GRADIENT DIAGRAM

Evening Post, Volume CVI, Issue 31, 6 August 1923, Page 3

GRADIENT DIAGRAM

ITS STORY ANALYSED

We are indebted to the Department of Railways for the privilege of photographing and of reproducing on a reduced scale the "gradient diagram" of the South Island Midland Railway (Christchurch-Grey'mouth). Christchurch is 13 feet above sea-level, Greymouth is 11; and the railway that now unites the two coasts, almost from sea-level to sealevel, rises to 2420 feet at Arthur's Pass station, and at the railway portal just west thereof to 2435 feet (Public Works Department's figures). Tba railway covers 87 miles in length in climbing from Christchurch to Arthur's Pass station. It covers 51 miles in rising from Greymouth to Otira. Add the intervening strip of about 8£ miles (including about 5£ miles Otira tunnel) and you can say that the Midland Railway is about 146 miles long; or 153 miles if you a-dd the ChristchurchLyttelton section with its mile-and-a-half tunnel—a monument to the Canterbury Provincial Council.

CROSS-SECTION OF SOUTH ISLAND.

When the reader looks at this diagram, he is not having a bird's eye view of the railway's straights, its curves, and its sinuosities. He is simply looking at line indicating gradients —a sort of side view that might be had from the sea if all the land on the northward side of the Midland Railwavy (that is, all the top half of the South Island) were to slip down to the j>lace Jlaui fished it up from. In this sense, the diagram is a sort of railway cross-section of the South Island. It is a railway line, not a contour line. If the Southern Alps peaks could be shown as a sort of background, Mount Rolleston would be seen immediately overlooking the tunnel, and towering to 9000 feet, or nearly four times the height of the highest portion of the railway line. Back of Uolleston would be Cook, 12----349 feet.

Between Christchurch and Rolleston the railway does not climb much. Rolleston is 177 feet above sea-level. The diagram shows a sharper climb up to Springfield (elevation 1252 feet). West of Springfield it shows that difficult section of country commented on in recent issues—a nine-mile length between Avoca and Otarama, carrying high viaducts; also tunnels short and long, the longest being about 2000 feet. PASS AND TUNNEL. Following the line westward is seen a sharp rise and fall between Craigieburn and Cass, imposing 1 in °53 gradient on west-bound traffic. A little way beyond Cass the front ascent begins, culminating at the point marked on the diagram as Arthur's Pass. (This is Arthur's Pass station, not the Pass itself • the Pass is hundreds of feet higher.) From the real Arthur's Pass traffic is now diverted, by the tunnel to Otira 4t the tunnel portal the East-West train .'egins.to descend. Landmarks along this n^TV a The, WeSt Coasfc art> Ot"-a 1260 feet) Jackson (GO7 feet, and only 12 miles from Otira), Stillwater (100 feet), Greymouth (11 feet). Now a word about gradients: There Springfield and the' East Coast, and between Jackson and the West Coast Between Springfield and Cora Lvnn, on the Canterbury side of the divide the east-bound traffic has nowhere a gradient worse than 1 in 60, but the west-bound traffic meets a 1 i n 30 crad- ' lent in places. Thereafter there is nothing worse" than 1 in GO until the tunnel (1 in 33) is reached. The Ldt ents between 6tira and Jackson Se 1 in ou. ....... (

It is clear that On the whole, the engineers have done very well. They have well and truly conquered the great di-