Drainage

Topographic influences

The drainage basins of most European rivers lie in areas originally uplifted by the Caledonian, Hercynian, and Alpine mountain-building periods that receive heavy precipitation, including snow. Some streams, notably in Finland and from southern Poland to west-central Russia, have their sources in hills of Cenozoic rocks, while others, including the Thames and Seine rivers, derive from hill country composed of Mesozoic rocks (i.e., those about 66 to 252 million years old). Drainage is directly, or via the Baltic and the Mediterranean seas, to the Atlantic and Arctic oceans and to the enclosed Caspian Sea.

The present courses and valley forms of the major rivers result from an intricate history involving such processes as erosion by the headstream, downcutting, capture of other rivers, faulting, and isostatic changes of land and sea levels. The Rhine, for example, once drained to the Mediterranean before being diverted to its present northerly course. The courses of many rivers—notably those of Scandinavia and the North European Plain—have been shaped since the Pleistocene Epoch (about 2,600,000 to 11,700 years ago). While the Alps, Apennines, and Carpathians provide watersheds, other mountain ranges have been cut through by rivers, as by the Danube at Vienna in Austria, Budapest in Hungary, and the Iron Gate and by the Olt in Romania. In the East European Plain the rivers are long and flow sluggishly to five seas. In western, central, and eastern Europe, rivers are largely “mature”; i.e., their valleys are graded, and their streams are navigable. Northern and southern Europe, in contrast, present still “youthful” rivers, as yet ill-graded and thus more useful for hydroelectricity than for waterways. The Atlantic rivers have scoured estuaries widening seaward, while, in the Baltic, Mediterranean, and Black seas, with minimal tidal influences, deltas and spits have been created. Since the end of the Pleistocene the upper Dnieper has failed to drain the low area of the Pripet Marshes effectively.

Hydrology

The water volume of and discharge from the rivers of Europe are governed by factors that include local conditions of precipitation, snowmelt, and rock porosity. In consequence, the rivers in the western area have more volume and higher discharges in the winter season and are at their lowest in summer. In areas of mountainous and continental climate, thanks to the runoff of snowmelt, the rivers are highest in spring and early summer. The longer rivers of the continent, notably the Rhine and the Danube, have complex regimes, since their basins extend into areas of contrasting climate. Although embanking measures have reduced the problem, flooding is a continued threat. Thus, the rivers of European Russia are liable to flood with the spring thaw, oceanic rivers after heavy or prolonged rain over the whole basin, and Alpine rivers when the warm foehn wind rapidly melts the snow. In the Mediterranean region some rivers—as in peninsular Greece—tend to dry up in summer through a combination of scant rainfall, evaporation, and porous limestone beds. In the Abruzzi region of central Italy, however, heavy rainfall, mainly in winter, permeable and porous rocks within the basin, and abundant snow combine to regulate the river regimes.

The Rhône River achieves a steady flow throughout the year, deriving a high input from the Cévennes Mountains—which experience heavy winter rain—plus abundant spring and summer snowmelt from the Alps via Lake Geneva. The Rhine and Danube tap supplies from the Alps in spring and summer, and the Rhine, especially, taps areas of winter rainfall maximum. The Volga River has its highest water in spring and early summer, thanks to snowmelt, and falls to a summer low. The Saône River, lying within the oceanic climatic area, tends to have a good flow year-round. The winter freeze of the east only rarely seriously affects the Danube and western European rivers.

Lake systems and marshes

Lakes cover less than 2 percent of Europe’s surface and occur mostly in areas subjected to Pleistocene glaciation. The Scandinavian Peninsula and the North European Plain account for four-fifths of the area of lakes, and in Finland lakes cover one-fifth of the surface. The other major zones of lakes lie marginal to the Alpine system, while Scotland has its many “lochs” and Ireland its “loughs.” Lakes survive where the inflow of water exceeds the loss from evaporation and outflow, but many eventually will disappear through alluvial accumulation. Their origins lie in the glacial excavation of softer rocks, in the building of dams by morainic material, and in tectonic, or deforming, forces, which may create depressions. The last explanation clearly applies to Alpine lakes, to many of those in the British Isles, including the small but scenic ones of the Lake District of England, and also to those of central Sweden. Volcanic crater lakes are found in central Italy, and small lakes of the lagoon type are found along the Baltic and Mediterranean shores, where spits have lengthened parallel to the coast and hence cut off sea access.

A cultivable zone (the Marschen) has formed along the low-lying, reclaimed marshes along the North Sea in Germany and the Netherlands, and characteristically the estuaries of Europe’s tidal rivers are edged by flat alluvial marshes. Fens, as exemplified by the polders in the Netherlands and the lowlands in eastern England, are made up of either alluvium or peat and stand too low to be drained effectively, except by continuous pumping. The continent’s largest marshland is the Pripet Marshes of Belarus and Ukraine.

Soils

The soil patterns of Europe are clearly and zonally arranged in the East European Plain but are much more complicated in the rest of the continent, which exhibits a more varied geology and relief. Tundra soils occur only in Iceland, in the most northerly parts of Russia and Finland, and in high areas of Sweden and Norway; they tend to be acidic, waterlogged, and poor in plant nutrients. South of that zone and extending around the Gulf of Bothnia and across Finland and Russia north of the upper Volga, cool-climate podzols are characteristic. Those soils, formed in a coniferous woodland setting, suffer from acidity, the leaching of minerals, hardpan formation and permafrost beneath the topsoil, and excess moisture; given the climate, they are virtually useless for crops.

The larger zone to the south stretches from central Russia westward to Great Britain and Ireland and southward from central Sweden, southern Norway, and Finland to the Pyrenees, Alps, and Balkan Mountains. In that region temperate-climate podzols and brown forest soils have developed in a mixed-forest environment, and those soils, which are highly varied, usually have a good humus content. Locally, the farmer recognizes soils of heavy to light texture, their different water-holding capacities, depth, alkalinity or acidity, and their suitability for specific crops. The soils within that zone that cover loess are excellent loams; lowland clays, when broken down, also exhibit high quality, as do alluvial soils; in contrast, areas covered with dry, sandy, or gravelly soils are more useful for residential and amenity purposes than for farming. In southwestern Russia, in portions of the Transcaucasus region, and especially in Ukraine, some soils that have been formed in areas of grass steppe are chernozems (black earths)—deep, friable, humus-rich, and renowned for their fertility. In the formerly wooded steppe lying to the north of the grass steppe in both south-central Russia and the lower Danubian lowlands, soils of somewhat less value are known as degraded chernozems and gray forest soils. At best, chestnut soils—some needing only water to be productive—and, at worst, solonetzic (highly saline) soils cover areas of increasing aridity eastward of Ukraine to the Ural River. Lastly, in southern Europe, where the countryside is fragmented by mountains, plateaus, and hills, much soil has been lost from sloping ground through forest destruction and erosion, and a bright red soil (terra rossa), heavy and clay-rich, is found in many valleys and depressions.

The origin, nature, variety, and classification of Europe’s soils raise highly complex problems. So many factors—bedrock, drainage, plant decomposition, biological action, climate, and time—are involved. Humans, moreover, have done much to modify soils and, with increasing scientific knowledge, to render soils of greater and continuing value by drainage, crop rotation, and the input of suitable combinations of chemicals. In such ways, naturally poor soils can—as has been shown in Denmark—be made productive. The practice of an enforced “resting” of soils, by leaving fields fallow to recuperate, began to disappear with the agricultural revolution of the 18th century, and agronomic science continues to show how the best results can be achieved from specific soils and also how to curtail soil erosion. Europe’s arable land lies mainly in the lowlands, which have podzolic, brown, chernozem, and chestnut soils, although the upper elevation level of cultivation, as that of animal husbandry, rises southward.