Northern outskirts of Prague with the Baba (PP) and the Šárka Brook valley in the centre, the Imperial Island with the waste water treatment plant on the right, and the Podhoří nature reserve (PR) in the background.
River Phenomenon
The Vltava, the principal river of Bohemia, ranks among those natural factors which have formed decisively Prague area and imprinted on it its characteristic appearance in the course of ages. To clarify the way in which it was done we have to stop for a general definition of the term phenomenon in the meaning used by geobotany and landscape ecology. In this meaning phenomenon is a set of specific processes and sites with characteristic flora and fauna, conditioned by geological substratum and ground relief of a certain area. The areas in which some phenomenon manifests itself usually differ maŕkedly from the average state of ambient landscape by the diversity and wealth of its nature or conspicuously different site conditions.
The valley of the Vltava is connected with the so-caled river phenomenon originating in sharply incised valleys with outcrops of various rocks in their faces, the properties of which influence significantly flora and fauna. In such valleys contrasting sites appear, differentiated by the slope orientation to cardinal points and the height above the valley floor. While the slope margins facing the south host xerothermal communities, the deep cuts provide favourable conditions for cold and moisture loving elements. This gives rise to the wealth and diversity of living nature by which the river valleys differ conspicuously from the much more monotonous peneplain in which the river valley has been cut.
The river phenomenon is fully developed in the Vltava canyon north and south of Prague. In the more open Prague basin it has subsided to a certain extent. Nevertheless it manifests itself even there by the existence of such formation as the Vyšehrad Rock, the steep slopes of the Petřín hill or the various rock outcrops in the Troja Basin.
The river phenomenon has contributed substantially to the wealth of Prague nature by having created in the course of past ages a highly diverse mosaic of the most varied sites providing adequate living conditions to the species with very different requirements. In the primeval past, when nature had not been influenced by man much, Prague area ranged among the naturally wealthiest parts of Central Bohemia, and even the big city development could not destroy this wealth completely. But the Vltava and its valley mediate also the connection with distant environs, as they represent a first class biocorridor along which various plant and animal species have migrated until recently. In this process a role of considerable importance was played also by the force of flowing water. Today such ways of communication are called stream corridors.
In Prague area, however, there is not only the Vltava. In its southern margin the Vltava is receiving the waters of the Berounka, an important waterway of SW Bohemia, a few miles futher south of the Sázava, coming from the SE from the Bohemian-Moravian Highlands. Along these rivers various submontane species have spred to Prague area, while the warm rocks and stony slopes enabled the expansion of xerothermal plants and animals far upstream these rivers. These migrations proceed even at present: the floodplain species of minor invertebrates from the Berounka and Sázava areas propagate into the secondary riverine woods along the Vltava which originated only after the Second World War.
The migration of various organisms is mediated also by the very course of the Vltava. Great role in this process is played also by human interference, particularly the upstream waterway transport and the construction of waterworks on the Vltava above Prague which has changed not only the flow rate, but also the temperature regime in the river. This is felt by all those who used to swim in the Vltava in summer and skate on its ice in winter. The river bank vegetation has changed, new species have appeared in its water, such as the river snail “Viviparus”, after the Second World War. Numerous bird species, which did not come to Prague in the past, winter on its water at present.
However, the Vltava influenced also the settlement and development of Prague itself. The broadened parts of its valley in less resistant Ordovician rocks and their mild slopes and terraces were directly predetermined for urban development, while the rocky promontories afforded ideal sites for castles and strongholds. They are represented by the Vyšehrad on the rock high above the river, as well as the Prague Castle on a steep promontory between the valleys of the Vltava and the Brusnice. In this way the inimitable panorama of the city has been formed in the course of ages on the foundations generated by the erosive and cumulative activities of the Vltava in the course of the last million of years. For instance, Bohnice or Suchdol are situated on the site occupied by the fluvial plain of the river about one million of years ago. On the other hand, the Old Town, the Lesser Town or Holešovice have been erected on the fluvial deposites from the last Ice Age dating from some 25 000 years ago, as well as the alluvia from the postglacial period which would continue to form until the present, had not the river been fettered by numerous dams.
The remainders of river activities can be encountered in Prague literally on every step. This is testified to by excavations uncovering Vltava gravel often high above its present water level and far from its present bed. Also the very Prague meander carrying Holešovice is the work of the Vltava. The panorama of Prague with Prague Castle, the Vltava, and Charles Bridge, as well as the Vítkov, Vyšehrad, Děvín and the slopes bordering the Troja Basin in the north, lend Prague inimitable originality which is not only the creation of man, but also - and primarily - of our biggest river, the Vltava.
Northern outskirts of Prague with the Baba (PP) and the Šárka Brook valley in the centre, the Imperial Island with the waste water treatment plant on the right, and the Podhoří nature reserve (PR) in the background.
The burning bush (Dictamnus albus) blossoms high above the river in the Podhoří (PR).
The steep slopes of the Podhoří (PR) were moulded by the Vltava.