Area info Balaton

General Information on Lake Balaton:

With a surface of almost 600 sq. km, Balaton is the biggest lake in central Europe. Its shallowness means it warms quickly and for 6 months of the year is a magnet to bathers. It is 77.8 km long and between 3 and 12.5 km wide. Its shoreline amounts to 195 km and the average depth is 3.14m. At Tihanyrév, the site of the North-South passenger and car ferry, the average depth is 3 m. Off Tihany, however, the lake is 12.2 m deep. Although a sea once rolled over the region Balaton now occupies, the lake is not a remnant of it but relatively young at around ten thousand years. Precipitation filled a once much larger geological depression. In comparison with many European lakes, the water of Balaton is very clean and rule number one is thus to protect it against the numerous perils of modern civilization. The strict Clean Water regulations - e.g. motor boaters must betake themselves to other waters - are appreciated by sailors, numerous sail boarders and obviously bathers. The water is often described as silky, or at any rate that is the sensation the skin conveys. This is not an illusion: the water is slightly alkaline and gentle - because of the fineness of its suspended matter and mineral particles it could as well be described as heavily diluted mineral water. The therapeutic sunbathing in the sun's rich rays, the microclimate and the non-salty but mineral rich water make bathing as enjoyable as in the sea - often from as early as May through to early autumn in October.

Hungary has a temperate climate, with alternating maritime and continental influences. In the southern part of the country and in particular around Balaton the Mediterranean influence prevails. Many plants and trees that can otherwise only be found in Mediterranean countries thrive in this pleasant climate. For example, on the south-facing slopes of the northern shore, almonds grow, figs ripen in many gardens and pomegranates frequently gleam through the foliage Within two decades, the population of the Balaton region has risen from 100,000 to almost 150,000 but in summer at least twice as many stay by the lake. Hence some shops and restaurants only open in the holiday season and in summer an increasing number of food shops are open on Sundays as well.

On the south side the railways run close to the shore, while on the north shore they take a loop around the Tihany peninsula and Badacsony Hills to return to the proximity of the lakeshore at Tapolca. A dense bus route network connects everywhere on Balaton . Foreign visitors arriving with their own cars generally use the M7 motorway from Budapest - a convenient link between the capital and the lake.

Coming from Vienna you do not merely save time and petrol by crossing Transdanubia via Sopron-Sarvar on Highway 84 or taking Highway 83 to Papa und Veszprem or Highway 82 to Varpalota at Györ - these routes also run through beautiful landscapes. There are also highways to Balaton from Graz, Zagreb and Belgrade on which you can avoid the heavy though- traffic to Western Europe and the Balkans. They have more than their fair share of natural beauty: attractive towns, interesting architectural memorials, pleasant staging points, little inns and homely pensions.

Bottom and ground conditions:

It is characteristic of the formation of the bottom of Balaton that the depth reaches 2.5 - 3 m close along the north shore and that this depth increases slowly and steadily toward the south-east. This slow change in the depth of the bottom extends up to the southern shoreline. Here it comes up against the 'ridges' which follow the shallow, gently shelving southern shoreline at a distance of 300 to 1000 m. The ridges are covered by water and are located between 40 and 60 m apart. Between them there are trenches with a relative depth of 60 to 120 cm. The southern shore is fringed by between 4 and 6 such ridges. The point where deep water encounters the first of them is known by Balaton's navigators and fishermen as the ledges. Off the northern shore such a bottom formation is unknown. In heavy weather when the depth of water cannot, as it were, be measured, the seas reveal the beginning of the dangerous shoals. The waves break along the line of the Cutters and the series of foaming seas indicates to some extent the limit of navigable depths. Along the northern shore, there are not inconsiderable cones of debris built up by the inflowing streams. These are clearly visible, even several hundred meters from the shore.

Hydrographic Features:

The level of water in the lake is determined by the amount of precipitation falling on its catchments region, evaporation and water level control by the Sió sluices in Siófok. The lake's catchments surface amounts to 5,774.5 km2. On this vast territory there falls an average of 3,176 million m³ of precipitation a year of which roughly 930 to 1000 million m³ end up in the lake. The water area receives an annual average precipitation of approximately 370 million m³. The streams feeding the lake and the River Zala between them contribute a water supply of approximately 17 m³/s to the maintenance of the level. The volume of water at a height of 104.84 m above sea level ( Adriatic ) - corresponding to the mean level of 75 cm -approaches 2 km³. On summer days this huge expanse of water evaporates vigorously and the fall in the water level caused by evaporation can be in the order of several centimeters.

Characteristic Water Movements:

The varied water movements are influenced by the large expanse of the lake, the formation of the terrain of the surrounding range, the dissimilarity and frequency of wind directions and strengths together with the subdivision of the surface of the lake into bays. The three typical water movements in which large volumes of water are involved are waves, surface drift resulting in oscillations and currents.

Sea state:

On water surfaces exposed to the effects of the wind, ripples arise with a height of between 0.5 and 3 cm depending on the wind strength ( the surface is ruffled ) and are caught by the wind. The occurrence of this process is promoted by the shallow depth of the lake. The body of water is heated to some slight extent by the influence of the sun. This relatively warm water is easily set in motion thereby giving rise to waves. Winds blowing in a direction at right angles to the long axis of the lake generally exhibit a gradual increase in wind strength and have a markedly intermittent effect. The fact that the valleys on the north shore run in the direction of these winds plays a considerable part in this. The fetch off these valleys, which to a large extent influences the development and intensity of the seas, increases proportionately in those areas that fall within the wind shadow effect of the mountains. In a seaway, the various wave motions play an important role. Peak wave height values have in almost all cases occurred during a brief, sudden lull. Because of the obstructions on the shore, the wind fluctuates greatly and hence high waves and short wave-free intervals follow one another in succession. The period of individual waves varies and their forms are very diverse. The waves reflected back off the bottom in the shallows off the shore are subject to an interference effect. When waves of different periods and forms run together in a sudden lull lasting a few minutes and the reflection from the bed of the lake occurs at the appropriate moment, especially high waves arise under the combined effect of these phenomena. Depending on such diverse effects of the factors affecting the sea state, short wave fronts of various forms develop. No clear-cut typical periodic interval can be determined for the seas on the lake. In the proximity of the shore the biggest wave to date with a height of 1.82 m was measured in a northerly wind. This exceptionally high wave occurred when a gust of 21.1 m/s (41.0 knots) was followed by a brief lull of 10 m/s (19.4 knots). In the middle of the lake the biggest wave of 1.95 m was observed in a northerly wind of average velocity 11.8 m/s (22.9 knots). The gust reached 19.5 m/s (37.9 knots) after which a relative calm occurred. At the same time a wave height of only 1.4 m was measured in the proximity of the shore. The average height of the seas caused by the wind is 100 to 130 cm, with wave lengths ranging between 2 and 12 m. The maximum wave heights occur in N-NW winds whose effect is at right angles to the long axis of the lake. In sudden, rapidly strengthening winds truly massive, high waves spring up but within 1 ½ to 2 hours of the wind ceasing, the sea also dies down. In winds that increase slowly and gradually, the seas comes up and grow parallel to the wind direction. The resulting wave heights are then generally less than average and the seas also die down gradually on a decrease in wind speed.

Surface drift - Oscillations:

Under the influence of the wind, the water in the lake moves in the wind direction resulting in a considerable drop in the water level. Depending on the wind direction the water level then falls on one shore and rises on the other. From the practical point of view surface drift must be taken into account in the immediate estimation of the navigability of individual harbours and channels as well as in grounding and floating off and when vessels are to be intentionally laid up. The greatest longitudinal oscillation is generated by WNW and ENE winds, which exhibit the same direction as the long axis of the lake. Depending on the wind direction and speed and the topographical features of the lake, the period of the resulting longitudinal oscillations ranges from 5.5 to 11 hours. In addition, the transverse oscillations and the oscillations of the various bays in the lake's shore have a considerable effect on the longitudinal oscillations. As a result of water oscillations, a substantial difference in water level can arise between two widely separated points on Balaton. In the largest observed fluctuation on 14 May 1962, a fall of 45 cm occurred at Keszthely in nine hours at the same time as a rise of 52.5 cm at Alsóörs. The greatest simultaneous difference in water level amounted to 80 cm at which time the speed of the longitudinal wind was 20 m/s (39 knots). Transverse fluctuations are most significant in the southwestern basin between Alsóörs and Siófok. In terms of size, that at the latter is the bigger and arises under the influence of the prevailing NNW wind as a result of the relatively great width and depth. The greatest fluctuation in level measured to date was 52.5 cm at Alsóörs and 37.5 cm at Siófok. At Siófok the oscillation lasts for approximately 1.5 hours.

Currents:

As a result of surface drift and water oscillation, currents of various magnitudes and directions occur in the body of the water of the lake. On the surface the water flows in the direction of the wind, close to the bottom against the wind because of the Earth's gravity as the surface strives to attain equilibrium. Significant currents determined by the various oscillations arise between the two basins and within the basins themselves. The strongest current may be observed in the section between the Tihany Peninsula and the Szantód shore where water is exchanged through the confined passage between the north-east and south-west basins. High stream rates occur at this point, in isolated cases reaching rates of 1.4 to 2 m/s (2.8 to 4 knots). In general the stream toward Keszthely runs less strongly than that toward Balatonkenese but persists for longer. There is a strong current off the entrance to Kesthely Bay and throughout the bay itself. Here weaker streams of 0.3 to 0.4 m/s (0.6 to 0.8 knots) may be observed. The inshore "circulating currents", which mainly flow close to the bottom, come about as a consequence of the fluctuations. Piers project into the path of these currents and, under the influence of the eddies and slack spots occurring behind them, harbour entrances become more or less silted up with debris.

Wind:

The prevailing wind on Balaton, known by the fishermen as the "main wind", is from between N and NW. In the eastern basin ( between Balatonkenese and Tihany) northwesterly predominate with northerly in the south-western region ( between Tihany and Keszthely ) SE and SW winds occur more frequently in autumn and winter. Storms are particularly dangerous to navigation since the wind increases suddenly with hardly any transition at all and sometimes attains a speed of 30 to 35 m/s (60 to 70 knots) within 10 to 20 minutes. The outbreak of storms is mostly preceded by a moderate or light southerly air stream. The wind veers to the NW accompanied by a dramatic increase in strength. In thunderstorms - when the falling air spreads out close to the water surface and gives rise to violent radial winds - the wind is strongest in the direction of the eye of the storm and more moderate on either side. A thunderstorm can last for 2 or 3 hours. On 13 July 1961, the strongest gust measured to date reached a speed of 36 m/s (70 knots). Such a hurricane-like wind can give rise to an average wind pressure of 94.4 kPa (12.8 lb/ sq. ft.). April is the windiest month on Balaton; storms (wind speeds exceeding 15 m/s or 30 knots) occur more frequently at the beginning of the summer ( on average one can reckon on storm gusts on one day in 3). The calmest month is September ( on average a storm can be observed only every 10 days). In the areas of the lake off the northern shore the wind-shadow effect of the mountains is of such intensity as to reduce the strength of the wind in particular instances ( e.g. between Balatonfüred and Siófok ) by as much as 60 %. In strong N and NW air flows strong winds from the valleys at right angles to the lake can be observed on the surface of the water. When the wind gets out over the lake, it fans out and its speed exceeds the surrounding average substantially. It follows from this that the area of the southern shore is windier than that of the northern one, especially in the summer months. Because of the considerable longitudinal dimension of the lake, mutually disparate weather conditions do occur in different areas. While calm reigns in one basin, a violent wind rages in the other. The National Weather Service warning observatory at Siófok deals with storm warnings for the Balaton area and between 1 May and 30 September operates the storm warning system. If the wind is liable attain a speed of 12 m/s (24 knots) within 3 hours, a Level I storm warning is ordered. If the wind speed will exceed 17 m/s (34 knots) immediately or within 1 - 2 hours, a Level II storm warning is ordered. Yellow lights indicating the meteorological conditions are displayed at 24 points along the shore. On the approach of a storm a yellow light flashing 30 times a minute indicates Level I, whereupon boats and water sports craft may only navigate within a 500 m wide zone off the shore. On the imminent occurrence of a storm, a yellow light flashing 60 times a minute indicates a Level II storm warning, whereupon a prohibition on navigation applies to small vessels of Class B under sail as well as boats and water sports craft.