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villages. For example, the guidelines require a minimum pipe diameter of 200 mm, with a minimum velocity of 0.5 m/s. For a minimum proportional depth of 10 per cent, the minimum velocity must be 0.30 m/s, a condition that in practice cannot be achieved because the flows are insufficient. Similarly, trenches must be at least 2 m deep, which causes stability problems during excavation. |
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The guidelines are also expensive to implement. The vast majority of villages in the Greek islands, in isolated settings and with small populations and narrow pathways, cannot find the necessary funds to construct such a sewer network. In some cases this has meant that the construction of a sewer network has had to be postponed despite the fact that a wastewater treatment plant had been built. |
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The network was designed with the following in mind: |
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Population Considerations |
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The population to be served by the network was calculated on: (a) the current permanent population, (b) the large number of existing and planned rooms in hotels and private houses; and (c) the planned construction of a desalination plant at Oia. Given that the design period of the project was 40 years, a trebling of the number of rooms was assumed. The calculated design population was 2500. |
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The mean daily water consumption during the 6-month summer period was estimated at 150 litres per caput per day (lcd). This value was broadly confirmed by measuring the mean daily consumption at a 30-room hotel complex, which was found to be 130 lcd. The maximum daily water consumption coefficient was estimated to be 1.5 (225 lcd). Assuming that 80 per cent of the water consumed becomes wastewater, the peak sewage flow was calculated at 0.0066 litres per second per caput. |
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Groundwater Infiltration. |
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This was not calculated because: (a) high density polyethelene pipes were to be used; (b) the network was to be very carefully constructed; and (c) there is no high water table. |
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