Hydrology of Lake Prespa
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UDK: 551.481.1 Originalni naučni rad HYDROLOGY OF LAKE PRESPA Cvetanka POPOVSKA University of Ss Cyril and Methodius, Civil Engineering Faculty, 1000 Skopje, Macedonia e-mail:[email protected] ABSTRACT developed, while the west part is rather poor. Around the Lake high mountains rise: in the West Galichitsa During the last century the Macro Lake Prespa Mountain (2.262 m asl.), Dry Mountain (1.863 m asl.), experienced a significant water level fluctuation. After and Petrinska Mountain (1.660 m asl.), in the east is its last peak (1963) and after the separation of the Micro Baba Mountain (2.601 m asl.), while in the north is Lake Prespa (1975), the level generally dropped by Bigla Mountain (1.990 m asl.). approximately 8 m (2002). This resulted to a loss in water volume and even more significant a loss of water The cumulative distribution of elevations in the surface. The effects and causes of the changes in the catchment has been defined on the basis of a 30x30 m Lake have been investigated in various studies carried Digital Elevation Model (DEM) and reflects the steep out by interested parties from shareholding countries. character of the watershed with moderately flat bottom. Most of these studies had to rely on the The elevation range is presented in Table 1. Mean hydrometeorological data that were not up-to-date or altitude of the watershed is 1.118,37 m asl, while the not complete. In this study, effort was made to collect mean slope is 21,37%. Main rivers in the Macedonian 2 long-term time series climatic and hydrological data and part of the watershed are: Golema (A=174 km ) and 2 to assess the vulnerability of Lake Prespa to climate Istochka (A=90 km ) on the North, and Kranska (A=74 2 2 change and human actions in the watershed. Monitoring km ), Kurbinska/Pretorska (A=8,6 km ) and 2 network and data quality and quantity is also discussed Brajchinska (A=74 km ) on the East. in the context of hydrological modelling and transboundary collaboration in integrated water Land use and land cover of the watershed is defined by resources management. Hydrological analysis is CORINE Land Cover (CLC) EU database which obtained using measured data for the period (1951- provides comparable digital maps on land cover, 2010) at Pretor meteorological station and Stenje biotopes, soil, and acid rain for over 22 countries in hydrological station. Europe. The map was created in GIS ARC/INFO format based on the interpretation of satellite images with land Kay words: Prespa Lake, hydrology, precipitation, cover types in 44 standard classes. The forests and semi 2 water balance natural areas cover 437,82 km (75,38%), agricultural 2 land participate with 120,53 km (20,81%), artificial 1. WATERSHED CHARACTERISTICS areas (urban, industrial and commercial units, mines, damps and construction sites) participate with 4,56 km2 The physical geographical characteristics of the Lakes (0,785%), and water bodies cover only 6,4 km2 (1,1%). Prespa watershed and sub-watersheds were defined on the basis of digital topographic maps in scale 1:25.000 Table1. Watershed characteristics of Lakes Prespa and satellite images with high resolution. The Macro Area Hmin Hmax Hav Slope 2 Lake Prespa catchment area is defined to be 1.110 km (km2) (m asl) (m asl) (m asl) (%) (including 278 km2 lake surface) and that one of Micro Lake Prespa is 253 km2 (including 48,5 km2 Lake Macedonia 761,00 844 2420 1118,37 21,37 surface) at Lake water level of 844 m asl. The Albania 261,19 844 2275 1207,41 26,23 Macedonian part of the catchment area is 52,1% and Greece 341,52 844 2161 1132,60 24,41 that of Lake surface is 65,7%. Northern and eastern parts of the watershed are well hydrographically Total: 1363,71 VODOPRIVREDA 0350-0519, Vol. 48 (2016) No. 279-281 p. 19-28 19 Hidrologija Prespanskog jezera Cvetanka Popovska Figure 1. Prespa Lake is recognised by the natural beauty and rare biodiversity 2. MONITORING NETWORK temperature, humidity, wind speed, and solar radiation. Rainfalls are measured at rain gauges at Asamati (860 m The monitoring in Macro Lake Prespa watershed has asl), Brajchino (1020 m asl), Carev Dvor (864 m asl), been established in accordance with the national Izbishta (980 m asl), Nakolec (850 m asl), Stenje (855 legislative in Macedonia: Law on Waters, Law on m asl). Unfortunately, there is no precipitation data for hydrometeorological affairs and Programme for higher region of the watershed. Also, data on snow are protection of Ohrid, Prespa and Dojran Lakes. The map not available on higher altitudes. of the existing hydrological and meteorological stations is presented in Figure 2. Hydrological stations for 2.1 Data availability and evaluation measuring the water level in the Lake are established at the villages: Stenje (1935), Asamati (1948) and Nakolec In vulnerability assessment of the Lakes and their (1954). All stations are equipped with water level ecosystem most important are historical data quantity recorders and water level gauges. Besides these there and quality. Hydrological and meteorological data are are three stations on the main rivers in the watershed: on basis in water balance modeling as one of the objectives Golema River in Resen (1947), Leva River (1986) and in vulnerability assessment and adaptation measures. In Brajchinska in Brajchino (1964). Recently (2012) in Table 2 are presented all kind of data that have been Resen has been established an automatic hydrological collected and tools used within this study. The input and station. Systematic groundwater monitoring doesn’t output components in the approximate water balance exist. For agricultural purposes there are have been model are obtained as it follows. constructed 7 shallow wells at Krani, Asamati, Resen, Krushje, Carev Dvor, Preljublje and Stenje. At these 2.1.1 Precipitation points there are sporadic groundwater and water quality measurements. Within the UNDP project The precipitations in the watershed have been analyzed “Hydrogeological Study for the Lake Prespa by collected monthly data for the period (1951-2010) Watershed” (2014/2015), 15 deep piezometers have from 7 rain gauge stations in the watershed: Asamati, been constructed with regular monthly water level Stenje, Izbishta, Carev Dvor, Nakolec, Brajchino and fluctuation and water quality monitoring. Pretor. The total amount of precipitation in the watershed is computed by the following expression: Meteorological monitoring is very important especially ⋅= APV in hydrological modeling of surface runoff and erosion p ∑ Δt (1) in the watershed. Climatologically station in Resen (881 m asl) is established in 1947 but stopped operation in Where (ΣPΔt) is the average precipitation sum in the 1993. Meteorological station in Pretor (993 m asl) is watershed for the time period (Δt), and (А) is the established in 1991. Since 2007 six automatic agro- watershed area. The average annual precipitation in meteorological stations have been established at Macedonian part of Lake Prespa watershed is 900 mm Jankovec, Resen, Dolna Bela Crkva, Krani, Lavci and obtained by the method of isohyets. Gorno Dupeni with hourly data on precipitation, air 20 VODOPRIVREDA 0350-0519, Vol. 48 (2016) No. 279-281 p. 19-28 Cvetanka Popovska Hidrologija Prespanskog jezera Figure 2. Monitoring sites in Macro Lake Prespa watershed 2.1.2 Water surface evaporation Three recommended formulas have been use: Penman, Rohwer and Mayer. Penman results showed the most Evaporation from free surface water in Lake Prespa stable distribution and have been considered as the most watershed has been computed by empirical formulas reliable to be used in future analysis. The average using data on air temperature, saturated vapour pressure, annual evaporation sum is obtained to be 798.02 mm. radiation, sunshine duration, wind speed, and albedo Comparing the annual amount of precipitation fall over effect. The total amount of evaporation from Lakes the Lake and evaporation it is concluded that evaporated Prespa water surface is obtained by the expression: water is less than precipitation. Figure 3 presents precipitation at Stenje for the period (1951-2004) and ⋅= AEI E Δt ∑∑ (2) computed evaporation using climatic data from Resen for the period (1952-1988). Monthly precipitation and Where (ΣEΔt) is the evaporated water from lakes’ evaporation distribution in an average year have shown surfaces for the period (Δt), and (ΣA) is a free surface that in April, May, June, July, August and September areas at normal water level (Macro Lake area A=278 the evaporation is greater than the incoming water from km2 and Micro Lake area A=48,5 km2 at 844 m asl). precipitation. VODOPRIVREDA 0350-0519, Vol. 48 (2016) No. 279-281 p. 19-28 21 Hidrologija Prespanskog jezera Cvetanka Popovska Table 2. Available data and tools used in evaluation Topographic Digital Elevation Model (DEM) (30G30 m) Land use CORINE Land Cover Climatic-meteorological Type of data Station Period Missing Precipitation Asamati 1951-1991 Stenje 1951-2004 Izbishta 1951-2004 Carev Dvor 1951-2004 1991-1995 1991-1993 Nakolec 1951-2004 1997-2002 Brajchino 1951-2004 Resen 1952-1993 Pretor 1991-2010 Temperature Resen 1952-1993 Pretor 1991-2010 Wind speed Resen 1952-1990 Pretor 1991-2010 Relative humidity Resen 1952-1988 Pretor 1991-2010 Sunshine duration Resen 1952-1988 Pretor 1991-2010 Hydrological Water levels Stenje 1951-2010 1400 1200 P_STENJE E 1000 800 600 400 200 Precipitation P (mm) / Evaporation E (mm) 0 1950 1960 1970 1980 1990 2000 2010 Time-T (year) Figure 3. Annual precipitation and evaporation distribution over the Lake 22 VODOPRIVREDA 0350-0519, Vol. 48 (2016) No. 279-281 p. 19-28 Cvetanka Popovska Hidrologija Prespanskog jezera 2.1.3 Evapotranspiration computed by Penman formula, Table 3.