PART 1
Surface water levels and flow ratesSurface water level recording in the hydrological year 2003 were carried out on 28 gauging stations on the Slovak side and 29 gauging stations on the Hungarian side (Tab. 1-1). On some of them flow rate calculations were performed as well. The situation of observation network is shown on Fig. 1-1a and Fig. 1-1b. The Parties in the intergovernmental Agreement have undertaken to mutually exchange data from agreed gauging stations. Joint flow rate measurements helped the joint evaluation of flow rates flowing into the Danube downstream of the Čunovo dam and into the Mosoni branch of the Danube. Based on mutual evaluation of joint measurements agreed time series data were accepted. These data create the basis for joint evaluation of measures and water supply realised according to Articles 1-3 of the Agreement. Table 1-1: List of gauging stations
In the frame of the intergovernmental Agreement, signed on April 19, 1995, a temporary water management regime was set up. It was agreed that in the case of average annual flow rate of 2025 m3s-1 at Bratislava-Devín the annual average of 400 m3s-1 should be discharged into the Danube old riverbed downstream of Čunovo. The daily amount of water is governed by the flow rate reaching the Bratislava-Devín profile, taking into consideration rules of operation described in the Annex 2 of the Agreement. The flow rate in vegetation period, depending on hydrological conditions, should fluctuate from 400 to 600 m3s-1; in the non-vegetation period the flow rate should not be less than 250 m3s-1. In case of floods the amount of water above 600 m3s-1 discharged through the inundation weir is not taken into consideration when the annual average is calculated. Additional 43 m3s-1 of water was agreed in the Agreement to be discharged into the Mosoni branch of the Danube and the right side seepage canal. The gauging station Bratislava-Devín plays the key role in determination of water amount discharged into the Danube old riverbed downstream of the Čunovo dam. The annual minimum flow rate occurred on September 8, 2003, when the average daily flow rate was 855.4 m3s-1, the annual maximum flow rate occurred on November 12, 2002, when it reached 5650 m3s-1 (average daily maximum flow rate was 5214 m3s-1). The average annual flow rate in this station in the hydrological year 2003 was 2000.75 m3s-1, which was close to the annual average flow rate considered in the intergovernmental Agreement (Tab. 1-2). However, considering the course of water levels and flow rates during the hydrological year 2003 it can be stated that it was an atypical year. Extremely water rich months occurred in the winter period (November 2002, December 2002 and January 2003). On the other side extremely water poor and water poor months occurred during the vegetation period (April-September 2003). Table 1-2: Average annual flow rates
Low flow rates in the Danube during the hydrological year 2003, in contrast to other years, occurred at the end of vegetation period in August and September 2003. November 2002 was extremely water rich and the average daily flow rates varied from 2733 to 5214 m3s-1. After the culmination in the middle of November 2002 the flow rates continuously decreased till the middle of December 2002. However, in the third decade of December flow rates, due to rich precipitation in the Danube catchment area, significantly increased and the average daily flow rate reached 4599 m3s-1. At the end of December 2002, after a sudden decrease, the flow rate started to increase again and the flow rate culminated in the first decade of January 2003, when the average daily flow rate reached 4318 m3s-1. Flow rates during the January significantly decreased, however at the end of the month, an increase occurred again. During the February the average daily flow rates continuously decreased and varied up to 1500 m3s-1. In March 2003 flow rates mainly varied from 1700 to 2200 m3s-1. The average daily flow rates in April fluctuated below, and during May, and during the first half of June oscillated around 2000 m3s-1. Considering the monthly average flow rates this period can be characterised as a dry period. At the end of June 2003 the average daily flow rates started to decrease and decreased till the middle of July, when they reached values below 1000 m3s-1. After a slight increase at the end of July and beginning of August 2003 the average daily flow rates steeply decreased and fluctuated around 1000 m3s-1. At the beginning of September the decrease continued and on September 8-9, 2003 the average daily flow rate reached the annual minimum values of 855.4 m3s-1. In spite of significant increase in the middle of September, the flow rates remained low till the beginning of October 2003. At the end of the first decade of October significant increase of flow rates occurred due to heavy rains and the average daily discharge reached 3658 m3s-1. However, after the culmination the flow rate till the end of hydrological year continuously decreased. Based on abovementioned facts it can be stated that in spite of the normal average annual flow rate extremely low flow rates were recorded during the vegetation period. The course of flow rates during the hydrological year 2003 at gauging station No. 1250 - Bratislava-Devín is shown in Fig. 1-2. 1.1. Discharge into the Danube downstream of ČunovoThe determination of the average daily amount of water discharged into the Danube downstream of Čunovo dam was based on average daily flow rates determined at stations Doborgaz and Helena (Fig. 1-3). The monthly characteristics of the daily average flow rates into the Danube in the hydrological year 2003 were as follows:
The average annual flow rate in the Danube at Bratislava-Devín profile in the hydrological year 2003 was 2000.75 m3s-1. Taking into consideration obligations envisaged in the intergovernmental Agreement the Slovak Party was obliged to release an average annual discharge of 395.21 m3.s-1 into the Danube riverbed downstream of Čunovo dam. The total average annual discharge released to the Danube downstream of Čunovo was 398.97 m3s-1. During the hydrological year 2003 it was necessary to release amount of water into the riverbed downstream of Čunovo higher than 600 m3s-1 only in one occasion due to high flow rate in November 2002 in the Danube. When subtracting the amount of water over 600 m3s-1, released during the flood events (1 value), the average annual flow rate of 397.94 m3s-1 is obtained. When evaluating the amount of water discharged to the Danube old riverbed, it can be stated that Slovak Party fulfilled the average annual discharge jointly agreed in the intergovernmental Agreement. Taking into consideration the minimal values prescribed in the Agreement (in the winter period not less than 250 m3s-1, in the vegetation period at least 400 m3s-1) it can be stated that the minimal daily average discharges in the winter period were lower during several days than the prescribed value. The minimal daily average discharges in the summer period, except of few occasions (in April), was satisfied. These differences came from belated update of Q-H curves at the reference profile on the Slovak side, where changes in riverbed morphology arose after floods in 2002. 1.2. Discharge into the Mosoni branch of the DanubeThe discharge into the Mosoni branch of the Danube according to the intergovernmental Agreement should be 43 m3s-1, which is composed by the discharge released to the Mosoni branch of the Danube through the intake structure at Čunovo and the discharge through the seepage canal. Discharge measurements are carried out downstream of the intake structure on the Slovak territory at 0.160 rkm and upstream of lock No. I on the Hungarian territory. The average daily discharges were agreed after the joint evaluation of joint discharge measurements performed at both profiles. In the evaluation the data measured just downstream of the intake structure were considered (Fig. 1-4). The monthly characteristics of the amount of water released into the Mosoni Danube through the intake at Čunovo in the hydrological year 2003 were as follows:
The average annual discharge was 42.56 m3s-1. The flow rate in the right side seepage canal was measured at two sites as well. The first is on the Slovak territory at Čunovo; the second is placed on the Hungarian territory at lock No. II. In the evaluation the data observed at lock No. II were considered. The monthly characteristics of the flow rates recorded at lock No. II in the hydrological year 2003 were as follows:
The average annual flow rate was 2.30 m3s-1. There was a continuous slow decrease of discharge observed in the seepage canal during previous years, so the hydrological conditions did not allowed continuous releasing of 3 m3s-1, which are envisaged in the Agreement. However, after the floods in March and August 2002 significant increase of seepage water amount can be observed. The average annual flow rate in the seepage canal approaches the average annual flow rate observed in 1998. The monthly characteristics of the total flow rate released into the Mosoni Danube in the hydrological year 2003, consisting of the amount of water released by the intake structure at Čunovo and amount of water in the right side seepage canal were as follows:
The total average annual flow rate was 44.87 m3s-1. Based on the evaluation it can be stated that the average annual discharge into the Mosoni Danube envisaged in the Agreement was fulfilled. 1.3. Water distribution on the Hungarian territoryThe goal of the water distribution on the Hungarian side is to provide continuous water supply into the inundation area, into the river branches on the flood-protected area and into the Mosoni Danube. 1.3.1. Water supply into the inundation area The inundation area on the Hungarian side can be supplied by water from two sources: a.) Through two openings in the Danube riverbank, by manipulating the water level increased by the submerged weir and the Dunakiliti dam. The total inflowing discharge is measured at Helena profile. b.) From the seepage canal through the lock No. V. Joint flow rate measurements by both Parties were performed at the Helena profile too. The measurements were jointly evaluated and average daily flow rate data were accepted. The monthly flow rate characteristics at Helena profile in the hydrological year 2003 were as follows:
The average annual flow rate was 58.31 m3s-1. The monthly flow rate characteristics at the lock No. V in the hydrological year 2003 were as follows:
The average annual flow rate was 13.68 m3s-1. The monthly flow rate characteristics of the total amount of water released into the inundation area in hydrological year 2003 (Fig. 1-5):
The total average annual flow rate supplied into the inundation area was 71.99 m3s-1. 1.3.2. Water supply into the Mosoni Danube The water supply into the Mosoni Danube is secured from the seepage canal through the lock No. VI (Fig. 1-6). The flow rate is measured at the profile downstream of the lock. The monthly characteristics of the flow rates through the lock No. VI in hydrological year 2003 were as follows:
The average annual flow rate in the Mosoni Danube at lock No. VI. was 27.41 m3s-1. During the non-vegetation period low water period was simulated in the Mosoni Danube as well. This was reached by redirecting of a large part of the water from the seepage canal into the inundation area through the lock No. V., while the water amount taken from the Danube upstream Dunakiliti was reduced. Besides the water supply function the lock No. I has also a flood protection function. It prevents floods to enter the flood-protected area. 1.4. The Danube water level characteristics on the Čunovo-Vámosszabadi stretchAccording to the prevailing influence the Danube stretch between Čunovo and Vámosszabadi can be divided into four different sections. These sections can be characterised by data obtained from the following gauging stations: Rajka and Hamuliakovo, Dunakiliti, Doborgaz and Dobrohoąť, Dunaremete and Gabčíkovo. Vámosszabadi and Medveďov. The characteristics of four sections on the Čunovo-Vámosszabadi stretch in the hydrological year 2003 are the following: a) Čunovo - Dunakiliti section. The water level in this section is impounded since construction of
the submerged weir. This impounded section allows the water supply into the
right side river branch system. The amount of water released to the river
branch system is determined by water level regulation at the Dunakiliti dam.
The water level is kept in the mid-water riverbed. The average flow velocities
fluctuated in the range between 0.25-0.60 ms-1. During the
hydrological year 2003 discharge over 600 m3s-1 into the
Danube old riverbed was released in two occasions. At November 13, 2002 because
of flood and at September 14-15, 2003 to keep the water level in the Danube
riverbed downstream of Čunovo dam higher due to technical reasons. b) Section between Dunakiliti and Dunaremete. This section of the Danube is not influenced by any measures and the water level is determined only by the flow rate in this riverbed section. In the upper part of this section the water level in the river branches is about 3 m higher than the water level in the main riverbed. The average daily water level at the Dobrohoąť gauging station (rkm 1838.6) fluctuated in the range from 116.93 to 119.95 m a. s. l. and the average annual water level was 117.99 m a. s. l. The average daily water level in the Dunaremete profile (1825.5) fluctuated from 113.27 to 115.90 m a. s. l. and the average annual water level was 113.91 m a. s. l (Fig. 1-8). The average flow velocities fluctuated in the range between 0.71-0.95 ms-1. c) Section between Dunaremete and Sap. The water level in this section is influenced by backwater effect from the confluence of the tailrace canal and the Danube old riverbed (rkm 1811). The water level changes, especially in the lower part of this section, are influenced by the flow rates in the tailrace canal. The length of the upstream section influenced by the backwater effect depends on the actual flow rate distribution between the hydropower station and the Danube old riverbed. At regular operation it can be stated that the backwater effect reaches the Dunaremete profile (rkm1825.5) at flow rates over 2500 m3s-1 at Medveďov. The average daily water level at the Gabčíkovo gauging station (rkm 1819) fluctuated in the range from 111.57 to 114.92 m a. s. l. and the average annual water level was 112.34 m a. s. l (Fig. 1-9). The daily water level fluctuation at Gabčíkovo gauging station in the Danube old riverbed, as a consequence of operation of hydropower station, can reach app. 20 cm. d) Sap – Vámosszabadi section. The flow rate in this section equals approximately to the flow rate at Bratislava and is additionally influenced by the operation of Gabčíkovo hydropower station. The daily water level fluctuation at this stretch (up to 30 cm) depends on the hydropower station operation. Higher changes occur at low flow rates in the Danube due to the ratio of the total flow rate and the capacity of one turbine, which is put into operation or stopped. The average annual flow rate at the Vámosszabadi – Medveďov profile in 2003 was 1944,21 m3s-1. The average daily water level at Medveďov profile (rkm 1806.3) fluctuated in the range from 109.14 to 114.73 m a. s. l. and the average annual water level was 111.25 m a. s. l (Fig. 1-10).
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