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Natural environment


Natural-geographical conditions

Budapest is Hungary's capital city, seat of Government authorities. It is an industrial and cultural centre of the country as well.

Due to its central location, it is the biggest and central transport junction of the country: this is the meeting point of all main roads and railways. The Danube, as a waterway, is of international significance. Its airport in rapid development is one of the most important air transport bases of Europe.

Population of Budapest*:
1 886 215
Population of the areas affected by Metro 4
District 8.
86 474
District 9.
69 547
District 11.
148 541 fő

Population of Budapest according to statistical data of January 1, 1997

In some areas of Pest side population density is more than 30,000 persons/sq. km., but it is not less than 10,000 even in the least dense units of the city development.

In the Buda districts affected by the Metro alignment it is rather 10,000 to 30,000 persons /sq. km., and only in a few districts could be established densities above or under this range.

Hydrological conditions

The area in question is located south of the Buda hills, and partly on the Pest plain. It is influenced by only one water flow, the Danube, which is at the same time its natural erosion basis. In the region of Budapest there are also several minor brooks, earlier water collecting streams of the Danube, now being unified into the same sewage system of the capital city and leading their water through the canals of this system, possibly transmitting it through pump stations to the Danube. There is no other important water stream whatsoever in the area concerned.

In Budapest, Danube water levels are checked at several water measurement stations.

Characteristic data from the water gauge stations in Vigadó tér
(Danube mileage 1646.5 km)
aBs - above Baltic sea level
0 pont
0 cm
94,98 m Bf
51 cm
95,49 m Bf
(November 6, 1947)
- 8 cm
94,909 m Bf
(January 13, 1954 ice)
845 cm
103,43 m Bf
(June 10, 1965)
867 cm
103,65 m Bf
(February 26, 1876, ice)
335 m
98,33 m Bf
259 cm
97,57 m Bf
309 cm
98,07 m Bf

Metro construction and operation cannot have any influence on the water level of the Danube, since no operation of this kind is to be carried out. Its utilisation for transport by waterways, and the direct drainage of the water from possible work pit dewatering can cause certain problems of water pollution. However, such - possibly - harmful effects can be prevented by due caution and periodic checks of the water quality discharged into the Danube.

In this area, there is no other live water stream except for the Danube. One branch of the regulated Hatr canal runs on the western side of Keleti railway station, app. in north-south direction, then joins the Danube as a surface trench along Kondorosi t. There is an engineering structure at its mouth.

Geological conditions

We provide an idealised set of layers enabling the description of the geological environment concerned.

  • Deep upper Triassic main dolomite of karni formation at the hill base. The main dolomite has a very outstanding position at the Buda side and medium section under the Danube with respect to the entire alignment.
  • The main dolomite has karstificated, with Eocene basis formation on its non-uniform surface, and detritus-free lime stone on the latter with Nummulithes and Lythothamniums, which is covered by only a thin Buda marl layer, compared to the thickness in the rest of Buda hills.
  • A Tardi set of Oligocene clayey-sandstone has developed from the Buda marl through a continuous transition, which is covered by mid-Oligocene Kiscelli set of clay and clayey-marl through another progressive transition.
  • On the Buda side, in a layer settled above the level of Metro 4, the Kiscelly clay and - along the Danube section - the Tardi and upper Eocene formations are only covered by quaternary sediments.
  • On top of the Kiscelly clay, upper Oligocene base sediments of open sea development have settled by continuous sedimentation, and the Trkblint set of mostly sand development of shallow sea - coastline origin is located partly on top of this Oligocene sediment, and partly serves as heteropicous facies.
  • The youngest member of the upper Oligocene formation, also representing the upper Miocene formation in respect of origin, both from lytho- and a bio-stratigraphic viewpoint, is the clay-sandy Egri set.
  • Egri sets are covered by lower Miocene aleurite of Eggenburg formation, and sandy agglomeration comprising gravel inclusions, with acute disconformity.
  • Thereupon, the oldest member of the Baden set of mid-Miocene origin, a fragmented and clayey "tuffigene" set is located, comprising rio-dacite and tuffit inclusions. On top, and also as lateral transition, there is the lensing, Baden "terrigene" set of stream water and tide origin with unexpectedly varying lithological character, with more and more frequent sea inclusions on its upper section, then later, sandy-clayey type "Rákosi-Lajta" developments of sea origin, comprising a few limestone inclusions, become predominant.
  • The upper Miocene, Szarmata set is developed with apparent sediment continuity out of a shallow sea upper Baden set, this Szarmata set is identical or very similar to the upper Baden sea formation in respect of its lithological character. Due to their similarity, these two formations can be separated almost exclusively on a palaeontological basis.
  • Older formations on the Pest side are entirely covered by Danube sediments, while on the Buda side older formations are covered mainly by Danube sediments, and partly by piedmont deposits.


Hydro-geological conditions

The ground water, as considered under its accurate definition, appears in a larger area and quantity on the Buda side only in areas within the early Pleistocene/Holocene floodplain. Ground water is generally supplied by rainwater, but ground water level and flow direction from the line of the 2nd terrace of the Danube towards the river (the border between the 2nd and 1st floodplain terrace is app. in the line of Fehrvri t) are influenced by the prevailing water level of the river, i.e. either increasing or lowering ground water level and affecting flow direction.

One of the main flow directions is the Danube, as leakage towards erosion base (the Danube is collecting ground water in a very similar manner to a gallery). Another main flow direction of ground water is in north-south direction, following the Danube valley.

The flow image described above is somehow modified by minor flows following the brooks coming from the hills. Such motions of the terrace water of brooks, towards valleys, will end up in the Danube as erosion base, however, at other locations they form mainly a north-south leakage field.

There is no sense in speaking of ground water in the section below the Danube, but the effect of the prevailing Danube water level cannot not be ignored. In case of average ground water level the ground water table descends towards the Danube, while in case of high water level the water of the Danube backfills the ground water or causes backwater effect. The effect range where backfilling height exceeds normal average water level oscillation, amounts to 400 m. This can be confirmed by the 1965 flood flow data, as well as by a study of the Miskolc University, which investigated the impact of the diaphragm wall section of the north-south Metro line on ground water.

On the Pest side, a specific border line separates two areas with ground water of different character, origin and motion. This is the supposed line of the eastern Danube embankment in the early Holocene era, as cut in into the Pleistocene Danube terrace.

This cutting effect of the Danube transformed the western border of the terrace into a quasi vertical river embankment. The area filled up with Holocene flood plain sediments of the ancient river is located towards the Danube from this former river bank (lower terrace levels), and east of this line the so called higher terrace levels are located.

The ground water mainly consists of infiltration precipitation waters, and just a small part is supplied by side flows of the same direction as the consequent slope direction of the Tertiary underlaying rock, as well as some live water flows (Szilas brook, Rkos brook). Erosion base of the area is the Danube, a hydrological element of generally good receiving capacity. At the same time, ground water is supplied by high water levels while it is lowered by low water levels in the river.

In terms of water quality, the Metro line can be divided into two sections:

  • The first section (Budars station to Móricz Zsigmond tér) is the area with slope and valley ground waters,
  • The second section (Móricz Zsigmond tér to Újpest station on the Pest side) is where the ground water of Danube flood plain appears.


Geotechnical conditions

In order to select optimal construction technology (out of both technical and economic viewpoints), also considering the geological conditions, three sections are to be differentiated:

  • Section 'A': in Buda, from Etele tér station to the platform end in Szent Gellért tér station
  • Section 'B': crossing under the Danube, from Szent Gellért tér to Fővám tér station
  • Section 'C': in Pest, from the short section following Fővám tér to the end of Keleti pu. station


The special requirements for tunnelling shields, obtained from detailed surveys carried out along line alignment, will be enforced by a contract concluded with the contractor, as set out in technical specifications complying with local geological and hydro-geological conditions.

When selecting shield type one of the important considerations is that the shield has to be suitable for the boring in all kind of soils identified by surveys between the stating point (Kelenfldi pu.) and the end point (Keleti pu.). Since the tunnel pair will lead on the Buda side in hard clayey marl and no aquiferous layers are expected to be crossed. That is why the so called open face, cutting-cross shield seem to be the most convenient solution in this area.

When driving the tunnel pair under the Danube, the karst water system should be disturbed as less as possible, excluding the mixing of thermal karst water and Danube water, and the penetration of significant water quantities into the tunnels. Thus, on the Pest side and under the Danube, under disturbed rock conditions, and in the expected ground and confined waters, tunnel driving is reasonably more advantageous with closed face support shields.

Up-to-date multi-purpose shields of our days can be modified from open to closed face support without dismantling the shield itself. This kind of modificaiton is planned by the designer at Szent Gellrt tr station. From here on, the shield advance with closed face support under the Danube and the entire Pest side. The closed face operation and the specific shield design guarantee that neither rock, nor large water quantity of any origin may penetrate inside the shield.

It is less probable, but due to the uncertainty in all surveys, it can be assumed that the shield would come across such a structural break or minor fissure in the lower part of the Tardi clay that can be related to deeper karst water storing rocks. Such possibilities can be anticipated by various preventing measures as early as before starting shield driving in order to avoid that unforeseeable geological - hydro-geological formations, obstacles cause environmental damages and slow down the driving progress by a considerable extent.

Seismic effects

A complex interpretation of existing seismic and regional geophysical data reveals that there is a certain stress accumulation in the Pannonian basin in our days, which can be released from time to time along more or less known structural lines. The magnitude of the seismic phenomena depends on how easily individual structural elements can move with respect to each other. Based on our earlier tectonic and seismic experience we can conclude that due to a significant cracking of the basin bottom any high stress accumulation has low probability. This can explain the rarity of earthquakes above grade 5.5 and the highest limit of grade 6.0 to 6.5 experienced so far.

The majority of earthquakes in the investigated area ranges between grade 3 and 5; higher seismic events are relatively rare and of local character. Accordingly, the region of Pannonian basin belongs to areas with medium seismic activities. Numerous foreign studies and experience can confirm that seismic waves cannot significantly damage any underground structure of circular cross section in this region.

In international practice it is quite frequent to design tunnels or underground facilities in the passive and even in the active break zone. In California, Turkey and Japan several earthquakes occurred in cities where metro lines are in operation, thus relevant experience is available.

According to other international experience, the corner joints of built structures reaching the surface are more sensitive to seismic effects, but tunnels of circular cross section are quite insensitive to such effects.

In case of deep tunnels the seismic effect acting on tunnel structures can be considered in design calculations. Seismic effect is simply one of the design parameters.

In addition to the seismic effect expected in Budapest, no other risk whatsoever is known for the tunnels. No special solutions are required for the section crosiing under the Danube. As proved by earlier situations, the ring segments have a relatively flexible behaviour, and their bolted connections can bear any static and dynamic effects.

Impacts on the ecosystem (animals and plants)

Investigations reveal that the natural ecosystem of the city centre is not endangered by the Metro, since no such ecosystem has been in existence for several decades in the area concerned.

Tunnel construction has no hazard for the parks. Gellrt hill is not affected by Metro construction.

An extension of the line towards Rkospalota has no detrimental consequence on the ecosystem, although some remains of the former vegetation are still present along Szilas brook, but most of the existing plants are weeds.

In the areas covered by the line extension towards Budars there are no more plants representing considerable natural values, not even in certain parts of semi-natural character. On the other hand, this area will soon be fully built in as indicated by the existing rate of constructions.

The envisaged alignment of Metro 4 will run north of the motorway, thus, it cannot endanger the protected area of about 24 hectares located southwards.

As for the fauna, a previous environmental impact study revealed that metro construction will have no hazardous effects since the valuable animals live in the regions with an undisturbed flora. Thus, their existence will not be affected by construction.