WATER RESOURCES MANAGEMENT IN THE ISLAND OF KALYMNOS
PLANNING WATER RESOURCES MANAGEMENT IN SMALL ISLANDS. THE CASE OF KALYMNOS, GREECE E. Kechagias1 and K. L. Katsifarakis2 Division of Hydraulics and Environmental Engineering, Dept. of Civil Engineering, A.U.Th, GR- 54006 Thessaloniki, Macedonia, Greece Tel: +302310995634 E-mail:
[email protected],
[email protected]
ABSTRACT Kalymnos is one of the largest islands of the Dodecanese, a rather dense island complex situated at the southeast corner of Europe. The development potential of the area is large. A serious restrictive factor, though, is fresh water availability. The latter has declined the last few years, due to increase in population and in per capita water demand. As a result, the already stressed groundwater resources have been overexploited, and salinization of many coastal aquifers has already taken place. Since water import from other areas is not a sustainable solution, optimization of the management of local water resources is necessary. This paper deals with both sides of the water balance of Kalymnos. First an estimate of the evolution of water demand is discussed. The use of a GIS tool, in order to estimate renewable water resources at the hydrologic basin scale, is presented next. Conjunctive use of surface and ground water resources, including traditional rainwater collection, is proposed. Water resources development in the hydrologic basin of Vathy, which is one of the largest of the island, is discussed in more detail.
keywords: GIS application, small islands, sustainable development, underground water storage, water demand, water resources management
1. INTRODUCTION Kalymnos is the fourth largest island of the Dodecanese, a rather dense island complex (Fig. 1), situated at the southeast corner of Europe. It has been populated since the ancient times, according to archaeological evidence and written sources, which mention the participation of its inhabitants to the Trojan war and to subsequent major events of ancient Greek history. The Kalymnians have actively participated in the major events of the history of modern Greece, too. But, despite their contribution to the Greek war of Independence and subsequent efforts, their island remained under Turkish occupation until 1911, when Italy took over the Dodecanese islands. It finally joined Greece in 1948.
Figure 1. The Dodecanese islands From the beginning of the eighteenth century, Kalymnos has been known as the island of the sponge-divers. Sponge collection and trade was until recently the major source of income. It still is an important financial activity, together with agriculture and tourism, the latter being on the rise, for some years now. Tourist activities have been supported be a remarkable effort to improve services, from health care to water supply. Meeting water demand is actually a very
challenging task, requiring careful development of all local water resources, since salinization of many coastal aquifers has already occurred. Administratively, the municipality of Kalymnos includes also Telendos and Pserimos, two adjacent smaller islands and a number of islets. It belongs in turn to the Dodecanese Prefecture and to the south Aegean Region, Greece. 1.1 The evolution of population With regard to population, Kalymnos ranks third among the Dodecanese islands (following Rodos and Kos). The evolution of its population, during the last 50 years is shown in Table 1 (based on data from the Greek Statistical Service). An increasing trend is evident since 1971. An important feature is the large number of children per family, which is in fact larger that the value provided by the GSS for the average Greek family. According to the latest nationwide census conducted in 2001, more than 41% of the Kalymnian families have 4 or more members, while at the same time the national average is 31%. Table 1. Evolution of the population of Kalymnos year population
1951
1961
1971
1981
1991
2001
13,712
14,249
13,281
14,457
15,842
16,573
The largest part of the population (around 11,000) lives in Pothia, which is the capital and main port of Kalymnos. There are 10 more communities on the island. The figures of Table 1 include the small communities of Telendos and Pserimos, with less than 100 people each.
2. THE HYDRAULIC BALANCE Kalymnos (as many other Aegean islands) exhibits a deficient water balance, which restricts both tourist and agricultural development. To arrive at meaningful solutions, both the demand and the supply side should be investigated and a variety of water resources should be taken into account (Kechagias and Katsifarakis, 2001). 2.1 The demand side of the water balance Both domestic and agricultural water demands play an important role in the water balance of Kalymnos. Satisfying the former is of course the top priority. Domestic water demand depends on population size and per capita water consumption. According to the data of the Greek Statistical Service, presented in Table 1, permanent population
has increased by almost 15% during the last 20 years. Assuming that this trend persists, we estimate that by 2020 the permanent population will exceed 19,000.
Seasonal population due to tourism is also an important component of domestic water demand. Data on tourist overnights, collected by the Hellenic Tourist Organization (HTO) are presented in Table 2. These account only for the above-average size tourist lodgings, leading us to believe that they should be multiplied by a factor close to 2, in order to take into account smaller tourist lodgings, that can be quite numerous. Moreover, many visitors are actually Kalymnians living abroad, who return almost every summer to the island to spend their vacations and are accommodated by their relatives. It should be mentioned in this context that the number of Kalymnian immigrants is quite large. A striking example is Tarpon Springs, a small town in Florida, USA, which can be considered a Kalymnian “colony”.
year overnights
Table 2. Number of tourist overnights in Kalymnos 1995 1996 1997 1998 98,637 66,404 68,507 75,776
1999 83,641
Based upon the aforementioned remarks, we estimated that the actual number of overnights in 1999 was close to 167,000. Since it is believed that their number is still low with regard to the potential of the island, a total increase of 40% over the next 20 years, which results in 235,000 overnights for the year 2020, is considered quite reasonable. Daily per capita water consumption can be taken equal to 200 lit, both for permanent and seasonal population. Some investigators tend to accept larger values for tourists, but we believe that plans for sustainable development should not try to accommodate wasteful practices. Current and projected annual domestic water demands appear in Table 3. In that table losses from water carrying pipes, amounting to 20% of the consumer demand, have been taken into account.
Year annual water demand (m3)
Table 3. Domestic water demand 2001 1,488,000
2021 1,721,000
Agricultural water demand is also substantial in Kalymnos. According to Eurosynergy Consulting (1994), it amounted to 1,594,200 m3 in the year 1994. Although agricultural development is and should remain an important financial activity, we believe that its further development should be based rather on water conservation, by means of improved irrigation systems. Thus we estimate agricultural water demand at 1,600,000 m3 per year.
2.2 Water supply Full development of water resources of Kalymnos is not an easy task. It is, after all, a small island. Moreover its shape is irregular and its terrain mountainous. All these factors favor quick surface runoff to the sea. A local survey, coupled with maps provided by the Institute of Mineral and Geology Exploration (IMGE) showed that permeable limestone, covering a large part of the island, favors infiltration of rainwater, but, unfortunately, offers quick access of groundwater to the sea, too. Up to now, increasing water demand has been met by pumping more groundwater. The pumping scheme is clearly not sustainable, since salinization of many aquifers has already occurred. The obvious choice is development of surface water resources, that is, construction of water storage facilities. One possibility is construction of detention ponds, for surface storage. Another possibility is underground storage. This can be achieved through construction of small dams, at selected sites of streambeds. Contrary to ordinary dam construction practice, soil upstream of the dams should be very permeable, in order to facilitate recharge of underlying aquifers. Moreover, locally available material should be used for dam construction, to reduce cost and impact on the landscape aesthetics. The concept of small “groundwater recharge” dams has been applied very successfully at the island of Naxos, as part of a pioneer project for protection of soil and water resources (Glezos et al., 2000). Naxos belongs to Cyclades, another island complex of the Aegean archipelago, situated just west of the Dodecanese complex. Compared to detention ponds, underground storage has three important advantages: a) Evaporation losses are much lower, b) Water quality is more protected, and c) land requirement is lower. Its main disadvantage is the difficulty of controling the resulting groundwater flow. Still, in our opinion, underground water storage should be considered as the first option. The trend to neglect traditional rainwater collection techniques should also be reversed, even through state funding of rehabilitation of old rainfall collection systems and construction of new ones. Rainwater is rather clean, since atmospheric pollution at the area is minimal. Thus, water quality can be satisfactory for most domestic water uses, like washing or bathing, if proper materials and some simple devices are used. Finally, seawater desalination, which has a significant contribution to the water balance of smaller islands like Nissyros (Kechagias and Katsifarakis, 2002) is not a viable option for Kalymnos, or any other island with substantial agricultural water demand. Energy consumption and the resulting water cost of reverse osmosis or distillation desalination plants are too high and outweigh any benefit from irrigation.
3. ESTIMATION OF AVAILABLE WATER The first step in any water resources development project is estimation of the available water quantity. GIS offer a very flexible tool for such a purpose, which can lead to quite reliable results. In our study, the MapINFO commercial package has been used. The process will be briefly described next.
Figure 2. Major streams and hydrologic basins of Kalymnos
Initially, maps for the island of Kalymnos were purchased from the Geographic Service of the Greek Army. In total, 23 maps, drawn at a scale of 1 to 5000, were used, depicting the whole of
the island along with nearby smaller patches of land. First they were scanned and digitized, so that they could be imported at the GIS tool, to be appropriately registered. Having projected all of the maps on a fixed coordinate system, the shores of the island were defined. In addition, major contour lines were located and recorded. From the resulting view of the terrain model, the most visible streams and rivers were identified, and the boundaries of their respective hydrologic basins were drawn. Work on the digitized versions of the maps was concluded with the delineation of the built-up areas of the island. The purpose of this task was to define zones where water collection works could or could not be constructed. In addition, this definition was very helpful in estimating construction costs for any suggested works. It has to be noted though, that built-up areas are underestimated up to a certain degree, since both the local population and the number of tourists have increased since the 70’s, i.e. when the maps were created. The aforementioned information appears on the map of Fig. 2 (in which the limits of built-up areas appear as broken lines). It should be mentioned that the GIS includes an additional layer with geological information, not shown in Fig. 2. In order to estimate the water availability at every hydrologic basin, the respective area was calculated electronically, along with a rough estimate of its average altitude. The latter was obtained as the weighted average of the areas within successive contour lines for each hydraulic basin. These values were then imported to a spreadsheet tool, where typical rainfall values per month were estimated. Hydrologic stations have been installed in Kalymnos rather recently and the respective data series are short. So, calculations are based on data from stations in the neighboring island of Kos, which are presented by Fantidis (1997a). Ground surface altitude is taken into account by means of an experimental formula, applied for some Dodecanese islands in the study of AN.DO. (1998). This formula reads: P = 2.0097⋅H + 243.9
(1)
where P is the precipitation (in mm) and H the altitude (in m). Another important parameter is evapotranspiration, which is quite high. Formulas to estimate it are summarized in many books (eg. Fantidis, 1997b, Shaw, 1998, Tsakiris, 1995). The problem is that different formulas may yield quite different results. To choose the most suitable for our case we have considered 7 of them, namely: •
the method of Thornthwaite,
•
the method of Hargreaves,
•
the method of Turc,
•
the method of Blaney (by FAO 24),
•
the method of Penman,
•
the method of Penman (by FAO 24)
•
the method of Penman – Monteith.
Only “high” rainfall months (from October to April) have been taken into account, since our study aims to calculate available water resources, not irrigation needs. Field measurements, which have not been reduced by any coefficient, have been considered as upper bound, that is, calculation results were acceptable if they did not exceed the respective measurements. Figure 3 demonstrates that most methods tend to provide evaporation figures higher than the measured ones quite frequently. The percentage of months (per method) when evaporation is overestimated is also shown in the graph. It can be seen that the Thornthwaite formula leads to the lowest
Exceedance of measured evaporation (%) 20 30 40 50 60 70 80 90
average exceedance of measured values, followed by the Hargreaves formula.
Ave. Evaporation Exceedance
Penm an
P-M
Penm an F AO
Blan ey F AO
Turc b
Turc a
Ha r g reav es
ite Thor nwa
0
10
Ave. Monthly Exceedance
Fig. 3: Comparative graph of the evaporation methods evaluated. We have finally chosen the Hargreaves method for two reasons: a) It fits measured values comparatively well and b) It has rather low input requirements, of the type available for the Dodecanese islands (i.e. temperatures). The Hargeaves formula reads:
Etr = 0,0023 * R a * (
Tmax + Tmin + 17,8) * (Tmax − Tmin ) 2
(2)
where Ra is the solar radiation (fixed by latitude and season), and Tmax and Tmin the highest and lowest daily temperatures (in 0C) respectively. Then, the maximum available water quantity for each hydrologic basin results as the difference between the respective rainfall and evapotranspiration values. 3.1 Application to the hydrologic basin of Vathy The use of the GIS tool, which has been described in the previous paragraphs, is illustrated through an application at the hydrologic basin of Vathy, one of the largest of Kalymnos. The respective hydrographic network appears in Fig. 4, together with the boundaries of the basin. The limits of the community of Vathy, one of the largest of the island, appear as broken line, starting from the seashore and extending in an adjacent hydrologic basin, too. Moreover, the Vathy basin has been divided in two parts, for water management purposes. The whole of the built-up area has been included in the lower part. The detention pond, which has been recently constructed, is not shown in Fig. 4.
Figure 4. The hydrologic basin of Vathy.
The areas of the Vathy basin and its upper and lower parts, easily calculated by means of the GIS tool, appear in Table 4. Estimated rainfall, based on average altitudes, appears in the next column. Effective rainfall comes next, resulting as the difference between rainfall and evapotranspiration
values, during the “wet period”, which lasts from November to April. Moreover, the water quantity retained by the soil at the end of the dry period is set equal to 90 mm and included in the calculations. Available water (in m3) appears in the last column of Table 4, calculated as the product of effective rainfall by the respective area. It should be mentioned that this value represents a practically unattainable upper limit, including both surface and groundwater resources, which can never be fully developed. Nevertheless, it is a useful indicator.
Hydrologic basin Vathy Lower Vathy Upper Vathy
Table 4. Results for the hydrologic basin of Vathy Rainfall Effective rainfall Area (km2) (mm/year) (mm/year) 20.23 741 207 9.3 611 112 10.93 852 288
Available water (m3) 4187610 1041600 3147840
With a surface runoff coefficient equal to 0.5, Upper Vathy could provide enough water to cover the domestic demand of the whole island. Of course, this result should be considered as approximate only, since it is based on a number of assumptions, regarding precipitation and evapotranspiration. Moreover, additional water losses due to evaporation from the surface of the detention pond may reduce drastically the available water quantity. Underground water storage, outlined in paragraph 2.2, is not recommended at this stage for the hydrologic basin of Vathy, since a detention pond is already in place. Its application should be considered, though, for the development of the water resources in other hydrologic basins of Kalymnos. Areas upstream of existing (and depleted or salinized) wells should be the first choice. 4. CONCLUSIONS A reasonable increase of the water demand should be expected in the years to come, due to the anticipated increase of population and of tourist and agricultural activities in Kalymnos. To meet this demand in a sustainable way, a well-designed conjunctive development of surface and ground water resources is necessary. Minor water sources (e.g. traditional rainwater collection) should not be neglected either.
ACKNOWLEDGEMENT This paper is part of a research program, which has been supported by the South Aegean Region. This support is gratefully acknowledged.The authors would also like to thank AN.DO S.A. for its kind help with collection of statistical data.
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