Showing papers in "Urban Water Journal in 2015"

Abstract: The management of urban stormwater has become increasingly complex over recent decades. Consequently, terminology describing the principles and practices of urban drainage has become increasingly diverse, increasing the potential for confusion and miscommunication. This paper documents the history, scope, application and underlying principles of terms used in urban drainage and provides recommendations for clear communication of these principles. Terminology evolves locally and thus has an important role in establishing awareness and credibility of new approaches and contains nuanced understandings of the principles that are applied locally to address specific problems. Despite the understandable desire to have a ‘uniform set of terminology’, such a concept is flawed, ignoring the fact that terms reflect locally shared understanding. The local development of terminology thus has an important role in advancing the profession, but authors should facilitate communication between disciplines and between regio...

Abstract: Flooding can cause major disruptions in cities, and lead to significant impacts on people, the economy and on the environment. These impacts may be exacerbated by climate and socio-economic changes. Resilience thinking has become an important way for city planners and decision makers to manage flood risks.Despite different definitions of resilience, a consistent theme is that flood resilient cities are impacted less by extreme flood events. Therefore, flood risk professionals and planners need to understand flood impacts to build flood resilient cities. This paper presents a state-of-the-art literature review on flood impact assessment in urban areas, detailing their application, and their limitations. It describes both techniques for dealing with individual categories of impacts, as well as methodologies for integrating them. The paper will also identify future avenues for progress in improving the techniques.

Abstract: Evapotranspiration (ET) is a key component of the hydrological cycle however it is also the most difficult factor to quantify. In recent decades, estimating ET has been improved by advances in remote sensing, particularly in agricultural studies. However, quantifying ET from mixed vegetation environs, particularly urban parklands, is still challenging due to the heterogeneity of plant species, canopy covers, microclimates, and because of costly methodological requirements. Several studies have recently been conducted in agriculture and forestry which may be useful for mixed landscape vegetation studies with some modifications. This review describes general remote sensing-based approaches to estimate ET and describes their advantages and disadvantages. Most of these approaches need extensive time investment, medium to high skill levels and are quite expensive. However, in addition to the reviewed methods, the authors recommend combining remotely sensed vegetation indices and ground-based techniques for ET ...

Abstract: This paper deals with numerical and experimental investigation of a gully under exceptional situations after the sewer system becomes pressurized. These results are useful for the calibration and validation of the linking elements found in Dual Drainage (DD) models. The experimental results were obtained in the MLE (Multiple-Linking-Element) experimental installation that allows the simulation of full surcharge flow through a gully. The installation consists of an 8 m long and 0.5 m wide channel, fitted with a 0.6 × 0.3 × 0.3 m gully with a 80 mm diameter pipe inlet at the bottom. The numerical results were obtained using a three-dimensional structured mesh simulated in the OpenFOAMTM Toolbox. The results characterization focuses mainly on the jet area, whereby pressure-flow relations were derived for this specific gully. The good agreement found between numerical and experimental results, allowed the extrapolation to larger flow rates.

Abstract: This paper explores whether a mixture of centralised and decentralised urban water systems is preferable for sustainable urban water management. This is of importance for developing countries where there is continued demand for expanding urban water infrastructure. Processes for determining the combination of centralised and decentralised urban water solutions remain largely ad hoc. Using the South West Pacific as a case study, a multi criteria decision analysis (MCDA) methodology drawing on expert elicitation was employed to assess the technical, economic, environmental and resilience performance of urban water infrastructure alternatives; assessing water supply, sewage and stormwater systems. The MCDA analysis was then systematically contrasted with both a series of recommended infrastructural investment plans and the desires of local technocrats in Port Vila, Vanuatu. Results demonstrate a high level of agreement between the MCDA outcomes and local stakeholders, favouring hybrid infrastructure. Convers...

Abstract: A hydraulic jump is the sudden transition from a high-velocity impinging flow into a turbulent roller in an open channel. Substantial amounts of air are entrapped at the impingement point, and significant free-surface fluctuations take place above the roller. In the present study, some physical modelling was conducted in a relatively large sized facility. The flow conditions included a wide ranges of inflow Froude numbers and Reynolds numbers (3.8 < Fr1 < 10.0, 2.1 × 104 < Re < 1.6 × 105). The fluctuating features of free-surface and roller position were investigated non-intrusively with a series of acoustic displacement meters. The characteristic frequencies of the fluctuating motions were documented, and some major roller surface deformation patterns were revealed. The air-water flow properties were investigated with an intrusive phase-detection probe. The void fraction and bubble count rate data were documented in the jump roller, together with the interfacial velocity distributions. The rate of ai...

Abstract: The impacts of floods on housing are increasing due to more frequent and severe weather events as well as the ongoing development of settlements in flood-prone areas together with the rising vulnerability of assets at risk. Therefore, the improvement of the resilience properties of buildings to better cope with flooding has become a key issue towards more flood resilient cities in European research in recent years. The implementation of flood resilience technologies (FReT) on the individual property scale provides a previously untapped potential to reduce flood damage to buildings due to insufficient transparency of their effects. To overcome this obstacle, the paper presents a four-step extension of a synthetic approach for flood vulnerability analysis to provide evidence on the potential effects of FReT uptake concerning flood damage mitigation. The proposed approach has been integrated in the GIS-based flood damage simulation model HOWAD to support the assessment of FReT alternatives. The simulation of...

Abstract: Small and medium sized water utilities (SMWU) are facing serious operational problems, and show less participation in benchmarking. Existing performance indicator (PI) systems developed for large water utilities need to be re-evaluated for SMWU. 114 Potential PIs were obtained in water resources and environment, personnel, operational, physical, water quality, quality of service and financial categories using a checklist. These PIs were evaluated against applicability, understandability, measurability and comparability criteria using the Elimination and Choice Translating Reality (ELECTRE) outranking method for multicriteria decision analysis. The criteria's weights and scoring of PIs were done through group decision making. The study results revealed that ELECTRE is a suitable method when the preferences between various alternatives based on small differences of evaluations cannot be established. The network maps based on outranking results provides an opportunity to the utility management to encompass t...

Abstract: Global flood management is a major issue for most cities which have to deal with worsening factors such as climate change and fast urban growth. Computer models have been used to model and understand urban flooding on a local scale in cities (25–50 km2). It has been practically impossible to model bigger cities in one go in sufficiently high resolution due to the heavy computations involved.The present paper describes a new modelling approach for urban flooding which allows modelling on large city scale (1000 km2) while keeping sufficient resolution, e.g. 5 m or 10 m grid. The multicell approach is applied for the city of Beijing for July 21st, 2012 flood event. Model results are compared to testimonials from the 2012 event. Comparison to traditional 2D urban flood computations shows that the multicell approach is much faster than standard detailed models while keeping a suitable level of precision.

Abstract: In this paper the sensitivity to small scale unmeasured rainfall variability (i.e. at scales smaller than 1 km by 1 km by 5 min in time, which are usually available with C-band radars) of a 1D/2D model with a 10 m resolution and a semi-distributed 1D model of the same 1.47 km2 urban area is analyzed. The 1D/2D model is the open source numerical platform Multi-Hydro, which couples (open source) distributed models of involved hydrological/hydraulic processes. The methodology implemented to evaluate the uncertainties consists of generating an ensemble of realistic rainfall fields downscaled to a resolution of 12.3 m in space and 18.75 s in time with the help of a stochastic universal multifractal model. The corresponding ensemble of hydrographs is then simulated. It appears that the uncertainty is significant and that Multi-Hydro unveils much more uncertainty than the simpler 1D model. This points out a need to develop high resolution distributed modelling in urban areas.

Abstract: This paper presents the pollutant build-up characteristics on road surfaces in residential, commercial and industrial areas in the southern part of Peninsular, Malaysia. Dust and dirt (DD) were collected using a vacuum cleaner for different numbers of dry days, ranging from 1 day to 10 days. The samples were weighed and analyzed for biochemical oxygen demand (BOD), chemical oxygen demand (COD), total phosphorus (TP), and particle size distribution. Sediment build-up generally reaches a maximum after five continuous dry days. The pollutant-solids ratios show high variation for all the road sites. Anthropogenic and traffic activities significantly influence the pollutant compositions. As the dry day period progresses, fine particle increasingly dominates the pollutant loading on road surfaces. Effective control of pollutant build-up on the road surface is necessary for reducing the urban stormwater runoff pollution into the receiving waters.

Abstract: Innovative analytical tools are needed to address complex sustainability challenges in securing water supply for water-stressed, expanding cities worldwide. Melbourne's Alternative Water Atlas is a spatial analytical model that integrates citywide data to evaluate the cost-effectiveness of alternative supply options and their environmental and social benefits. This study presents the methodology employed in the Atlas model to evaluate supply options from four sources (rainwater, stormwater, centralized wastewater recycling, decentralized recycling) to meet the long-term water demand for a range of non-drinking uses in Melbourne. The results of the Atlas analysis highlight preferable options at the local scale with regards to multiple criteria, in order to guide strategic decision-making. Site-specificity and transferability of the Atlas approach are discussed. The Atlas approach can serve as a basis for other international locations to build a locally adapted analytical framework to evaluate the potential...

Abstract: The pollution reduction opportunities of a drainage basin, located in Barcelona (Spain), were analysed as a case study in order to assess strategies for optimised management of sewerage networks in the Mediterranean region. The analysis results show that the introduction of a large storm tank against combined sewer overflow significantly reduces the negative impacts associated with discharges during rainy weather. The total annual mass into the receiving waters is reduced by 45%, measured in terms of suspended solid and chemical oxygen demand. The performance of large storm tanks can be optimised taking advantage of the natural sedimentation of the retained rainwater. At optimum stratification conditions, the annual regulation capability can be increased by 15% compared to the traditional operating conditions. Apparently, the environmental impacts associated with the materials used in the construction of the tank will also be reduced per unit volume of regulated water with the increasing annual regulation...

Abstract: We present a new hydrodynamic modelling framework capable of fully exploiting modern graphics and central processing units (GPUs and CPUs) from any of the mainstream vendors, to be used in the design and assessment of sustainable drainage systems. A finite-volume Godunov-type scheme is combined with the HLLC Riemann solver to create a robust numerical model which correctly addresses wetting and drying and transient flow conditions, and is suitable for application to a wide range of flood simulations. The software is tested with a three day flood event in Carlisle during 2005, at resolutions from 25 m to 2 m. Run-times are significantly reduced without compromising numerical accuracy. Excellent agreement is found between the simulation results and a comprehensive post-event survey. Changes in sensitivity to Manning's n are examined at different resolutions, with changes to the floodplain found to have little influence at 2 m resolution.

Abstract: Drop manholes, a typical element of urban drainage networks in steep catchments and in reaches of supercritical flow, enhance air entrainment and entrapment. The air flow across drop shafts can be remarkably high.This paper discusses the air transport phenomena and the effects of ventilation absence in drop manholes. Based on an extensive experimental study, air entrainment mechanisms have been accurately described and air demand has been evaluated in different flow regimes. In addition, the effects of ventilation absence on the hydraulics of circular drop manholes, with emphasis on sub-atmospheric pressure onset and pool depth raising, have been investigated. The effects of a possible air flow recirculation have also been evaluated. Issues regarding any scale effects have been discussed.The influence of the main hydraulic and geometric parameters on drop manhole performance was contemplated to provide improved design concepts for sewer systems.

Abstract: Flow regime transition is observed in closed conduit when there is a transition between free surface and pressurized flows. This condition is often observed in stormwater storage tunnels undergoing rapid filling. Such tunnels provide stormwater control inurbanized areas, relieving the stormwater collection system during intense storms. Operational issues have been reported in such tunnels during intense rain events, some of which linked to air pocket entrapment. These issues motivated development of flowregime transition models and more recent models attempt to improve predictions by accounting for air effects in formulations. However, no comparative study has been performed between recent models that account for air pockets and earlier models that don't include this feature. This work aims to address this gap, focusing on an actual tunnel geometry that was proposed for the city of Washington, DC. Results indicate that including air in model formulation yielded more realistic predictions of low pressures.

Abstract: The effects of water meter age and private tanks on the apparent losses due to metering errors were evaluated by experimental and theoretical analyses. A monitoring campaign on a small district metered area (DMA) was carried out to determine the causes of apparent losses and implement a numerical model. Metering errors are affected by the flow rate passing through the meter, which is dependent on the network pressure and water level of the private tank. A node model that reproduces the effect of private tanks was coupled with EPANET and was applied to the DMA. The proposed modelling approach was used to identify where apparent losses are higher and to schedule maintenance. The model predicted the results of the installation of a device that minimises the effect of private tanks on apparent losses, the unmeasured flow reducer (UFR), the economic impact of losses and substitution programmes.

Abstract: Flood control detention facilities are widely used for stormwater control in urban areas. Standard design procedures are in most cases based on the design storm approach: a single flood event at a time is considered, at the beginning of which the facility is assumed completely empty. The possibility of pre-filling from previous events is then neglected and underestimation of storage volume may occur. In this paper an analytical probabilistic approach to estimate the probability of pre-filling is presented and its effects, due to outflow rate and storage volume, are investigated. Two different strategies for the outlet control are analysed. Results are validated on a case study.

Abstract: A small size laboratory test-bed was realized at the University of Genoa in order to evaluate the drainage capacity of permeable pavements by monitoring inflow, runoff and sub-surface outflow. The laboratory test programme was designed to investigate the influence of rainfall intensity and pavement slope on the hydrologic response of permeable pavements. Four permeable pavement systems combining two paving types (concrete cell and pervious brick) with two filter layers made of recycled glass aggregate and a mix of gravel and coarse sand are tested. The hydrologic response of permeable pavements is analysed by using a dimensionless volume index (discharge coefficient) and a timing index. Laboratory results reveal that the hydrologic performance is fairly consistent for all the investigated permeable pavements. The recycled glass aggregate turns out to be a valid solution. No surface runoff occurs even at 98 mm/h rainfall intensity.

Abstract: Following the worldwide flooding episodes from the last decade, we have witness a gradual change from the international community. Academics, practitioners and policy makers are moving away from th...

Abstract: The paper presents an alternative approach regarding the spatial allocation of the actual water demand (at node level) when developing a pipe network's hydraulic simulation model. The process takes into account the respective demand patterns of the various types of water users, considering the water being lost through leaks/breaks occurring, as a competitive use. This new method accurately approximates the demand allocation of a network when there is no GIS data, thus having a significant impact on its cost effectiveness. Kos Town (Greece) water pipe network is used as the case study to demonstrate the entire process and the problems encountered. Finally, to prove its effectiveness the results of the new method were compared to MW-Voronoi diagram method's results and to field measurements.

Abstract: An attempt has been made to develop a fuzzy expert system capable of establishing a criterion for predicting water quality index (WQI) in the various zones of municipal distribution system using pH, alkalinity, hardness, dissolved oxygen (DO), total solids (TS) and most probable number (MPN). The proposed expert system includes a fuzzy model consisting of IF-THEN rules to determine WQI based on water quality characteristics. The fuzzy models are developed using triangular and trapezoidal membership functions, with centroid, bisector and mean of maxima (MOM) methods for defuzzification. Further, the performance of fuzzy models is compared with adaptive neuro fuzzy inference (ANFIS) models. ANFIS models are developed by using triangular, trapezoidal, bell and Gaussian membership function. The study reveals that fuzzy models outperform ANFIS models for all water quality classes. Out of twenty nine zones in the study area, for twenty two zones fuzzy model with triangular membership function performs better th...

Abstract: The overall objective of this paper is to contribute to the standing debate concerning the advantages of separate sewer systems compared to traditional combined sewer systems. By a case study this investigation reveals that transformation of part of a town from being serviced with combined sewer systems to become serviced with separate sewer systems decreases the volumes of storm water and pollutants diverted to the waste water treatment plant and discharged as combined sewer overflow. This happens at the expense of an increase in volumes of storm water and pollutant loads diverted to local receiving waters when detention ponds are not built-in the new separate sewer systems. It is concluded that consequences can be fatal for receiving waters, if no retention of pollutants is integrated into the system.

Abstract: Treating and reusing municipal wastewater for urban agriculture raises water productivity. This paper developed a methodology to quantify water flows and productivity of a proposed infrastructure including water supply, sanitation, wastewater treatment and water reuse for agriculture. The methodology consists in calculating the pathogen reduction achieved with wastewater treatment, designing a crop scheme for the irrigation with treated water, modeling irrigation requirements and quantifying water flows with mathematical material flow analysis. This methodology was applied for the current state and with the planned facility in semi-arid Namibia. This infrastructure has the potential to raise water productivity by +10% as household water use increases with improved sanitation. Compared to not reusing the water for agriculture, water productivity can be raised by +39%. This methodology allowed the consideration of the impact of facility user behavior on water flows and found that water productivity increase...

Abstract: This paper contains results of a depression storage investigation based on simulations of runoff using SWMM 5 software and measurements from a real urban catchment in Poznan, Poland. The catchment area is 6.7 km2 and its average imperviousness has been evaluated as 29 %. Altogether, 46 rainfall events, registered by tipping-bucket raingauges in years 2006–2010 in three stations, have been analysed. The best agreement of the computed outflow hydrographs with the results of measurements has been obtained for a depression storage depth of 1.5 mm. The influence of spatial distribution of impervious surface depression on the shape of the computed hydrographs has been found to not be significant.

Abstract: A new sample collection system was developed to improve the representation of sediment in stormwater by integrating the entire water column. The depth-integrated sampler arm (DISA) was able to mitigate sediment stratification bias in storm water, thereby improving the characterization of particle size distribution from urban source areas. Collector streets had the lowest median particle diameter of 8 μm, followed by parking lots, arterial streets, feeder streets, and residential and mixed land use (32, 43, 50, 80 and 95 μm, respectively). Results from this study suggest there is no single distribution of particles that can be applied uniformly to runoff in urban environments; however, integrating more of the entire water column during the sample collection can address some of the shortcomings of a fixed-point sampler by reducing variability and bias caused by the stratification of solids in a water column.

Abstract: Faced with the severe leakage and chaotic water management situation in developing countries, this research is committed to provide an appropriate and practical water audit calculation method for most water companies so as to guide their leakage control management. It prepares a recommended basic standard terminology for calculation of real and apparent losses, which can be consistent with practice in China. Due to more detailed subdivision of unmetered water along with water component analysis, the water consumption of SA city can be calculated more accurately. The proportion of water loss in SA is 18.02%, while unbilled authorized consumption contributes no more than 1% to the total water consumption. Meanwhile, the “Neighbourhood Metering Area (NMA)” project in SA city also suggests that metering inaccuracies and leakage on service connections up to the point of customer metering can be prioritized for active leakage control in China.

Abstract: The effect of urban form on Curve Number (CN) use in rainfall-runoff modelling is explored in an arid wadi watershed in Oman. The standard hydrologic CN used in the Soil Conservation Service method may not be appropriate to use in urbanized arid wadi regions since the land-use characteristics are different than those for which the CN method was developed for. In this paper a new method is described to develop regional CN for arid wadi regions. The modified CN are then used to predict peak-flow and time-to-peak in a wadi watershed and are compared to results from the standard CN method. The regional values produce higher peak-flow (an increase of 19% or 7.4 m3/s, on average) with shorter time-to-peak (a decrease of 16% or 86 minutes, on average), mimicking the flash-floods seen in the region. In addition, the regional CN were used to model the change in hydrology caused by urbanization.

Abstract: Despite the common use of stormwater infiltration systems, there is still only limited data available evaluating the long-term hydraulic function of such systems. The hydraulic performance of twelve stormwater infiltration systems (vegetated and unvegetated concrete grid pavers, unvegetated interlocking concrete pavers and grassed swales) was therefore investigated in field and laboratory environments in Vaxjo, Sweden. The systems investigated had not been subjected to regular maintenance to sustain infiltration capacity. Due to this, and the fact that, for most systems, an inappropriate joint filling material was used and (at the swales) there was severe compaction, most systems showed a reduced infiltration capacity. Despite this, especially the older vegetated systems, were still capable of infiltrating intense design rainfalls. This study showed the influence of some factors (type and age of the system, the type of joint filling material (grass and macadam) and the distance from the edge of the paveme...

Abstract: A severe storm event occurred over the western area of Mexico City causing the rupture of a drainage tunnel, resulting in surface flooding, severe infrastructure damage and three deaths. This paper describes the methodology followed in order to validate the diagnostic of the event. The detailed investigation comprised in situ observation of the system, as well as hydraulic and structural analyses. In this case, severe pressure oscillations inside the tunnel caused by rapid filling and sudden air leakage through a large orifice (manhole) were recognized as the direct cause of the conduit burst. Further, the low strength of the concrete pipes of the tunnel, constructed without reinforced steel, and the low confinement by the dead load due to the soil above the tunnel also contributed to the rupture. The numerical results show a very unfavorable stress distribution along the tunnel stretch where the accident occurred, sufficient to cause the rupture.