Abstract: In this paper, a dimensionless methodology for the optimal design of domestic rainwater harvesting systems (DRWH) is presented.
The methodology is based on the results of daily water balance simulations carried out for 17 rainfall gauging stations in Sicily (Italy).
A novel dimensionless parameter to describe the intra-annual rainfall patterns is introduced and easy-to-use regional regressive models are developed to estimate water savings and overflows from harvesting systems in the region. A minimum-cost-based approach together with obtained regressive models is used to evaluate the optimal DRWH tank size. Results of the approach point out that the economical convenience of large tanks decreases as rainwater availability decreases.
Abstract: 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.
Abstract: 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.
Abstract: The paper presents the results of an experimental investigation aimed at estimating the water saving obtained by reusing washbasin grey waters for toilet flushing in domestic bathrooms. Six Italian households characterised by different number of users largely heterogeneous in age, gender, occupation and customs were selected for the experimental campaign. Washbasin and toilet uses for each selected household were monitored recording chronological series of time instants of washbasin tap opening/closure and of toilet flushing operations. On the basis of water balances on a short time scale, acquired data enabled the evaluation of water saving and unused grey water deriving by the adoption of a simple grey water reuse scheme. Specific dimensionless variables were adopted to present the results and to enable their use within the ranges of practical applications.
Abstract: This paper presents the head reconstruction method (HRM), a new technique that can be used within the finite volume framework to make shallow water models well balanced, i.e., to correct the imbalance that exists between flux and source terms in the equation discretization in the case of irregular bathymetry thus providing unphysical solutions. This technique, based on considering, within each computational cell, the total head of the flow (i.e., the sum of the elevation, pressure and kinetic energies per unit weight of the fluid) as an equilibrium variable, enables the preservation of dynamic equilibria under subcritical, transcritical, and supercritical flow conditions. The new technique is applied to the one-dimensional total variation diminishing (TVD) MUSCL-Hancock scheme and the conservation property is then proven mathematically for this scheme under static equilibrium conditions. Furthermore, the effectiveness of the HRM is tested and compared with two other well balancing techniques based on considering the water elevation as an equilibrium variable in various steady flow case studies. In the end the robustness of the HRM is tested in the simulation of dam-break flow over irregular bathymetry.
Abstract: This paper reports the results of a numerical investigation aimed at assessing the effectiveness of the real-time control (RTC) of valves in reducing leakage in water supply networks. The investigation was carried out considering the head-driven simulation of a network under successive steady conditions. A literature bench-test case-study was used for the simulations enabling the comparison with other methodologies proposed by previous writers and based on the use of optimization algorithms. The performance of RTC was evaluated in terms of pressure and leakage reduction with respect to uncontrolled conditions in the network. Further elaborations showed the better flexibility of RTC, with respect to optimization algorithms, in adjusting valve regulation under variable daily water demand conditions.
Abstract: 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.
Abstract: 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 generalise the results of the experiments and to compare the capturing performances of analysed baffle configurations.
Abstract: Prediction of urban water consumption can help to improve the performance of water distribution systems. Despite the obvious presence of uncertainty in measurements and in assumed model types/structures, most of the existing water consumption prediction models are developed and used in a deterministic context. Methods for more realistic assessment of parameter and model prediction uncertainties have begun to appear in literature only recently. A novel application of the Shuffled Complex Evolution Metropolis algorithm (SCEM-UA) for the calibration of a water consumption prediction model is proposed here. The model is applied to a case study of the city of Catania (Italy) with the aim to predict daily water consumption. The SCEM-UA algorithm is used to calibrate the parameters of the artificial neural network based prediction model and in turn to determine the associated parameter and model prediction uncertainties. The results obtained using the SCEM-UA ANN approach were compared to the corresponding results obtained using other predictive models developed recently by the authors of the paper. When compared to the these models, the SCEM-UA ANN based water consumption prediction model shows similar predictive capability but also the ability to identify simultaneously the prediction uncertainty bounds associated with the posterior distribution of the parameter estimates.
Abstract: Hydraulic flushing gates have recently been successfully adopted for the removal of sewer sediments. A large number of researches are aimed at the evaluation of the performances of these devices in the case of granular sediment deposits, but little information exists about the effectiveness of flushes on cohesive sediments as yet in literature. The current paper reports the results of an experimental investigation on the erosive performances of flushing waves on cohesive sediment beds. Experiments were performed in a laboratory flume adopting two flushing hydraulic conditions and comparing the erosive effects on cohesive and granular sediment beds. Different behaviours of cohesive sediments were observed during flushing operations: in particular, erosive effects in cohesive sediment beds were observed to be smaller than in granular sediments during initial flushes whereas erosion in cohesive sediments proved to be higher during subsequent flushes.
Abstract: The assessment of water resources in a region usually must cope with a general lack of data, both in time (short observed series) as well as in space (ungauged basins). Such a lack of data is generally overcome by combining rainfall - Runoff models with regionalization techniques in order to transfer information to sites without or with short available observed series. The present paper aims to analyze applicability and limitations of two regionalization procedures for estimating the parameters of simple rainfall - Runoff models respectively based on a "two-step" and on a "one-step" approach, for the estimation of monthly streamflow series in ungauged basins. In particular, an application to a Sicilian river basin of multiple regression equations according to a "two-step" and a "one-step" approaches and of a "one-step" approach based on neural networks is reported. For the investigated region, results indicate that models based on the "one-step" approach appear to be robust and adequate for estimating the streamflows in ungauged basins.
Abstract: The various hydraulic and environmental problems related to the accumulation of solids have recently drawn increasingly attention to deposits in the management of sewer systems. Among the mechanical and hydraulic devices used for deposit removal, hydraulic flushing gates have proved to be a cost-effective solution and have been adopted in several sewer networks. This paper reports the results of an investigation on the scouring performance of flushing waves produced by hydraulic flushing gates. A numerical model based on the De Saint Venant-Exner equations in dimensionless form was validated by using data derived from laboratory experiments and was then utilized in this investigation. Simulations were carried out considering various values of the dimensionless parameters involved in the analysis, in order to obtain indications for the design and positioning of flushing devices in sewer channels. The problem of optimal flushing frequency was also investigated.
Abstract: 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.
Abstract: 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.
Abstract: In the management of urban drainage networks, great interest has been recently addressed to the removal of sediment deposits from sewer collectors. In particular, sewer cleansing can be carried out by flushing devices able to discharge a great volume of water during a short period of time. In this paper an experimental and numerical investigation on the scouring effects of flushing waves on sewer sediment deposits is presented. Experiments were carried out on a laboratory channel adopting a simple flushing device and considering different flushing conditions. Accurate measurements on the evolution of mobile-bed deposits and on sediment transported during the flushing operations were carried out. Subsequently, a numerical model was specifically developed for the analysis of the flushing wave propagation and for the description of the sediment scouring on mobile-bed channels. The model is based on the semi-coupled solution of the complete De Saint Venant equations for the water flow and of the Exner equation for the sediment continuity. Numerical results were compared with the experimental measurements in order to derive indications on the scouring processes consequent to flushing operations.
Abstract: 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.
Abstract: 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.
Abstract: The application of real time control (RTC) to wastewater systems may be useful if both operational problems exist and idle capacity is available. One of the more frequently applied RTC techniques in combined sewer systems (CSS) is the activation of in-line storage capacities by positioning regulators such as moveable weirs and gates into the collectors. If adequately controlled, these regulators can improve the system response during storm events eventually providing both improved flow control and significant overflow reduction. This paper presents the results of the application of RTC by using an advanced hydraulic model. Both local and global strategies for the control of moveable weirs are investigated. A simple two-step procedure to fix the weirs setup in the system and an application to the Roma-Cecchignola CSS are presented. Based on obtaining the maximum activated storage capacity, the procedure can easily be extended to any other CSS. Comparison of the results obtained with the tested strategies has shown that, according to other authors' results, a global control strategy allows for reducing overflows considerably more than a local control strategy.
