The Upper Navigable Level
In 1773 an upper navigable level was created by widening the original drainage sough with a finished length of 1.75 miles (2.8 km) and draining into the main navigable level. A sloped branch was driven from the upper level to the surface at a gradient of 1 in 4 to allow boats to be drawn up and lowered down. This incline was later continued downwards to the main level. Further navigable levels were dug below the main level to serve deeper seams; these were 57 yards (52 m) and 83 yards (76 m) deeper.
Read more about this topic: Worsley Navigable Levels
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