Velitchko Tzatchkov

GRAPH THEORY BASED ALGORITHMS FOR WATER DISTRIBUTION NETWORK SECTORIZATION PROJECTS

Water distribution network sectorization projects, in process in Mexican cities in the last two decades, consist in dividing the large interconnected city distribution network in smaller networks with one (or two in exceptional cases) supply points. Known water distribution network models are routinely applied to revise any proposed sectorization. For large network sectorization projects, however, additional algorithmic capabilities are needed, such as connectivity and source contribution analysis. This paper presents algorithms of that type, based on graph theory, for obtaining the number of independent sectors in a network layout, the set of nodes belonging to each sector, the set of disconnected nodes, and the source to node contribution. The algorithms are implemented in a computer AutoCAD-based system. Real sectorization project in two cities, where the proposed algorithms are applied, are then commented.

INTEGRATING DISTRIBUTION NETWORK MODELS WITH STOCHASTIC WATER DEMANDS AND MASS DISPERSION

An Advection-Dispersion-Reaction model, ADRNET, is developed to perform dynamic water quality simulation in complex pipe networks. The network hydraulic functions in the EPANET toolkit are incorporated and used as hydraulic engine to simulate the extended period pipes flows in ADRNET based on the time-averaged stochastic demands. An Eulerian-Lagrangian scheme is combined with a numerical Greens Function technique to numerically solve the ADR equation efficiently in network conditions. Verification with analytical solution shows that ADRNET achieves excellent performances of numerical convergence and stability. ADRNET is applied to an all-pipes network with stochastic water demands to compare against results obtained by EPANET advection-reaction water quality model and field observations. Both models achieve similar results at locations where turbulent flows prevail. However, the ADRNET provides better agreement with field observations than EPANET at locations where laminar flows dominate. The ADRNET proves to be a valuable tool for managing water quality practice in water distribution network. This paper was presented at the 8th Annual Water Distribution Systems Analysis Symposium which was held with the generous support of Awwa Research Foundation (AwwaRF).

Stochastic Demand Generated Unsteady Flow in Water Distribution Networks

This paper presents an attempt to analyze the complex unsteady flow behavior of water distribution networks subject to demand pulses. Relevant elementary concepts from the Poisson Rectangular Pulse model and the elastic water column unsteady flow theory, used later in the analysis, are first presented. Engaging an appliance causes a rapid flow raise and related pressure drop and that propagates with high speed (celerity) along the pipes. Similarly, disengaging an appliance causes a propagating pressure raise. Each of those propagating pressure changes is transformed when a junction node is encountered. Depending on the relation of the areas of the pipes that join at the junction, a portion of the moving pressure change enters into the upstream pipes, and the rest is reflected. On this basis, the unsteady flow behavior following opening or closing of an individual water-using appliance inside a home is discussed, concluding that it may be important in in-home piping and service lines. Arriving at the connection of the service line to the street water main, however, only a small portion of the pressure and flow changes enters the main, since its cross sectional area is normally much larger compared to that of the service line. Because of that, the operation of a single water appliance inside a home is almost imperceptible in water mains and larger distribution network pipes. The subsequent analysis of the unsteady flow in pipe networks shows that the demand pulses deform in their path from the demand point to the pipe supplying the entire network, or the corresponding part of it. This way the commonly used approach to obtain the flow in pipes supplying a group of water users as a simple sum of the downstream demand pulses, is not always justified. The actual effect of the unsteady flow on a particular network depends on the length of the network pipes, the distance from the supplying pipe, the wave celerity and the number of branching points in the path. Since water users are located in different points throughout the network, the travel time and the network topology need to be considered too, as well as the effect of simultaneous demand pulses.

Assessment of a Water Utility Agency: A Multidisciplinary Approach

This chapter describes the methodology for an action plan for solving the water supply problems of a city of around 400,000 inhabitants, with a semi-dry climate and a subterranean supply system. This plan was based on a diagnosis of the supply sources, the demand for drinking water, the operation of water treatment plants, and the commercial and accounting system, as well as the analysis of possible alternative supply sources for the city and its adjacent urban areas. The actions that have been proposed in this action plan are focused on increasing the supply of water, both in terms of quantity and quality, to meet the needs of the population and to operate the supply system more efficiently.

Importance of Dispersion in Network Water Quality Modeling

This paper applies numerical models to simulate more realistic network conditions and develop preliminary new guidelines on the conditions under which dispersion is important in pipe networks. Instead of adopting the “usual” one-dimensional Advection-Dispersion-Reaction (1D-ADR) model, a two-dimensional AdvectionDiffusion-Reaction (2D-ADR) model is selected. This eliminates the error caused by estimation of the enigmatic dispersion coefficient, an essential parameter of the 1DADR model. Numerical results from the 2D-ADR model are compared against numerical results from a 1D-AR (Advection-Reaction) model to identify differences caused by dispersion-related factors, such as time history of source strength, solute reaction rate, pipe diameter and flow pattern. Several source load scenarios are simulated using the 2D-ADR numerical code in order to confirm a theoretical orderof-magnitude analysis of each term in the simplified 1D-ADR equation. This comparison highlights the relative importance of advection, dispersion and reaction in solute transport during low flow conditions. Results confirm that dispersion is just as important as advection and, therefore, should not be ignored when modeling water quality in laminar flow dominated zones of the water distribution system.

Hydraulic Behavior of Pipe Network Subject to Random Water Demands

A Poisson Rectangular Pulse (PRP) process is used to simulate instantaneous indoor and outdoor residential water use during a 55-hour period at 135 demand nodes in an all-pipes water distribution system. The corresponding network equations are then solved with an ad hoc program to generate unsteady flow rates in each pipe. This computational approach yields an unprecedented level of detail, affording new insights into the hydraulic behavior of municipal pipe networks. Results of simulation experiments include the frequency of stagnant, laminar, transition and turbulent flow, the number of flow direction reversals, the coefficient of variation of the flow rate, the minimum and maximum rates of flow and other hydraulic statistics for any link in the pipe network. These hydraulic characteristics are compared against similar data generated by a standard network progam using a one-hour extended period time resolution.