Existing practices on water resources
The annual rainfall and snowfall for Crete has been estimated by IGME to 7.2 billion m3 of water. From this amount of water, 3.6 billion m3 are lost, 1.6 billion m3 are moved by channels toward the sea and the remaining 1.6 billion m3 is percolating underground. A closer look of the water network of Crete shows that Crete faces severe water problems due to uneven distribution of the water resources between Western and Eastern Crete. In addition, the uneven distribution of rainfall during the winter months and the high demand for water during the summer months creates water management problems.
Although precise estimations of the available water resources in Crete have not been made, most related entities agree that the water consumption and use constitute only a small percentage (less than 5 %) of the annual precipitation. However, in many cases a severe water imbalance occurs due to unequal temporal and regional distribution of precipitation. This is intensified during the summer months by the increased water needs for irrigation and water consumption due to tourism. Most of the annual precipitation occurs in the western mountainous of Crete, while transport of water to the other areas exhibits technical, social and cost limitations.
It is estimated that water consumption in Crete is increased more than 4 % per year. Most of the total water consumption is used in agriculture for irrigation. Further Rural Development mainly depends on water availability. The increased demand of water, either for urban or agricultural use, cannot be always met despite adequate precipitation. Water imbalance is often experienced, due to temporal and spatial variations of the precipitation, the increased water demand during the summer months, and the difficulty of transporting water due to the mountainous terrain. In Crete there are regions, mainly the coastal and eastern ones, where there exists severe need on freshwater resources due to spatial and temporal uneven distribution of relatively high annual precipitation and run-off. In some cases this is exaggerated by especially high demand due to tourism and agriculture.
The main water uses in Crete is irrigation corresponding to 82 % of the total consumption. Total water consumption for 1980 was 225 million m3 of water. It has increased to 375 million m3 in 1991, while an additional 30 % increase is expected by the end of this decade (Angelakis, 1993). The demand for irrigation water is high, while at the same time only 27 % of the available agricultural land is irrigated. On the other hand, there are major losses (seepage, evaporation, leakage, etc.) from water delivered to the agricultural sites for irrigation and the municipal sites for domestic use. In some cases, these losses are estimated to be as much as 50 % of the delivered water.
Messara valley catchments
The Messara Valley comprises three catchments (Underbill, FAO, 1970a); the west Messara catchment with a drainage area of 398 kmē, the main river is Geropotamos and the discharge outlet is at Phaistos; the east Messara catchment with a drainage area of 95 kmē, the main river is Anapodaris and the discharge outlet is at Demati; and the Timbaki Plain with a drainage area of 218 kmē. The basic catchment areas are shown in Figure 10 numbered as 60 and 61.
Figure 10: Watersheds of Eastern Crete (Dept. of Development, 1989)
The discharges differ from year to year within a range of about 0.4 to twice the annual average, depending on the precipitation. From the total annual volume of 200 mil. m3 of water, a maximum of 160 mil. m3 can be diverted and supplied to the fields, the remainder being lost by evaporation from reservoir lakes, by seepage from canals and storage reservoirs, and by the uncontrollable flow of some minor streams.
Although the Valley receives on average about 600 mm of rainfall per year it is estimated that about 65 % is lost to evapotranspiration, 10 % as runoff to sea and only 25 % goes to recharging the groundwater store. Rainfall increases with elevation from about 500 mm on the Plain to about 800 mm on the Valley slopes while on the Ida massif the annual precipitation is about 2000 mm and on the Asterousian mountains is 1100 mm.
Pan evaporation is estimated at 1500 ą 300 mm per year while the winds are mainly westerly. The potential evaporation is estimated at 1300 mm per year (Vardavas et al., 1996) and so the ratio of mean annual rainfall to potential evaporation for the Valley is about 0.5 and hence it is classified as dry sub-humid according to UNCED (1994) definitions. The Plain contains several aquifers and aquicludes of complex distribution and properties. Groundwater levels are maximum in March or April with long recessions until recharge occurs in winter. The aquifers were high yielding with discharge rates as high as 300 m3/hr in the early seventies but now are reduced to about one tenth of this.
Before the installation of the groundwater irrigation system, the average discharge out of the Valley was about 20 Mm3/yr corresponding to 50 mm of the annual rainfall lost as runoff to the sea. It is estimated that the annual recharge of the groundwater store was about 60 MnrVyr (150 mm) and evapotranspiration loss was about 160 Mm3/yr (400 mm).
Chania region
In Western Crete the vast water resources come from the Lefka Ori (White Mountains) which have a limestone and dolomites geological formations. The Lefka Ori take advantage of the fact that surrounding the northern perimeter of the mountains and the ocean there is a non porous rock formations that created an integrated underground water formation that is trapped within the mountains. This complex system of underground water results in a series of natural springs on the north of the mountains. These springs with large capacities include Koleni, Meskla, Agia, Anabalontas, Zourbo, Armenon, Stilos, Kourna, and Argiroupolis. The yearly capacity of these springs is estimated at 350 million m3. A small portion of this is used yearly due to the lack of adequate infrastructure to capture and store the water, the rest is lost to the ocean. The karst geomorphology of the area allows regular annual feedback and further enrichment of the aquifers
OADYK is a major water distributor but also a water provider for irrigation and for drinking water. OADYK has a main pipeline that runs from Spilia, Kolymbari to the plain area of Chania. The existing unified network covers the lower elevations with its unified pipeline. The main pipeline ends in Spilia and is able to irrigate the surrounding area up to an elevation of 60-65 meters. This is referred to as the "low" zone. OADYK provides water to the higher zone in the Voukolies area.
The high season runs from mid-May until September, the driest month with the biggest water demand are July-August and September. The peak water demands can run from 5-7 months. In general, the water demands for olives is 3000m3/ha and orange trees are estimated at 4500 m3/ ha. Water is applied in olive groves and citrus or avocado plantation mainly by drip irrigation system.
