PART 1
Surface water levels and flow ratesMonitoring of surface water levels and discharges in the hydrologic year 2011 continued without changes. Water level observations and discharge measurements have been carried out in the same extent as in previous years. The evaluation of surface water regime relates to the hydrologic year (period from November 1 of the previous year to October 31 of the evaluated year). Surface water level observations were carried out at 28 gauging stations on the Slovak side and 29 gauging stations on the Hungarian side (Table 1-1). Discharge measurements and calculations were performed at 10 gauging stations on each side. The observation network is presented in Fig. 1-1a, Fig. 1-1b. Parties in the intergovernmental Agreement have agreed to mutually exchange data from these gauging stations. Joint discharge measurements helped the common evaluation of flow rates discharged into the Danube downstream of the Čunovo dam and into the Mosoni branch of the Danube. Based on mutual evaluation of common measurements, time series data of surface water levels and flow rates 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
The intergovernmental Agreement, signed on April 19, 1995 set up a temporary water management regime. Parties has agreed that in case of annual average flow rate of 2025 m3.s-1 in the Danube at the Bratislava-Devín gauging station an annual average of 400 m3.s-1 of water should be discharged into the Danube old riverbed downstream of the Čunovo weir. The actual daily amount of water is governed by the discharge reaching the Bratislava-Devín cross-section, taking into consideration the rules of operation described in Annex 2 of the Agreement. The flow rate in vegetation period, depending on hydrologic conditions, should fluctuate between 400 and 600 m3.s-1; in non-vegetation period the discharge should not be less than 250 m3.s-1. According to the specification agreed in the Joint Annual Report in 2004, in case of flow rates over 5400 m3.s-1 the amount of water above 600 m3.s-1 discharged through the Čunovo weir is not taken into consideration when the annual average is calculated. An additional 43 m3.s-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 a key role in determining the current amount of water to be discharged into the Danube old riverbed downstream of Čunovo weir. The annual minimum flow rate of 1016 m3.s-1 occurred on October 6, 2011, when the daily average flow rate was 1044 m3.s-1. The lowest daily average flow rate occurred on October 4, 2011, when it reached 1040 m3.s-1. The annual peak discharge occurred on January 16, 2011, when it reached 7214 m3.s-1, with a daily average discharge of 6885 m3.s-1. The annual average flow rate at this station in hydrologic year 2011 reached 1782 m3.s-1, which belongs to below-average flow rates on the Danube and represents the third lowest discharge since operating the Gabčíkovo Hydraulic Structure (Table 1-2). Considering the course of water levels and discharges during the hydrologic year 2011 it can be stated that no extraordinary values occurred, however one high flood occurred in mid of January 2011. The course throughout the year was not typical – rather big flood occurred in the winter period; flow rates mostly deeply below average were registered from mid February to mid July, without more significant discharge waves, only in August occurred higher flow rates exceeding 3000 m3.s-1. Extremely dry months in hydrologic year 2011 were April, May and June. March, July, August and September 2011 belonged to dry months. November 2010 and February 2011 were moderately wet months, while December 2010 and October 2011 belonged to wet months. January 2011 belonged to extremely wet months. Table 1-2: Annual average flow rates
As mentioned above, the discharge regime on the Danube was not typical in hydrologic year 2011 - i.e. discharges in the winter period oscillated around and above the long-term daily average values; rather big flood occurred in January; the water bearing of "winter months" (November 2010 - February 2011) ranged from moderately wet to extremely wet, while the spring, summer and autumn months (March 2011 - September 2011) were dry or extremely dry. The Danube flow rates in November 2010 were balanced and mostly fluctuated on the level of long-term daily average values. The discharges at the beginning of December 2010 slightly decreased, but at the end of first decade a discharge wave occurred, when daily average discharges exceeded 2700 m3.s-1. Another discharge wave occurred at the end of month, with daily average discharge of 2300 m3.s-1. Following a slight decrease at the beginning of January 2011 significant flood wave occurred on the Danube, due to warming and huge precipitation in the German and Austrian catchment area. The flood wave peaked on January 16, 2011 at 7214 m3.s-1 (the daily average discharge was 6885 m3.s-1). Following the culmination the flow rate rapidly declined till end of the month. At the beginning of February the discharge fluctuated around 1700 m3.s-1, but due to warming and slight precipitation a discharge wave occurred, with flow rate exceeding 2300 m3.s-1. After passing the discharge wave the flow rates continuously decreased till mid of March, when the lowest discharges in the winter period occurred. At the end of the second decade in March a discharge wave occurred, with daily average flow rates exceeding 2500 m3.s-1. However except this, the flow rates fluctuated significantly below long-term daily average values. Flow rates during April continued in decline and at the end of month they fluctuated at the level of lowest long-term daily average values for this month. The decrease continued also in May and discharges till mid of May reached the lowest long-term daily average values. At the end of May one discharge wave occurred with the daily average value of 2700 m3.s-1, however, neither this value has exceeded the long-term daily average. Flow rates generally fluctuated deep below the long-term daily average values. Similar course had the flow rates in the first half of June, when they again fluctuated at the level of the lowest long-term daily average discharges. In the third decade of June two discharge waves occurred due to heavy rains, when the flow rate exceeded 2500 m3.s-1, but it did not reached values of the long-term daily average discharge. Due to precipitation the flow rate at the beginning of July increased again, but after the culmination till the end of the second decade it decreased to the level of lowest long-term daily average discharges. In the third decade of July a discharge wave occurred due to huge precipitations in the German and Austrian catchment area, having several peaks (daily average discharge reached 3305 m3.s-1). The daily average flow rates exceeded the long-term daily average values for the first time in the vegetation period of the year 2011. The flow rates decreased after passing the discharge wave, but thanks to heavy rains at the end of the first decade of August another discharge wave occurred, with daily average flow rate of 3200 m3.s-1. Subsequently the flow rates decreased till the end of the month and at the end of the month they again fluctuated at the level of the lowest long-term daily average discharges. Flow rates in September increased two times, but only the second increase exceeded the long-term daily average discharge values (daily average discharge above 2400 m3.s-1). After passing the discharge wave the flow rates at the beginning of October declined to the level of lowest long-term daily average values. The lowest daily average flow rate occurred on October 4, 2011, with a value of 1040 m3.s-1. Annual minimum occurred on October 6, 2011 at 1016 m3.s-1. At the beginning of the second decade of October significant discharge wave occurred due to precipitation in the Austrian Danube catchment area, peaking on October 11, 2011 at 4386 m3.s-1. The highest daily average discharges occurred on October 12 and 14, 2011, when they exceeded 3700 m3.s-1. After passing the discharge wave the flow rates continuously declined till the end of the hydrologic year. The course of flow rates during the hydrologic year 2011 at gauging station No. 1250 - Bratislava-Devín is shown in Fig. 1-2. 1.1. Discharge into the Danube downstream of Čunovo weirThe determination of average daily amount of water discharged into the Danube downstream of Čunovo weir was based on daily average flow rates determined at gauging stations Doborgaz and Helena (Fig. 1-3). At these stations joint flow rate measurements were performed to determine the flow rate supplied into the Danube old riverbed. The monthly characteristics of daily average flow rate into the Danube in hydrologic year 2011 were as follows (calculated from daily average data):
The in the Danube at Bratislava-Devín profile in hydrologic year 2011 was 1782 m3.s-1. Taking into consideration obligations envisaged in the intergovernmental Agreement, the Slovak Party was obliged to release an annual average discharge of 352.0 m3.s-1 into the Danube riverbed downstream of Čunovo weir. The total annual average discharge released to the Danube downstream of Čunovo was 424.4 m3.s-1. During the hydrologic year 2011 it was necessary to release an amount of water exceeding 600 m3.s-1 into the riverbed downstream of Čunovo due to flood wave in January 2011. Higher discharges were released in the period from January 14 to 18, 2011 (5 days). Discharges above 600 m3.s-1 were also released in September (4 days), when technical maintenance on the power plant was performed. According to the modified method of annual average discharge calculation, accepted in the Joint Annual Report on the environment monitoring in 2004, reduction of discharge released to the Danube old riverbed was done for 4 days (reduction to 600 m3.s-1). According to this the annual average flow rate in the Danube old riverbed corresponded to 409.2 m3.s-1, which represents 116.3 % of the amount requested by the Agreement. If we would reduce the discharge in September, whereas the higher flow rate was released due to maintenance works on the power plant (reduction for 4 days), the average annual flow rate in the Danube old river bed would be 404.0 m3.s-1, what is also significantly higher than the amount prescribed by the intergovernmental Agreement (114,8 %). The annual average minimum of 232.5 m3.s-1 in the Danube old riverbed was measured on October 28, 2011; the annual average maximum of 2789 m3.s-1 was recorded on January 16, 2011. Based on the above evaluation of water amount discharged to the Danube old riverbed, it can be stated that Slovak Party fulfilled the annual average 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 m3.s-1, in the vegetation period at least 400 m3.s-1) it can be stated that considering the accuracy of the measurements (±7 %) discharges below 250 m3.s-1 in the winter period did not occurred and discharge below 400 m3.s-1 in the summer period occurred once at the beginning of April. On the other side discharges above 600 m3.s-1 in the summer period occurred several times in June, July and August. 1.2. Discharge into the Mosoni branch of the DanubeAccording to the intergovernmental Agreement, the discharge into the Mosoni branch of the Danube should be 43 m3.s-1, which is composed of both, the discharge released to the Mosoni branch of the Danube through intake structure at Čunovo, and the discharge through seepage canal. Discharge measurements are carried out downstream of intake structure on the Slovak territory at 0.160 rkm and also upstream of lock No. I on the Hungarian territory. The daily average discharges were agreed after joint evaluation of common discharge measurements performed at both profiles. In this evaluation, data measured downstream of intake structure were considered (Fig. 1-4). The monthly characteristics of water amount released into the Mosoni Danube through intake at Čunovo in hydrologic year 2011 were as follows (calculated from average daily data):
The annual average discharge was 39.54 m3.s-1. The minimal daily average discharge was 22.70 m3.s-1; the maximal daily average discharge was 44.77 m3.s-1. The flow rate in right side seepage canal was measured at two sites as well. The first is on Slovak territory at Čunovo; the second is on Hungarian territory at Lock No. II. In the evaluation the data observed at Lock No. II were considered. The monthly characteristics of flow rate recorded at Lock No. II in hydrologic year 2011 were as follows (calculated from average daily data):
The annual average flow rate was 2.05 m3.s-1. The minimal daily average discharge was 1.08 m3.s-1; the maximal daily average discharge was 3.18 m3.s-1. The monthly characteristics of total flow rate released into the Mosoni Danube in hydrologic year 2011, consisting of water amount discharged through the intake structure at Čunovo and water amount flowing in the right side seepage canal, were as follows:
The total annual average flow rate was 41.40 m3.s-1, which represents 96.3 % of the agreed amount. The minimal daily average discharge was 24.50 m3.s-1; the maximal daily average discharge was 46.77 m3.s-1. Taking the maintenance works on turbines into account it can be stated that the water amount released into the Mosoni branch of the Danube envisaged in the Agreement was fulfilled. 1.3. Water distribution on the Hungarian territoryThe goal of water distribution on the Hungarian side is to provide a continuous water supply of the branches in inundation area, the river branches on flood-protected area and the Mosoni Danube. The Hungarian Party determined the actual water distribution on the basis of flow rate reaching the Bratislava-Devín cross-section and according to the seasons, as described in Operation rules for water distribution. 1.3.1. Water supply into the inundation areaRiver branches in inundation area on Hungarian side can be supplied by water from two sources:
These two sources are summed to get the total amount. Criteria for water distribution were set up at right-side river branch system revitalization planning. The reference status was determined at the end of nineties with the involvement of stakeholders. Taking various needs into consideration the water distribution reflects the hydrologic regime of fifties. Water levels characteristic for this period was targeted in the river arms of inundation area. The actual daily flow rate was determined as a function of flow rate entering the Bratislava - Devín cross-section. The environmental status of Szigetköz in the reference period was determined as the most similar to a state, which can be sustained on a long run, and serves adequate information on riverbed morphology and hydro-geological regime for determining the reference status. This is in full harmony with recommendations of the Water Framework Directive and goals of the River Basin Management. Joint discharge measurements by both Parties were performed at the Helena gauging station. The measurements were jointly evaluated and the daily average flow rate data were accepted. The monthly flow rate characteristics at Helena gauging station in hydrologic year 2011 were as follows (calculated from daily average data):
The annual average flow rate was 64.85 m3.s-1. The minimal daily average discharge was 7.78 m3.s-1; the maximal daily average discharge was 349.0 m3.s-1. The monthly flow rate characteristics at lock No. V in hydrologic year 2011 were as follows (calculated from average daily data):
The annual average flow rate was 14.23 m3.s-1. The minimal daily average discharge was 0.00 m3.s-1; the maximal daily average discharge was 32.30 m3.s-1. The monthly flow rate characteristics of total water amount released into the inundation area in hydrologic year 2011 (Fig. 1-5), consisting of water amount flowing through the Helena cross-section and water amount flowing through the Lock. No. V in the right side seepage canal, were as follows (based on average daily data):
The total annual average flow rate supplied into the river branches in inundation area was 79.08 m3.s-1. The minimal daily average discharge was 37.52 m3.s-1; the maximal daily average discharge was 349.0 m3.s-1. In 2011 artificial flooding of inundation area on both sides was not realized. Natural flood occurred in mid of January. The water amount distributed in the Hungarian river branch system created water stages corresponding to the reference status in the upper part of the inundation area – in the Tejfaluszigeti river branch system. In the middle part – Cikolai and Bodaki river branch systems, the water levels were slightly above the reference status. Water stages in the Ásványi river branch systems corresponding to the reference status can only be achieved with technical measures implemented in the water supply system or in the Danube old riverbed. Based on the above mentioned it can be stated that for the low and medium flow rate periods the target values of the reference status were fairly well achieved. However, in the lower part of the river branch system reference water levels cannot be achieved; technical measures are needed for achieving the desired status. 1.3.2. Water supply into the Mosoni DanubeThe 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 cross-section downstream of the lock. The monthly characteristics of flow rate through the lock No. VI in hydrologic year 2011 were as follows (calculated from average daily data):
The annual average flow rate in the Mosoni Danube at lock No. VI. was 25.07 m3.s-1. The minimal daily average discharge was 9.78 m3.s-1; the maximal daily average discharge was 41.00 m3.s-1. The water supply regime is regulated by rules of operation and follows the Danube’s water regime. In non-vegetation period a low water period was simulated in the Mosoni Danube. This was realised by redirecting a greater part of water amount into the inundation area. 1.4. The Danube water level characteristics on Čunovo-Vámosszabadi stretchThe Danube stretch between Čunovo and Vámosszabadi can be divided into four different sections according to the prevailing influence. These sections can be characterised by data obtained from following gauging stations: Rajka and Hamuliakovo, Dunakiliti, Doborgaz and Dobrohoą», Dunaremete and Gabčíkovo. Vámosszabadi and Medveďov. The characteristics of four sections on Čunovo - Vámosszabadi stretch in hydrologic year 2011 are the following:
|
|||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
