Rita Ugarelli

Optimal Scheduling of Replacement and Rehabilitation in Wastewater Pipeline Networks

To fulfill the objective of providing acceptable level of service to customers, the water managers have to plan how to operate, maintain, and rehabilitate the system under budget constraints. The model presented in this paper uses risk cost as an appropriate framework to define the optimal replacement time prediction based on the balance between investment for replacing and expenditures for maintaining the asset. An economic analysis compares the costs associated with maintaining an existing pipe in service, being completely depreciated or not, to the cost of replacing or rehabilitating the pipe. On this basis, the right time in the future to rehabilitate the pipeline can be determined. The costs associated with an existing pipe include direct operational and maintenance costs and indirect costs, such as those associated with risk of failure. The optimal replacement time is identified as the year in which the cost to maintain the existing stock of pipes exceeds the investment to replace it. A dynamic prog...

Assessing mechanical vulnerability in water distribution networks under multiple failures

Understanding mechanical vulnerability of water distribution networks (WDN) is of direct relevance for water utilities since it entails two different purposes. On the one hand, it might support the identification of severe failure scenarios due to external causes (e.g., natural or intentional events) which result into the most critical consequences on WDN supply capacity. On the other hand, it aims at figure out the WDN portions which are more prone to be affected by asset disruptions. The complexity of such analysis stems from the number of possible scenarios with single and multiple simultaneous shutdowns of asset elements leading to modifications of network topology and insufficient water supply to customers. In this work, the search for the most disruptive combinations of multiple asset failure events is formulated and solved as a multiobjective optimization problem. The higher vulnerability failure scenarios are detected as those causing the lower supplied demand due to the lower number of simultaneous failures. The automatic detection of WDN topology, subsequent to the detachments of failed elements, is combined with pressure-driven analysis. The methodology is demonstrated on a real water distribution network. Results show that, besides the failures causing the detachment of reservoirs, tanks, or pumps, there are other different topological modifications which may cause severe WDN service disruptions. Such information is of direct relevance to support planning asset enhancement works and improve the preparedness to extreme events.

Statistical analysis and definition of blockages-prediction formulae for the wastewater network of Oslo by evolutionary computing

Oslo Vann og Avløpsetaten (Oslo VAV)-the water/wastewater utility in the Norwegian capital city of Oslo-is assessing future strategies for selection of most reliable materials for wastewater networks, taking into account not only material technical performance but also material performance, regarding operational condition of the system.The research project undertaken by SINTEF Group, the largest research organisation in Scandinavia, NTNU (Norges Teknisk-Naturvitenskapelige Universitet) and Oslo VAV adopts several approaches to understand reasons for failures that may impact flow capacity, by analysing historical data for blockages in Oslo.The aim of the study was to understand whether there is a relationship between the performance of the pipeline and a number of specific attributes such as age, material, diameter, to name a few. This paper presents the characteristics of the data set available and discusses the results obtained by performing two different approaches: a traditional statistical analysis by segregating the pipes into classes, each of which with the same explanatory variables, and a Evolutionary Polynomial Regression model (EPR), developed by Technical University of Bari and University of Exeter, to identify possible influence of pipes attributes on the total amount of predicted blockages in a period of time.Starting from a detailed analysis of the available data for the blockage events, the most important variables are identified and a classification scheme is adopted.From the statistical analysis, it can be stated that age, size and function do seem to have a marked influence on the proneness of a pipeline to blockages, but, for the reduced sample available, it is difficult to say which variable it is more influencing. If we look at total number of blockages the oldest class seems to be the most prone to blockages, but looking at blockage rates (number of blockages per km per year), then it is the youngest class showing the highest blockage rate. EPR allowed identifying the relation between attitude to block and pipes attributes in order to understand what affects the possibility to have a blockage in the pipe. EPR provides formulae to compute the accumulated number of blockages for a pipe class at the end of a given period of time. Those formulae do not represent simply regression models but highlight those variables which affect the physical phenomenon in question.

Effect of climate change on navigation channel dredging of the Parana River

This paper presents an analysis of the effect of climate change on modifying the dredging cost to maintain the navigation channel at the actual capacity of the Parana waterway (Argentina). The Parana−Paraguay Rivers system is one of the most important inner navigation waterways in the world, where approximately 100 million tons of cargo are transported per year. Maintenance of the navigation channel requires continuous dredging by Hidrovía SA (limited liability company), which is responsible for ensuring the minimum water depth for navigation. A failure event occurred during January 2012 when a bulk cargo carrier ran aground, interrupting fluvial trading for 10 days. Numerical models were applied to simulate hydro-sedimentation processes at the Lower Parana River to estimate dredging costs for a given flow discharge. The resulting function relates the sedimentation rate (i.e. the dredging effort required to keep the present depth for vessel draft) to forcing hydrology conditions. This function and the statistical evaluation of climate scenarios were used to calculate the probability of failure for navigation and the associated cost of channel maintenance. The most appropriate dredging effort was estimated by detecting the minimum total cost (i.e. dredging plus failure) to varying the yearly average discharge and by analysing the sensitivity of the total cost to different degrees of economic impact.

WASTEWATER NETWORK CHALLENGES AND SOLUTIONS

Sewer and storm water systems in cities worldwide suffer from ageing and inappropriate wastewater networks. This challenge has to be met by systematic upgrading and preventive maintenance. It is necessary to analyse the current performance of the wastewater networks, to determine the system bottlenecks that cause system vulnerability on floods in city areas and pollution of receiving waters. The next task is then to use this information for selecting and ranking upgrading projects to improve the situation. CARE-S is a computer based system developed to meet this challenge. It is designed for sewer and storm water network rehabilitation planning. It provides fundamental instruments for estimating the current and future condition of sewer networks, ______ * Sveinung Saegrov, SINTEF, Dept. Water and Wastewater, Klaebuveien 153, NO-7465 Trondheim, Norway, phone +47-73592349, fax +47 73592376, e-mail: sveinung.sagrov@sintef.no

Historical analysis of blockages in wastewater pipelines in Oslo and diagnosis of causative pipeline characteristics

The city of Oslo is evaluating strategies for the selection of appropriate materials for the pipelines and manholes of its wastewater network. The overarching motive is to minimise construction-related failures over the system lifetime and also ensure that it is able to avert flooding events. This paper analyses the blockage records of the last 16 years (1991–2006) in the wastewater pipeline network of Oslo. For the purpose of the analysis, the pipeline stock is categorised on the basis of pipe diameter, material of fabrication, slope and age. Proneness to blockages is studied and attempts are made to correlate the same to the size, material, slope and age. The analyses performed confirm that older and small diameter sewage pipelines made of concrete, laid almost horizontal to the ground surface are the high-priority candidates, and more importantly enables one to compare among the different categories and classes of pipelines.

Integrated Urban Water System

This chapter presents the challenges faced by the water utilities to provide safe, secure and reliable service to meet the Water Framework Directives 2000/60/EC and the water safety plan (WHO [16]). These directives among others will form framing conditions for the risk and vulnerability analysis to be conducted. The analysis approach follows standard methodology for risk and vulnerability described in Chap. 3 of this book. In order to structure the analysis, it is common to split the system into the various water cycle components. For each of these components, hazards and threats are identified, probability and consequences assessed, and finally, the total risk picture presented. Practical examples from the Oslo case study are presented to support the approach.

Displacement Of Non-Newtonian CompressibleFluids In Plane Porous Media Flow

Displacement of non-Newtonian fluid in porous media is of paramount importance in the flow modeling of oil reservoirs. Although numerical solutions are available, there exists a need for closed-form solutions in simple geometries. Here we revisit and expand the work of Pascal and Pascal [4], who analyzed the dynamics of a moving stable interface in a semi-infinite porous domain saturated by two fluids, displacing and displaced, both non-Newtonian of power-law behavior, assuming continuity of pressure and velocity at the interface, and constant initial pressure. The flow law for both fluids is a modified Darcy’s law. Coupling the nonlinear flow law with the continuity equation considering the fluids compressibility, yields a set of nonlinear second-order PDEs. If the fluids have the same consistency index n, the equations can be transformed via a selfsimilar variable; incorporation of the conditions at the interface shows the existence of a compression front ahead of the moving interface. After some algebra, one obtains a set of nonlinear equations, whose solution yields the location of the moving interface and compression front, and the pressure distributions. The previous equations include integrals which can be expressed by analytical functions if n is of the form k/(k+1) or (2k-1)/(2k+1), with k a positive integer. Explicit expressions are provided for k = 1, 2; for other values, results are easily obtained via recursive formulae. All results are presented in dimensionless form; the pressure distribution and interface positions are studied and discussed as a function of the self-similar variable for different values of the mobility and compressibility ratios.