Managing Uncertainty in Operational Control of Water Distribution Systems

1. Introduction Operation of water distribution systems requires a variety of decisions to be made. There are system development decisions: where, when and what new elements of the distribution system need to be built. There are system management decisions concerning the regulatory measures such as water pricing principles, effluent standards, legislative measures etc.. There are operational decisions determining such things as water pumping schedules, reservoirs' operation and pressure control in a distribution network. These decisions are made at different time intervals and with very different time horizons in mind. The development planning spans a time horizon of 1-10 years and depends on forecasts of water demands, but it is also linked very strongly to regional planning through data on future social and economic conditions and future environmental conditions. The management control, while it influences system development, concentrates on achieving optimum performance from the existing system. In this sense there is an interplay between system management regulations and operational decisions. The difference is in the possible or practical frequency of intervention: the prices, standards and other regulatory measures of a legislative nature cannot be changed too often and, in particular , they are not adjusted to actual hydraulic conditions and short term forecasts. The expected time horizon of management control is within the range 1-12 months. As compared to this time scale, operational control decisions need to be made very frequently. For example, the decision to activate/deactivate pumps is made in response to measurements of reservoir levels or system