Geography of Sheffield (Totley Brook passes south of Totley and meets Old Hay Brook at Needham's Dyke). The Sheaf flows northwards to join the River Don near Blonk Street Bridge in the city centre. This lower section of the River Sheaf together with the River Don, between the present Blonk Street and Lady's Bridge, formed part of the perimeter of Sheffield Castle. Porter Brook's source is just inside the Peak District National Park, to the west of the city, at Clough Hollow, also near Ringinglow. From here it flows eastward to meet the Sheaf, at a point now located underneath Sheffield Midland Station.
Sheffield city is in the eastern foothills of the Pennines, and the valleys of the River Don and its four tributaries, the Loxley, the Porter Brook, the Rivelin and the Sheaf. Sixty-one percent of Sheffield's entire area is green space, and a third of the city lies within the Peak District national park. There are more than 250 parks, woodlands and gardens in the city, which is estimated to contain around 4.5 million trees. In the 19th century, Sheffield gained an international reputation for steel production. Known as the Steel City, many innovations were developed locally, including crucible and stainless steel,