Anatoli Vassiljev

Calibration of a model of an operational water distribution system containing pipes of different age

The aim of the paper is to demonstrate that the Levenberg-Marquardt algorithm can give successful results when operational water distribution systems are calibrated with the proper selection of parameter increment for the calculation of partial derivatives. The functional dependence of pipe roughness on age, which describes linear and nonlinear dependences, is proposed for the calibration of a model of a water distribution system containing pipes of different age. It is also shown that the visualization of response surface on a coarse grid is very useful for the analysis of the results.

Use of modelling error dynamics for the calibration of water distribution systems

The calibration of a water distribution system remains a complex task. Leakages create additional difficulties if their proportion is high. Not all leakages are real. A part of them are apparent leakages. An optimization procedure is proposed to obtain the proportions of real and apparent leakages. The distribution of the leakages over a WDS may be made easier by analyzing the dependence of modelling errors on water flow. It is suggested that pressure measurements should be ranked according to the closeness of measurement to the water source and that modelling errors should be analysed separately for the measurements of different order (from the first to the highest). The advantage of this approach is that the analysis is confined within points of measurements of one order and it allows to redistribute fluxes of leakages (real and apparent) more reliably. Nonlinear optimization with linear constraints is used for the redistribution of leakages over a WDS. The methodology proposed allows to exclude the influence of systematic errors on the result of calibration.

Estimation of real-time demands on the basis of pressure measurements by different optimization methods

The aim was to estimate real-time demands in a water distribution system on the basis of pressure measurements. The task was formulated as an optimization procedure to find water flows correcting typical demands that will minimize differences between measured and modelled pressures. The Levenberg-Marquardt algorithm (LMA) and the Genetic algorithm (GA) were tested to solve the problem. Results showed that the LMA works much faster than the GA. It was also found that the higher the demands the lower is the sensitivity of the results to random errors in pressure measurements. Measurements in an operational WDS were used in calculations.

Real-time demands and calibration of water distribution systems

All computer models of water distribution systems (WDS) have to contain information about demands. Usually demands are derived based on customers water meters weekly or monthly readings. It gives information only about the average demand. Dynamics of hourly, daily and weekly demands are usually estimated based on typical demand patterns of different type of consumer groups like domestic households, hospitals or hotels. Estimation of demand dynamics by this manner inevitably decreases precision of calibration. Calculations show that differences between real-time and typical demand can influence results of calibration. The paper proposes some methods to minimize this influence. Special software has been developed for estimation of real-time water demands in a WDS. Algorithms and software checked on an operational WDS.

Estimation of real-time water fluxes in water distribution system on the basis of pressure measurements

Experience in calibration of water distribution system (WDS) models shows large uncertainties of demands estimated on the basis of typical hourly values for different types of consumers. The typical dynamics of demands, which are used for the lack of more detailed information, differ from real-time demands in time and in space. It makes it difficult to estimate real-time water fluxes in WDS which are necessary for evaluation of the propagation rate of the contaminated zones in case of deliberate or accidental chemical or biological threats. The aim of this investigation was to test the possibility of estimating real-time water flow fluxes in District Meter Areas (DMAs) on the basis of pressure measurements. Results have been tested on the operational WDS.

Optimization of pump efficiencies with different pumps characteristics working in parallel mode

This paper concentrates on an algorithm for the prediction of steady running variable speed pumps (VSPs) working in parallel to keep them running close to the best efficiency point (BEP) provided by the pump manufacturer. Special focus is on the pumps that have different efficiency and performance characteristics. The complex optimization task to maximize the total efficiency of the pump system and thereby minimize energy consumption was solved with the customized optimization software using the Levenberg-Marquardt algorithm (LMA). Three different theoretical scenarios were analyzed: with working pumps having identical, slightly and largely different characteristics. The transition curves are proposed on the basis of optimization that indicate water discharge and pressure head when an additional pump should be switched on to ensure the highest total efficiency of the pump system.

Controlling Stormwater Runoff from Impermeable Areas by Using Smart Inlets

Climate change and rapid urbanization are driving the need for improved urban stormwater runoff strategies. Urban stormwater drainage systems are severely affected by the changing climate bringing along inter alia more intense rainfall events. The pipeline system, usually having limited capacity, is unable to cope with these excessive flows and becomes surcharged. This may trigger overland flow from the drainage manholes and activate combined sewer overflows. Both events have negative consequences and therefore should be avoided. There are available effective solutions, like low impact development techniques for the catchments under development. However, options for retrofitting the existing drainage facilities are much more limited. Enlarging the pipelines, which has been a traditional response for rising demands is often financially unrealistic due to the large scope of the work. Therefore, recent advances in “smart” water system technologies are considered as an opportunity to meet the future challenges. In this study the concept for controlling stormwater outflow from impervious catchment areas, i.e. parking lots is developed. The target is to find a solution that is affordable and can be implemented with minor disturbances in the area. For that, a novel approach of controlling water flow by regulating the inflow to the manholes is analysed. The adjustable gullies are real time controlled by coupling rule-based algorithms with distributed model predictive control. The concept is successfully tested in a 12 ha impervious catchment area in Tallinn.

Modelling of nitrogen leaching from watersheds with large drained peat areas

Abstract The SOIL and MACRO models with different versions of SOILN initially developed for small field-scales were used to simulate the water flow and nitrate N concentrations in two watersheds in Estonia that contain large areas of peat soils. Monitoring data show that nitrogen concentrations tend to increase in some rivers even where the human activity is very low. This may be connected to soil self-degradation processes taking place in drained peat soils where it is difficult to use most of the hydrological models. Results show that SOIL, MACRO and SOILN may be successfully applied at the watershed scale to model the water quantity and quality on watersheds with high content of peat soils. The analysis revealed that the nitrate nitrogen level trends depend considerably on the meteorological conditions.