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Hydrography

Most of Catalonia belongs to the Mediterranean Basin. The Catalan hydrographic network consists of two important basins, the one of the Ebro and the one that comprises the internal basins of Catalonia (respectively covering 46.84% and 51.43% of the territory), all of them flow to the Mediterranean. Furthermore, there is the Garona river basin that flows to the Atlantic Ocean, but it only covers 1.73% of the Catalan territory.

The hydrographic network can be divided in two sectors, an occidental slope or Ebro river slope and one oriental slope constituted by minor rivers that flow to the Mediterranean along the Catalan coast. The first slope provides an average of 18,700 cubic hectometres (4.5 cubic miles) per year, while the second only provides an average of 2,020 hm (0.48 cu mi) /year. The difference is due to the big contribution of the Ebro river, from which the Segre is an important tributary. Moreover, in Catalonia there is a relative wealth of groundwaters, although there is inequality between comarques, given the complex geological structure of the territory. In the Pyrenees there are many small lakes, remnants of the ice age. The biggest are the lake of Banyoles and the recently recovered lake of Ivars.

The Catalan coast is almost rectilinear, with a length of 580 kilometres (360 mi) and few landforms —the most relevant are the Cap de Creus and the Gulf of Roses to the north and the Ebro Delta to the south. The Catalan Coastal Range hugs the coastline, and it is split into two segments, one between L'Estartit and the town of Blanes (the Costa Brava), and the other at the south, at the Costes del Garraf.

The principal rivers in Catalonia are the Ter, Llobregat, and the Ebro (Catalan: Ebre), all of which run into the Mediterranean.