Modelling a controlled water system as a sampled data system with events

Automatic control of water systems such as canals for shipping, irrigation systems, drainage systems, or sewer systems, is a complex problem. While the system state is continuously changing, in almost all cases the weir, gates, or pumps are adjusted only at set times. This mixes continuous and discrete time. Moreover, it may be necessary to take action in response to the occurrence of an event in the system. So, part of the system evolves continuously, another part changes stepwise at given times, while yet another part responds to events in the system or its surroundings that may occur at arbitrary times.

Basic limitations on controlling these systems when ignoring their hybrid nature are demonstrated for the case of a Dutch sewer system. The control schemes under discussion are: local event driven control for a group of pump stations, sampled data control for a group of pump stations, hierarchical control with sampled data control for the group, and event driven control for the individual stations.