Sectores objetos de armonización según “el antiguo enfoque”

The Athens external water supply system (Figure) extends over an area of around 4,000 km2

including both surface water and groundwater resources and is operated by EYDAP (Kozanis et al., 2012). The hydrosystem comprises an extensive network of surface water reservoirs, boreholes, aqueducts, pumping stations, hydropower plants and water treatment works and is characterised by a high level of complexity.

0 10 20 30 km Mornos reservoir Evinos reservoir Marathon reservoir Vassilika boreholes Hylike boreholes NE Parnitha Boreholes Hylike reservoir Mornos Aqueduct Hylike Aqueduct Connecting Aqueduct Mandra WTP Galatsi WTP Kiourka MEN Menidi WTP Evinos – Mornos tunnel City of ATHENS

Figure 9.3. The Athens external water supply system

Water resources and storage

The majority of water resources used for supplying water to Athens come from surface sources, which are stored in the four reservoirs of the hydrosystem, Mornos, Evinos, Hylike and Marathon reservoirs (Table 9.2). Out of these reservoirs only Hylike is a natural lake, the rest are artificial.

Mornos and Evinos, which represent the main sources used for the Athens water supply, are used in conjunction with one another, as most of the surface runoff received by Evinos is diverted to Mornos via the Evinos – Mornos tunnel (Figure 9.3) due to its relatively small net storage capacity in comparison to the mean surface runoff received from the upstream catchment area (Table 9.2).

Hylike and Marathon reservoirs both represent auxiliary water sources. Specifically Marathon is mainly used for storing an emergency water supply volume due to its proximity to the city of Athens. On the other hand the reservoir’s water levels need to be kept below a certain threshold in order to minimise flood risk of the downstream populated areas. Therefore, tight limits have been set for Marathon’s water level fluctuation (Efstratiadis et al., 2009).

Table 9.2. Main characteristics of the Athens water system surface water sources and reservoirs

RESERVOIR

NAME CATCHMENT AREA (km2₎ MEAN _ANNUAL SURFACE RUNOFF (hm3₎ TOTAL STORAGE CAPACITY (hm3₎ NET STORAGE CAPACITY (hm3₎ MEAN ANNUAL ABSTRACTIONS (hm3₎ Mornos 588.1 234.1 763.71 630.23 291.0 Evinos 351.9 276.1 137.63 112.05 202.4 Hylike 2466.6 294.1 594.75 584.75 83.3 Marathon 118.0 13.4 42.85 32.20 68.8

Source: Makropoulos et al. (2010)

Groundwater from three aquifers is used today as a back-up water source. EYDAP currently holds approximately 70 boreholes that are classified in six different groups. These have a total power of 17 360 Hp and pumping capacity of approximately 390 000 m3_/d

(Efstratiadis et al., 2009). Aqueducts

The Athens external water supply system includes an extensive and in some case complex network of aqueducts that conveys water from the different water resources to the four water treatment plants supplying the city of Athens. The external aqueduct network includes open channels, tunnels, siphons and closed pipes; the total length of the all water conveying elements is approximately 440 kilometres (Table 9.3).

The primary external aqueduct network includes two main branches; the north and south branch (Figure) (Rozos and Makropoulos, 2013). The north branch conveys water from Hylike Lake, Marathon reservoir and the boreholes groups of Ougra, S.W. Hylike and Mavrosouvala towards Kiourka and Galatsi water treatment plants. This is an energy intensive branch as it requires the use of pumping stations at various locations along the network. However, its use is required in order to minimise losses from Hylike lake that increase as water are high (Katerinopoulou, 2009). The south branch conveys water from Evinos and Mornos reservoirs, as well as from the borehole group Vassilikon-Paroriou towards Mandra, Menidi and Galatsi

water treatment plants. The water is transported through gravity and currently five hydropower plants exploit the hydropower potential of the south network branch.

Table 9.3. Main characteristics of external aqueduct network

TYPE OF AQUEDUCT

AQUEDUCTS TOTAL

LENGTH (KM)

Main Mornos, Evinos, Hylike, Kakosalesi, Marathon - Galatsi

300 Connecting Marathon connecting, Distomo,

Kiourka – Menidi, Kremmada – Kleidi

105

Auxiliary Vasilikon – Paroriou GW, SW Hylike GW, Ougra GW, Viliza GW, Hylike floating, Diversions (Viliza, Malakasa)

34

Source: Makropoulos et al. (2010)

Besides the primary aqueduct network, the hydrosystem also includes connecting and auxiliary aqueducts. The most significant connecting aqueduct is the Marathon connecting aqueduct that links the south and north branches via Kleidi (Table 9.3). Despite the fact that the particular connecting aqueduct has been designed to allow bi-directional flow between the main branches, at the moment only the gravity flow direction actually functions due to technical problems (Makropoulos et al., 2010). There are also other connecting aqueducts allowing water transfers between the four water treatment plants. Auxiliary aqueducts include among others pipes that transport water abstracted from the boreholes to the main network and diversions.

Pumping stations

The pumping stations along the Athens external aqueduct network enable the water transfer from sources of lower elevations (Hylike lake, boreholes) towards higher elevations (Marathon, Mornos aqueduct). The operation of pumping stations is of particular importance for this study that explores the water energy nexus of the Athens hydrosystem.

The total installed power of the pumping stations of the external water supply network amounts to 97660 Hp; the most significant ones are (Efstratiadis et al., 2009):

• Hylike central pumping station and Hylike floating pumping station: These two

pumping stations transfer water from Hylike Lake towards Hylike aqueduct. Both pumping stations operate when the lake’s water level falls below 71.0 metres. The central pumping station is also used for the conveyance of groundwater abstractions from the borehole groups of SW Hylike and Ougra.

• Viliza pumping station: This pumping station in conjunction with a series of other smaller ones conveys water towards Marathon reservoir via Hylike aqueduct.

• Distomo pumping stations (AD1, AD2 and AD3): These pumping stations transfer

water abstracted from the borehole group Vasilikon – Paroriou towards Mornos aqueduct.

• Kremmada and Asopos pumping stations: The two pumping stations transfer water

from Hylike to Mornos aqueduct. Hydropower plants

Currently five small hydropower plants are in operation on the south branch of the Athens external water supply system, on Mornos aqueduct.