Engineering Wonders of the World
Volume I

IRRIGATION WORK IN THE UNITED STATES. 97 WHEAT ON LAND IN THE NEIGHBOURHOOD OF THE GUNNISON RIVER TUNNEL. Difficult Levelling Work. cameras, and provisions went down with the floods. The notes contained data sufficient to indicate the feasibility of diverting the Gunni- son, for they showed that the elevation of that stream was considerably above the Uncom- pahgre valley. The final mapping of the canyon by En- gineer I. W. M‘Connell was fully as exciting and dangerous as the exploration work of Mr. Fellows. Mr. M‘Connell had to be lowered into the canyon so that he could make a map of it—a real topographic map, with contour lines, levels, and bench marks, as clear and easy to trace as any good map of a ward of a city. Then he established precise levels at both ends of the proposed tunnel. Only an engineer can appreciate the difficulty of this job. To aid the layman’s understanding, a few of the details which M‘Connell had to consider are appended. First, the tunnel must be planned with the exact slope necessary to carry the proper amount of water into the valley. To do this, levels had to be run over the mountain to the valley, and back from the mountain to the bottom of the canyon. The work was repeated again and again, and measurements were taken each time until the exact slope required had been determined. (1,408) This was really only preliminary to the more difficult task of ascertaining the exact length of the tunnel. Between the ends of the bore is a hill 2,000 feet high, as rough a bit of country as lies out of doors. The tunnel goes right through that hill. M‘Connell first meas- ured it by triangulation, and then “ slope boarded ” it. The latter process is the easier to understand, as it is used to determine the horizontal distance between the head and the foot of a flight of stairs. M‘Connell and his men followed a plan similar to this. They had a long board scaled off to a hair’s-breadth. In the middle of the board was set a spirit- level, so that the measuring edge of the board could be set true. With a man at each end of the board, and one at the middle to watch the spirit-level, they started from a precisely GOVERNMENT ROAD INTO GUNNISON CANYON, . COLORADO. This road, one of the most remarkable highways in the world, was made to enable materials for work on the Gunni- son Tunnel to be brought to the scene of operations. 7 VOL. II.