Nantes
Hydrology

The Loire is about 1,000 kilometres (620 miles) long and its estuary, beginning in Nantes, is 60 kilometres (37 miles) in length. The river's bed and banks have changed considerably over a period of centuries. In Nantes the Loire had divided into a number of channels, creating a dozen islands and sand ridges. They facilitated crossing the river, contributing to the city's growth. Most of the islands were protected with levees during the modern era, and they disappeared in the 1920s and 1930s when the smallest waterways were filled in. The Loire in Nantes now has only two branches, one on either side of the Isle of Nantes.

The river is tidal in the city, and tides are observed about 30 kilometres (19 miles) further east. The tidal range can reach 6 metres (20 feet) in Nantes, larger than at the mouth of the estuary. This is the result of 20th-century dredging to make Nantes accessible by large ships; tides were originally much weaker. Nantes was at the point where the river current and the tides cancelled each other out, resulting in siltation and the formation of the original islands.

The city is at the confluence of two tributaries. The Erdre flows into the Loire from its north bank, and the Sèvre Nantaise flows into the Loire from its south bank. These two rivers initially provided natural links with the hinterland. When the channels of the Loire were filled, the Erdre was diverted in central Nantes and its confluence with the Loire was moved further east. The Erdre includes Versailles Island, which became a Japanese garden during the 1980s. It was created in the 19th century with fill from construction of the Nantes–Brest canal.
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