CEMEPE , Skiathos island, Greece , June 24 to 28, 2007

1. CEMEPE, Skiathos island, Greece, June 24 to 28, 2007 A novel systemic approach to water resources optimization in areas with limited water resources E. Kondili1*, M. Mentzos2, C. Papapostolou1 1Optimisation of Production Systems Lab, Mechanical Eng. Dept., TEI Piraeus 2 Lab of Soft Energy Applications & Environmental Protection, TEI Piraeus

2. Objective of the work • To propose an optimization method for the distribution of water resources under constrained conditions as they appear in the Aegean Islands • Technical and environmental parameters are taken into account on the optimization problem, as well as cost variations of the different supply sources and water uses accordingly • The proposed approach may form the basis for a water planning decision support system in areas with limited water resources

3. Water shortage, an urgentproblem… • This year, the problem of limited water recourses has been widely discussed, due to the intense character of the water shortage. • Many infrastructure projects have been planned for the islands (especially desalination plants) • If the current weather dominates during the next year, then the availability of water in the proper quantity and quality, will become a vital and in some cases an unfeasible problem

4. Description of the problem 1/2 • In Greece, and more specifically in the Aegean Islands, water demand and supply is a difficult problem that needs to be assessed and has either a temporal character (appears only in summer months) or a permanent one in extreme cases (through out the year)

5. Description of the problem 2/2 • Optimization models, as well as decision support systems have been implemented either for the optimal allocation of water resources or for the optimization of water systems. Nevertheless limited research work has been conducted in the field of the water supply chain management • The water shortage problem occurs when the demand exceeds the local availability and different users have conflicting demands

6. Water resources management in the Aegean Islands 1/3 Extended water shortage problems are faced in Cyclades and Dodecanese Islands mainly due to: • the geomorphology of the area • the low precipitation rate • the temporal increase of the population (tourists arrival especially in the summer months) How can this problem be assessed? • with infrastructure projects (dams, reservoirs, or desalination plants) • or by ship transfer

7. Water resources management in the Aegean Islands 2/3 • Cyclades complex, is mainly constituted from many small and in their majority arid islands • The medium- large sized ones i.e. Syros, Naxos, etc cover their water needs by desalination plants, dams and the existing groundwater resources • The small ones, acquire the demanded water by ship transfer and storage in inland water tanks • During the last decade a water volume of 1,620,000m3 has been transferred to Cyclades with an overall cost 12,524,000 €

8. Water resources management in the Aegean Islands 3/3 • In Dodecanese islands, only the large ones, like Rhodes and Kos, have their own water resources • The rest acquire the demanded quantity through transfer from the large ones • The last years some desalination plants have been constructed • The imported quantity in Dodecanese Islands during the last decade has been 1,620,000m3 with an overall cost 12,524,000 €

9. A Decision Support System implemented in water management… The proposed optimization model taking into account: • The needs of the various users associated with the type of the water use (agriculture, urban uses, industry) • Their priorities • The type and the availability of water supply resources Will allocate the water • Maximizing its total value and • Seeking to the optimal exploitation of the available water resources

10. Basic characteristics of the proposed model 1/2 Typical approach: • Construction of new infrastructure projects or • Water transfer through ships (expensive and unsustainable solution) In this work an optimization mathematical model has been developed • For the management of the water demand (prioritizing of the needs) and the optimal use of the existing water resources Criterion: • the maximization of the water value

11. Basic characteristics of the proposed model 2/2 The objective of this model is to determine: • The appropriate water quantities allocated to each user • The optimal output flows, from each on of the available supply sources

12. The proposed mathematical model 1/5 Parameters

13. The proposed mathematical model 2/5 Variables

14. The proposed mathematical model 3/5 Optimization criterion Maximize Total Value of Water = Total Benefit = Total Cost = Supply Cost + Penalties for the discrepancy between demand and real supply to the users including environmental costs

15. The proposed mathematical model 4/5 Optimization criterion • The benefits represent the water value, and they may be varying with time • They are determined by the specific area, the time interval and the efficiency of the water uses.

16. - The proposed mathematical model 5/5 Model constraints The continuity equation in the water storage tank: Upper and lower bounds of the water in the reservoir: Capacity limitations of each supply scheme: Flows allocated to each user should not exceed the corresponding Demands. Furthermore, it may be desirable to assign a minimum water quantity to some users.

17. Case study – Data 1/2 Case study data:

18. Case study – Data 2/2 Monthly water demand Benefits from the water use(€/m3)

19. Case study – Results Results, water allocation in the users Model results – water storage The water is mainly distributed to the water users with the highest water value. Consistently the water quantities stored in the tanks are greater during the winter whilst practically annihilating during the summer

20. Conclusions • The current model sets the fundamentals for a Decision Support System which will be able to support the allocation of the water flows from each supply source, compromising the demands and priorities that are assigned to each user. • This approach of water systems planning provides the capability of an integrated study and investigation of the role of all the system parameters and gives a better insight to the problem of the optimal allocation of water resources, considering the value and priorities of the water usage.

21. Support • This research has been conducted within the framework of the ARCHIMEDES II Environment Funding of Research Groups, cofunded by the EU and the Greek Ministry of Education.