Real time control of water distribution networks: A state-of-the-art review.

This paper presents a review of the current state of the art of real time control (RTC) of water distribution networks (WDNs). After proving the basic concept and terms of RTC and presenting sensors, regulation devices and controllers typically used in WDNs, the paper goes on by describing the most frequent control objectives, which mainly include service pressure regulation, control of tank filling and energy production in each WDN district. Various control methodologies recently proposed in the scientific literature are presented and discussed, along with experimental and numerical results achieved. Also, aspects related to the cost-effectiveness of RTC are critically analyzed. The paper ends by giving an outlook into potential future developments in the area of RTC for WDNs.

Modelling the erosive effects of sewer flushing using different sediment transport formulae.

A numerical investigation to simulate the cleaning effects of successive flushes over sediment beds in prismatic channels is presented in this paper. The 1D De Saint Venant-Exner equations were used to describe the temporal evolution of the sediment bed after each flush. The predictive capacity of two sediment transport formulae was explored against experimental results from laboratory tests. Results show that the adopted model can successfully describe the evolution of the sediment bed due to the flushes exerted during the experiments, with differences between the used transport formulae depending on the channel invert slope and on the flush energy.

Designing domestic rainwater harvesting systems under different climatic regimes in Italy.

Nowadays domestic rainwater harvesting practices are recognized as effective tools to improve the sustainability of drainage systems within the urban environment, by contributing to limiting the demand for potable water and, at the same time, by mitigating the generation of storm water runoff at the source. The final objective of this paper is to define regression curves to size domestic rainwater harvesting (DRWH) systems in the main Italian climatic regions. For this purpose, the Köppen-Geiger climatic classification is used and, furthermore, suitable precipitation sites are selected for each climatic region. A behavioural model is implemented to assess inflow, outflow and change in storage volume of a rainwater harvesting system according to daily mass balance simulations based on historical rainfall observations. The performance of the DRWH system under various climate and operational conditions is examined as a function of two non-dimensional parameters, namely the demand fraction (d) and the modified storage fraction (sm). This last parameter allowed the evaluation of the effects of the rainfall intra-annual variability on the system performance.

Regional scale analysis for the design of storage tanks for domestic rainwater harvesting systems.

A regional scale analysis for the design of storage tanks for domestic rain water harvesting systems is presented. The analysis is based on the daily water balance simulation of the storage tank by the yield-after-spillage algorithm as tank release rule. Water balances are applied to 17 rainfall gauging stations in Sicily (Italy). Compared with literature existing methods, a novel dimensionless parameter is proposed to better describe the intra-annual character of the rainfall patterns. As a result, easy-to-use regional regressive models to evaluate the water saving performance and the overflow discharges from the tank are provided along with a stepwise procedure for practical application. The regional models demonstrate good fits between model predictions and simulated values of both water savings and overflows from the tank.

A simplified approach for the design of infiltration trenches.

The use of infiltration trenches has proven to be useful to reduce runoff in urban surfaces. The design of these structures is based on the continuity equation taking into account inflow, outflow and detention water volumes. Basic procedures evaluate entering flow rates and relative volumes directly as a function of rain event characteristics, without taking into account rain-runoff processes occurring in the watershed. An improved simplified procedure, based on the kinematic model for the description of rain-runoff processes, has been developed here using a dimensionless approach. The procedure and the relative applicative design graphs are presented and discussed.

Laboratory investigation on the performances of baffles for the capture of sewer floatables.

The use of baffles in sewer systems enables the capture of floatables, which could be responsible for both malfunctioning of water treatment plants and aesthetic pollution of receiving bodies when discharges through combined sewer overflow devices occur. An experimental contribution to the understanding of capturing processes of floatable elements by means of baffle devices is presented in this paper. Experiments were carried out using different baffle configurations. The limit equilibrium conditions of various types of floatables, i.e the condition beyond which upstream intercepted floatables start to escape the baffle, were investigated. The dimensional analysis was used in order to generalize the results of the experiments and to compare the capturing performances of analysed baffle configurations.

P controller calibration for the real time control of moveable weirs in [corrected] sewer channels.

In this paper, a detailed study on the local real time control of moveable sharp-crested weirs in sewer channels is presented. Firstly, an experimental analysis aimed at determining the hydraulic behaviour of the regulator under both free flow and submerged flow conditions was carried out. Then, a numerical investigation into the calibration of proportional (P) controllers for the weir control was performed. In particular, suitable values were evaluated for the controller proportional parameter in order to obtain quick regulations and avoid the occurrence of permanent water level oscillations behind the weir. A dimensionless approach was adopted for the generalisation of the results.

Experimental analysis of the hydrass flushing gate and laboratory validation of flush propagation modelling.

Periodical cleansing operations prove necessary inside sewer systems in order to reduce hydraulic and environmental problems owing to the accumulation of deposits on the bottom of channels. For this objective, new effective hydraulic devices based on the scouring effects of flushing waves have been recently set up and adopted in many sewer systems. In this paper, the results of an experimental and numerical investigation on the hydraulic operation of the Hydrass flushing gate are reported. The experimental analysis has been carried out using a laboratory channel and a reduced scale model of the gate, in order to characterise the flushing waves generated by the device. The numerical analysis has been performed using a mathematical model specifically developed for the simulation of flushing waves inside sewer channels. The comparison of numerical results and experimental data has allowed evaluation of the applicability under unsteady flow conditions of the outflow relations determined for the Hydrass gate in a previous investigation under steady flow conditions.

Experimental analysis of the hydrass flushing gate and field validation of flush propagation modelling.

As well known, a periodical cleansing of sewers results necessary in order to avoid or reduce many unpleasant consequences due to the presence of sediments, such as the solid re-suspension during rain events and the reduction of the channel flow capacity. For this purpose, different systems based on flushing techniques have been adopted in sewers. In the present paper, the results of an analysis of the hydraulics of a flushing device, the Hydrass gate, is presented. In particular, an experimental investigation on a scale model under steady conditions was carried out in order to determine the behaviour of the device during the flushing phase. Outflow relations were derived for the different outflow conditions. A numerical model was finally set up for testing the relations under unsteady conditions, using for validation the experimental data of a previous measurement campaign carried out in a sewer reach of the city of Lyon, France.

Flow velocities and shear stresses during flushing operations in sewer collectors.

Many relevant problems of drainage systems such as first flush pollution, flow capacity reduction and consequent risks of surcharges are worsened by sediment accumulation in sewer collectors. For the solution of these problems several sediment cleansing methods and techniques, e.g. mechanical methods, traps and flushing devices, have been developed and applied in the last decades. In particular, simulation studies and experimental campaigns have shown the effectiveness of flushing methods as preventive cleansing strategy in sewer collectors. In this paper the results of a numerical investigation for determining flushing waves characteristics both in terms of duration and flow rate are presented. The collector section lengths where flow velocities and average shear stresses determined by flushing waves exceed minimum threshold values are evaluated using a dimensionless approach. The results, related to the operative ranges of the practical applications, are exposed by means of graphs and regressive equations.

PID and PLC units for the real-time control of sewer systems.

Moveable gates for the real-time control (RTC) of sewer systems storage capacities are usually operated by controllers which, on the basis of local water level or flow velocity measurements, calculate the regulation errors of the monitored variables, determining the necessary regulator movements to lead the flow conditions to the desired set point. In this paper the results of an investigation on the influence of proportional-integral-derivative (PID) controllers and programmable logic controllers (PLC) for the RTC of moveable sluice gates positioned into sewer systems are presented. The analysis of response time, damping and regulation errors provided information on the PID parameter calibration values and on the PLC control function performances. A comparison between the two kind of controllers has also been carried out.