Snow cover is the predominant source of food for the rivers of Polissya.
In Ukraine there are almost 4 thousand small rivers (up to 100 km long), 123 – medium (100-500 km), 14 – large (over 500 km)
Surface waters include rivers and canals, lakes and reservoirs, swamps.
Rivers are the most active part of the land waters. They return most of the precipitation to the sea, are the main source of water for household and domestic needs, as well as transport routes and a source of energy.
The rivers are unevenly distributed throughout the country. This is due to the nature of the terrain, climate, water permeability of rocks, vegetation and other natural factors. For comparison, use the density of the river network, which is determined by the ratio of the total length of rivers to the area. Its highest density is in the Carpathians (up to 1.1 km / km2), and in the steppes between the rivers Dnieper and Molochna this indicator is the lowest – 0.25 km / km2.
The vast majority of Ukraine’s rivers belong to the Black and Azov Seas and only 4% to the Baltic Sea Basin. This is due to the general slope of the surface of Ukraine. In the west of the country is the Main European Watershed, which divides the basins of Ukrainian rivers between the basins of these seas.
The fall and the average slope of rivers, the speed of their flow, the structure of river valleys depend on the relief.
Mountain rivers of the Carpathians and Crimea are characterized not only by a significant slope and speed, but also by deep (up to 900 m) valleys with steep slopes, rapids and waterfalls. Thresholds and gullies are formed on some plain rivers that cross the Podolsk and Dnieper hills. Due to the small slope of the rivers of Polissya, their currents are very slow, which significantly increases the wetlands of the surrounding areas.
The greater the slope of the river, the more work it does, eroding and transporting solid particles of destroyed rocks, and at the mouth they can form a delta. Among the rivers flowing through Ukraine, the Danube River has a well-formed delta.
In the north of Ukraine in the forest zone the turbidity of the water was low. It does not exceed 20-50 g / m3, which is due to excessive moisture, poorly cut terrain, low river slope. In the forest-steppe, where there is a lot of loamy deposits and high plowing of the adjacent territories, the annual value of river water turbidity is 100-250 g / m3. Maximum turbidity values reach 3000 g / m3. In steppe rivers the turbidity of the water is average, the concentration of sediments in the water here reaches 250-500 g / m3.
In the Carpathians and the Crimean Mountains, water flows from forested slopes have a turbidity of 250,500 g / m3. If they flow down from bare slopes, the turbidity is not less than 5-10 g / m3. Due to heavy rains, mudflows can be formed – short-term, with a high level rise and a high content (10-75%) of solid material, streams that have great destructive power. Sometimes they destroy roads, buildings, arable land.
The main source of food for the rivers of Ukraine is precipitation. The main share (50-80%) in the supply of plain rivers falls on melting snow water, and mountain – on rainwater. Underground supply of rivers in most parts of the territory is 10-20% and only for some areas – up to 50%. Thus, the rivers of Ukraine have mainly mixed supply – melted snow, rain and groundwater. This is the type of power supply in which no source of water is more than 50%. If the value of one of the sources is from 50 to 80%, it is called predominant, if more than 80% – exceptional.
On the territory of Ukraine there are some differences in the nature of river nutrition. Snow cover is the predominant source of food for the rivers of Polissya. The value of rainwater supply on plain rivers decreases from north to south from 10 to 1%. In the same direction, the rate of groundwater supply decreases approximately.
The water regime of the plain rivers of Ukraine clearly reflects the spring floods and winter and summer lows. In autumn there is a slight rise in water level. The summer low is sometimes disturbed by minor rain floods, and the winter – by thaws. The flood period begins in birch in April and lasts on large rivers for 2-3 months, and on small – 10-15 days.
The formation of the flood regime of mountain rivers is due to heavy rains and a significant slope of watercourses. The Carpathian rivers are flooded throughout the year, and in the Crimean mountains – mainly in winter and spring.
Icefall on the rivers of Ukraine is formed in December. Its average duration is 2-3.5 months, in severe winters – up to 4 months. The mountain rivers of the Carpathians do not have a stable ice cover, and it is not formed on the Crimean rivers. Clearing and ice drift on the rivers of the plain part of Ukraine lasts from 5 to 25 days.
The richest river in Ukraine is the Dnieper. Its average annual water flow at the mouth is 1700 m3 / s. The annual runoff of the Dnieper is 53.5 km3.
The magnitude of the annual runoff of rivers depends on the climate. In western Ukraine, where the moisture content is close to one, the annual runoff is the highest, and it is lowest in the southern lowland areas of the sea coast, where the moisture content is significantly less than one.
The amount of runoff is also influenced by the geological structure of the river basin, its relief, soil and vegetation.
Australia: general characteristics of the continent. Abstract
Discovery, research and development of Australia. Great Barrier Reef. The fauna of Australia
Discovery, research and development of Australia
The existence of a large continent in the extreme south of the Earth was mentioned by the ancient Greeks (Ptolemy, etc.). They placed it on maps of the time south of the Indian Ocean.
Europeans learned about the existence of Australia in the era of the Great Geographical Discoveries. The discovery by the Portuguese of islands south of Asia – Sumatra, Java, Borneo (Kalimantan), Celebes (Sulawesi), and most importantly – the extremities of New Guinea suggested that these islands may be part of the unknown Southern Continent.
Gradually, there was a strong belief that in the far south of the globe there is buy comparative essay now a continent. It was called Australia (more precisely "Terra Australius is incognito" that is "Unknown southern land"). On the map of the famous Dutch cartographer Ortelius (1570) the southern continent is depicted by a huge part of the world. On this legendary continent dreamed of finding gold.
The unknown continent was especially attractive to Spanish sailors. After conquering Peru, the Spaniards often traveled west from here along the route that Magellan paved to the Philippine Islands.
Confidence in the existence of the Southern Continent was further strengthened after the Spanish navigator Mendanya in 1568 discovered the Solomon Islands archipelago. Mendanya, who discovered the islands of Santa Cruz during his second voyage, still did not find the Southern Continent.
In December 1605, three ships headed by Pedro Quiros set sail from the port of Callano (Peru) in search of Australia. Having passed among "clouds of islands" of the Tuamotu (Lowland) archipelago, Kiros reached the island group of Santa Cruz. From here he turned south and saw a mountain "great land" with dense forests, gorges, turbulent streams and settlements of black people.
Cyrus called this land Australia the Holy Spirit. He was convinced that he had discovered a great continent. The Christian city of New Jerusalem was solemnly founded on the new land. Hence the Christian faith was to spread among blacks "Australia holy spirit"… Rejoicing at his discovery, Cyrus abandoned two ships and secretly left them on his ship in Peru. He decided to be the first to inform the Spanish authorities about the discovery of Australia and get the right to govern it. In fact, Cyrus discovered an archipelago of islands that are now called the New Hebrides.
Meanwhile, the Portuguese Torres, the captain of one of the ships abandoned by Cyrus, explored the islands and led the ships west, crossing the Coral Sea for the first time.
On June 14, 1606, he approached the southern coast of New Guinea and discovered a strait that separated the island from an unknown land that ran south. This was the real Australia. The cape that Torres saw in the south is now called York, and the strait between New Guinea and Cape York was named in the 18th century. Torres Strait. When Torres informed the Spanish authorities in the Philippines about his discovery, it was decided to keep it a secret, and for more than 150 years no one knew about Torres’ discovery. Only after the capture of Manila did the British find Torres’ message in the archives. It was published only after James Cook in the 18th century. for the second time passed through the strait between New Guinea and Australia.
So, Spanish sailors approached Australia from the east. But this does not mean that no one has seen the coast of Australia from the west. On secret Portuguese maps of the 16th century. the shore of a large unknown island was depicted "Great Java" which by its geographical position corresponds to the coast of Australia west of the Gulf of Carpentaria. It is possible that the Portuguese did not approach this shore themselves, but heard about it from the locals and, in their words, depicted it on maps.
At the beginning of the 17th century. the northern shores of the Southern Continent became known. But what is this continent? Does it extend to the South Pole, as shown on the map of Ortelius?
The answer to these questions was formed gradually, as the study of the mainland.
In 1616, the Dutchman Dirk-Hartogson approached the island later named after him (Dirk-Hartog), located on the western outskirts of Australia at 26 ° S. w.
But the most important discoveries were made by the Dutchman Abel Tasman. In 1642, he left Batavia with the firm intention of finding out whether Australia was reaching for the South Pole. After passing the island of Mauritius in the Indian Ocean, he headed east and, to his surprise, went to the Pacific Ocean. Along the way, he saw only the southern coast of a land he called Vandimenova. It later emerged that it was a large island called Tasmania.
Tasman bypassed Australia from the south and east and found that it is an independent continent that does not connect in the south with the land near the South Pole. Discovering New Zealand along the way, Tasman took it for the edge of the southern Antarctic continent.