AVERAGE ANNUAL RIVER DISCHARGE ASSESSMENT, YANTRA RIVER, NORTH BULGARIA

Elena Kirilova Bojilova

National Institute of Meteorology and Hydrology

Corresponding author: E. Bojilova, National Institute of Meteorology and Hydrology, Bulgaria, 1784 Sofia,

Tzarigradsko chausses Avenue 66, Elena.kirilova.bojilova@gmail.com 

INTRODUCTION

The study was performed for the needs of Danube river basin directorate in Bulgaria. The object of investigation

is Yantra river basin situated in North Bulgaria.  

The Bulgarian Ministry of Environment and Water was provided the points for each effluent or water abstraction facility. For all points it was requested to evaluate 10% of multiannual average river discharge. For the drainage basin of Yantra river the points are 195. The selected cross section (points) are along the main river body and also on the main river tributaries. The majority of the points are located in the drainage basins of Vidima, Rositza, Belitza and Drianovska rivers.  

Three homogeneous regions were determined: upper mountain tributaries; middle part and lower part of Yantra river basin. Map with determined homogeneous regions for the drainage river basin is elaborated. The obtained results are discussed.

YANTRA RIVER BASIN

Yantra river basin belongs to Danube river basin directorate in Bulgaria. By the size of the catchment area (approximately 7 862 km2), the Yantra River is the second largest in the Danube River Basin. The watershed of river Yantra is situated between Osam river basin from West direction, Rusenski Lom and Kamchia rivers from East, form North the border is Danube river. To the south Balkan mountain is a water divide with the rivers Maritsa and Tundja. The Yantra River originates from Mount Hadji Dimitar (Balkan mountain), approximately 1 340 m above mean sea level. The river length is around 285 km. Up to Veliko Turnovo town the river flows in north-east direction. After Veliko Turnovo the river turns in east direction making curve and since that is flowing in north direction. Yantra joins Danube River near Krivina village at approximately 18 m altitude.

The Yantra River has thirty tributaries over 10 km in length (for example: Rositsa River, Stara Reka, Djulyunitsa River, etc.). The average altitude for the entire catchment area is 470 m and the average slope varies from 10.6 ‰ (Stara reka River) to 48 ‰ (for the Plachkovska River). River Yantra has an average slope of about 34 ‰ in its upper stream, while at the mouth it reaches 0.25 ‰, where it is also characterized by a high coefficient of curvature.

The relief in the upper part of the catchment is mountainous and abounds in high mountain ridges and peaks. The middle part is characterized by many hilly heights. The lower stream, which crosses the Danube Plain, is characterized by smooth rounded hills, which cross the low terraces near the Danube.

Authors (see Dimitrov et al., 2017) worked on trends assessment of hydrometeorological elements in Nort-western Bulgaria. The stochastic modelling in water resources management was performed (for example Yordanova A. et al., 2017). The TOPKAPI model for Ogosta river in Nort Bulgaria was applied and further used for short term river forecasts (Yordanova V. et al., 2017). Ninov and Karagiozova (Ninov et al., 2014; Karagiozova et al., 2017) investigated technology for determination of annual surface water resources in Bulgaria. In 2012 Hristova (Hristova N., 2012) made an overview of river runoff of Bulgaria. Furthermore, Hristova and Seymenov (Hristova et al., 2019) worked on annual flow dynamics in river basins with different sizes located in North Bulgaria. Furthermore, Orehova and Vasileva (Orehova et al., 2014) studied the atmospheric chloride deposition in the Danube hydrological zone of Bulgaria.

 INFORMATION PROVIDED FROM THE MINISTRY

From the Bulgarian Ministry of Environment and Water are provided the points for each effluent or water abstraction facility. For all points it was requested to evaluate 10% of multiannual average river discharge. For the drainage basin of Yantra river the points are 195. The selected cross sections are along the main river body and also on the main river tributaries. The majority of the points are located in the drainage basins of Vidima, Rositza, Belitza and Drianovska rivers (Fig. 1). There is a number of points along the main river body too.

Fig. 1. Points (cross sections) for investigation (in red)

HYDROLOGICAL INFORMATION

The monitoring network of National Institute of Meteorology and Hydrology for the catchment of Yantra River consist of 13 hydrological gauge stations (see Table 1). Three of them are located on the main body of Yantra River and others are on its tributaries. More significant tributaries are: the Rositsa River, 164 km long and catchment area of 2 265 km2; Lefedja River - 92 km in length and catchment area 2 424 km2; Dzhulunitsa River - 85 km in length and area of 892 km2. In terms of area, the hydrological stations cover the whole catchment area, with their density in the upper and middle part of the catchment being greater than in the lower flat part.  

The author performed extended studies concerning integrated river basin modelling of Upper Yantra River (Bojilova, 2010). The high flows in drainage basin of Yantra River were evalueted (Bojilova, 2016). Furthermore, inter-annual distribution for the basin was investigated (Bojilova, 2017).

For the purposes of the study, time series with average annual water discharges from all stations are used. For the differentiation of the individual regions a comparative expert assessment of the conditions for formation of the runoff in the entire catchment was made. The upper stations are alpine with a large slope and a small catchment area. Gradually the slope decreases, but the area does not grow so fast. Midrange stations have a smaller slope but have a larger area.  

ESTIMATION OF 10% OF THE AVERAGE ANNUAL DISCHARGES AT THE POINT OF ANY EFFLUENT OR WATER ABSTRACTION FACILITY IN THE YANTRA RIVER BASIN

The 1981-2014 time period is executed. Data from all available hydrological stations are used. The database is 34 years of records. 10% of the average annual discharges at the point of any effluent or water abstraction facility in the Yantra River basin are calculated.  

Table 1. Used hydrological stations in Yantra River basin

The method of hydrological regionalization has been used. The method is statistical by applying regression analysis. With its help, regional regression equations are created. Regression establishes a statistical relationship between the runoff (in this case 10% of the average annual runoff) and selected water catchment characteristics (in this case the catchment area).

The methodology for hydrological regionalization does not allow determination of runoff in isolated water bodies with extremely small area (few km2), since it is possible that the determined water quantity is not within the tolerable error for the method. Therefore, in the present study for catchments below 10 km2 the water values have not been determined.

HOMOGENEOUS REGIONS

After a detailed analysis of the basin of the Yantra river there were identified three homogeneous regions using the regional correlation method as follows: upper mountain tributaries; middle part and lower part of the Yantra river basin.  

Region 1 – Upper mountain tributaries

For the region of upper mountain tributaries four stations are utilised: the station at Vaglevzi village (23030) for Belitza River; Ostrezka River at Aprilovzi village (23200); Rositza River at village Valevtzi (23450) and Yantra River at Gabrovo city (Fig. 2).

Region 2 - Middle part of the Yantra River basin

The following stations are used: Lefedja River (Stara Reka) at Slivovitsa village (23100), Vidima River at Sevlievo city (23250), Dryanovska River - Tsareva Livada (23350), Djulyunitsa river (station 23400), Rositsa River at Sevlievo (23500) and Yantra River – Veliko Tarnovo town, in the district of Cholakovtsi (23700). The area is characterized by a gradual increase in the catchment area and homogenous factors for generation of river discharge (Fig. 3).

Fig. 2. Regional relationship for Region 1

Fig. 3. Regional relationship for Region 2

Region 3 - Lower part of the Yantra River basin  

The stations used are: Yantra river at village Karantsi (23850), 23570 closed station, Golyama Reka river near Strazhitsa village (23150) and Rositsa River near the village of Vodoley (23550). The resulting regional relationship is presented in Fig. 4.

After determination of the three homogeneous regions 10% of multiannual average river discharge for the points for each effluent or water abstraction facility were evaluated. Data for 195 points were calculated and presented to the Ministry. For visualization, the map with the homogeneous regions in Yantra river watershed was prepared (see Fig. 5).

Fig. 4. Regional relationship for Region 3

Fig. 5. Main homogeneous regions in Yantra catchment area for estimation of 10%
of the multiannual average river discharge

RESULTS AND DISCUSSIONS

The Bulgarian Ministry of Environment and Water was provided the points for each effluent or water abstraction facility. For all points it was requested to evaluate 10% of multiannual average river discharge. For the drainage basin of Yantra River, Danube River basin directorate, the points are 195.  

The method of hydrological regionalization has been used. With its help, regional regression equations were created. Regression establishes a statistical relationship between the 10 % of the average annual runoff and the catchment area.

Three homogeneous regions were determined: upper mountain tributaries – region 1; middle part – region 2, and lower part of Yantra River basin (region 3). Map with determined homogeneous regions for the Yantra River basin was elaborated.  

REFERENCES

Bojilova E. Upper Yantra River Basin Modelling. Bulgarian Journal of Meteorology & Hydrology (BJMH), Volume 15, ISSN 0861-0762, number 3, 2010. P. 93-104.

Bojilova E. High flows in drainage basin of Yantra river, Proceedings of the international conference BALKANERECO’16, Vol 9, №1, ISSN 1311-2783, 2016. P. 125-127.

Bojilova E. Inter-annual distribution for Yantra river basin, North Bulgaria. E-book with full paper from XXVII Conference of The Danubian Countries “On Hydrological Forecasting and Hydrological Bases of Water Management”, 26-28 September 2017, Golden Sands, Bulgaria, ISBN 978-654-90537-2-2, 2017. P. 346-355. www.danubeconference2017.org 

Dimitrov Y., Yordanova A. Trends assessment of meteorological factors, river flow and droughts in North-western Bulgaria. E-book with full paper from XXVII Conference of The Danubian Countries “On Hydrological Forecasting and Hydrological Bases of Water Management”, 26-28 September 2017, Golden Sands, Bulgaria, ISBN 978-654-90537-2-2, 2017.  www.danubeconference2017.org

Karagiozova Tz., Ninov P. Determination of water resources in the national park Rila in the absence of a monitoring network. E-book with full paper from XXVII Conference of The Danubian Countries “On Hydrological Forecasting and Hydrological Bases of Water Management”, 26-28 September 2017, Golden Sands, Bulgaria, ISBN 978-654-90537-2-2, 2017.  www.danubeconference2017.org

Ninov Pl., Karagiozova Tz.  Technological Approach to determine the water resources of river water bodies - using hydrological monitoring network. Hydrological International Scientific Conference „Adaptation to climate change, from source to river basin”, Bucharest, 2014.

Orehova T., Vasileva T. 2014. Evaluation of the atmospheric chloride deposition in the Danube hydrological zone of Bulgaria. Environmental Earth Sciences, 72, 4, 1143-1154, Springer, ISSN 1866-6280, DOI:10.1007/s12665-013-3032-5

Нели Христова. Речни води в България. 978-954-723-000-4, Издателска къща „Тип-топ прес“, 2012. 500 p. [Neli Hristova. River flow in Bulgaria, Tip-top press, 2012. 500 p. in Bulgarian]

Hristova N., Seymenov K. Annual flow dynamics in large and small drainage basins in Northern Bulgaria during the last two decades. SocioBrains. ISSN 2367-5721, journal homepage: www.sociobrains.com, February 2019. issue 54, P. 123-131.

Yordanova A., Niagolov I., Ilcheva I. Aspects of stochastic modeling in water resource management. E-book with full paper from XXVII Conference of The Danubian Countries “On Hydrological Forecasting and Hydrological Bases of Water Management”, 26-28 September 2017, Golden Sands, Bulgaria, ISBN 978-654-90537-2-2, 2017.  www.danubeconference2017.org 

Yordanova V., Balabanova Sn., Stoyanova V. Application of the TOPKAPI model on the Ogosta river basin. E-book with full paper from XXVII Conference of The Danubian Countries “On Hydrological Forecasting and Hydrological Bases of Water Management”, 26-28 September 2017, Golden Sands, Bulgaria, ISBN 978-654-90537-2-2, 2017.  www.danubeconference2017.org 

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