The time dimension is a crucial aspect of an effective pipe rehabilitation strategy because of ongoing (and often independent) deterioration mechanisms that affect pipe structural integrity and hydraulic capacity. For instance, hydraulic analysis of a waterdistribution system may show that the hydraulic capacity of a pipe should be improved, and relining the pipe may be found to be the least cost solution. However, if deterioration in the structural integrity of the pipe is considered, it may be economical to replace this pipe in say, five or ten years due to the costs associated with high breakage frequency. Thus, it may be more economical to replace the pipe at the appropriate time in the future while in the meantime the hydraulic capacity of the network is improved by rehabilitating another pipe. This scenario may be further complicated if a future increase in demand is expected, in which case it may be more economical to replace the pipe with a larger diameter pipe in the future. Kleiner et al. (1998a, 1998b) proposed an approach in which the network economics and hydraulic capacity is analyzed simultaneously over a pre-defined analysis period, while explicitly considering the deterioration over time of both the structural integrity and the hydraulic capacity of every pipe in the system. A brief description of this approach is provided here with a special emphasis on the computer program created for the application of this approach, including description of the data structure, program flow chart and speed of execution. Comments are provided about the application of the approach to large systems.
Keywords: Secure sensor networks; Robust simulation models; Resilience assessment.
WaterDistribution Systems (WDSs) are critical infrastructures that may fail to distribute drinking water of adequate quantity and quality. Given their distributed topology and interconnectivity with other infrastructure systems, such as power supply and telecommunication, WDSs are exposed to a variety of risks including terrorist attacks, natural hazards and widespread technical failures that may be caused by cascade effects. The ResiWater project  aims to improve prevention, surveillance and response regarding realistic case studies of collapse of WDS, water quality deterioration and cascade effects between water, energy and IT infrastructures.
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Leak detection methods for plastic waterdistribution pipes
Hunaidi, O.; Chu, W. T.; Wang, A.; Guan, W.
Water loss from waterdistribution systems is a major concern to water utilities. Water utilities around the world are becoming more focused on adopting a proactive approach to managing water loss. The amount of lost water can be significant, reaching levels as high as 50% of production. However, water loss management is still not widely practiced by utilities in North America. Water balance analysis is the most widely used method for quantifying water losses. Guidelines and standard procedures for performing water balance analysis is mainly provided as a best practice (BP) document by the International Water Association (IWA). Experience shows that successful implementation of this BP depends to a large extent on the ability to efficiently collect and integrate data from various sources. These data sources include metered and un-metered consumption records, water supply data, and water network asset inventory. It will also require an understanding of various components contributing to the water loss, and the significance and inter-relationships of computed performance indicators (PIs).
In this paper, we address the pumping station design problem precisely, with an optimization approach combining the strengths of both previous strategies. While the overall approach is generic, the operational level is presented in the context of the FRD network, a branched network that is described in details in [ 3 ]. The approach is built on a decomposable formulation of the problem in- cluding the operation scheduling subproblem as a large-scale non-convex mixed- integer non-linear program with uncertain data. We apply a stabilized Benders’ decomposition [ 1 ] to solve the problem and propose different approximations for the subproblem to reduce its complexity while maintaining some performance guarantees. First, we decompose the multi-year scheduling horizon in a restricted set of seasonal representative days. This common assumption in long-term plan- ning models fits well with the daily periodicity of drinking waterdistribution, and allows to separate the scheduling subproblem in independent daily sub- problems (once a pump configuration is given). As optimizing iteratively each subproblem would remain too time consuming, we propose to relax the integral- ity constraints and to convexify the hydraulic constraints. This results in convex continuous non-linear programs providing under-estimates of the operation costs and dual information to derive Benders cuts. Second, we handle the long-term uncertainties by enforcing the robustness of the solution on hypothetical stress days characterized, e.g., by a high water demand and the outage of one pump. By disregarding optimality but forcing feasibility on stress days we can, for the class of networks in consideration, aggregate identical pumps and, therefore, reduce the size and complexity of the subproblem. Furthermore, we exhibit a dominance relation between pump combinations that allows to generate multiple feasibility cuts from one infeasible solution. Our experiments on the FRD network show the accuracy of our approximations: the impact of the horizon decomposition is negligible while the continuous convex relaxation induces a deviation of the optimum lower than 4.3%. Finally, the annual savings (in terms of investment and operation costs) expected from the rehabilitation are estimated to 32%.
Leak inspectors listen to leak sounds and document sound levels together with other standard descriptors such as pump or other mechanical noise or high-pitch noise (normally corresponding to ﬁ re hydrant leaks). Sound levels are input into a geographic information system (GIS) for the pipe network to produce coloured contour maps of leak sound levels. These maps enable leak managers to easily compare the latest sound levels with those previously collected to identify zones where more detailed surveys are needed. The maps also provide a visualization of leak noise patterns, which can help identify the presence of multiple leaks in a particular zone. Subsequently, managers can effectively plan the work of leak inspectors for pinpointing and validating suspected leaks. Zones with validated or conﬁ rmed leaks are re-inspected after leak repair and leak noise is re-mapped to detect remaining leaks. The process is repeated until no detectable leaks remain in the waterdistribution network.
Distribution Infrastructure Impacts
The deterioration of drinking waterdistribution infrastructure is among the main causes of the loss of quality and quantity of water at the consumers tap. However, since a major portion of the distribution infrastructure is underground, its deterioration does not present the same visual urgency as other visible infrastructure. Since deterioration of the distribution infrastructure adversely impacts the water quality, PWSs must not invest costs and efforts to treat water to potable levels and then transmit it through deteriorating distribution system. Some of the most critical water quality issues related to waterdistribution infrastructure deterioration were highlighted in a series of white papers produced by the USEPA, AWWA (American Water Works Association) and AWWSC (American Water Works Service Company). These white papers underline the importance of pro-active management of distribution systems to maintain water quality at an acceptable level (Scharfenaker 2002).
Modeling of heterotrophic bacteria in a waterdistribution system
Alex Francisque * , Manuel Rodriguez*, Luis Miranda* and Rehan Sadiq**
For routine microbiological monitoring of water quality in distribution systems (DS), heterotrophic plate count (HPC) constitutes a standard indicator that’s widely used. (Grabow 1996; Edberg and Allen 2004; Pavlov et al. 2004). HPC are, generally, non-pathogenic bacteria that can appear in DS in particular when pipes are dirty or when levels of residual disinfectant are insufficient (Edberg 1997; Russin et al. 1997; Zhang and Digiano 2002; Berry et al. 2006). The growth of bacteria in the DS depends on a number of physical, chemical and operational conditions (Zhang and DiGiano 2001), as well as on seasonal fluctuations (Berry et al., 2006). The main influential factors are residual free chlorine, the presence of assimilable organic carbon (AOC), water temperature, pH, the nature of pipes, the presence of corrosion and the shear in the biofilm-liquid interface (LeChevalier et al. 1990, 1993; Ollos 1998; Zhang and DiGiano 2001; Ndiongue et al. 2005). Some authors also mention the distance with regard to the water treatment plant (WTP), thus, the residence time of the water within the DS, conductivity and turbidity (Carter et al. 2000; Momba et al. 2004).
The viability of deploying microturbines for energy recovery and downstream pressure dissipation in waterdistribution systems was examined. A simple, yet representative, system that included a source with surplus head and a conduit of moderate size was used to ascertain the financial viability of using a microturbine to dissipate pressure. Discharge through the system was the most important factor contributing to the turbine’s performance, which was analyzed probabilistically using Monte Carlo simulation with system demand as a random variable. The roles of diurnal demand patterns and a random annual demand growth rate were also considered.
Environmental Systems Engineering, University of Regina, Regina, SK, Canada
Waterdistribution pipes constructed in expansive clay soils are often subjected to severe distress subsequent to construction. Seasonal variations in climatic conditions cause alternate saturation-desaturation in soils that can result in periodic swelling and shrinkage of the expansive soils. The volume changes may cause severe differential movement that will eventually lead to pipe failures. Field instrumentation was installed to monitor the soil conditions around a section of waterdistribution pipe in an area with expansive soil and where pipe failures were known to be frequent. The instrumentation included sensors to measure in situ soil water content and soil suction, soil movement, soil stress and temperature. This paper presents the data from the first year of monitoring and discusses implications of the preliminary findings.
In many waterdistribution systems, a significant amount of water is lost due to leakage from distribution pipes. To reduce water loss, system operators conduct systematic programs to locate and repair leaks. Acoustic leak detection equipment is normally used to locate the leaks. Initially, listening rods and aquaphones are used to detect the sound induced by water leaks by placing them in direct contact with the pipes or their appurtenances, e.g., fire hydrants or control valves. Ground microphones are then used to pinpoint suspected leaks by listening for leak sounds on the pavement or soil directly above water pipes. Leak noise correlators, which are state-of-the-art computer- based devices, are also used to accurately pinpoint the location of suspected leaks. Several makes of acoustic leak detection equipment are commercially available.
The AC pipes installed in Regina drinking waterdistribution systems are classified as Type II, which contains about 15 to 20% of asbestos, 45 to 51% Portland cement and 32 to 34% of silica. When these components mixed and hydrated, about 1% of free lime was produced. Initial pH of the AC pipe is greater than 12.4, due to presence of free lime. Degradation of AC pipe is a combination of biological and chemical processes and these processes often facilitate each other. For example, the chemical process in the beginning caused reduction in pH of inner pipe wall from greater than 12 to about 9, which made it possible for bacterial communities to establish on the pipe surface (Bastidas-Arteaga et al., 2008). Once these microbes established, they started to acquiring nutrients from the flowing drinking water and from pipe surface to multiplying in population. SLYM bacteria may have first harbored and thrive as biofilm on the pipe surface around the voids and cracks. As biofilm further developed, other bacteria in the flowing water can be intercepted and joined in the biofilm. Together, they form a community as patina developed. Within this community, each group would play specific functions. After more than many years, this bacterial community became mature and stable, and played important roles in the destruction processes of AC pipes.
Unidirectional ﬂushing is a widely used method to remove sedimented particles from waterdistribution systems and prevent water discolouration events. However, it shows low ef ﬁciency in cases of high pressure losses, usually requires large volumes of water, and does not remove incrustations. Air scouring is known for being very effective in particle removal with minimal impacts from pressure loss, requiring little water and improving hydraulic capacities by removing soft incrustations. Flushing sequences of unidirectional ﬂushing and air scouring were performed in similar conditions on 18 pipe sections from four waterdistribution networks located in the province of Quebec, Canada; unidirectional ﬂushing was also performed on 14 additional pipe sections located in three other waterdistribution networks. Total suspended solid concentration, water ﬂow and pressure of ﬂushed water were recorded to estimate the amount of ﬂushed particles, the required water volume and the evolution of hydraulic capacities. Within the studied networks, the water requirements for air scouring were approximately 8-fold less than for unidirectional ﬂushing and did not signi ﬁcantly improve the hydraulic capacity of the cleaned pipes.
Sophia Antipolis, France email@example.com
This paper presents a generic non-compact linear program- ming approximation of the pump scheduling problem in drinking waterdistribution networks. Instead of relying on the binary on/off status of the pumps, the model draws on the continuous duration of activation of pump combina- tions, whose entire set is computed in a preprocessing step by ignoring the pressure variation in the water tanks. Pre- processing is accelerated using network partition and sym- metry arguments. A combinatorial Benders decomposition- based local search takes the approximated solution as input to derive a feasible solution. Our experiments on two differ- ent benchmark sets, with fixed- or variable-speed pumps, show the accuracy of the approximated formulation and the ability of the matheuristic to compute near-optimal solutions in seconds, where concurrent, more specialized approaches need minutes or hours.
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There has been a growing body of evidence that ARC waterdistribution pipelines are affected by deterioration processes that are evident by the decrease of the wall thickness from the inside out. These deleterious process usually have the following common elements in ARC pipes: (1) decreased thickness of the pipe wall reduces pipe strength; (2) while the concrete becomes thinner or softer the reinforcing asbestos fibers start to expose as the concrete corrodes away; and (3) patina develops on the inner surface of pipes, generally with the exposed asbestos fibers interfacing between the patina coating and the corroding concrete wall of the pipe. This investigation examines the microbiologically-influenced mechanisms that can be associated with both the patina development and the deterioration of the internal pipe walls. The assessment involves the determination of the forms of any microbiological activity as detected by the newly developed biological activity reaction test - visual BART reader (VBR72) system. (Droycon Bioconcenpts Inc.). Subsequent identification of the bacterial species or communities utilized the Rapid Agitation and Static incubation techniques, followed by modified MIDI procedures and then referred to Sherlock ® library. Additionally synthetic patina biomass was grown using a section of ARC pipe.
• In the medium to long term, fundamental research in modeling the deterioration of water quality in pipes as a function of the condition of pipes is required in order to incorporate water quality considerations into the decision making model.
• Waterdistribution pipes are but one component of a larger infrastructure system that includes also sewer pipes (sanitary and storm), and power and communication networks. Some or all of these systems typically reside under the road pavement. Interactions exist between the various systems both physical (e.g., pipe failure may cause subsequent road failure) and economical (e.g., it is cheaper to replace a pipe in conjunction with road renewal, and conversely, installing a pipe in an existing pavement will shorten the useful life of this pavement). An all-encompassing DSS should consider all infrastructure components as one system. Although we are currently a long way from such a DSS, we should remember that this is the strategic goal of all the research that is pursued in the area of rehabilitation of infrastructure systems.
Biofilms inevitably develop on the internal surfaces of drinking water pipelines, regardless of the presence of disinfectant residual (Geldreich, 1996). Biofilms are composed of microbial cells that are embedded in an exopolymeric matrix in a manner that makes the enumeration of these microorganisms difficult (Lazarova and Manem, 1995). It has therefore been very challenging to determine the community structure of microorganisms in the biofilms. As a consequence of these limitations, evaluation of microbiologically influenced pipe corrosion rates has been scarce. Previous studies of biofilm formation in distribution pipes have been focused on its effect on bulk water quality, including the bacteria detached from the biofilms, which was shown to cause increased bacterial counts in the drinking water (Van der Kooij, 1992). In some cases, it was believed that the formation of biofilms on corroded pipes might have provided protection to the pipe materials by restricting further oxidation (LeChevallier et al., 1993; Dubiel et al., 2002). In a study of the effect of various pipe materials on fixed bacterial biomass on pipe surfaces, Niquette et al. (2000) determined that the density of bacterial biomass on AC pipe was around 0.1 µg C/cm 2 , which was much higher than polyethylene, PVC, cemented steel, cemented cast iron and tarred steel pipes. The microbiological effects on the degeneration of the drinking waterdistribution network, particularly the AC pipes, still remains largely unknown.
Performance evaluation: The quality of WDS sub-zoning is evaluated and the methods are compared based on the visual and quantitative performance measures previously presented.
Final outcome: The final outcome of this work resulted in a web-based tool accessed by the authorized PUB operators, that enables choosing the desired number of sub-zones or, alternately, the size of the sub-zones, for a selected waterdistribution network. The output provides a summary of the network partition to sub-zones including the number of nodes, number of intra and inter cluster edges, and the daily demand; and an interactive map demonstrating classification of network nodes (using colormap) to sub-zones showing their inter-connecting links and a supporting aggregated network layout. An example of an output for Network1 using GP algorithm for k = 5 sub-zones is shown in Table 3. Figure 3 graphically shows the partition of the network to 20 sub-zones aggregated network layout (a) and map view (b).
Initially, leak detection crews roughly bracket leaks in water-distribution systems by listening on all accessible contact points with the distribution system such as fire hydrants and valves. Suspected leaks are then pinpointed by listening on the ground surface directly above the pipe at very close intervals (about 1 m). Alternatively, suspected leaks can be pinpointed automatically by using modern leak noise correlators, which have become popular in recent years. Normally, leak noise correla- tors are more efficient and more accurate than listening devices.