BALWOIS 2004 Ohrid, FY Republic of , 25-29 May 2004

Hydrology Of Prespa Lakes

Molnar Kolaneci Hidrometeorological Institute Tirana,

Abstract The levels of the Prespa Lakes follow an annual cycle with peak levels in May and June and the low water levels in autumn. Superimposed on this annual cycle are longer period fluctuations caused by particularly wet or dry periods. After 1988 it is observed a continuing and fast decrease of water level in Big Prespa Lake. Up to this year the amplitude of level oscillation from the beginning of the regular observations (1952) was about 4 m with maximum of 852.91-m a.s.l. in 1963 and minimum of 848.91 m a.s.l. in 1978. In 1989 started a fast decrease and is still going on. For the period from 1988-1989 to 1995-1996 (7-8 years) it was observed the amplitude of 4.17 m, the same as it was observed for the period of 36 years (1952- 1988). After a short period of 4 years (1997-2000) of stagnation with small increasing of water level, restarted the decreasing and as consequence the minimal historic water level of Big Prespa Lake is observed in 2002. This phenomenon caused the separation of Small Prespa from Big Prespa Lake. In last years the communication of these two lakes is interrupted. This is a serious problem and constitutes a big threatens for the Prespa Lake ecosystem. Exchanging of hydro meteorological data between the three neighbouring countries and cooperation between professional institutions is the only possible way to define a real water balance of Prespa Lake. Concerning the water inflow from Albanian part, there are not natural surface inflows into both lakes. In Small Prespa in Greek territory there are small temporary streams that inflow into the lake. There are several rivers flowing into Big Prespa Lake: River in Greek territory and Golema, Kranjska, Brajchinska and Istocna River in Macedonian territory. There are no natural outflows by surface way in all Prespa Lakes. However, there has been considerable human modification of the hydrology of the area, which has to be taken in consideration. So, in 1976 in Small Prespa was created a channel which a water from Devolli River has been is turned in during the wet and withdraw water from the lake for irrigation during the dry period. However, due to the existing artificial channels, the level in Small Prespa Lake is less oscillating. The water balance of Small Prespa Lake shows a good equilibrium between inflow and outflow elements for the long-term period even some of these elements require more accurate estimations. The water balance of Big Prespa Lake demonstrates that the most interesting and in the same time the most difficult element of the outflow by underground way is not yet defined properly. Also in this case the same elements require more accurate estimations.

Introduction Prespa Lakes (Big and Small) and Ohrid Lake constitute the biggest water system in Balkan. The surface area of Big Prespa is about 253 km2 and about 47 km2 is the surface area of Small Prespa. Prespa Lakes are situated in an altitude of ca. 850 m a.m.s.l. with high mountains (up to 2000 m) around them. Big Prespa and Small Prespa are linked by a small channel, which traverses the alluvial isthmus that separates the lakes. It is well known, the water communication of all these lakes by both: surface and underground ways. The last one is due to the presence of a deep and very developed karst region between Prespa and Ohrid Lake (Galichitsa Mountain in Macedonia and Dry Mountain in Albania. The fact that three countries, Macedonia, and Albania, share this complex water system, make more difficult a real hydrologic analyse. For example the way of water connection between two Prespa is in the Greek territory, the outflow of Big Prespa is through the well-known Zaveri abyss (Albanian territory) to St. Naumi springs (Macedonian part) and Tushemishti springs (Albanian part), the outflow of Ohrid Lake is Black Drini River in Macedonian part. In all this facts must be taken in account the artificial flow-out-

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BALWOIS 2004 Ohrid, FY Republic of Macedonia, 25-29 May 2004

pumping water for irrigation from Prespa Lake (Big and Small) in all three countries. This situation needs good collaboration between researchers of the three countries and exchange of scientific information in order to create a Unique Database of this system.

Level oscillation in Prespa Lakes The water levels of the Lakes follow an annual cycle with maximum levels in May and June and the low water levels in autumn. This is a typical character of continental water regime. Superimposed on this annual cycle are longer period fluctuations caused by particularly wet or dry periods. After 1988 it is observed a continuing and fast decrease of water level in Big Prespa Lake (see fig.1). Up to this year the amplitude of level oscillation from the beginning of the regular observations (1952) was about 4 m with maximum of 852.91-m a.s.l. in 1963 and minimum of 848.91 m a.s.l. in 1978. In 1989 started a fast decrease and in one year it was observed a falling of more then 1 m of mean annual water level. This decrease is continuing up to minimal historic, which is observed at the end of 1995 and the beginning of 1996. For the period from 1988-1989 to 1995-1996 (7-8 years) it was observed the amplitude of 4.17 m, the same as it was observed for the period of 36 years (1952- 1988). After a short period of 4 years (1997-2000) of stagnation with small increasing of water level, restarted the decreasing and as consequence the minimal historic water level of Big Prespa Lake is observed in 2002. This phenomenon caused the separation of Small Prespa from Big Prespa Lake. In last years the communication of these two lakes is interrupted. Different specialists have discussed the causes of this catastrophic continuing falling of water level in Big Prespa Lake. Until now, three would be the main hypothesis about this spectacular phenomenon: - Tectonic falling of the lake bottom - Widening of underground channels connecting the two lakes - Influence of meteorological parameters For the first hypothesis, the geologic researchers must tell their opinion. Probably the two other hypotheses are more close to the reality. The widening of underground channels hypothesis can be proved by detailed analyse of discharge measurements in St. Naumi and Tushemishti springs for the period 1988-1996, especially for the years1989-1990. In Albanian part the discharge measurements made in Tushemishti springs during this period show net decreasing of water flow, even the number of measurements is scarce. After 1996 seemed that the tendency is going to the normality concerning the spring discharges but not on water levels in Big Prespa Lake (little increasing). For the third hypothesis must be analysed accurately all meteorological parameters for the same period (1988- 1996), even the diagram showing the distribution of the precipitation during all the observation period of Liqenas station (in Albanian part) doesn’t agree with this idea; the fluctuation in long term period has no trend. The fact that in Small Prespa Lake this phenomenon was not observed (see fig. 2), decreases the chances that this hypothesis being true. However the phenomenon we are discussing is extremely complex and none of hypothesizes must have priority above the others. To simplify the question, the problem is to find how are disappeared more then 800 million m3 in Prespa Lake in order to protect this natural ecosystem, in which, we all are common owners.

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Water levels Big Prespa H m. a.s.l. 1952 - 2002 854.0 853.0 Max. historical level 852.91 m a.s.l. (1963) 852.0 851.0 850.0 Mean 849.0 Min 848.0 Max 847.0 Max. Amplitude 8.49 m 846.0 845.0 844.0 Min. historical level 844.42 m a.s.l.(2002) 843.0 1950 1955 1960 1965 1970 1975 1980 1985 1990 1995 2000 2005 Years

Figure 1 Water levels of Big Prespa at Liqenas

Water level of Micro Prespa Lake

H cm 1955-2002 400

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50 Mean Min 0 Max

-50 1950 1955 1960 1965 1970 1975 1980 1985 1990 1995 2000 2005 Years

Figure 2 Water levels Small Prespa at Tren

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BALWOIS 2004 Ohrid, FY Republic of Macedonia, 25-29 May 2004

Rainfall Gorica 1951 - 2002 R m m

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0 19 5 1 19 5 6 19 6 1 19 6 6 19 71 19 7 6 19 8 1 19 8 6 19 9 1 19 9 6 2 0 0 1 year

Figure 3 Distribution of rainfall Gorica station

Rainfall Liqenas 1951-2002

R mm

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0 1951 1956 1961 1966 1971 1976 1981 1986 1991 1996 2001

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Figure 4 Rainfall of Liqenas (Pusteci) 1951-2002

Water balance of Prespa Lakes The method of water balance can be very useful for determining one element when the others are known. In case of Prespa Lake is not possible to define a real water balance without exchanging of hydrometeorological data between three countries and co-operation between professional institutions. The previous studies made on water balance in each country are a good base and will serve as reference points for the future.

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The distribution of hydrometeorological elements is not uniform in this region. It seemed that in western part of Big Prespa Lake (Albanian and Macedonian part) the amount of rainfall is higher than in the other parts. The range of precipitation in the field area of this region is from around 600 mm to more then 900 mm. The difference will be also for temperature and so on. In the fig. 3 is given the distribution of rainfall for Liqenas (Pusteci) station during 1951-2002. Another important element of water balance is inflow and outflow in this lakes system. Prespa Lakes system has a complex and specific hydrographical network. There are no outflows by surface way in all Prespa Lakes. There is outflow only by underground way from Big Prespa down to in Tushemishti and Driloni springs in Albanian part and Saint Naumi springs in Macedonian part. Concerning water inflow from Albanian part there are no natural surface inflows into both lakes. In Small Prespa in Greek territory there are small temporary streams that inflow into the lake. There are several rivers flowing into Big Prespa Lake: Agios Germanos River in Greek territory and Golema, Kranjska, Brajchinska and Istocna River in Macedonian territory. There has been considerable human modification of the hydrology of the area, which has to be taken in consideration. So, in Small Prespa was created in 1976 a canal, in Albanian part, which can input water from Devolli River during wet period and withdraw water from the lake during dry period for irrigation. The data of these artificial inflow and outflow are not well evidenced in all cases and as result the values of these elements will be not so reliable. The water balance is calculated for each lake separately because they are considered independent hydrological speaking. The canal linking Small and Big Prespa will serve once as outflow (Small Prespa) and after as inflow (Big Prespa).

Water balance of Small Prespa Lake 1 Lake area of Small Prespa is 47.4 km2 (essentially in Greek territory) and his catchment area is 189 km2.

Inflow: Precipitation, surface and underground flow The inflow elements for Small Prespa Lake are as follow: - contribution of precipitation (direct on water mirror) - runoff from catchment area - underground inflow - artificial inflow from Devolli River (Albania)

Precipitation on surface lake The rain gauge stations near water mirror of Small Prespa Lake are all in Greek territory2 fig 5: Koula 572 mm Kalithea 646 mm Mikrolimni 685 mm Average 634 mm The all over averages of rainfall on surface area of lakes is accepted the arithmetic average of 634 mm, which means an amount of 30*106 m3 of water coming in the Small Prespa Lake from rainfall.

1 The water balance of Prespa Lakes will be calculated for long-term period 2 , Northwestern Greece: A Unique Balkan Wetland. (Developments in Hydrobiology 1997 Kluwer Academic Publishers)

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Figure 5 Distribution of rain gauge stations in coastline of Prespa Lake

Runoff from catchment area The catchment area of Small Prespa Lake (189 km2) is dominated by limestones and dolomites on the western and southern sides, while on the eastern side they are predominantly granites and gneisses. For our purpose is better to use the definitions: infiltrated area (karst) and non-infiltrated area. According Greek data and studies (IGME), infiltrated area in the catchment area of Small Prespa is around 140 km2 and the runoff (surface flow) is no more then 10% of precipitation. For the rest (always by Greek studies) is applied a specific discharge of 8 l/s/km2. The most difficult problem is to calculate the average precipitation for whole catchment area of Small Prespa, taking into account that is not enough number of rain gauges in the catchment area and the existing stations are located on the plain around the lake. There are no meteorological stations or rain gauges in the surrounding mountains and so the existing stations are not representative for whole catchment area. In this case is adopted a value of 742 mm taken from other studies3. After calculations there are 10.4 106 m3 of water coming from infiltrated area and 12.4 106 m3 of water from the rest area. In conclusion, the total amount of water coming from whole catchment area of Small Prespa is 22.8*106 m3.

Inflow by underground way This element is not important (to be neglected).

Artificial inflow In Albanian territory is constructed in 1976 a canal which can input water from Devolli River into the lake during wet period (October-May) and withdraw water from the lake during dry period (June- September) for irrigation. According to the data taken from Directorate of Water Management in Ministry of Agriculture results an average volume of 55-60*106 m3 of water per year, which flow into the Small Prespa lake.

Outflow : evaporation, surface or groundwater outflow, irrigation The outflow elements for Small Prespa Lake are as follow: a) evaporation from open water surface, b) surface or groundwater outflow, c) outflow by irrigation.

3 Lake Prespa, Northwestern Greece: A Unique Balkan Wetland. (Developments in Hydrobiology 1997 Kluwer Academic Publishers)

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Evaporation The evaporation from open water surface is an important element and many researchers have dealt with it. In the same time the results of the calculation are different among themselves. For that reason in this study is applied Penman Formula for open water evaporation which is a unique formula and worldwide used. Also are used the data of the evaporation pan in Koula station and evaporation pan in Vegoritis Lake in the east of Prespa Lake in Greece. a) Open water evaporation from Prespa Lake Equation of Penman Combined approach (Mass transfer method + Energy balance approach)

s RN + cp ρa (ea – ed)/ra Eo = C/L *  s + γ -1 where Eo open water evaporation mm d C constant to convert units from kg.m-2.s-1 to mm.d-1 -2 RN net radiation at earth’s surface in W.m L latent heat of vaporization (L = 2.45*106 J.kg-1) s slope of the temperature-saturation vapour pressure curve (kPa.K-1) -1 -1 cp specific heat of air at constant pressure (cp = 1013 J.kg .K ) -3 ρa density of air (ρa = 1.2047 kg.m at sea level) ed actual vapour pressure for the air at 2 m height in kPa ea saturation vapour pressure for the air temperature at 2m height in kPa γ psychrometric constant (γ = 0.067 kPa.K-1 at sea level) -1 ra aerodynamic resistance in s.m The required data for Penman formula are as follows (monthly averages; where appropriate 24 hour): latitude altitude sunshine duration relative humidity minimum air temperature maximum air temperature wind speed at 2 m height Results of calculations and monitoring of open water evaporation (per year): Equation of Penman ...... 1180 mm (Koula data) 4 Evaporation pan (Koula station)...... 1090 mm (2 years of data) 5 Evaporation pan Vegoritis Lake……..1113 mm (8 years of data)5 As a final estimation is accepted the average of these three values, 1128 mm, or expressed in volume that means a total volume of 53.5*106 m3 of water, evaporated from water mirror of Small Prespa Lake.

4 Lake Prespa, Northwestern Greece: A Unique Balkan Wetland. (Developments in Hydrobiology 1997 Kluwer Academic Publishers) 5 is unknown the type of the pan used for the monitoring

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Evaporation from Prespa Lake Penman Formula Evaporation mm

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0 12345678910 Months

Figure 6 Monthly evaporation from water mirror of Small Prespa Lake

Outflow by surface or groundwater way a) Outflow by surface way In Albanian part there is no surface outflow, meanwhile in Greek territory is the canal linking Small and Big Prespa from which outflows a total annual volume of 41*106 m3 of water (last ten years data) 6. b) Outflow by underground way From Small Prespa not exist outflow by underground way.

Irrigation Albanian part 10*106 m3 (annually for last ten years) Greek part 5*106 m3 (annually) Total 15*106 m3 of water

Summary results of Water Balance Small Prespa Elements Inflow Outflow 106 m3 106 m3 Precipitation 30 Runoff (catch. area) 22.8 Surface flow 55 –60 41 Groundwater - - Evaporation 53.5 Irrigation 15 TOTAL ≈ 110 ≈ 110

6 Greek data (IGME)

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BALWOIS 2004 Ohrid, FY Republic of Macedonia, 25-29 May 2004

Water balance of Big Prespa Lake Lake area 253.6 km2 Catchment area 1058 km2

Inflow: Precipitation, surface and underground flow, irrigation The inflow elements for Big Prespa Lake are as follow: a) contribution of precipitation (direct on water mirror), b) runoff from catchment area, c) surface or underground inflow.

• Precipitation on the surface lake The contribution of the precipitation according to the available data (long-term averages) for all meteorological station around the coast of the lake is as follows (see fig. 5):

Albania Liqenas 849 mm south-west side Gorice 910 mm west side Greece Koula 572 mm south side Ag. Germanos 638 mm south-east side Macedonia Asamati 614 mm north-east side Nakoleci 596 mm east side Stenje 868 mm west side Pokvernik 820 mm north side

Average for all surface area 733 mm After calculations result a total amount of 186*106 m3 of water coming in water mirror of the lake only by precipitation

Inflow from catchment area (runoff) The catchment area of Big Prespa Lake is not uniform (rainfall distribution speaking). In the west part of this catchment area the precipitation are higher than the east part, showing a value in the range of 800 – 950 mm /year for the all catchment area. The problem of the distribution of the meteorological stations in whole catchment area (especially in surrounding mountains) of Big Prespa is the same as for Small Prespa. The calculation of the inflow from the catchment area was evaluated according to the land characteristics and in the same time are taken into consideration the flow rate measurements in some stream flows in Greek territory (Ag. Germanous river) and Macedonian territory (Brajcinska, Kranska, Resenska and Istocka rivers). The whole catchment area was divided in three sub areas in the base of land characteristics concerning infiltration capability. The value that has been founded for the specific discharge of the east and southeast sub area (in total amount of 487 km2) was 13 l/s/km2 i.e. 199*106 m3 as a total inflow volume. The calculation of the inflow for the west and south–west sub area (in total surface of 327 km2) was based on the specific characteristics and hydrogeological approach (Karst formation), assuming a value of 10 % of the total rainfall which in this case is accepted 950mm/y and the value of 31*106 m3, was received. For the remaining catchment area of 244 km2 and the previously adopted value of 9 l/s/km2, an amount of 69*106 m3 has been obtained. On the basis of the above calculation has been received the value of 299*106 m3 as a total inflow from catchment area.

Surface or groundwater inflow As surface inflow in this paragraph is intended the amount of water coming from the Small Prespa Lake through the canal linking both lakes. Is the same water, which in the case of Small Prespa was considered as outflow and now for the Big Prespa is considered as inflow, so this amount is 41*106 m3.

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Concerning the underground inflow, according to the performed study on south part of the catchment area of the Big Prespa in Greek territory, the underground inflow of 8*106 m3 has been estimated7. In total there are 49*106 m3 of water coming by surface and groundwater way.

Outflow : evaporation, outflow by surface or groundwater way, irrigation

• Evaporation Concerning the evaluation of the open water evaporation in Big Prespa Lake the scenario is the same as for the Small Prespa Lake. Estimated value based on Penman Equation with Albanian data is 1180 mm. Greek Evaporimeter pan ………………………………………….. 1100 mm On the basis of the Environmental Isotope Study (balancing the δ8Οand δ 2Η values) performed in the past by the researchers of F.Y.R. of Macedonia, Anovski et al. (1987), for Big Prespa Lake, a value of 1000 mm has been received for the open water evaporation. Taking into account the average value of 1100 mm, total outflow due to the evaporation is estimated 279*106 m3.

Irrigation In Albanian part and Greek part the water of Big Prespa Lake used for irrigation is not important. In Macedonian part, according data furnished by Macedonian colleagues are used 10*106 m3 of water from Big Prespa Lake.

Outflow by surface or underground way In the Big Prespa Lake doesn’t exist outflow by surface way. Meanwhile the outflow by underground way is very important for the Big Prespa Lake. This outflow is through the well-known Zaveri abyss (very interesting and the only known because is visible) in Albanian part of Big Prespa Lake and the St.Naumi springs (Macedonian part) and Tushemishti springs (Albanian part) and some other underwater springs in Ohrid Lake. According the Hydrometeorological Institutes in Macedonia and Albania the long-term averages of the discharge of St. Naumi and Tushemishti springs are respectively 7.5 m3/s and around 2 m3/s. For the underwater springs in both countries it is not possible till now to estimate their discharges. Referring the conclusions of the isotopes studies caring out in the frame of “Study of Prespa Lakes using nuclear and related techniques” are obtained the percentages of the waters of Big Prespa Lake containing in the waters of St. Naumi and Tushemishti springs. According these conclusions it results that 40% of the discharge of St. Naumi springs belongs to the waters coming from Prespa Lake and for Tushemishti springs the conclusion is 54% of his discharge comes from Prespa Lake. In conclusion, the discharge of waters for the both springs, resulting coming from Big Prespa Lake, is 4.08 m3/s, that means a total volume of 129*106 m3. Note: In this amount of water is not included the contribution of the underwater springs (sublacustrine) in Ohrid Lake (unknown in our dates).

Summary water balance Big Prespa Elements Inflow Outflow 106 m3 106 m3 Precipitation 186 Runoff (catch. area) 299 Surface flow 41 Groundwater 129 Evaporation 279 Irrigation 10 TOTAL 526 418

7 IGME Data

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This is the first attempt for the calculation of water balance of Big Prespa Lake. The data, which are used, are not so reliable in some cases and the computation is hazardous. The differences between inflow and outflow can be explained by sublacustrine springs that are not possible to measure. With more reliable data is possible to compute better the elements of water balance of Big Prespa Lake in order to determine more accurately the contribution of sublacustrine springs. PS: During the last year of this Project was made a tentative to calculate the water balance of Big Prespa Lake for a short (fixed) period, i.e. for the year 1994 or 1995. Even in this case was not possible to find complete data for all elements in three countries. Conclusion on hydrological behaviour and water balance of Prespa Lake 1. The location of Prespa lakes between three countries inhibits intensive integrated studies. 2. Relatively little climatological or hydrological data in the region 3. Total absence of data for the mountains areas – hazardous computation. 4. Human activity in the area are not well evidenced in all three countries. 5. Water level of Big Prespa Lake is in continuing decreasing up to date and none of hypothesis has priority. The last hypothesis: The cycle of variation of water level may be longer that our observation period. Some paths under the water, observed during last fieldwork, serve as indicator of this hypothesis. 6. Hydrometeorological monitoring is required in Prespa region. In the hydrometeorological monitoring program must be included: - Three meteorological station for all elements: Gorica, Pretor and Koula. - All existing rainfall station must be continuing. Three rainfall instruments in altitude must be installed. - Hydrometric stations in the main rivers: Golema, Brajchinska (or Kranjska) and Ag. Germanos and a hydrometric station in channel linking two Prespas. All these stations must be equipped with auto recorder water level (rating curve). - Hydrometric stations in St. Naumi and Tushemishti springs.

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