Development of Multi-Period Response Management Model to Suddenly Contaminated Urban Water Distribution Networks

Abstract

In this study, a simulation-optimization model is used for multi-period consequence management of sudden contamination in urban water distribution network. The tools used in the management of consequences in this study are to discharge contaminated water by hydrants, to cut or plug the pipes to control the flow path in the network or to isolate the different areas, as well as to switch the pumps on or off to regulate the water flows pressure into the network. EPANET software is used for simulation and single-objective genetic algorithm is used for optimization. In this study, the three objective functions are to minimize system return time to normal situation, minimize the mass of contamination consumed, and minimize the number of infected nodes. Each of the objective functions mentioned is executed for two different management scenarios. In the first scenario, the status of the hydrants, valves and pumps is constant from the beginning to the end of the management period. In the latter scenario, the status of the hydrants, valves and pumps can be changed periodically from the beginning to the end of the management period. The number of decision variables in this study was 54, which included determining whether the hydrants were open or closed, whether the pipes were closed or connected, and whether the pumps were on or off. The contamination loading is injected from the three candidate nodes into the network. The results show that alternating situations of hydrants, valves and pumps, compared to the situation where the hydrants, valves and pumps are in constant condition, decreases the return time to a normal state between 13 and 26.5 percent, the amount of contaminated water consumed between 12 and 20 percent and the number of infected nodes between 6 and 21 percent. It should be noted that in all scenarios, the minimum water pressure at the nodes of the network is controlled from the minimum permissible value and the increase in the number of management responses actions is controlled from the maximum permissible value. The alternation of the opening and closing of the hydrants and valves, as well as the switching of the pumps on or off, helps to improve the target functions to an acceptable extent.