A.G. Kolechkina

Speed of discrete optimization solvers for real time sewer control

In the project ‘Integrale sturing afvalwater en oppervlakte water Hoeksche Waard’ (integral management of the drainage and sewer system on the island ‘Hoeksche Waard’) in the southwestern Netherlands a central controller was developed for small sewer systems. The aim was the improvement of water quality through the reduction of combined sewer overflows. Two field tests of the controller went very well. Extension to a larger system resulted in timing problems. This paper investigates these problems. The controller minimizes the deviation from proportional distribution of the volume of sewage over the system. The pumping stations contain several pumps that can be either on or off, so the variables to be optimized do not vary continuously, but are only allowed to have integer values. The computational cost is investigated for different solvers. This cost determines the applicability of a solver for a given system size and time step.

A problem in hydrological model calibration in the case of averaged flux input and flux output

This paper shows that the uncertainty due to derivation of fluxes from integral model input can be at least as large as that due to uncertainty in the measurements. The method used to illustrate the problem is interval arithmetic. During calibration hydrological models often seem to perform equally well for two or more sets of parameters that differ considerably. There are many ingredients that may contribute to this. One of those ingredients is a mismatch of information present in input and output data and information used by the model. In this paper we examine one particular case where this occurs. We assume that the input data sets are time series of fluxes integrated over fixed or variable time intervals, while outputs can be the result of continuous or discrete, direct or indirect flux measurements. We assume that for model calibration purposes each output value represents a value at a specific point in time. We show that even for a linear reservoir the process of averaging and sampling may make recovery of its sole parameter impossible. We also show that these problems can be diagnosed and for this simple model also solved through the use of interval arithmetic.

Agile Design of Sewer System Control

We describe the first part of an attempt to include stakeholder participation in the design of a central automatic controller for a sewer system in a small pilot project (five subcatchments) and present lessons learned so far. The pilot is part of a project aimed at the improvement of water quality management through central automatic control of sewer systems and surface water systems.

A controlled sewer system should be treated as a sampled data system with events

Abstract Arguments are presented in favor of modeling sewer systems and in particular Dutch sewer systems as a sampled data system with events. Basic limitations on controlling these systems when ignoring their hybrid nature are stated. The traditional control scheme for the Dutch systems is given as an example of event driven local control. Basic limitations on systems using a sampled data approach without an event driven component are derived. To provide context a brief description of a sampled data controller for a sewer system based on set-point tracking is given. This is followed by an explanation of how the absence of event driven control limits its effectiveness.

Room for automatic control in combined sewer systems

Abstract Combined sewer systems in low lying areas, such as those in the Western part of the Netherlands, have very specific characteristics. Due to a lack of available head gravity driven flow is possible only over short distances, so pumps are needed throughout the system. Lack of available gradient also means fairly large diameter pipes are needed to transport the maximum design flow, so storage volume is usually available. Systems tend to respond quickly and prevention of combined sewer overflows is strongly dependent on available pump capacity and storage volume. For a simplified system model a mathematical proof is given that for a system, designed by Dutch rules of thumb under spatially homogeneous load, local control is nearly as effective as central control when it concerns the prevention of CSO events.