SYSTEM DYNAMIC METHODOLOGY APPLICATION IN URBAN WATER SYSTEM MANAGEMENT

http://www.iaeme.com/IJCIET/index.asp 93 [email protected]

International Journal of Civil Engineering and Technology (IJCIET) Volume 6, Issue 7, Jul 2015, pp. 93-112, Article ID: IJCIET_06_07_011 Available online at http://www.iaeme.com/IJCIET/issues.asp?JTypeIJCIET&VType=6&IType=7 ISSN Print: 0976-6308 and ISSN Online: 0976-6316 © IAEME Publication ___________________________________________________________________________

SYSTEM DYNAMIC METHODOLOGY APPLICATION IN URBAN WATER SYSTEM

MANAGEMENT Jure Margeta and Snježana Knezić

University of Split, Faculty of Civil Engineering, Architecture & Geodesy, Water Resources and Environmental Management

Department, 21000 Split, Matice Hrvatske 15, Croatia

Željko Rozić Faculty of Civil Engineering, University of Mostar, BiH

ABSTRACT Urban water system management is a complex task which takes place

within a number of constraints. It is particularly related to developing

countries with limited amount of available data when important decisions

have to be made regardless of such unfavourable situation. Therefore, for

decisions regarding urban water system management it is important to know

the consequences on all segments of the management system in the future

period. Various methods and models of system engineering are used in order

to achieve this. The work presents the application of System Dynamics (SD)

methodology for analyse of the urban water system. The methodology was

implemented in the water system of Mostar in Bosnia and Herzegovina. The

system dynamics model is a mathematical realization of the developed

interactions among different system variables, quality and quantity, over time

and is comprised of two physical subsystems namely water supply and

wastewater and subsystem. The object-oriented programing (OOP) has been

use for the SD methodology realisation. The obtained results confirm that SD

methodology and OOP can be successfully applied in the management of the

urban water system in developing countries. The method is very flexible and

easy to adapt to system characteristics and objectives of the analysis. It has

been found that application of object-oriented programming is suitable tool

which cans help create policies for urban water system management.

Key words: Urban Water System, System Dynamic Methodology, Object-Oriented Programming, Sustainability, Price of Water, Mostar, Bosnia and Herzegovina.

Cite this Article: Margeta, J., Knezić, S. and Rozić, Ž. System Dynamic Methodology Application in Urban Water System Management. International

Jure Margeta, Snježana Knezić and Željko Rozić


Journal of Civil Engineering and Technology, 6(7), 2015, pp. 93-112. http://www.iaeme.com/IJCIET/issues.asp?JTypeIJCIET&VType=6&IType=7

_____________________________________________________________________

1. INTRODUCTION The world today is faced with a growing number of inhabitants, concentrated in all major cities, mostly in the coastal marine zone [1] and [2]. Cities should strive for urban areas that contribute to local, regional, and global sustainable development. Naturally, this also applies to urban infrastructures and services, including Urban Water System (UWS), Figure 1. Thus, sustaining UWS is an imperative because it is of existential importance for urban areas. The UWS comprises: water supply infrastructure, sanitation infrastructure, drainage infrastructure, natural water bodies, institutional and non-institutional stakeholders, and mechanisms for financing, operation and managing the infrastructure.

The challenge of urban development is to absorb urban growth while solving the environmental and social equity problems arising from economic and physical concentration. Water supply and sanitation, drainage and flooding prevention, pollution control, are infrastructures which significantly reduce environmental health problems and thus contribute to the sustainability of cities and sustainable development in general. The biggest challenge for UWS operation is to keep water and wastewater flowing at affordable rate, without threatening the urban and wider natural environment. It means that is necessary to apply integrated urban water management that is based on the recognition that the UWS is best designed and managed in a holistic manner. Urban water system management is an important segment of growth and sustainability of every city especially in developing countries. The social-economic state of urban midst, its sustainability and productivity, depend on the state and development stage and efficiency of the UWS. Management and development of the UWS is a complex task which is solved within a number of constraining frames: financial, personnel, infrastructure, legislative, environmental, cultural, civilization, etc.

The traditional management model, mainly based on experience acquired throughout years of work, is neither sufficient nor productive any more. The systems are complex, especially large ones, with a whole range of elements and processes, which could not be effectively managed nor controlled with such models. Like all complex problems and systems, UWS is also solved by system analysis process. The problem solving methodology includes various methods and techniques, which can be divided into two main groups [3]: (i) optimizing techniques and methods; (ii) simulation techniques and methods. Simulation is necessary for describing and understanding the system and processes within, while optimization is used to improve its aspects, such as performance, efficiency, or quality. Both methods are generally used, through development and implementation of adequate decision support system. A feature of these models is that they can't adequately include in process simulations non-technical system elements, social, cultural, economic and others which affect the UWS sustainability, such as simulation of the effect of increased water prices. Second problem is that reliability of such models depends on huge amount of quality data and important decisions have to be made regardless of the fact that less developed UWS lacks of such data.

System Dynamic Methodology Application in Urban Water System Management


Figure 1 Conventional coastal UWS boundaries and direction of extension [2]

There is a need for appropriate management tools which take into consideration such situations as well as all system elements, functional connection of different parts of the system and physical infrastructure, city areas and associated water resources, as well as social economic aspects of the problem. In view of the aforesaid, it is obvious that particular attention must be given to proper management and control of the UWS, respecting the needs and plans for sustainable growth and development of cities, as well as all constraints, primarily those related to environment. These systems and problems are solved with the System Dynamic (SD) methodology [4]. That is simulation methodology based on system theory. The main advantage of such approach is in analysis of the entire system that leads to more sustainable solutions then separate design and management of elements of the system [5].

This paper will present this approach and a modelling tool, ''Object-Oriented Programming'' (OOP) [6], used in UWS management in a holistic manner. It represents a new way of problem approach with a group of models based on real world concept. Implementation of OOP in integrated UWS management will be presented, i.e. its possibilities and characteristics [7]. The paper begins with the description of basic characteristics of SD methodology, OOP and continues with description of the development of an integrated model and case study for the city of Mostar. Second part of the paper shows a segment of the results and experiences gained during the implementation to UWS analysis.

2. SYSTEM DYNAMIC METHODOLOGY AND OBJECT-ORIENTED PROGRAMMING Modelling of complex systems such as UWS requires a specific approach, because processes in which management policies are defined must count on full understanding of the effects of the proposed solution and possible system feedback. UWS modelling can be divided into two main groups: (1) mathematical modelling of certain technical subsystem, such as pipeline, network, water reservoir, etc. and (2) modelling of the system in a wider sense, representing expansion of a classical technical view of other non-technical system elements (economic, organizational etc.). The SD methodology

Conventional Boundaries of Urban Water System

Sewerage

Stormwater

Drinking

Water supply WATER

SOURCES

RIVER

BASIN-

OTHER USES

SEA WATER MARINE

RESOURCES –

ECOSYSTEMS

URBAN AREA

NATURAL ENVIRONMENT



is the approach that helps create management policies in a holistic manner [5]. The SD principle is applied to all types of systems, which can be described as systems with feedback, and enables understanding of the system, not only in the context of technical-technological solutions, but also in the context of social, political and economic conditions [8]. The origin of the paradigm ''system dynamics'' lies in Forrester's work on systematic approach as an intellectual tool for modelling complex systems and consists of the process of recognizing the objects and their connections within the system, in order to simulate its functioning [9] [10]. The SD is mathematical realization of the developed interactions among system variables over time and is comprised of four sectors, system environment, UWS infrastructure, consumer and finance. From the technical point of view, many intuitive solutions develop in the context of the so-called negative first-order feedback loops which seek solution within one objective and based on one state variable of the system. During modelling of dynamic behaviour of the model, four basic structures should be recognized: (1) system limit, (2) feedback, which is the basic structural element within the limits, (3) system state variables that represent accumulation within the feedback, (4) variables that represent the course and show activities within the feedback.

Both SD methodology and OOP have been applied in UWS management. N. Grigg [11] presents a retrospective view to SD methodology, thus showing how to apply quantitative analysis to the urban water supply system using OOP. Junying [12] applied OOP on urban water infrastructure management. The model comprises water demand, perspectives for urban development. Recently, the methodology of system dynamics has been presented for studying water and wastewater network management with respect to the financially sustainable management of UWS [12], [13].

Object-oriented programming (OOP) is a very suitable programing for system dynamic model development. The type of programming in which programmers define not only the data type of a data structure, but also the types of operations (functions) that can be applied to the data structure. In this way, the data structure becomes an object that includes both data and functions. In, addition, programmers can create relationships between one object and another. OOP are widely implemented in areas of engineering and programme software and have been introduced to meet the requirements of complex and dynamic systems. The advantages of the OOP lie in its simplicity [8], because ''what if'' scenarios can very easily be constructed and, therefore, insight to system behaviour can be gained. On the other hand, the principles of ''system dynamics'' are uniformly applied to social, natural and physical systems.

In this paper OOP is applied to UWS management of the city of Mostar, in order to make the complex system more understandable to both managers and decision makers. The platform ''STELLA'' has been foreseen. Dynamic behaviour of the system is generated within feedback loops, Figure 2a [7] [14] [15]. Feedback loop consists of stock – state variable of the system and course that represents inflow of information and matter. Equations which express system policies, and explicitly or implicitly contain objectives, are assigned to flows through regulators. The flow regulator equation represents a detachment from the objective and formulates action which is the result of that detachment. Stock and flow, i.e. flow regulators, are the main functional elements of the system structure. Levels serve as sources, but can also serve as constraints and inseparable part of the flow. The other two basic elements are converter and connector (Figure 2b). The converter converts input data into output data and can represent information or material quantities. The connector connects



stock and converters, stock and flow regulators, interconnects converters, and transfers numerical values, i.e. information. Symbols ''cloud'' are sources or destinations of flows, going from or to external surroundings and are controlled only by conditions within the system.

The simple loop of feedback Complex loop with one converter

Figure 2 The loops of the model

Interrelations and connections of various previously described objects, presented by the model are a reflection of functional dependencies within the system, and dependences with external interaction systems and surroundings. The conceptual system development generally consists of four phases:

• system analysis (problem identification and defining system functions);

• creation of simulating system (development of the overall architecture of the system);

• creation of system objects (development based on demand analysis); and

• implementation – programming (transfer of object groups and links into the programme).

The results of process are three models:

• object model (describes the physical structure of the system);

• dynamic model (describes profane connections in the system); and

• functional model (describes functional connections among the variables of the system being simulated).

The presented steps of system modelling have been applied in UWS management of the city of Mostar.

3. URBAN WATER SYSTEM MODEL DEVELOPMENT Unlike other methods and techniques, the described methodology starts from a unique modelling approach of all segments (elements) of the system, so that their integration would be on the same level of abstraction, and therefore facilitate and improve that part in development and analysis of the system. The application of ''system dynamics'' paradigm and implementation through OOP enables implementation of planning and control process of UWS, by unique treatment of entity as an object, regardless whether entities represent consumers, concepts, models, or other parts of consumer interface; and connecting all those objects (system elements) into one integral system.



In preparation of the UWS management model the start-up point should be system component analysis, followed by analysis of all elements, starting with operative-physical level, through management and strategic level (Figure 3). After that, the flow of information connection system should be established, i.e. interdependence between various systems and subsystems and defining their functional dependence through relation connections and ratios. The connections and ratios are simple algebra functions combined with logical and special – adjusted application functions.

EXTERNAL STRATEGIC FRAME

MANAGEMNET FRAMEWORK

Figure 3 General concept of integral urban water system management in a holistic manner

The system is modelled gradually in three subsequent steps. The simplest, but basic model of water in the UWS is prepared first, by which the following is simulated: state and changes of water quantity in the whole system, i.e. water supply system from intake to users; collecting/sewerage system, wastewater treatment plant and outflow into the recipient.

In the second step water quantity model is expanded by introducing water quality parameters/variables including mass balance and water quality parameters concentration calculations in the system. Finely a more complex model is then worked out by expanding the quantity and quality model with economic and managerial factors, or social-economic factors and policies. Thus, an integral model for analysis of urban water operation is obtained, which contains all infrastructure system elements (configuration), describes main changes of water quality and quantity variables in the system, and social-economic processes. The model can be more or less complex, depending on requirements and characteristics of the system as well as available data. At the beginning of the problem-solving process a simpler concept of the system and problem is modelled in order to familiarize with the behaviour of the system and model. In the next steps, the system expands to include other elements and processes of the system according to the needs and objectives of the planed research. The first step is to develop a system configuration model or physical infrastructure sector.

PHYSICAL

FRAME –

DEVELOPED

URBAN WATER

SYSTEM WITH

SURROUNDINGS



3.1. Model 1. – Urban water system configuration and water balance

The Model I describes UWS configuration and includes the following main structural elements of the system:

1. The system of main model levels with flow and influence rates consists of the following elements:

(i) water resources – water intake, (ii) inhabitants and other users of the system, (iii) recipient.

2. The system of main converter elements with connectors and defined directions of connectors consists of:

• water intake,

• water supply system (capacity, system state, losses),

• need for water – demand for water,

• potable water purification plant,

• industry consumption,

• public consumption,

• total water consumption,

• wastewater quantity,

• other water,

• sewerage system (capacity, system state, losses),

• wastewater treatment plants.

The purpose of the model is to determine the amount of water in all main elements of the UWS based on input and output quantities and their respective processes of transformation (converters). The system is divided into subsystems and for each subsystem a dynamic water balance is modelled, that is used to define the state of the amount of water in the entire planning period in accordance with the established trends of changes of input variables and conditions/development of the system. Subsystems and components of their water balance are:

1. Water supply subsystem:

- Water intake – water intake balance, - Water use – water consumption balance, - Water losses – water loss balance,

3. Wastewater subsystem:

- Wastewater generation – balance of inflowing wastewater into the subsystem, - Sewerage system – balance of wastewater in sewerage network

4. Surface water subsystem:

- Surface water generation– balance of inflowing rainwater, - Drainage system − water balance in the drainage system, - Overflow – overflow balance.

5. Wastewater treatment subsystem:

- Wastewater treatment plant– water balance in treatment plant, - Outflow – balance of water out flowing into the recipient.



The balance is determined for the key variables that determine the balance of individual components of the subsystem, the subsystem as a whole and the system as a whole, for each fiscal year in the planning period, using the mass balance equation

V = Qin – Qout (1)

V – Accumulation

Qin – Input

Qout – Output

Appropriate convertors are introduced in the model, as well as capacity constraints of individual components in the system (for example water intake):

Qreq; for Qreq ≤ Qava

Qreq = { (2)

Qava; for Qreq > Qava

Qreq – Q needed

Qava – Q available

In this way, by changing certain input values it is possible to obtain the balance state of system components, as well as the system as a whole and the dynamic trend of changes in the entire analyzed period. For example, changes of: the number of inhabitants and other users, water use quantity per capita/tourist, % of connection to the network, water losses, capacity of water sources, rehabilitation of sewerage system etc. It is possible to analyze a full range of development scenarios and thus the situation in the urban area, UWS, environment and the impact of management decisions in the entire planning period. All information is given as numerical values and graphical display (trend of changes) so that changes are easily visible to all participants.

The main components of this model are shown in Figure 4 (black colour). The developed model comprises more elements than presented here. An abbreviated version is presented for the purpose of a better overview of structure model. In the next step Model 1 is upgraded with components that describe the state of quantities of certain parameters of water pollution.

3.2. Model 2. Water quality characteristics in the system

Upgrading enables the analysis of water quality and dynamic balance of certain substances in the whole UWS and related environment; water supply, wastewater and surface water subsystem and receiver. The following is modelled in the water supply system: changes in water quality in the system, work of drinking water treatment plant, including water disinfection. A balance of waste substances found in certain parts of the sewerage system are determined, as well as of those that flow to the wastewater treatment plant, in the whole planning period. Afterwards, the plant sub-system/plant operation and balance of certain pollution parameters and discharge of treated water into the recipient and the state in the recipient are described. All this is performed by using the equation of mass balance and certain types of reactors



(convertors). In a similar way it is possible determine pollution load generated by a system of surface waters and the burden of pollution in the recipient (river) is determined throughout the whole planning period.

In the presented example only the BOD5 parameter in wastewater system has been presented. The main components of this model are shown in Figure 4 (blue colour). The issue of water quality in the water supply system or rainfall sewage is treated similarly.

Figure 4 Model of the urban water system; black colour – Model 1; blue colour – Model 2; red colour – Model 3

All indicators of the state of wastewater quality can be expressed with the following values:

• average quantity of organic matter in wastewater (kg/day), and

• Concentration of certain parameters – pollution indicators (mg/l or kg/m3).

It should also be stressed that, for the purpose of simplicity and good layout of the model, only one indicator has been included in this presentation – the water quality indicator BOD5. Naturally, the model can analyse other indicators (total suspension solids, COD, NH3, N – nitrates, P – phosphorus, etc.). Based on the analysis of wastewater, state of recipient and the selected degree and mode of wastewater



treatment, all components and their interference, as well as the state of the recipient, can be analysed.

3.3. Model 3. Management component of the urban water system

The following upgrading of the model refers to the use of the model to obtain information necessary for the economic and financial analysis and creation of management policies for the system. The upgrading of the water quality and quantity model includes non-technical control variables. This primarily refers to the economic system, i.e. to economic factors as the main drives of development and system sustainability. For example, the impact of water fee changes on the water balance, concentration of waste substances in UWS, plant pollution load and impact on the environment are analyzed. In a similar way, it is possible include other variables and management issues (e.g. climate change). In this example only key parameters that characterize the economic system will be used for extension. The main components of the model are shown in Figure 4 (red colour).

The presented model can be expanded and include a number of other processes in solving the problems of sustainability of the UWS. Once the model has been developed, it can be used for various analyzes, by introducing new variables and processes. Modelling start with simpler analyzes and gradually expand them to the desired level of complexity, according to the needs, but also to the available data. In this way, the user gradually familiarizes with the system and its behaviour. The model is supplemented based on new information and analysis is more efficient and useful. It is a great advantage of the presented procedure.

4. CASE STUDY The developed system dynamics UWS model can be used by water utilities to achieve a variety of utility short and long-term objectives as well as to establish appropriate utility policies. As an example of possible application UWS of the city of Mostar have been used. Mostar is the largest city in the region of Bosnia and Herzegovina, situated on the river Neretva. The city and its water infrastructure suffered great damage in the last war, partly due to destruction and partly due to lack of maintenance. The UWS is underdeveloped, especially sewerage system. Throughout the last decade great efforts are being made to improve the system and increase its efficiency. Parts of this process are research works and some results are presented in this example.

4.1. Main input data

• Population: 80000 − 87000 (growth trend 0, 55 – 0,30 %);

• specific consumption: 250 l/inhabitant/day, depending on civilization factor which is within the range of 1,0 – 1,7 for the period of 20 years;

• Industry water consumption: 100 l/s (with annual consumption increase of 0,5 %);

• Public water consumption: 80 l/s (with annual consumption increase of 0,5 %);

• losses in water supply system: 60 %;

• development level of water supply system: 95 %;

• wastewater quantity: 80 % of specific consumption;

• development level of sewerage system : 85 %;

• losses in sewerage system: 30 %;

• water resources: average outflow in the Neretva River basin 150 m3/s and average groundwater abundance of the Neretva for the Mostar area: 0,4 m3/s;



• total number of equivalent inhabitants (PE)

• recipient flow (the Neretva River – critical dry period − min. flow): 50 m3/s;

• discharged wastewater: obtained as output parameter of the water quantity model in the system;

• concentration of BOD5 of recipient on upstream section: 2,0 mg/l;

• unit load of BOD5: 60 gr/PE/day (actual state and increased up to 65 gr/PE/day for the planned period);

• wastewater mixing/dispersion coefficient in recipient: Y (from 0 to 1,0), depending on hydraulic parameter and distance of measuring section from discharge point;

• load of recipient : 9 600 kg/day – measured on upstream section;

• permitted concentration for river water category II of the Neretva: 4,0 mg/l;

• planning period is 15 years, and time step is 1 year.

The analysis has been made in order to answer three basic policy questions:

• What would be the result/state of UWS in the next 15 if the current way of managing continued;

• In what way and how much do certain factors affect the behaviour, state and sustainability of the system as a whole in that period;

• Which are the main factors, i.e. factor ranking in relation to positive effect on system sustainability.

Currently the biggest problems related to the functioning of the system are related to:

1. large water losses in the water supply system, (ii) low level of payment of services, (iii) an increase in water use per-capita, (iv) direct and indirect pollution of the river due to low level of population connected to the sewerage system, permeability of the sewerage system and insufficient treatment of waste water and overflow waters from combined sewerage system.

4.2. Analyses of the impact of population and water consumption rate change on the UWS characteristics The OOP utilization of analyses can be simple and complex. Simple analyses include the estimate of the system behaviour in the planned period, such as water demand in the coming planned period (Figure 5), wastewater quantity analysis (Figure 5), water losses and estimate of effects which specific consumption has on water requirements (Figure 6), if retaining the current level of system development, technological features (water losses, infiltration in sewers, etc..), the price of services and collection of fees for services.



Effects on population increase on water consumption (l/s)

Effects on population increase on wastewater quantity (l/s) for the planned period

Figure 5 Effects on population increase on water consumption and wastewater quantity (l/s) for the planned period

Effects of per capita water use in the planned period on water consumption (l/s)

Effects of per capita water use in the planned period on wastewater quantity (l/s)

Figure 6 Effects of per capita water use in the planned period on water consumption and wastewater quantity (l/s)

These results clearly show the changing water balance in UWS in the future period with a planned increase of the city and its population and the existing level of technological development of the system.

More complex analyses are estimates of effects of the system on water quality and wastewater quantity flowing to the treatment plant and the recipient, Figure 7.



a)Effects of population increase on generation of BOD5 in wastewater system and at the plant

(kg/day)

b)Effects of population increase on load of BOD5 (kg/day) discharge in recipient, case without

wastewater treatment

Figure 7 Effects of population increase on generation of BOD5 in wastewater system and recipient

The model provides direct analysis of population effect on BOD5 concentration in the recipient (mg/l). Figure 8 shows two cases: (i) wastewater is not treated and (ii) wastewater is treated at treatment degree of 90%, (wastewater mixing coefficient in recipient is Y=0,6).

Figure 8 graphic presentations of population increase effects on BOD5 concentration in the recipient for the case when wastewater is not treated (1) and when it is fully treated (2)

A simple and realistic graphic presentation of results and trends of change of the system state facilitates in the planning period, contributes to a better understanding of the problem and making sustainable decisions. Namely, data and number of information increase significantly, enabling full perception of the problem.

The result of the analysis is the fact that the UWS is unsustainable. All trends of parameter changes in the planning period are negative in relation to the desired sustainability of the system and the environment. The system must be improved in



order to be functional and sustainable. Someone might say that it could be known without analysis. True, it is obvious to experts but the difference is that implementation of the displayed enables us to follow the trend of changes and the situation in the future, as well as interdependence/impact of individual parameters. Trends of changes and the situation are easy to understand for decision makers. By application of the presented model it is possible to quickly implement a whole range of analyzes of various scenarios and management decisions, with the aim of minimizing the use of resource inputs into the system, maximizing the desired effects and reducing adverse impacts. For example, the analysis of the effects of reduction of water losses from the water supply network and sewerage system, increase of % of connections to the system, on the water balance, wastewater and economic state of the company and pollution of the river.

4.3. Analyse of water fees change impact on UWS characteristics Analyses of effects the economic and financial factors such as water fees have on the state and behaviour of the system are of particular importance. These analyses are important, because they give a full image of the user-owner relation. These several examples of possible analyses are presented. The economic system structure is composed of the following components: water price (Figure 9), water tariff collection, municipality income, municipality income per capita, system operating and maintenance costs, general standard, etc.

Figure 9 Perspectives of water price growth for the planned period; KM/m3 (KM-BiH currency)

The main driving factor of the existing economic system is water price. The creation of normal market and economic relations in the UWS requires formation of a certain water services price, which includes full costs of the system. The change in water price creates new circumstances in view of establishing the new organizational and institutional management unit, as well as in water demand processes, i.e. water consumption. Increase of water price up to a certain limit (depending on social conditions) creates the sufficient and required condition for sustainable development of the UWS. Following is the information regarding water fee changes, relevant for decision makers:

• reduction of losses in water supply network;

• reduction of specific water consumption, or total water intake;

• increase of municipal income (if the municipality is the owner);



• total wastewater quantity;

• BOD5 load of wastewater system;

• BOD5 concentration in river; etc.

The main presumptions, built in the model are:

• more money or higher revenue, better maintenance and operation of the system and therefore less water losses and less leakage of wastewater;

• more money, better connection of inhabitants to water supply and sewerage system;

• Higher price, higher saving and reduction of per capita water consumption.

Relations describing these interdependences are defined in the model based on experience and data from literature. Each particular case requires specific research and definition of functional connections among these factors. The example of the effect of water price change on overall water consumption is presented in Figure 10. The difference in total consumption is observable, i.e. the effect of economic factor, ''water price'', as the key economic parameter. Economic factors affected the reduction of:

• per capita water consumption and

• water losses in water supply network.

Figure 10 Water consumption (l/s) in settlements: 1. price increase of 1–4 KM/m3; 2. water price unchanged, 1 KM/m3

Based on that parameter solely (water price) a detailed analysis can be conducted for determining the overall tariff system, where optimal water price would be defined for such system, i.e. cost-effectiveness, efficiency, productivity, etc. would be determined. Similar analysis could be conducted for other parameters and their sensitivity and effect on the overall system could be seen, Figure 11.



Figure 11 Wastewater quantities in planned period (l/s): 1. price increase of 1–4 KM/m3; 2. water price unchanged 1 KM/m3

Figure 12 presents the analysis how economic factors affect the quantity and intensity of wastewater flowing to the treatment plant and recipient, i.e. the conditions of wastewater discharge.

a) Concentration of BOD5 (mg/l) in wastewater flowing to the treatment plant: (1) water price

increase; (2) price unchanged

b) Quantity of BOD5 (kg/day) in wastewater flowing to the treatment plant: (1) water price

increase; (2) price unchanged

Figure 12 Change of quantity and concentration level of BOD5 at wastewater treatment plant influenced by economic factors.

In the context of the previous analysis, the effect of economic factors, i.e. ''water price'', on load and concentration of BOD5 of the recipient, can be perceived; Figure 13. The initial state of BOD5 concentration in the recipient is 4,0 mg/l for both models. At the end of the planned period the BOD5 concentration increase is higher in the first case (4,8 mg/l), than in the second (4,35 mg/l), as the result of change in quantity and concentration of wastewater.



Figure 13 Change in concentration of BOD5 (mg/l) in recipient, with treatment degree of 0 % and Y = 0.6 for the cases of: (1) price increase; (2) unchanged price

The model enables simulation and changes of municipality income from service charge; Figure 14. The income increases in both cases, and at the end of the planned period it is 1.3 × 106 KM/month, which is also a significant increase in municipal budget. This creates more favourable conditions and bigger possibility for rehabilitation of urban infrastructure (water supply and sewerage), as well as for construction of new infrastructure.

Figure 14 Increase of municipality income (KM/month) from water services charge in two cases: (1) water price increases from 1,0 KM/m3 to 4,0 KM/m3 (model MM-UWS); (2) water

price is constant and is 1,0 KM/m3 for the entire planned period

Based on the analysis of effects of various components on the system itself and the surroundings, the following conclusions can be drawn:

Income from water services charge, with defining the water price and its increase until the end of the planned period, which results in increase of municipality budget,



and on the other hand, reduces water consumption. It is the only possible and sustainable approach to water use;

By introducing the economic category in the UWS management model, all other relations are created within the system, as well as in economic relations, i.e. in the society as a whole;

Municipal income (or income of the company managing UWS) increases considerably, enables a number of activities regarding organization and functioning, and provides rehabilitation measures for the existing infrastructure and measures regarding construction and improvement of the new water supply and sewerage network;

All changes of parameter values within the system are the result of ''water fee'' increase; therefore, it is the main managerial element for sustainability of the system.

The aforesaid does not present all analyses which have been conducted by application of the developed system dynamics model. Presented methodology enables analysis of both system behaviour and its influence to natural and socioeconomic environment in a situation with a limited budget, as it is usual in developing countries like Bosnia and Herzegovina. Such approach fully supports making feasible decisions in given circumstances. Other numerous analyses are also possible, which improve significantly the level of information of decision makers and managers, considerably improving the management reliability and sustainability.

6. CONCLUSION Based on the aforesaid, it can be concluded that the system dynamic methodology is suitable, acceptable and desirable for the management of the UWS equally in developed as well as less developed urban areas and therefore should be used more. Design and management of the UWS based on an analysis of the entire urban water system as it is presented will lead to more sustainable solutions then separate design and management of the system elements. This particularly applies to cases when the local owner is indebted and when there is a need for a more complete analysis of the effects of indebtedness and investment on the sustainability of the communal water system. Similar refers to the analysis of the impact of climate change on UWS and similar problems where equal importance is given to economic, ecological and social features of the problem and input data are global and imprecise [16]. The biggest advantage of this procedure is that useful information for management can be obtained based on a restricted data fund as it is case in less develop areas as it is Mostar in Bosnia and Herzegovina.

The actions identified as needed as the result of the study include:

• Reduction of water losses from water supply systems to the acceptable level of 15–20% soon as possible

• Introduction of economic prices of water uses

• Providing of alternative water sources for the water supply systems supplied only from one source

• Proclamation of sanitary protection zones for water intake

• Controls on pollution from solid waste by implementation EU directives

• Modify existing predominately combined sewerage system into separate system

• Control of surface water flow within urban areas by development of appropriate storm water drainage system.



The OOP is flexible programming tool, very easily adaptable to the dynamic system methodology, using a whole range of interconnected and interdependent parameters and elements. One of the principal advantages of OOP techniques over procedural programming techniques is that they enable programmers to create modules that do not need to be changed when a new type of object is added. A programmer can simply create a new object that inherits many of its features from existing objects. Therefore, it can be concluded that implementation of the OOP has the following advantages:

• simple approach in preparing a full and comprehensive (integral) management model,

• faster and simpler formulating of new alternatives or management scenarios then traditional simulation and optimization techniques,

• easy and simple system transformation and adjustment to other conditions and states of the system,

• possibility of planning and forecasting the state of the water system for a certain period of time.

Modelling is simple and has the features of "learning by working" so that at the beginning of the problem solving process it is not necessary to have all the information, but only basic. During the development of the model and by gradual problem analysis, the model and system are upgraded on the already achieved results so that the process is rational and reliable. All stakeholders can be involved in the implementation of the model and ongoing analysis of the problem during the whole period of operation. Because of the graphical representation of the system and dynamic characteristics of the process being analyzed, as well as the visibility of the cause and effect connection in the system, everything is easily recognizable even to non-professionals. Stakeholders can quickly and accurately see a result of a certain policy proposal for the state of the system as a whole and related environment. Therefore, stakeholders can easily participate in the whole process of analysis and problem-solving which is very important for decision makers and is a main perquisite for sustainable development. The platform STELLA is simple and easy to apply.

The biggest criticism that engineers usually have relates to the fact that the model is not based on complex hydraulic or similar technological models used for operation simulation of the UWS. They described object systems as overly simplistic models of the real world. However, the purpose of the presented modelling is not an analysis of hydraulic state of the system, but getting information necessary to create system management policies, for which comprehensive technical system modelling is not always necessary, although it is always advisable if there are good input data. The developed models enable enhancing the sustainability of the system in situations where all the technical details of the system and related environment are not well known. We hope that the presented will be useful for engineers and researchers.

REFERENCES

[1] Leslie Roberts, 9 Billion?. Science, Vol. 333(6042), 29. July 2011, pp. 540–543.

[2] UNEP/PAP, Integrated Coastal Urban Water System Planning in Coastal Areas of the Mediterranean, Priority Actions Programme, 2007.

[3] Margeta, J. Book Water resources management. Faculty of Civil Engineering, University of Split, Croatia 1992, (in Croatian).



[4] Elshorbagy, A. and Ormsbee, L. Object-oriented modelling approach to surface water quality management. Environmental Modelling and Software, 21(5), 2006, pp. 689–698.

[5] Stave, K. A. A system dynamics model to facilitate public understanding of water management options in Las Vegas, Nevada. Journal of Environmental

Management, 67, 2003, pp. 303–313.

[6] Simonovic, S. Tools for Water Management One View of the Future. Water

International, 25(1), 2000, pp. 76–88.

[7] Rozić, Ž. Optimization of the performance of urban water system, Ph.D. Dissertation, University of Mostar, Bosnia and Herzegovina, 2009. (in Croatian).

[8] Odanaka, T. Environment system and dynamic management decision. Applied

Mathematics and Computation, 120, 2001, pp. 255–263.

[9] Forrester, J. W. Urban Dynamics. Cambridge: MIT Press, 1971.

[10] Forrester, J. W. Industrial Dynamics. Cambridge: MIT Press, 1961.

[11] Grigg, N. S. Systemic Analysis of Urban Water Supply and Growth Management. Journal of Urban Planning and Development, 123(2), 1996, pp. 23–33.

[12] Rehan, R., Knight, M. A., Haas, C. T. and Unger, A. J. A. Application of system dynamics for development financially self-sustaining management practices for water and wastewater systems. Water Research, 45(16), 2011, pp. 4737–4750.

[13] Rehan, R., Knight, M.A., Haas, C. T. and Unger, A. J. A. Development of a system dynamics for financially sustainable management of watermain networks. Water Research, 47(20), 2013, pp. 7184–7205.

[14] Surendra, H. J. and Deka, P. C. Effects of Statistical Properties of Dataset in Predicting Performance of Various Artificial Intelligence Techniques for Urban Water Consumption Time Series. International Journal of Civil Engineering &

Technology, 3(2), 2012, pp. 60–69

[15] Costanza, R., Duplisea, D. and U. Kautsky. Ecological Modelling on modelling ecological and economic systems with STELLA. Ecological Modelling, 110, 1998, pp. 1–4.

[16] Costanza, R. and Voinov, A. Modelling ecological and economic systems with STELLA: Part III. Ecological Modelling, 143(1–2), 2001, pp. 1–7.

SYSTEM DYNAMIC METHODOLOGY APPLICATION IN URBAN WATER SYSTEM MANAGEMENT

Engineering

Transcript of SYSTEM DYNAMIC METHODOLOGY APPLICATION IN URBAN WATER SYSTEM MANAGEMENT