diversion of the River Frome in the 1240s into an artificial deep channel known as "Saint Augustine's Reach", which flowed into the River Avon. Saint Augustine's Reach became the heart of Bristol's docks with its quays and wharfs. The River Avon within the gorge, and the River Severn into which it flows, has tides which fluctuate about between high and low water. This means that the river is easily navigable at high tide but reduced to a muddy channel at low tide in which ships would often run aground. Ships had no option but to be stranded in the harbour for unloading, giving rise to the phrase "shipshape and Bristol fashion" to describe how ships and their secured cargo were capable of taking the strain of repeated strandings on the mud. As early as 1420, vessels from Bristol were regularly travelling to Iceland and it is speculated that sailors from Bristol had made landfall in the Americas before Christopher Columbus or John Cabot. After Cabot arrived in Bristol, he proposed a scheme to the king, Henry VII, in which he proposed to reach Asia by sailing west across the north Atlantic. He estimated that this would be shorter and quicker than Columbus' southerly route. The merchants of Bristol, operating under the name of the Society of Merchant Venturers, agreed to support his scheme. They had sponsored probes into the north Atlantic from the early 1480s, looking for possible trading opportunities. In 1552 Edward VI granted a Royal Charter to the Merchant Venturers to manage the port. By 1670, the city had 6,000 tons of shipping, of which half was used for importing tobacco. By the late 17th century and early 18th century, this shipping was also playing a significant role in the slave trade. Construction of the floating harbour In the 18th century, the docks in Liverpool grew larger and so increased competition with Bristol for the tobacco trade. Coastal trade was also important, with the area called "Welsh Back" concentrating on trows with cargoes from the slate industry in Wales, stone, timber and coal. The limitations of Bristol's docks were causing problems to business, so in 1802 William Jessop proposed installing a dam and lock at Hotwells to create the harbour. The £530,000 scheme was approved by Parliament, and construction began in May 1804. The scheme included the construction of the Cumberland Basin, a large wide stretch of the