European Water 60: 293-298, 2017. © 2017 E.W. Publications

Low flow conditions evaluation within the western Morava river basin

Z. Simić* and B.B. Matić Jaroslav Černi Institute for the Development of Water Resources, Belgrade, 11226, * e-mail: [email protected]

Abstract: The largest share of renewable internal fresh water resources in Serbia is located within the Western Morava River basin in central part of Serbia. Despite of the favourable natural conditions and water resources abundance, in last few years noticeable shortage in drinking water supply is detected in some regional water supply systems within the river basin, in particularly during the peak seasons, namely summer and autumn. Thus, like in many other parts of the world, consequences of observed changes in low flow accompanied with significant seasonal fluctuations in precipitation and runoff, emphases necessity for trough evaluation and analyses of the observed precipitation regime, runoff and low flows seasonal fluctuations within the drainage area. Moreover, evaluation of land use, hydrogeology and soil type provides better insight into natural retention capacity of significance for ground and surface water sources. Established correlation among precipitation, runoff, and natural retention capacity as a result of land use practices indicated significant differences of season low flow conditions. The results presented in this paper manifest necessity of comprehensive regional hydrological low flow investigation for future drinking water supply infrastructure and other water management facilities to sustain sustainable water resources management at the watershed level.

Key words: Low flow conditions, drinking water sources, natural retention capacity, seasonal fluctuations

1. INTRODUCTION

The Western Morava River basin (15,796 km2) is mainly located within the Serbian territory with small share (446 km2) located in Montenegro. Moreover, it has the largest share of renewable internal fresh water resources in Serbia and presents the most immense drinking water source reserves in the country that results in development of several large drinking water supply systems, e.g., water supply system, Gazivode water supply system, water supply system, Djetinja water supply system, Kragujevac water supply system (Republic of Serbia Water Management Master Plan, 2001; Water for 21st Century, 1999). Thus, assessment of low flows and natural retention capacity are of great interests given the noticeable shortage in existing drinking water supply systems located within the river basin. The Western Morava drainage area stretches south – north direction with well-developed hydrographic network (Figure 1). The river originates in Požeška ravine at the 300 m a.s.l. as the confluence of Moravica (1,513 km2), Djetinja (1,210 km2) and Skrapež (630 km2) rivers. Ibar River is the main Western Morava tributary with drainage area of 7,925 km2, followed by Rasina (990 km2), Čemernica (629 km2), Gruža (617 km2), etc. Despite the abundance good quality of fresh water the water shortage during the low flow conditions is detected, very likely due to competition among different users (water supply, hydropower, agriculture, industry). In addition, possible alteration in hydrological cycle (Houghton et al., 1996) and water resources will have adverse effects on sustainable water resources management. Multipurpose dams that serve many of the typical water management functions (Lindström et al., 2012) together with natural retention capacity as one the hydrological ecosystem service (UNEP, 2008, 2009; Burkhard et al., 2014) advance water resources resilience to diverse pressures and changes. At the present, there are several multipurpose dams within the drainage area. Reservoir Gazivode (average flow 13.5 m3/s) on river Ibar that serve for water supply, irrigation, hydropower. Ćelije 294 Z. Simic & B.B. Matic reservoir results from damming of river Rasina and is utilized for water supply, flood control and sediment management. It has average flow of 5.9 m3/s and uniform environmental flow of approximately 0.56 m3/s. reservoir located on Djetinja river main goal is city of Užice drinking water supply combined with flood control and environmental flow regulation for downstream locations. With respect to different users’ water supply there are few large reservoirs, e.g., Ovčar Banja, Medjuvršje, and Gruža for Kragujevac and Kraljevo drinking water supply. Finally, the regional drinking water supply system Rzav is located within the studied drainage area.

Figure 1. The Western Morava drainage area with main tributaries and evaluated hydrological stations

2. LOW FLOW FREQUENCY ANALYSES

At the present, 45 hydrological stations exist within the river basin. There is rationale to evaluate average monthly low flow data for selected 30 hydrological stations (Figure 1) that fully portray Western Morava drainage area hydrological regime. For selected localities observed data are fitted with theoretical distributions (Pearson, log Pearson, log Normal and Gumbel) to generate best fit curves for low flow probabilities. The low flow assessment is based on criteria that 95% of average minimum flows have to be maintained with purpose to set permit discharge limits downstream (Matić and Simić, 2016) of evaluated stations. To provide more uniform approach low flow probabilities at each hydrological station are normalized by equation:

NQLF (1-30) = Qlf (1-30) / A (1-30) (1) (1) where NQlf is the normalized low flow probability, QLF is low flow probability derived from the European Water 60 (2017) 295 observed data and A is hydrological station contributing drainage area. The summary results for all evaluated hydrological stations are exhibited in Figure 2.

5.5 5.0 4.5 4.0 3.5 2 3.0 2.5 l/s/km 2.0 1.5 1.0 0.5 0.0 50 55 60 65 70 75 80 85 90 95 100 probability (%)

Preljina Brđani Ribarići/Batrage Požega Guča Raška Kraljevo˛M.Most Kosjerić Trstenik Ušće Lopatnički Lakat Krat.stena&G.Most Kruščica Arilje Kruščica Bogutovac Šengolj /Radobuđa Novi Pazar Biljanovac Ušće Mlanča Devići

Figure 2. Normalized average monthly low flow probability values for evaluated hydrological stations

0.035

0.030

0.025 ) 2 0.020 s/km / 3 0.015 q (m 0.010

0.005 T (month) 0.000 1 2 3 4 5 6 7 8 9 10 11 12 Preljina Brđani Ribarići/Batrage Požega Guča Brus Bivolje Ravni Raška Kraljevo˛M.Most Kosjerić Trstenik Ušće Jasika Lopatnički Lakat Krat.stena&G.Most Stapari Kruščica Ivanjica Arilje Arilje Kruščica Bogutovac Šengolj Roge/Radobuđa Novi Pazar Biljanovac Ušće Mlanča Devići

Figure 3. Normalized average monthly low flow values within the Western Morava River Basin for hydrological stations

Based on Figure 3 that exhibits results for average monthly low flows analyses at each location it is evident that highest low flows are observed from August to October on River Lopatnica followed by upper part of River Ibar, etc. 296 Z. Simic & B.B. Matic

Since the scope of study is low flow evaluation within the whole river basin, the results presented above are grouped in four categories and the Western Morava river basin in divided in 4 zones with respect to that: 2 n Zone 1: with NQLF, >2.5 l/s/km 2 n Zone 2: 2.5 l/s/km2> NQLF>1.5 l/s/km 2 n Zone 3: 1.5 l/s/km2>NQLF>1.0 l/s/km 2 n Zone 4: NQLF < 1.0 l/s/km

Figure 4. Delineation of the Western Morava River basin

Spatial presentation on Figure 3 indicates that Zone 1 is located in the middle part of the Western Morava basin which is quite surprising it was expected that the largest reserves are located along the basins’ perimeter. Zone 2 is located within the Rzav catchment in western part. Zone 4 is comprised of smaller rivers catchments located on the north part and main share of Ibar River on the south. The remaining part of Western Morava basin is within the Zone 3. Given that based on available data and methodology the Zone 1 has the largest water yield during the low flow conditions.

3. NATURAL CONDITIONS EVALUATION WITHIN THE DEFINED NORMALIZED LOW FLOW ZONES

Introduction of the natural retention capacity is simplified by evaluation of main natural features within the four defined NQLF Zones e.g. precipitation, land cover, etc., with no intention to go in detailed assessment of it, since it is the beyond the scope of this paper. The four Zones natural characteristics located in Western Morava Basin are summarized in Table 1 and Figures 3 and 4 exhibits graphically natural features, elevation, hydrogeology, slope and land use practices, in a given order. European Water 60 (2017) 297

Table 1. Natural characteristics of evaluated zones within the Western Morava River Basin

Zone 1 Zone 2 Zone 3 Zone 4 Area (km2) 809 2351.7 4962.27 7673.05 Precipitation (mm/god) 912.1 841.7 768.6 820.6 Average basin elevation (m.a.s.l) 1123.16 839.59 545.48 754.79 Average slope (%) 24.48 19.66 13.29 13.76 Forest (311+312+313) 65.69% 53.68% 40.63% 44.31% Pedology distric distric distric kam. mix Broad-leaved forest (311) kambisol34.86% kambisol44.27% (19)35.42% and 41.15% Land principally occupied by 11.91%(19) 23.64%(19) pseudogley20.23% 14.33% Complexagriculture cultivation (243) patterns (242) 4.72% 7.58% 20.42%(23) 12.91% Transitional woodland-shrub (324) 12.05% 7.75% 6.29% 7.22% Non-irrigated arable land (211) 0.25% 0.32% 5.73% 10.65% Mixed forest (313) 16.93% 5.34% 2.85% 1.58% Coniferous forest (312) 13.91% 4.07% 2.35% 1.58% Natural grasslands (321) 2.86% 4.01% 1.47% 3.43% Discontinuous urban fabric (112) 0.00% 0.77% 2.12% 2.36% Pastures (231) 2.00% 1.77% 1.38% 2.22%

Figure 5. Slope (%) and CLC Corine 2012

Based on overview of data and information presented above the Zone 1 has the highest NQLF and natural retention capacity given the average precipitation, during the low flow conditions given the average precipitation of 912 mm, 66% land covered by forest and low urbanization. Although the Zone 2 have favourable values with respect to NQLF and natural conditions (54% land covered by forest) the shortage in water supply is observed there during the peak seasons (summer and autumn) likely due to highest percentage of agricultural activities (24%). Zone 3 is more urbanized in comparison to Zone 1 and 2 and has less than 50% of forests in addition to lowest average precipitation. The outputs for Zone 4 are quite interesting since the average precipitation, percentage of land covered by forest are higher than in Zone 3.

4. CONCLUSIONS

The study of low flows within the Western Morava River Basin emphasizes existence of four normalized low flow (NQLF) zones. The findings indicated that the highest NQLF is observed in central part of the drainage area where in addition to precipitation other features relevant for natural 298 Z. Simic & B.B. Matic retention capacity (land cover, low urbanization, the highest elevation). The quite interesting findings refer to Zone 2 in which water shortage exists during the peak seasons (summer and autumn). The general overview of potential natural retention capacity based on available data and information underlined necessity for its more comprehensive evaluation as a part of contemporary water resources management. It is of particular interest for drinking water supply, since it requires enough quantity of water that corresponds to high quality standards. The new drinking water supply systems within Western Morava River should be located in the Zone 1 at the First place, followed by Zone 2, 3 and 4. Moreover, the environmental protection criteria should be the most inflexible in the Zone with highest NQLF and natural retention capacity. The methodology developed in this study that comprises of low flow analyses and natural retention capacity general overview is suitable for any large river basin. The more comprehensive and detailed analyses and evaluation are more applicable at the sub basins level and smaller river basins. Outcomes presented here are useful for strategical planning and delineation of the most significant locations for drinking water supply.

ACKNOWLEDGMENTS

Hydrological data presented in this study are based on available data and Jaroslav Černi Institute for Water Resources Development research, studies, and reports are supported by Ministry of Education, Science, and Technological Development of Serbia projects ТR 37013 (Development of decision support system for large dam maintenance in Serbia) and TR 37005 (Assessment of climate change impacts on water resources in Serbia).

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