Tápió
The hydrology of Hungary is mostly determined by Hungary's lying in the middle of the Carpathian Basin, half surrounded by the Carpathian Mountains. All parts of the country have some outflow. All surface water gravitates towards its southern centre, and from there, is united in the Danube, which flows into the Black Sea. The whole of Hungary lies within the Danube drainage basin.
The total length of all the irrigation systems and inland waterways in the country is about 26,000 km (16,000 mi).
The annual water balance of the country shows a surplus. Yearly about 100 km3 (3.5×1012 cu ft) of water leaves the country towards the Black Sea. From that, precipitation amounts for only 10%, the rest being provided by the incoming rivers of surrounding countries.
Hydrographically Hungary can be divided into two roughly equal parts: the drainage basins of the Danube and the Tisza.
The present network of Hungary's rivers began to take shape at the end of the Tertiary and the beginning of the Quaternary periods when the Pannonian Sea retreated from the basin.
The rivers in Hungary reach their lowest level at the end of the summer, the beginning of the autumn, or sometimes in the winter.
Both the Danube and the Tisza have two regular floods each year, the early spring "icy flood" and the early summer "green flood". The "icy flood" is the result of the thaw in the mountains surrounding the Carpathian Basin, when the rivers in the plain are usually still frozen. Before the river flows were controlled, the piled-up ice sheets of the river could form tremendous barriers, which in turn could cause devastating floods. This phenomenon can still be a real danger after cold winters, and a small fleet of icebreakers is used on the two rivers to fight against ice barrages. The "green" flood in the early summer carries a much larger amount of water, not only the torrents from the Alps, but also the surface runoff water from the May and June rains.
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Wikipedia