Showing papers in "Urban Water Journal in 2016"

System interactions of stormwater management using sustainable urban drainage systems and green infrastructure

Abstract: This study explores system interactions of stormwater management solutions using Sustainable Urban Drainage System (SuDS) and Green Infrastructure (GI) within the wider urban landscape. A series of interdependencies between urban components relating to stormwater management are identified. These include physical interdependency, geographical interdependency, cyber interdependency and logical interdependency, as defined by Peerenboom (2001). Stormwater management using SuDS/GI are viewed according to their Hydrological, Ecological and the Built Environment functions during events up to the design rain (non-flood condition) and during controlled exceedance and uncontrolled inundation (flood condition). The inclusion of SuDS/GI into the urban fabric is shown to modify urban functional and relational interdependencies under both these conditions. Within the context of the UK, there are fragmented responsibilities across planning scales created by SuDS/GI solutions which have not addressed the relational compl...

Water distribution systems flow monitoring and anomalous event detection: A practical approach

Abstract: Methods to detect outliers in network flow measurements that may be due to pipe bursts or unusual consumptions are fundamental to improve water distribution system on-line operation and management, and to ensure reliable historical data for sustainable planning and design of these systems. To detect and classify anomalous events in flow data from district metering areas a four-step methodology was adopted, implemented and tested: i) data acquisition, ii) data validation and normalization, iii) anomalous observation detection, iv) anomalous event detection and characterization. This approach is based on the renewed concept of outlier regions and depends on a reduced number of configuration parameters: the number of past observations, the true positive rate and the false positive rate. Results indicate that this approach is flexible and applicable to the detection of different types of events (e.g., pipe burst, unusual consumption) and to different flow time series (e.g., instantaneous, minimum night flow).

Flood damage assessment in urban areas. Application to the Raval district of Barcelona using synthetic depth damage curves

Abstract: This paper presents a detailed flood damage assessment in the Raval district of Barcelona. The implementation of a new 1D-2D coupled model is used to obtain flood depths, and new stage damage curves are developed to estimate the direct tangible damages. The curves have been validated using data from surveys and actual reported damages to the Spanish re-assurance. Finally, combining hazard and vulnerability levels by using a GIS-based toolbox, the expected annual damage of the area is obtained. This enables the determination of the critical points of the district in terms of flooding impacts, and highlights the need to implement strategies to cope with these impacts.

Modelling sewer discharge via displacement of manhole covers during flood events using 1D/2D SIPSON/P-DWave dual drainage simulations

Abstract: In urban areas, overloaded sewers may result in surcharge that causes surface flooding. The overflow from sewer systems mainly starts at the inlets until the pressure head in the manhole is high enough to lift up its cover, at which stage the surcharged flow may be discharged via the gap between the bottom of the manhole cover and the ground surface. In this paper, we propose a new approach to simulate such a dynamic between the sewer and the surface flow in coupled surface and sewer flow modelling. Two case studies are employed to demonstrate the differences between the new linking model and the traditional model that simplifies the process. The results show that the new approach is capable of describing the physical phenomena when manhole covers restrict the drainage flow from the surface to the sewer network and reduce the surcharge flow and vice versa.

Integrated rehabilitation planning of urban infrastructure systems using a street section priority model

Abstract: Due to the changes in water management, from the construction of new systems to the rehabilitation of existing networks, integrated strategic rehabilitation management has become more and more important. Consequently, this paper shows a method that considers sewer and water distribution networks against environmental factors (e.g. street network and connected buildings) in a priority model. This approach aids in not only identifying areas where rehabilitation is technically necessary but also economically recommendable (e.g. completely depreciated). This is achieved by implementing factors of structural resiliency, vulnerability of the network, capital value and other network components (e.g. manholes, house connections). This model is applied to a medium sized case study in which the rehabilitation areas identified by the developed model are compared to the actual rehabilitation plans of the water and sewage companies. Results also show the application of the estimated ranking for rehabilitation ...

Assessment of evolutionary algorithms in predicting non-deposition sediment transport

Abstract: In this article, the densimetric Froude number of the flow is estimated using the parameters of volumetric sediment concentration (CV), the relative depth of flow (d/R), dimensionless particle number (Dgr) and the overall sediment friction factor (λs). The particle swarm optimization (PSO) and imperialist competitive algorithms (ICA) were used to estimate the densimetric Froude number. To study the effects of sediment transport parameters on the densimetric Froude number, six different models are presented. The PSO algorithm with root mean square error (RMSE) = 0.014 and mean absolute percentage error (MAPE) = 5.1% present the results with a relatively good accuracy. The accuracy of the results presented for the selected model by the ICA algorithm is also in the form of RMSE = 0.007 and MAPE = 5.6%. Although both algorithms return good results in estimating the densimetric Froude number for the selected model, it should be mentioned that for all the six presented models ICA returns better results than...

The combined use of resilience and loop diameter uniformity as a good indirect measure of network reliability

Abstract: The aim of this paper is to show that the combined use of the resilience index (Todini, 2000) with a loop based diameter uniformity index (here formulated) yields a good indirect reliability measure, which can be conveniently used within the optimization processes of the water distribution system design. The methodology adopted to show the advantages of the combined use of the two indexes consists of (a) a three-objective optimization performed in order to simultaneously minimize costs (first objective function) and maximize both the resilience and the loop diameter uniformity indexes (second and third objective functions respectively); (b) a retrospective assessment of performance indicators relative to critical operational scenarios on the solutions of the Pareto surface obtained at the end of the optimization process. Applications were performed considering a simple case study, which made it possible to easily compare the new approach, based on a three-objective optimization, with the two-objective opt...

Decision-making for sewer asset management: Theory and practice

Abstract: Operational decision-making for sewer asset management has hardly been empirically analysed, hampering the current challenge for cost-effectiveness in the urban drainage sector. This paper analyses how decisions for sewer replacement are actually made and to what extent complexity of the decision-making environment is addressed. Decision argumentation of 150 sewer replacement projects in the Netherlands was obtained by interviews. The decision process was analysed by the rational and streams model. The decision argumentation is a relatively wide variety of information sources, of which the majority is case-specific. Yet, decision-making does not rely purely on data analysis; it also includes negotiations between involved infrastructure managers. Then, replacement planning of a sewer asset manager depends on other public works. Consequently, individual cost-effectiveness as an evaluation criterion should be expanded to include group utility.

Use of green roofs to solve storm water issues at the basin scale – Study in the Hauts-de-Seine County (France)

Abstract: At the building scale, green roof has demonstrated a positive impact on urban runoff (decrease in the peak discharge and runoff volume). This work aims to study if similar impacts can be observed at a basin scale. It is particularly focused on the possibility to solve some operational issues caused by storm water.For this purpose, a methodology has been proposed. It combines: a method to estimate the maximum roof area that can be covered by green roof, called green roofing potential, and an urban rainfall-runoff model able to simulate the hydrological behaviour of green roof.This methodology was applied to two urban catchments, one affected by flooding and the other one by combined sewage overflow. The results show that green roof can reduce the frequency and the magnitude of such problems depending on the covered roof surface. Combined with other infrastructures, they represent an interesting solution for urban water management.

Prediction of boundary shear stress in circular and trapezoidal channels with entropy concept

Abstract: Relying on the power law to develop new relationships, the present study developed the Shannon entropy concept to predict shear stress distribution. The presented method was evaluated and compared with valid laboratory results and the shear stress distribution surveyed through this concept in circular, circular with flat bed and trapezoidal channels. By increasing the flow depth in circular channels, the model presented herein gives an improved prediction of shear stress distribution, while in circular channels with flat bed it is better in predicting shear stress both at lower flow depth and subcritical flow conditions. In comparison, in trapezoidal channels the model is much better in predicting the shear stress distribution at lower flow depths. Accordingly, with a mean error percentage of 1.99% in circular channels, 3.69% in circular channels with flat bed and 4.1% in trapezoidal channels, this novel model shows good ability in predicting shear stress distribution.

Water leakage detection using remote sensing, field spectroscopy and GIS in semiarid areas of Cyprus

Abstract: Water pipelines need to be systematically monitored in order to minimize losses from possible leakages. In this paper, remote sensing techniques have been exploited in semiarid areas of Cyprus. In addition, ground spectroradiometer has been used to define the leakage's threshold values. The data were analysed in a GIS environment. Two known leakage problems have been examined. In the first case study, a high resolution QuickBird image was used for the detection of the exact point of leakage. In the second case study a multi-temporal analysis was performed using SPOT images. This methodology was able to record 10 possible leakage points along the pipeline. Throughout the 25 km length of the pipeline, the in-situ observations were minimized to only 0.4%. In both studies the Normalised Difference Vegetation Index (NDVI) was applied. The final outcomes highlight the contribution of remote sensing to the early detection of leakages especially in difficult and near inaccessible areas.

Source characterisation and loads of metals and pesticides in urban wet weather discharges

Abstract: Contaminants in urban wet weather discharges originate from a number of sources such as materials from wet and dry atmospheric deposition, wastewaters, urban surface erosion, traffic-related activities, in-sewer deposits, etc. In the current study, four contributions (rainwater, dry atmospheric deposition, dry weather discharge and catchment surface + possible erosion of in-sewer deposits) to the total concentrations of priority substances have been assessed at the outlet of two urban catchments (one residential catchment with a combined system and one industrial area with a separate stormwater system) for 12 storm events (six for each catchment). Mass balances were calculated for seven metals and four pesticides, as well as for total suspended solids and chemical oxygen demand. The respective contributions of dry and wet atmospheric deposition, wastewater and catchment surface differ for each pollutant type, corresponding to different land use, activities, environments and sewer systems. For most of the ...

Climate, land use and hydrologic sensitivities of stormwater quantity and quality in a complex coastal-urban watershed

Abstract: We determined reference hydro-climatic and land use/cover sensitivities of stormwater runoff and quality in the Miami River Basin of Florida by developing a dynamic rainfall-runoff model with the EPA Storm Water Management Model. Potential storm runoff in the complex coastal-urban basin exhibited high and notably different seasonal sensitivities to rainfall; with stronger responses in the drier early winter and wetter late summer months. Basin runoff and pollutant loads showed moderate sensitivities to the hydrologic and land cover parameters; imperviousness and roughness exhibited more dominant influence than slope. Sensitivity to potential changes in land use patterns was relatively low. The changes in runoff and pollutants under simultaneous hydro-climatic or climate-land use perturbations were notably different than the summations of their individual contributions. The quantified sensitivities can be useful for appropriate management of stormwater quantity and quality in complex urban basins under a c...

Exploring forecast-based management strategies for stormwater detention ponds

Abstract: Dry detention ponds are commonly implemented to mitigate the impacts of urban runoff on receiving water bodies. They currently rely on static control through a fixed limitation of their maximum outflow rate. This study investigated the performance of several enhanced management strategies for a dry detention pond located at the outlet of a small urban catchment near Quebec City, Canada. Among the enhanced scenarios studied are some previously developed real-time control (RTC) strategies, and new operating rules relying on a daily manual adjustment of the outlet gate. Both types of control make use of rainfall forecasts originating from the initial or downscaled Canadian global ensemble prediction system. Different ways of using the forecasts' ensemble spread were considered to take action. The pond performances were investigated considering three different volumetric capacities (including the existing volume). The RTC scenarios are very promising. The value of taking rainfall forecasts into account to pre...

Operational management of trunk main discolouration risk

Abstract: Despite significant on-going investment, water companies continue to receive an unacceptable number of discolouration related customer contacts. In this paper, data from intensive distribution system turbidity monitoring and cluster analysis of discolouration customer contacts indicate that a significant proportion of these contacts are due to material mobilising from the trunk main system, and operational flow increases are shown to have a higher discolouration risk than burst incidents. A trunk main discolouration incident highlighting this risk is discussed, demonstrating the need for pro-active trunk main risk assessments. To identify the source of the material event flow rates were modelled using the PODDS (prediction of discolouration in distribution systems) discolouration model. Best practice pro-active management is demonstrated in a case study where the PODDS model is used to implement managed incremental flow changes on a main with known discolouration risk with no discolouration impact to cust...

Pressure as a predictor of occurrence of pipe breaks in water distribution networks

Abstract: Sudden bursts in water distribution networks may lead to costly consequences. As pressure is one of the causes of such events, pressure management could reduce the probability of failure. In this work, a methodology is proposed to analyse the relationship between pipe breaks and water pressure by means of pressure-related indicators. The objective is to identify the most influential indicators for the probability of occurrence of pipe breaks. The methodology compares the cumulative distribution function (CDF) conditioned to breaks and 100 random sets of the same size sampled from the CDF of the indicator. The most influential indicators are related to the greatest number of rejected cases of the Kolmogorov-Smirnov test. Moment indicators and their calculation period emerge from sensitivity analyses. The methodology is applied to six sectors of Madrid (Spain) while two sectors are used for validation. Results show that the pressure range is the best indicator of breaks.

Reliability-based layout design of sewage collection systems in flat areas

Abstract: The sewer layout in flat areas significantly influences the final design which is desired to be optimized for the construction and operational costs. This study introduces a model for designing the layout of sewer networks considering their reliability. A reliability criterion is introduced and optimized using a simple simulated annealing scheme. The best layout with the maximum reliability represents an optimum sewer layout in which clogging in a sewer has the least effect on its upstream lines. A case study is solved using the proposed model. Then, for the obtained layout, the sewer specifications are designed using a dynamic programming model. The reliability somehow reflects the operational costs that can be taken into account in the system design by the proposed model. Furthermore, it is concluded that the network's reliability and construction cost are in conflict with each other such that more reliable layouts lead to more expensive designs.

Hard rain gonna fall: Strategies for sustainable urban drainage in informal settlements

Abstract: Inadequate drainage of stormwater, greywater and sewage plagues informal settlement ‘slum’ dwellers throughout the developing world. Residents, local governments and others find drainage solutions hard to come by due both to physical challenges – densely packed shack homes and few roads or open spaces – and social challenges associated with the often contentious, turbulent and legally uncertain nature of informal settlements. While concepts of sustainable urban drainage systems (SUDS) and integrated water resource management (IWRM) hold promise for informal settlements, we find little practical guidance available for their application in these contexts. To begin filling this gap, we propose a simple model for understanding various informal settlement contexts and ‘upgrading’ strategies that affect drainage development strategies. We then use this model to report on a series of small projects in South Africa that illustrate social and structural dynamics and practical techniques relevant to implementing co...

Water recovery from treated urban wastewater by ultrafiltration and reverse osmosis for landscape irrigation

Abstract: Techno-economic feasibility of water recovery from secondary effluents of an urban wastewater treatment plant (WWTP) for landscape irrigation was investigated considering two distinctive strategies: ultrafiltration (UF)/chlorination and UF/reverse osmosis (RO). Experimental performance evaluations were conducted separately for UF membranes and for different RO trans-membrane pressures. The quality of the effluent recovered by the UF/RO system was in accordance with the national and international guidelines. The produced reuse water was first class quality according to the national guideline for all parameters except sodium adsorption ratio (SAR), which can be eliminated readily by direct addition of KCl into the recovered water. Estimated field-scale costs indicated that UF/RO yielded a total cost of US$12,500,000–13,600,000 with annual operating cost being US$482,000–533,000 at 5–20 bar. The economic estimations guaranteed reimbursement with US$7,600,000–7,400,000 net present value, 0.22–0.39 year paybac...

Willingness to pay for reliable supplies of safe drinking water in Guatemala: A referendum contingent valuation study

Abstract: Unreliability of water systems has become a major concern in many developing countries. A referendum-format contingent valuation (CV) survey was implemented to investigate household preferences, in monetary terms, for improved water services in the small town of San Lorenzo, Guatemala. A random sample of 500 households report that they currently adopt a variety of averting measures (e.g. in-home water storage and treatment) to cope with service interruptions and low water quality. Findings also indicate that households are willing to pay an increase of more than 200% in their water bill for reliable supplies of safe drinking water.

Simulating the effects of climate change, economic and urban planning scenarios on urban runoff patterns of a metropolitan region

Abstract: Urban development and climate change are expected to have significant effects on urban stormwater runoff. In this study, the Dynamic Urban Water Simulation Model (DUWSiM) is applied to Dublin, Ireland, to explore urban runoff patterns under varying urban growth and climate scenarios. Results show that annual urban runoff could decrease by 3.0% from climate change and monthly runoff could increase by 30% in winter and decrease by 28% in summer. Results also indicate that urban growth could increase annual runoff by up to 15%. The combined effect of climatic and land-use change generated runoff may potentially increase annual totals from between 2.9% to 21%. Monthly changes in runoff totals could increase by up to 57%. Accommodating these variations in runoff between the scenarios, flexible decentralised systems such as green roofs and pervious pavements, have a vital role in increasing the adaptability and long term sustainability of water infrastructure.

Management of chlorine dosing rates in urban water distribution networks using online continuous monitoring and modeling

Abstract: The aim of this study is to present the results of a research which was undertaken to manage chlorine dosing rates in a real water distribution network using online continuous monitoring and modeli...

Risk-based water resources planning in England and Wales: challenges in execution and implementation

Abstract: In this paper we describe the execution of a risk-based analysis on a simple, small-scale water resources planning problem. We aim to understand whether a risk-based approach could underpin the regulated water resources planning process in England and Wales. We demonstrate the practical feasibility of the approach and identify clear benefits over the conventional planning methods. We also identify several nontrivial challenges for scaling up and caution against the view that better quality decisions would emerge naturally from risk-based analyses. Useful future research might focus on: (1) the development of practical methodologies for applying these approaches to larger, more complex resource zones; (2) identifying and overcoming problems associated with regulating a risk-based water resources planning process; and (3) developing methods of economic options appraisal that can deploy the outputs of a risk-based analysis to inform planning decisions.

A stochastic approach for the water demand of residential end users

Abstract: Reliable hydraulic modeling of water distribution networks requires a deep knowledge of water demand. In the past few years, technical literature has been enriched with many contributions aimed at realistically representing the residential water demand of end users. The proposed models generally represent water demand through rectangular pulses, describing demand as the sum of the requests from single domestic appliances. This paper proposes a new stochastic model - Overall Pulse (OP) - which allows the generation of the overall domestic demand as displayed at the house water meter. The proposed model allows the taking into account of the randomness of the arrivals rate and the demand persistence phenomenon. The effectiveness of the proposed model has been tested, comparing the generated data series with those measured for residences with different lifestyles. The generation of the synthetic data series has been made by means of the OP model with the Monte Carlo method.

Optimal design of urban water supply pipe networks

Abstract: This paper approaches the optimisation of looped water distribution networks supplied from one or more sources, according to demand variation. The pipe networks have concentrated outflows or uniform outflow along the length of each pipe. An optimisation model coupled with a computational iterative procedure of optimal discharges through pipes is developed on the basis of linear programming for the design of new or partially extended water distribution networks. The optimum solution obtained by this model consists of one or two pipe segments of different discrete sizes between each pair of nodes. The improved linear optimisation model guarantees a high reliability. Also, it is possible to take into account the network pipes with variable discharge on route. Additionally, the paper compares the linear optimisation model to some others, such as the classic model of economical velocities, the Moshnin model and a nonlinear model. This shows a good performance of the proposed model.

GreenValve: hydrodynamics and applications of the control valve for energy harvesting

Abstract: Energy harvesting from dissipation processes during flow control is a challenge for many different applications. Common usage of many plants and systems requires control valves to dissipate overpressures. GreenValve is an innovative control device designed to control the flow and harvest the energy that is normally wasted during the throttling process. A vertical axes water turbine resides within the valve body to improve regulation efficiency and recover part of the energy that would be dissipated. In the present work, GreenValve and the results of an experimental campaign to characterize its functioning are discussed. Then some real scenarios have been considered as potential applications. Regulation as a function of time has been considered to calculate the instantaneous energy dissipated through the throttling process and evaluate case by case the amount of harvestable energy. At the end some considerations on the effectiveness of the GreenValve are presented.

Which factors determine water saving behaviour? evidence from spanish households

Abstract: In this paper we propose to answer the following questions: What does the adoption of water saving measures by Spanish households depend on? Which factors have the most influence on water saving behaviour? To this end we have conducted an empirical study in which a binary model (probit/logit) with interaction effects between city size, educational level and climatic area, along with other quantitative and qualitative variables, is estimated using household level data. The results of this estimation, together with the evaluation of probability changes that occur when any of the qualitative factors change, suggest that the level of income, the size of the city where the dwelling is, the educational level of the reference person and the climatic location of the city are factors that influence the attitude towards saving water.

Review of models and procedures for modelling urban snowmelt

Abstract: A literature review of selected snowmelt models or algorithms was undertaken to identify which of these tools could be readily used, or easily modified, for simulating urban snowmelt. In this context, the urban factors influencing snowmelt were classified into three categories: human activities, land use, and the origin of deposited snow; and served to develop a classification of urban snow covers with characteristic properties influencing snowmelt. Finally, the assessment of capabilities of the surveyed models or algorithms to simulate snowmelt for these covers indicated that: (i) only two of the tools addressed the critical characteristics of urban snow covers (for specific cases only), (ii) urban runoff models with snowmelt subroutines offered best operational flexibility, though modifications and/or guidance on input values would be required for satisfactory simulations, and (iii) the review findings should help modellers in choosing a snowmelt simulation tool best serving their task with respect to u...

Gross solids from combined sewers in dry weather and storms, elucidating production, storage and social factors

Abstract: Variation in rates of sanitary hygiene products, toilet tissue and faeces occurring in sewers are presented for dry and wet weather from three steep upstream urban catchments with different economic, age and ethnic profiles. Results show, for example, that total daily solids per capita from the low income and ageing populations are almost twice that from high income or ethnic populations. Relative differences are verified through independent questionnaires. The relationship between solids stored in sewers prior to storms, antecedent dry weather period and the proportion of roof to total catchment area is quantified. A full solids’ flush occurs when storm flows exceed three times the peak dry weather flow. The data presented will assist urban drainage designers in managing pollution caused by the discharge of sewage solids.

Statistical analysis of public perceptions of water infrastructure sustainability in shrinking cities

Abstract: Population contraction has afflicted a number of U.S. cities, presenting problems as the infrastructure becomes overbuilt for shrinking populations. Civic authorities have options to make infrastructure sustainable in light of urban decline including decommissioning or raising service costs to sustain existing infrastructure. This paper conducts a survey and statistical analysis of public opinions towards water infrastructure decommissioning and raising costs in U.S. shrinking cities, to identify groups likely to oppose these alternatives and hamper sustainability efforts. The analysis found a range of socio-economic factors affecting residents' likelihood of opposition and that their impacts vary considerably across the population. One critical finding is that only approximately 50% of respondents are aware their city is shrinking and that these residents have significantly different views on sustainability options. The statistical findings provide important initial information on how residents are likel...