Aspetti economici nelle strategie di gestione delle perdite idriche

L’obiettivo logico di ogni gestore efficiente è quello di eliminare completa-mente le perdite della rete di distribuzione, in quanto queste si associano ad incrementi di costi per la produzione e la distribuzione delle risorse, in termini di sovradimensionamento dei serbatoi, degli impianti di trattamento e delle tubazioni della rete. Tuttavia la completa eliminazione è impossibile, e in realtà va individuato il livello di perdite che si può tollerare e controllare. La definizione teorica dei livelli economici delle perdite idriche non è nuova. Già Parry nel 1881 discusse i costi e i benefici di una strategia di ridu-zione degli sprechi con ispezioni, uso di materiali e infrastrutture di buona qualità evidenziando i primi risultati della misurazione delle perdite ottenuti nella città di Liverpool. In quel tempo in vaste zone di Londra l’approvvigionamento idrico era «imperfetto e intermittente» e la priorità del gestore era garantire la continuità del servizio. Anni dopo, nel 1957, Gledhill studiò gli aspetti economici legati alla ricerca perdite ed elaborò alcune delle teorie ancora oggi in uso. Nel 1980 il Report 26 (Technical Group on Waste of Water) metteva a confronto il rapporto costi/benefici delle diverse forme di controllo delle per-dite: il controllo passivo, le ispezioni regolari, la misurazione degli sprechi. Il Report 26 recitava: «È chiaramente antieconomico fare in modo che non vi siano perdite lungo le reti e presso i serbatoi. È altresì chiaro che esiste un li-mite economico di perdite idriche che dovrebbe essere tollerato». Nel 1988 Shore propose un metodo di definizione degli obiettivi basato sul calcolo dei costi ottimali. Nel 1994, a cura del WSA/WCA Engineering and Operation Commitee, fu pubblicato il Managing Leakage – Report C che definiva il livello economico di perdite, come «quel livello di perdite per il quale il costo marginale per il controllo attivo delle perdite è pari al co-sto marginale dell’acqua persa». È importante evidenziare come tutti gli approcci seguiti siano simili. Nel grafico che segue (Farley e Trow, 2003) è rappresentata la relazione generale esistente tra la spesa per interventi finalizzati alla gestione delle perdite e i costi di produzione unitari dell’acqua in funzione del livello delle perdite. In ogni caso i diversi autori sono concordi nel ritenere che una efficiente strategia di gestione delle perdite idriche si debba basare sulla raccolta di un numero di dati sufficienti a definire questa relazione per ogni zona di approvvigionamento o distretto del sistema di distribuzione. In questo contesto gestire praticamente la problematica delle perdite si riconduce allo sviluppo di strategie e pratiche di gestione appropriate, definendo target economicamente sostenibili in termini di livello di perdite di riferimento fissato dal gestore che deve essere nel tempo monitorato e mantenuto. L’attività di controllo delle perdite interagisce in maniera articolata con le diverse strutture operative di un’azienda idrica: gli addetti specializzati nel settore sono interessati all’ottimizzazione della metodologia, i gestori della rete ai benefici indotti dalla gestione della pressione, dalla distrettualizzazione e dalle misure che si rendono disponibili, mentre gli addetti alla gestione delle fonti di approvvigionamento sono interessati alle implicazioni sul bilancio idrico per pianificare le azioni finalizzate a soddisfare la domanda idrica

Screening Investments to Reduce the Risk of Hydrologic Failures in the Headwork System Supplying Apulia (Italy) – Role of Economic Evaluation and Operation Hydrology

The paper introduces and applies a methodology to screen investments aimed at reducing water supply risks due to hydrologic failures in headwork systems for municipal use, based on the principles of cost-benefit analysis. As risk includes both the probability of a failure and its effect, the methodology combines a simulation module of the system, fed by a stochastic hydrologic input to reproduce the probability distribution of the failures, with a metric for supply failure damage provided by the price – demand relationship for municipal water. Benefits are assessed as the averted damage compared to a base case without investments. This approach is then combined with the classic discounted cashflow approach of cost– benefit analysis to allow for the dynamics of both water supply and demand due to trends in population growth, individual consumption and, above all, planned reduction of losses in water distribution networks. The methodology is applied to screen a number of different supply-side projects for the headwork system supplying Apulia, in southern Italy featuring both regulated surface and groundwater resources and providing drinking water to over 4,000,000 persons. The procedure allows both ranking of single projects by their economical performances and the economic evaluation of combinations of different projects. The study also aims to assess the impact of the selected time scale, of cross-correlation among production sites, and of the specification of the demand function on projects' economic indicators. Results show that each modelling assumption has a considerable impact on the value of the economic indicators in absolute terms, but ranking of the different projects seems to be less sensitive to such modelling aspects

A simulation/optimization model for selecting infrastructure alternatives in complex water resource systems

The paper introduces a simulation/optimization procedure for the assessment and the selection of infrastructure alternatives in a complex water resources system, i.e. in a multisource (reservoirs) multipurpose bulk water supply scheme. An infrastucture alternative is here a vector X of n decision variables describing the candidate expansions/new plants/water transfers etc. Each parameter may take on a discrete number of values, with its own investment cost attached. The procedure uses genetic algorithms for the search of the optimal vector X through operators mimicking the mechanisms of natural selection. For each X, the value of the objective function (O.F.) is assessed via a simulation model. Simulation is necessary as the O.F. contains, besides investment costs, also incremental operation costs and benefits that depend on the incremental water amounts which the alternative can provide. The simulation model transforms a thirty-year hydrologic input at daily/monthly scale in water allocations, accounting for the usual non-negativity constraints and using some simple, sytem-specific rules aimed at reducing spills and at sharing water deficits among demand centres. Different O.Fs and constraints have been tested, such as incremental financial cost/benefit minimization under various maximum water deficit constraints scenarios or cost/benefit mimization including scarcity costs. This latter approach has the advantage of implicitly allowing for the magnitude of deficits, but requires the assessment of deficit-scarcity cost relationships. The application of the procedure to a water resources system in south-western Sicily shows that the model is able to converge to results that are consistent with the planning options expressed by the selected O.Fs

Multi-year drought frequency analysis at multiple sites by operational hydrology - A comparison of methods

This paper compares two generators of yearly water availabilities from sources located at multiple sites with regard to their ability to reproduce the characteristics of historical critical periods and to provide reliable results in terms of the return period of critical sequences of different length. The two models are a novel multi-site Markov mixture model explicitly accounting for drought occurrences and a multivariate ARMA. In the case of the multisite Markov mixture model parameter estimation is limited to a search in the parameter space guided by the value of parameter k to show the sensitivity of the model to this parameter. Application to two of the longest time series of streamflows available in Sicily (Italy) shows that the models can provide quite different results in terms of estimated return periods of historic droughts, although they seem to perform more uniformly when it comes to simulate drought-related statistics such as drought length, severity and intensity. The role of parameter selection for the multisite Markov mixture model and of the marginal probability of generated flows in providing results consistent with the characteristics of the observed series is discussed. Both models are applied to the system of sources supplying the city of Palermo (Sicily) and its environs showing the applicability of the newly developed multisite Markov mixture model to medium-to-large scale water resources systems

Sensitivity of regional water supply systems models to the level of skeletonization – a case study from Apulia, Italy

Simulation models supported by state-of-the-art software packages are nowadays available to explore operation rules of regional water supply systems or to select structural alternatives for improving long-term service performances. Given the, sometimes high, complexity of these systems, model calibration can become a lengthy procedure and many runs are necessary before obtaining convincing results. However, even after calibration, depending on system's complexity and the number of time steps investigated, a single run can take up to several minutes, even on state-of-the-art computers, so that simulation time can become a true bottleneck if such models are to be coupled with metaheuristic optimization techniques, such as genetic optimization. This paper investigates the possibility to reduce computational time through skeletonization of the models. The regional water supply system of Apulia, Southern Italy, was adopted as a case study and the software package AQUATOR was employed to model the syste

Linee guida per la redazione del progetto di fattibilità tecnica ed economica da porre a base dell’affidamento di contratti pubblici di lavori del PNRR e del PNC (Art. 48, comma 7, del decreto-legge 31 maggio 2021, n. 77, convertito nella legge 29 luglio 2021, n. 108)

Nel quadro dell’innovazione normativa e procedurale introdotta dal PNRR e dal decreto-legge 31 maggio 2021, n. 77, le Linee Guida sono volte a definire il contenuto essenziale dei documenti, degli eventuali modelli informativi digitali e degli elaborati occorrenti alle Stazioni Appaltanti per l’affidamento sulla base del Progetto di Fattibilità Tecnico-Economica - PFTE, secondo quanto stabilito dall’art. 48, comma 7

The “Diabetes Comorbidome”: A Different Way for Health Professionals to Approach the Comorbidity Burden of Diabetes

(1) Background: The disease burden related to diabetes is increasing greatly, particularly in older subjects. A more comprehensive approach towards the assessment and management of diabetes’ comorbidities is necessary. The aim of this study was to implement our previous data identifying and representing the prevalence of the comorbidities, their association with mortality, and the strength of their relationship in hospitalized elderly patients with diabetes, developing, at the same time, a new graphic representation model of the comorbidome called “Diabetes Comorbidome”. (2) Methods: Data were collected from the RePoSi register. Comorbidities, socio-demographic data, severity and comorbidity indexes (Cumulative Illness rating Scale CIRS-SI and CIRS-CI), and functional status (Barthel Index), were recorded. Mortality rates were assessed in hospital and 3 and 12 months after discharge. (3) Results: Of the 4714 hospitalized elderly patients, 1378 had diabetes. The comorbidities distribution showed that arterial hypertension (57.1%), ischemic heart disease (31.4%), chronic renal failure (28.8%), atrial fibrillation (25.6%), and COPD (22.7%), were the more frequent in subjects with diabetes. The graphic comorbidome showed that the strongest predictors of death at in hospital and at the 3-month follow-up were dementia and cancer. At the 1-year follow-up, cancer was the first comorbidity independently associated with mortality. (4) Conclusions: The “Diabetes Comorbidome” represents the perfect instrument for determining the prevalence of comorbidities and the strength of their relationship with risk of death, as well as the need for an effective treatment for improving clinical outcomes

Antidiabetic Drug Prescription Pattern in Hospitalized Older Patients with Diabetes

Objective: To describe the prescription pattern of antidiabetic and cardiovascular drugs in a cohort of hospitalized older patients with diabetes. Methods: Patients with diabetes aged 65 years or older hospitalized in internal medicine and/or geriatric wards throughout Italy and enrolled in the REPOSI (REgistro POliterapuie SIMI—Società Italiana di Medicina Interna) registry from 2010 to 2019 and discharged alive were included. Results: Among 1703 patients with diabetes, 1433 (84.2%) were on treatment with at least one antidiabetic drug at hospital admission, mainly prescribed as monotherapy with insulin (28.3%) or metformin (19.2%). The proportion of treated patients decreased at discharge (N = 1309, 76.9%), with a significant reduction over time. Among those prescribed, the proportion of those with insulin alone increased over time (p = 0.0066), while the proportion of those prescribed sulfonylureas decreased (p < 0.0001). Among patients receiving antidiabetic therapy at discharge, 1063 (81.2%) were also prescribed cardiovascular drugs, mainly with an antihypertensive drug alone or in combination (N = 777, 73.1%). Conclusion: The management of older patients with diabetes in a hospital setting is often sub-optimal, as shown by the increasing trend in insulin at discharge, even if an overall improvement has been highlighted by the prevalent decrease in sulfonylureas prescription