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CEMEPE , Skiathos island, Greece , June 24 to 28, 2007. A novel systemic approach to water resources optimization in areas with limited water resources. E. Kondili 1 *, M. Mentzos 2 , C. Papapostolou 1 1 Optimisation of Production Systems Lab, Mechanical Eng. Dept., TEI Piraeus - PowerPoint PPT Presentation
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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
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
Water shortage, an urgentWater shortage, an urgent problem…problem…
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
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)
Description of the problem 2/2Description 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
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 or by ship transfer
Water resources management in the Water resources management in the Aegean Islands 2/3Aegean 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
0
50000
100000
150000
200000
250000
300000
350000
WA
TE
R Q
UA
NT
ITY
(m
3 )
1997 1998 1999 2000 2001 2002 2003 2004 2005*
YEAR
IMPORTED WATER QUANTITY IN CYCLADES ISLANDS
During the last decade a water volume of 1,620,000m3 has been transferred to Cyclades with an overall cost 12,524,000 €
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 €
0
100.000
200.000
300.000
400.000
500.000
600.000
700.000
800.000
WA
TE
R Q
UA
NT
ITIE
S (
m3 )
1997 1998 1999 2000 2001 2002 2003 2004
YEAR
IMPORTED WATER QUANTITIES IN DODECANESE ISLANDS
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
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
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
The proposed mathematical model 1/5
Parameters
Bjt Benefit for the use of the water from user j at time interval t (in €/m3)
Djt Demand of water from user j at time interval t (m3)
QjtMIN Minimum water flow to user j at time interval t (m3)
Sit Capacity of the supply source i (m3) at time interval t
Pjt Penalty for not satisfying the demand of user j at time interval t (€/m3)
Vmax Maximum volume of water that can be stored in the storage tank (m3)
Vmin Minimum volume of water that should be stored in the storage tank (m3)
Cit Cost of water from supply source i at time interval t (€/m3)
The proposed mathematical model 2/5
Variables
Fit Flow of water from supply source i at the time interval t (m3)
Qjt Water flow allocated to user j at time interval t (m3)
Vt Water volume stored in the reservoir at time interval t (m3)
The proposed mathematical model 3/5
Optimization criterionMaximize 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
∑∑ *j
jtjtt
QB
The proposed mathematical model 4/5
Optimization criterion
The benefits represent the water value, and they may be varying with timeThey are determined by the specific area, the time interval and the efficiency of the water uses.
The proposed mathematical model 5/5
Model constraintsThe continuity equation in the water storage tank:
∑+= 1i
ittt FVV - ∑j
jtQ
Upper and lower bounds of the water in the reservoir:
maxmin <=<= VVV t
Capacity limitations of each supply scheme:
itit SF <=
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.
jtjtjt DQQ <=<=min
Case study – Data 1/2
Case study data:
Time horizon 12 months, time step 1 month
Water supply sources
1:Desalination 2: Ground reservoir, 3: Transfer by ships
Water Users A: Urban Use, B: Irrigation
Water Demand (Figure 1)
Benefits (Table 1)
VMAX, VMIN 1.000.000 m3 and 10.000 m3 respectively
Capacity of water supply
S1=300000, S2=200000m3/month, S3=1000000 m3/year
Water supply cost C1t= 3 €/m3, C2t= 4,4 €/m3, C3t= 7 €/m3
Case study – Data 2/2
0
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200
300
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500
600
700
1 2 3 4 5 6 7 8 9 10 11 12
months
Wate
r Vol
ume
(in
1000m
3)
Urban
I rrigation
Monthly water demand
Months
1 2 3 4 5 6 7 8 9 10 11 12
BAt 5 5 5 15 20 25 25 25 10 5 5 5
BBt 5 5 5 5 5 5 5 5 5 5 5 5
Benefits from the water use (€/m3)
Case study – Results
0
100
200
300
400
500
600
700
1 2 3 4 5 6 7 8 9 10 11 12
months
Wat
er V
olum
e (in
100
0m3)
Urban Use
I rrigation
0
100
200
300
400
500
600
1 2 3 4 5 6 7 8 9 10 11 12
months
Wat
er V
olum
e (in
100
0 m
3)
months
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
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.