The Architecture of the WSM Decision Support System
and the GIS Database

1       The architecture of the Decision Support System

The Decision Support System has been implemented in Visual Basic .NET using the Arc Objects COM technology by ESRI, which is also the platform for the GIS Database. The tool was designed according to the four step schema presented in Fig. 1 that involves: (a) the database; (b) the object model linked to mathematical models for water allocation, quality and economic estimations, (c) a logical coordination unit, responsible for the communication with external models, and (d) the user interface that allows for the definition of data and simulation parameters, and the presentation of results through customizable charts, tables and maps.

Special attention has been given to the portability of the DSS. The developed object model and the linked mathematical models can easily be transported to other GIS environments while most GIS functions are generic, implemented outside the modelling procedures and algorithms.

The user of the DSS is not necessarily a hydrologist, an engineer or an economist; such expertise however can be useful during the setup stage when defining the case study region.

Figure 1. The WSM DSS architecture

2         The GIS Database

The GIS Database is the heart of the spatial information system and provides the central storage system that allows communication and intermediate storage between the models. The Database is strictly interrelated with the methodology applied in analyzing and simulating water resource systems and consequently with the WSM Decision Support System. The Data Model has been developed under Arc GIS 8.1. The main output of the data model is an Arc Info geodatabase, which stores information on all spatial and non-spatial attributes and classes included within the model.

Besides the accommodation of available data and the selection of the appropriate platform for facilitating data collection and entering, the GIS Data Model has been developed keeping in mind the final goal of the WSM DSS, which is the analysis of water management strategies in the project case study area. To this end, the Data model is able to:

• to accommodate all data related to the simulation of different water availability scenarios and demand forecasts, including forecasts of pressures;

• to store information on the different water management instruments proposed for the different case studies of the project.

Since the spatial scale of the case studies is variable ranging from a river basin in Portugal (Ribeiras do Algarve) to a small Greek island in the Aegean Sea, one primary aim achieved during the development and the implementation of the data model was to allow for the modelling of those very different systems under a unique but flexible framework.

In this context, the design of the Database was performed in such a way as to adequately describe any system in terms of water resources availability, demand, infrastructure and management options and developmental policies to be formulated within the scope of the analysis.

Within the model, logically related features are grouped together. Thus, the model extends the basic distinctions between water resource systems, demands, infrastructure and administrative structures. The core components of the Data Model are:

• Basic Regional Data, organizing general information of the case study area.

• Water Bodies, representing the most important water bodies, as those are classified in the Water Framework Directive, and the monitoring network.

•  Water Network Data, for modelling the water resource system and infrastructures of the case study region.

•  Administrative Structures, standing for the administrative organization of the region.

•  Time Series, modelling time series data, mostly related to water network objects.

It should be noted that in the approach adopted during the development of the WSM Data Model, some features are represented both as simple features (i.e. points, lines and polygons) and as a complex water network. This allows for the accurate representation of the physical entity (e.g. a lake) and for the particular modelling requirements set out by the Decision Support System.

3 The Object Model of the WSM Decision Support System

The Object Model of the WSM DSS is formulated around the concept of an ESRI geometric network. A geometric network is described as a set of junctions (points) and edges (polylines) that are topologically connected to each other. The network is used to describe the connectivity of flow through the modelled system, incorporating different supply sources, demands and requirements as well as treatment points or monitoring stations.

In the Object Model junction elements are conceptualized as water nodes while the edges that stand for the connections between them are the water links. The objects and their functionality are strictly related to the Water Allocation procedure and algorithms.

Water nodes are classified into three categories (Figure 2):

• Supply nodes, standing for alternative water supply sources and characterized by the monthly available supply;

• Demand nodes, modelling water uses and flow requirements and,

• Transhipment nodes, representing treatment plants and generic network junctions.

Supply nodes conceptually provide water to demanding users through the outgoing links, thus having a water source function, but some of them also have ingoing links, functioning as water accumulators or final receptor bodies. Those are:

• Renewable Groundwater, representing shallow, free groundwater that is continuously recharged by the hydrological cycle. A renewable groundwater is a water source with the further roles of accumulator and receptor body of return flows (end node).

• Coastal Zone, conceptualising a coastal area where seawater is abstracted for desalination, or quality status such as eutrophication is monitored. A coastal zone is a water source and also an end node. As a receptor body, it can receive the return flows from consumptive uses and recharges from aquifers.

• River Reach.  For the modelling purposes of the DSS a river and its tributaries are divided into “river reaches” by a certain number of cross sections. Each river reach is characterised by a physical branch of the river and by its downstream section. A river reach is schematically represented by one river node.

• Reservoir (Storage + Small + Natural Lake), conceptualising three types of reservoirs: a man-made storage reservoir fed either by a natural water course or by pipelines, a small artificial reservoir built to collect rainfall or run-off from a catchment area, or a natural surface lake. A reservoir is a water source with the further roles of accumulator and receptor body.

• Importing, standing for water transfers from a neighbouring area. As a supply node it has the role of water source.

• Fossil Groundwater, conceptualising deep, confined groundwater that is not recharged by the hydrological cycle. Fossil groundwater is a water source but not an accumulator or an end node because it has a no recharge.

Demand nodes are:

• Settlement, conceptualising the civil urban population and infrastructures of a defined area, i.e. a city, a town or a village.

• Tourist site, representing a tourist community exerting a seasonal water demand.

• Irrigation site, standing for the activity of cultivating land either for the survival of land-owners or for commercial purposes.

• Industrial site, representing a productive site producing or supplying goods, services etc. An Industrial Site can be public or private, and is also characterised by its field of application: Petrochemical, Electronics, Aerospace, Food and Beverage, Pulp and Paper, Textile etc

• Animal Breeding, describing the activities of livestock breeding.

• Exporting, representing the amount of water to be exported to a neighbouring area.

• Hydro-electricity production, which takes into account the amount of water requested by a single plant or a group of plants to generate electricity from falling or fast-flowing water.

• Environmental, recreation and navigation requirements, representing non-consumptive demand nodes aiming to address the minimum water requirements of rivers, or the water needs for recreational purposes and navigation.

Three types of Treatment Plants are considered in the DSS:

• Drinking Water Treatment Plant,  standing for a plant treating water in order to make it safe and acceptable for human consumption.

• Wastewater Treatment Plant, describing a plant treating water in order to remove or at least abate pollutant concentrations before water is re-used or discharged into a body of surface water.

• Desalination, conceptualising a plant removing dissolved salts from seawater, brackish water or highly mineralized groundwater.

Two Transhipment nodes have been formalised:

• Network Reservoir, which represents a physical reservoir of very small capacity, which is used to serve the needs of settlements, tourist sites etc. Its contribution in the water allocation is not significant at the monthly time scale used within the WSM simulations. However, as a part of the infrastructure, it has costs for construction, operation etc that can be accounted for.

• Generic network junction, used for maintaining network connectivity and used as an intersection point between links.

Figure 2. Overview of the object model for water nodes

The Water Links of the conceptual water network have two generic characteristic variables:

• the link capacity, which represents the maximum monthly flows allowed, and

• the monthly flow rate, that is the decision variable of the Water Allocation algorithm.

Water link objects are classified in four categories based on the connectivity rules of the network and the particular modeling requirements of the DSS:

• Supply links (pipelines and canals) conveying water from supply sources to demand nodes,

• Groundwater interaction links (recharge and discharge links), representing the natural interaction between surface and groundwater bodies,

• Return flow links, conveying return flows from consumptive demand uses to receptor bodies (surface or groundwater) or wastewater treatment plants, and

• River links representing the natural course of a river water body.

The WSM Data and Object Models implicitly specify a number of connectivity rules, in order to ensure the proper modelling of a water resource system and its correct simulation by the WSM Decision Support System. Modelling requires that some types of edges (water links) have a specific type of start or end junction, or both. For example, groundwater recharge links can only originate from surface water nodes (reservoirs and river reaches) and should end only at renewable groundwater nodes. Additionally, junctions modelling particular types of water sources such as non-renewable (fossil groundwater) or importing from neighbouring regions cannot have incoming edges of any type. To ensure therefore the integrity of network data within the database, network connectivity is modelled within the WSM Decision Support System, with a set of rules that specify which type of junction can be connected to on other junction type, and with what type of edge.