The irregular curved lines shown on the diagram are contours of the original surface, the cutting planes being parallel and horizontal and having a perpendicular interval of 4 ft. The zero or datum line was taken at the line between the cut and fill portion of the construction marked 00 and shown dotted on the diagram, the elevation of the various contours above or below this elevation is given in the margin at the end of each contour.

The top of the embankment portion being 10 ft. wide, this width was carried level around the Reservoir basin as shown, making the excavation part of the reservoir a level strip 10 ft. wide between the top of the inner or basin slope and the bottom of the outer slope. The elevation of this level strip which is marked “GRADE” on the diagram was taken at the same height as the zero plane of the surface Contours.

The slopes of the finished work both embankment and excavation being all taken as having a ratio of 1½ to 1, the straight broken lines on the diagram are the lines of intersection of the same set of cutting planes as produced the surface or original contours with the slopes of the final or finished Reservoir surfaces and are the “final contours” or contours of the final surface.

The problem then is to measure the volume of the material which must be excavated and filled in, in order to bring the original surface of the ground to the desired finished surface or in other words to find the number of Cu. yds. of excavation and embankment required in order to construct a reservoir of the size and shape shown on a site whose surface is shown by the original contours.

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