ISSUE 6
OCT-DEC 2004

Groundwater Exploitation in Paros

The construction of new boreholes to provide additional water supply is the method that has been used most frequently in the case of Paros, as until recently the groundwater reserves were adequate, the costs entailed in the use of boreholes are significantly lower than those of major structural solutions, such as reservoir construction or desalination, and the solution was quick and easy to implement. As a result, the island today is perforated by a large number of boreholes, most being used for irrigation purposes. The size of this potential water management intervention as a component of the comprehensive scenarios for Paros was defined in the basis of the local geological structures and the current exploitation patterns. Since little or no data are available for abstracted water volumes from irrigation, the option is examined for domestic use only. Very low priority is given to the new supply source.

As in the case of Network Unifications, the size of such an intervention cannot be varied on the basis of demand conditions, since it depends more on available quantities for abstraction. Thus it was the schedule of implementation (see Annex) that was defined by the demand – availability conditions in the area, and formed the extent for the application of the option.

The locations that could be selected for the application of this intervention were:

The Agairia – Alyki area. This area does not face water deficit, and thus can provide water for other parts of the island. However, this can only be effected in conjunction with network unifications, as this water network is currently isolated.
The Archilohos area. This area faces small, periodic deficits, and exhibits low water exploitation. An additional borehole yielding about 47,000 m³/yr can be constructed.
The Kostos area, in order to supply water to the main town of Paroikia and its suburbs. A maximum of two new boreholes can be constructed here, based on current estimates, yielding about 75,000 m³/yr each.
The Glysidia area. However, the local aquifer is non-productive and vulnerable to salinisation; to that end, it is estimated that a borehole yielding only 7,000 m³/yr should be constructed.

Option details and results

The yields and costs of the proposed interventions are summarized in Table 1.

Table 1. Yield and construction costs for new boreholes

Borehole	Yield (m³/yr)	Construction Cost (€)
Arhilohos	47,000	40,000
Glysidia	7,000	20,000
Kostos 1	75,000	40,000
Kostos 2	75,000	40,000
Total	204,000	140,000

Figure 1 presents quantities abstracted from the new drillings for the BAU+Normal scenario. The month variation of water production for a normal, dry and wet year (2009 under the three scenarios) is presented in Figure 2.

Figure 1. Additional Groundwater Abstractions (BAU+Normal scenario)

The new boreholes are assigned a very low supply priority with respect to existing supply sources. For this reason, under all three scenarios the new boreholes operate after the peak summer months, when the traditional supply sources have been depleted. During the peak season, supply normally originates from the existing groundwater drillings.

Figure 2. Monthly variation of abstractions from the new boreholes (2009)

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Effectiveness

The coverage of Domestic demand shows some improvement where the option is applied, which is once again diminished as the demand grows over time (Figure 3). Although the traditional practice of groundwater exploitation can assist in meeting some domestic requirements, this effect is almost diminished in cases of drought, as it is depicted from the results of the BAU+HD scenario (Figure 4).

Figure 3. Percent demand coverage effectiveness of Groundwater exploitation to Domestic use

Figure 4. Percent Improvement of deficit in Domestic use with respect to the reference scenarios

In general, irrigation deficits are not significantly affected, with the exception of the high dry scenario (Figures 5 and 6).

Figure 5. Percent demand coverage effectiveness of Groundwater exploitation to Irrigation use

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Direct and Environmental Costs

Overall the direct cost increases are similar to those of the network unification option. A small average increase of about 3.5-5% is common among all three scenarios. Infrastructure construction costs are low; the increase is due to the augmentation of water abstracted and delivered to domestic use, which incurs a proportional increase in annual operating costs

Figure 7. Total direct cost difference of the Groundwater exploitation option under the three scenarios (Present Value – Million €)

The total environmental cost records a substantial increase due to the increase of groundwater abstractions. In all cases, it is considerably higher than the respective reference case, with the highest values recorded for the high dry scenario (Figure 8).

Figure 8. Total environmental cost difference of the Groundwater exploitation option under the three scenarios (Present Value – Million €)

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