of-the-technology literature and current practice review on water pipe condition, deterioration and failure rate prediction models in order to identify the gap between the models found in literature and those currently used by utilities around the world. Researchers have developed various methodologies in determining pipe condition and failure prediction over the last three decades. Their efforts are discussed in many literatures and articles but are not summarised by one document. In this report, more than 50 articles were reviewed from the last decade and are presented based on the type of methodology utilised. Nine utilities across the world with significant undertakings of water pipe infrastructure management are also presented which underline the current practice. In summary, both the literature and current practice are summarised to identify the gap between the models found in literature and water utility asset management practices.

Rainwater harvesting to control stormwater runoff in suburban areas. An experimental case-study

Abstract: On a 23 ha urban watershed, 10 km East of Paris, rainwater tanks have been installed on 1/3 of the private parcels to prevent stormwater sewer overflows. This paper investigates the macroscopic effect of rainwater harvesting on runoff, and thus the potential of this technique for stormwater source control. The analysis is performed using the SWMM 5 model, calibrated on rainfall- runoff measures from two measurement campaigns, before and after the equipment. The availability of two data-sets allows the authors to point out changes in the catchment's behaviour. The main findings are that: (1) catchment's evolution, mainly caused by individual land-cover modifications, produces non-stationarity of the hydrologic behaviour; (2) the rainwater tanks installed, although they affect the catchment hydrology for usual rain events, are too small and too few to prevent sewer overflows in the case of heavy rain events.

Evaluation of the effects of greywater reuse on domestic wastewater quality and quantity

Abstract: This simulation study, based on experimental and literature data, evaluates the influence of onsite greywater reuse on domestic wastewater quality and quantity. For this, three scenarios were studied: no reuse; reuse for toilet flushing; reuse for toilet flushing and garden irrigation. Light greywater reuse reduced the daily household wastewater flows by 25–40%. These reductions mainly occurred during the morning and evening peak wastewater generation. Although daily loads of all pollutants decreased, their concentrations in the discharged wastewater increased owing to exclusion of potable water from the wastewater and replacing it by treated light greywater. The proportional concentration increase of most pollutants was lower than the decrease in wastewater discharge, due to degradation during treatment. The highest concentration increase occurred during the morning peak, coinciding with the highest flow reduction. This study is a first step towards quantification of the effects of onsite greywater reuse...

Identification of the optimal entry points at District Metered Areas and implementation of pressure management

Abstract: Nowadays, the implementation of pressure management in District Metered Areas (DMAs) is considered one of the most effective tools for leakage control, particularly in large networks and in systems with deteriorated infrastructures and with high pressure. The goal of the methodology proposed in this paper is to identify the optimal entry points at DMAs, determine the network needs in terms of reinforcement/replacement, and fix both the location and settings of different types of Pressure Reduction Valves (PRVs) for leakage control. This methodology is based on an optimisation model, which is solved by a Simulated Annealing algorithm, and the solutions obtained always fulfil the minimum pressure requirements for the network. The objective function comprises the total cost of the DMAs implementation and the economic benefits that can be achieved by pressure management. Finally, the results for two case studies are presented and discussed.

Fast network multi-objective design algorithm combined with an a posteriori procedure for reliability evaluation under various operational scenarios

Abstract: This paper presents a methodology for the optimal design of water supply networks. It features a multi-objective optimisation (aimed at minimising costs and maximising resilience) and a subsequent ‘retrospective’ evaluation of network reliability under various operational scenarios. The multi-objective optimisation is based on an algorithm specifically developed for the design of real networks which feature a very high number of nodes and pipes. The ‘retrospective’ evaluation of network reliability is assessed considering resilience contrasted with several other indexes adopted to describe the operational performance of the network under critical scenarios such as segment isolation or hydrant activation, and different water demand conditions. In the applications two case studies, made up of a simple benchmark network and a real network respectively, are considered for the multi-objective optimisation; the ‘retrospective’ evaluation of reliability is performed only on the real network. The latter example c...

Assessing the combined benefits of water recycling technologies by modelling the total urban water cycle

Abstract: This study investigates the potential benefits of new technologies, modern appliances, and innovative techniques that help to improve the performance of the urban water cycle. Urbanisation is a major source of additional pressures (both qualitative and quantitative) on the environment. For example abstractions to cover the increased demands for water supply or alterations of the topographic and geomorphologic properties of the land cover result in considerable changes to the dynamics of the hydrosystem (change of average and maximum values of flows). Sustainable, water-aware technologies, like SUstainable Drainage Systems (SUDS) and rainwater harvesting schemes, can be implemented to reduce these adverse effects. These technologies introduce interactions between the components of the urban water cycle. Rainwater harvesting for example, apart from the potable water demand reduction, may have a significant influence on the generated runoff. Consequently, an integrated modelling of the urban water cycle is n...

Exploration of the relationship between water main breaks and temperature covariates

Abstract: Water utilities (especially in colder climates) often experience an increase in water main breaks in colder seasons. Some observers argue that this increase largely occurs during the period when there are sudden and prolonged changes in water and air temperatures, which typically occur during the late fall to early winter (temperature drop) and late winter to early spring periods (temperature rise). This paper examines the impact of temperature changes on observed pipe breakage rate for three pipe materials, namely, cast iron, ductile iron and galvanised steel. Several water and air temperature-based covariates were tested in conjunction with a non-homogeneous Poisson pipe break model to assess their impact on water main breaks, using data sets from three different water utilities in the USA and Canada. Temperature-based covariates, such as average mean air temperature, maximum air temperature increase and decrease, and how fast the air temperature increase and decrease over a specific period of days, wer...

Cost-benefit analysis – leakage reduction by rehabilitating old water pipelines: Case study of Oslo (Norway)

Abstract: Water saving is not just the responsibility of the consumer. While demand-side management prescribes several good practices for water-consumers, the supplier also understands that leakage reduction on its part is a more effective mode of saving large quantities of water, by having to abstract, treat and supply less. It is not just water which is saved, but money spent on chemicals and energy expended on treatment and pumping. The economic aspect apart, this also means that there are possibilities of significant reductions of environmental impacts upstream in the chemicals production and energy generation processes. However, it is not an easy task to perform a comprehensive cost-benefit analysis, by taking into account all the direct and indirect costs and benefits. Benefits besides are not just multi-pronged but also distributed over time. In this paper, the author compares the direct costs incurred in rehabilitating old water pipelines in Oslo, with the direct benefits of leakage reduction which accrue t...

External corrosion to concrete sewers: a case study

Abstract: The aim of this study was to investigate the deterioration of concrete sewers and identify responsible factors; this investigation was a part of an ongoing asset evaluation for Rennes (France). The sewer studied was a 300 mm spun concrete pipe laid in 1992. Core samples (D 28 mm, L 40 mm) were taken from different areas of a pipe (invert, crown and side wall) and analysed to quantify the condition of the concrete and the extent of damage to the internal and external surface of the pipe. Physical and mechanical properties of the material were characterised. The depassivation of the concrete was measured by testing with a phenolphthalein solution. The study showed that in this particular case the external corrosion was extensive with minimal internal corrosion. It is proposed that the corrosion was possibly linked to the use of a contaminated backfill or organic acids in the ground water. Recommendations are proposed concerning the direction of future research.

Stormwater management challenges as revealed through a design experiment with professional landscape architects

Abstract: Despite a number of potential benefits, using the urban landscape for managing stormwater runoff is spreading rather slowly. As urban planners and landscape architects are considered key protagonists of this trend, the objective of the study was to identify the challenges they confront when asked to retrofit an urban landscape for the management of stormwater runoff. Monitoring a two-week design experiment involving six teams of professional landscape architects identified 11 challenges, including sizing of elements, estimating costs, understanding water dynamics, aspects of biodiversity promotion, and dealing with land administrations and ownership issues. Measures to address the challenges are discussed. It should be noted that all six teams approached the stormwater management challenge in an energetic and focused way, applying their technical, personal and site-specific knowledge, and delivered innovative, flexible and coherent solutions. This emphasizes that the design process constitutes a strong an...

Development of the standardised precipitation index for Greece

Abstract: The use of standardised precipitation index (SPI) may lead to an understanding of a droughts magnitude and duration and thus contributing to integrated drought management options. Greece, a semi-arid country, has very often faced the hazardous impacts of droughts. The worst drought on record lasted from 1989 to 1993, and affected all the country, particularly the urban water supply of Athens metropolitan area. Rainfall time series from 41 rain stations were used to calculate SPI, for time scales of 3, 6, 12 and 24 months. Forty eight (48) interpolation surfaces were produced and assessed using historical data and statistical parameters for the SPI spatial visualisation through GIS kriging of the 1989–1993 drought. The results suggest the use of SPI as a drought monitoring tool, namely in areas with a distinct dry season, supporting drought forecasting and assisting integrated strategies for drought management.

Valuing the environment in developing countries: modelling the impact of distrust in public authorities' ability to deliver public services on the citizens' willingness to pay for improved environmental quality

Abstract: In this paper, we employ the choice experiment method to estimate citizens' valuation of an intervention that proposes to improve the quality of the wastewater deposited in the Ganges River, India. We interviewed 150 randomly selected citizens of Chandernagore, along the banks of the Ganges River, to elicit their willingness to pay (WTP) for this intervention, measured in terms of higher municipality taxes. The findings reveal that almost all of the citizens value wastewater quality, though majority protested the intervention, and stated that they donot trust the authorities for effective management of funds. These protest responses were controlled for with the nested logit model. The results reveal that the citizens are willing to pay significant amounts for improved wastewater quality. Municipalities could rely to some extent on their citizens' WTP higher taxes but municipalities' performance, trustworthiness, accountability, as well as the citizens' perceptions of these, should be improved.

A composite indicator for water meter replacement in an urban distribution network

Abstract: In water supply management, volumetric water meter are typically used to measure users' consumption. With water meters, utilities can collect useful data for billing, assess the water balance of the system, and identify failures in the network, water theft and anomalous user behaviour. Despite their importance, these instruments are characterised by intrinsic errors that cause so-called apparent losses. The complexity of the physical phenomena associated with metering errors in aging water meters does not allow meter replacement to be guided by single parameters, such as the meter age or the total volume passed through the meter. This paper presents a meter replacement strategy based on a composite ‘Replacement Indicator’ (RI) that aims to reduce apparent losses. The performance of a meter during its operating life was analysed by means of this indicator, which signals when the meter needs to be replaced. To test the reliability and robustness of the proposed indicator, a Monte Carlo uncertainty analysis ...

Influence of wind-driven rain on the rainfall-runoff process for urban areas: Scale model of high-rise buildings

Abstract: The hydrological response of impervious urban areas with varying building densities to the combined action of wind and rain is not well understood. Exploratory laboratory simulations were conducted using a scale model of a hypothetical high density urbanized area with high-rise buildings. Seventy two runs were conducted for static and moving storms in upstream and downstream directions, with and without wind, for different building densities and for an average rainfall intensity of 120 mm/h. The laboratory experiments show that building density and the spatial and temporal distribution of rainfall that results from wind and storm movement have a clear influence on the hydrological response to rainstorms. Increased urbanization promotes a higher peak discharge, a longer base time and reduces the slope of the hydrographs rising limbs, while wind-driven rain attenuates these effects. Downhill storm movement promotes a faster hydrological response and a higher discharge peak than uphill movement.

Reliability based optimal design of water distribution networks considering life cycle components

Abstract: Water distribution systems play an important role in supplying water to consumers in a timely and efficient manner. The importance and complexity of such systems lead to extensive research in the area of optimal design of water distribution networks. Traditionally, only system costs are considered in design with few models incorporating environmental impacts. This paper presents a model for designing sustainable water distribution networks by minimising life cycle costs and life cycle CO2 emissions, while ensuring hydraulic reliability for the life time of the system. The model integrates a multi-objective genetic algorithm with water network simulation software, EPANET. A traditional benchmark water distribution network is used to demonstrate the model. Eight scenarios have been developed to test and validate the model for a variety of objectives with different constraints. Trade-offs between life cycle costs and life cycle emissions, along with hydraulic reliability of the system are illustrated.

An organisational innovation perspective on change in water and wastewater systems – the implementation of the Water Framework Directive in England and Wales

Abstract: This paper presents an assessment of how the European Water Framework Directive (WFD) is stimulating change in water and wastewater management. The paper aims to provide an organisational innovation contribution towards understanding the processes by which policy and legislation stimulate change in water and wastewater systems. Results were produced by analysing interviews with environmental managers from all water and sewerage companies in England and Wales. Results show that integrated water supply approaches are emerging in response to the WFD, while wastewater approaches are not changing to the same extent. Reasons for this difference are located in a mix of factors including: economic regulation; conflicting national and EU regulations; uncertainty; lock-in to infrastructure; the way in which different WaSCs frame business problems and opportunities, and a lack of technological knowledge. Results are discussed against an international review of water sector change and against government reviews of the water sector economic regulator.

Performance of a dry detention pond: case study of Kota Damansara, Selangor, Malaysia

Abstract: The Urban Stormwater Management Manual for Malaysia (MSMA) was published in 2001 by the Department of Irrigation and Drainage (DID), which promotes Best Management Practices (BMPs) aimed at stormwater management at the source. The construction of detention ponds has been strongly encouraged for water quantity control for new housing developments. This study focuses on the evaluation, using the InfoWorks Collection Systems (CS) model, of the effectiveness of a constructed dry detention pond built in 1996 located at Kota Damansara, Selangor. Hydrological and hydraulic data were collected for model calibration and verification. The study indicates that the dry detention pond can achieve its design goals, catering the flow from a 100-year Average Recurrence Interval or ARI storm and complies with the design requirement in the MSMA for major urban stormwater systems.

Development of two indices for determining hydrologic implications of land use changes in urban areas

Abstract: Simple metrics are needed by decision makers to quantify hydrologic impacts of land uses as a result of urbanization. Two indices to evaluate hydrologic implications of land use changes were developed and demonstrated in case studies. The first index, pre-development versus post-development index (PPH), compares pre-development to post-development hydrologic conditions for time of concentration, peak runoff for a 2-year 24-hour storm and a 10-year 24-hour storm, and average annual runoff volume. The second, extent of maximum index (EH), compares post-development with potential minimum and maximum hydrologic conditions of a site. The indices were applied in three case studies of residential subdivisions in Lafayette, Indiana. These case studies illustrate how to interpret the resulting index values. The Orchards subdivision, which was designed with conservation principles, scored the best for both indices. Although the two indices can be used separately, it is advised to use them together.

Generalising urban runoff and street network density relationship: A hydrological and remote-sensing case study in Israel

Abstract: This paper describes the relationship between urban road network density and urban runoff coefficient in the coastal plain of Israel. The study assessed 30 years of recorded changes in rainfall-runoff coefficient in an urban catchment in the coastal plain of Israel. Rain and runoff were measured and sampled at measurement stations. Insight into the factors affecting urban runoff was gained by applying GIS and remote-sensing analysis, including street network density assessment and urban impermeable area recognition. Street network density was found to be a reliable indicator for both urban impermeability (R2 = 0.83) and runoff (R2 = 0.92) change dynamics, showing a strong linear correlation. Thus the urban street drainage network can help explain the dynamics of change in urban runoff. To prevent urban flooding hazards, and to help conserve water resources, regional planners should take into consideration road network density in built-up areas.

Quality assurance and quality control practices for rehabilitation of sewer and water mains

Abstract: As part of the US Environmental Protection Agency (EPA)'s Aging Water Infrastructure Research Program, several areas of research are being pursued including a review of quality assurance and quality control (QA/QC) practices and acceptance testing during the installation of rehabilitation systems (USEPA 2011). The objectives of this research effort were to collect, analyze and summarize information on the installation and QA/QC practices for the trenchless rehabilitation of sewer and water transmission mains. In addition, consideration was given to practices related to water service lines, sewer service laterals, force mains, siphons, sewer manholes, pumping stations, associated wet wells and other appurtenances. This review was accomplished primarily by conducting interviews directly with rehabilitation technology vendors, design engineers and water and wastewater utilities that have a track record of using trenchless rehabilitation technologies within their network. This paper provides an overview of ho...

Solid wastes drained in an urban river sub-basin

Abstract: Inadequate disposal of solid wastes in urbanised areas may cause water body pollution and the obstruction of drainage canals. This may lead to floods, health problems and economic impacts. The study aimed at quantifying and qualifying the solid wastes transported in a river sub-basin and relating them to rainfall data. A gravimetric analysis of the urban solid wastes captured showed that they were constituted by 73% organic matter and 27% inorganic matter, and that 14% of the volume retained was plastic. The results observed showed major human interference in the basin and the environmental risks to the Esperanca stream. The development of tools to evaluate the effectiveness and impact of actions generates information which will help the municipal managers' decision-making process.

Determination of leakage inside buildings with a roof tank

Abstract: Buildings with a roof tank are common in countries with intermittent water supply. For these buildings, it is difficult to determine the leaks inside with the methods developed for pressurised networks of drinking water. A proposed alternative is Continuous Automatic Tank Gauging. Although commonly used to check the tightness of gasoline storage tanks, this method still has not been used to determine water leaks. This study explains how to set up the method and shows its application to six buildings. As expected, the leak magnitude was found to increase with the size and age of buildings. In practice, the method can estimate (within ± 30%) a leak as small as 1 l/h in buildings with a small roof tank and 20 l/h in buildings with a large roof tank.

Evaluation of non-user benefits towards improvement of water and sanitation services in informal settlements

Abstract: Many municipalities in developing cities are faced with the challenge of providing water and sanitation to ever-growing populations that cannot afford to pay for the services. This challenge calls for solutions that link equity considerations to cost recovery, and may require society to re-evaluate its perspectives on the value of urban water services. This paper explores the potential of non-user benefits as drivers of value and measures the trade-offs that “non-poor” residents were willing to make for the reductions in public health, social and economic costs when levels of service in informal settlements are improved. The study finds that people are sensitive to the public health impacts, and when given the choice of location of settlement to improve, and the means through which to make payment, would be willing to pay 6500 UGX (approx. $2.83) per household per month to install yard facilities in an informal settlement located nearest to their neighbourhood and with payment made through a special purpo...

Full cost recovery in the urban residential sector according to the Water Framework Directive

Abstract: Full cost recovery is a major and complex issue that has gained high recognition in recent years. The Water Framework Directive promotes the idea that water charging should act as an incentive for the sustainable use of water resources. Thus, all Member States should take into consideration the principle of recovery of the total cost of water services, which includes environmental and resource costs as well. In order to evaluate various aspects of current water policy, to investigate the perspectives of water saving, to explore new approaches toward sustainable water management in the water supply sector and to evaluate water price elasticity, a survey has been performed recently in the city of Volos, concerning the residential sector. The influence of some selected variables is examined, residential water demand curve and water price elasticity are calculated. Estimations of future water demand under different pricing policies are also performed. Finally, the full water cost for the city of Volos is esti...

A rapid fuzzy optimisation approach to multiple sources water blending problem in water distribution systems

Abstract: This paper proposes a Fuzzy Response Surface Optimisation (FRSO) approach for the water blending problem of multiple sources to maintain the water quality in water distribution systems. In the proposed approach, instead of the more precise and complicated nonlinear equations, the response surface models are used to describe the harmful reaction kinetics. The objectives of this study are to minimise the harmful reactions in the water network. A fuzzy linear programming using the min-operator approach is applied to handle the multiple objectives. Due to the FRSO only containing quadratic models, this approach is easy to apply and the optimisation is performed rapidly. Hence, the FRSO can be used to dynamically estimate the optimal blending ratios of water coming from multiple sources. Finally, a case study and two comparisons demonstrate the FRSO's advantages as to computational efficiency and simultaneous optimisation.

Integrated river flow modelling: A case study

Abstract: The paper presents a holistic approach to river flow modelling in which catchment rainfall-runoff, sewer hydrodynamic and river hydrodynamic models are linked together and applied to the Bradford catchment (UK). The catchment features steep gradients, flashy supercritical flow in combination with dry bed condition and is highly urbanised. Given this complexity and the paucity of data, a holistic approach was found essential, although its application proved challenging. Most important uncertainties inherent in each sub-model were assessed individually as well as propagation effects through the integrated model. The relative contribution of uncertainty sources to the total uncertainty in river flow predictions was quantified using the concept of variance decomposition. The results show that uncertainties in model structure and rainfall input in the rainfall-runoff model were significant. However, within the river hydrodynamic model, uncertainties propagated from the rainfall-runoff model were less apparent ...

Promoting the reuse of stormwater runoff in the Maltese islands

Abstract: The Maltese Islands have long suffered from a water resource problem to the extent that extensive reliance is made on desalination by reverse osmosis technology. Whilst this has solved the quantitative problem, it is undoubtedly amore expensive technology when compared to groundwater extraction. Moreover, the carbon footprint of desalinated water is much higher than that of groundwater due to the energy intensive nature of desalination. Notwithstanding, groundwater resources have been exploited to such an extent that current estimations of an annual extraction of 34 hm3 are 11 hm3 in excess of sustainable extraction levels. The Maltese Islands are also highly urbanised and it is estimated that, in urban areas, up to 80% of runoff could be lost to the sea depending on the geography and land use of the catchment. This resource could potentially be useful in recharging existing aquifers. The aim of this paper is to characterise the quality of stormwater derived from one of Malta's most urbanised catchments w...

Modelling the urban water chain: Incentives and cost recovery in wastewater treatment in developing countries

Abstract: To improve surface water quality in developing countries new approaches to design wastewater treatment schemes have been developed. We identify a compliance problem in these schemes which threatens their success. To analyze this problem, we integrate a compliance game into a model of the urban water chain. We illustrate the model with a numerical example on small scale leather processing. We find that the compliance problem indeed threatens the overall success of the treatment scheme and show under which conditions this is so. With an empirical calibration our model is a ready to use tool to provide quantitative results that can inform planners of urban wastewater treatment schemes.