Some Engineering Problems Of The Panama Canal In Their Relation To Geology And Topography

10 ENGINEERING PROBLEMS OF PANAMA CANAL. into cars. The site of another quarry near Fri joies was first picked out by the writer from a railroad train because of its steep ridge- like topographic expression. On further exploration the ridge was found to be composed of basalt, but the rock was a little too much jointed for the desired use, the facing of a breakwater. The hills and higher areas, because of their steep slopes, contain, no stag- nant water in which mosquitoes and other pests can breed, and have good drainage, hence, where convenient, they were utilized as camp sites. By clearing the jungle cover off the tops of the higher hills they became convenient, triangulation stations for the surveys of the Canal Zone. Plate IV indicates the location and area of the hilly region, which is practically coextensive with the areas of igneous rocks, and Plates I and II convey some idea of its character. COASTAL-PLAIN TYPE. Coastal plains locally border both the Atlantic and the Pacific coasts of Central America. In the Canal Zone this type of land form is principally on the Atlantic side and comprises five kinds of subtypes. They are: (1) Coastal swamps, of considerable depth, composed of soft dark mud and organic matter, and inland swamps and alluvial basins; (2) coral reefs, awash at half tide, and coral flats, composed largely of coral débris, slightly above high-tide level; (3) river flats of alluvium in the lower valleys; (4) bars at and near the mouths of rivers, beaches, sand spits, etc.; (5) seaward-tilted relatively smooth plains, low hills, and higher dissected remnants of former plains. A discussion of the origin of the land forms of the isthmian region is not within the scope of this report. The first practical relation between tho engineering work and this type of topography was tho groat difficulty of making surveys through the unhealthful black-mud and grecn-wator swamps. Next came the construction of the Panama Railroad lines across the swamps. A feature of this construction was tho necessity of vast fills with, wide bases. The extra width was to obviate tho sinking of the fill, with accompanying bulging of tho swamp material on either side of the sunken part. Another most important matter was tho building up of a groat coral flat from its original high-tide level to 3 or 4 feet above, in order to furnish a site for the town of Colon and the Atlantic tormina! plant of tho canal and the Panama Railroad. On the other hand, the flats formed mostly of coral débris, unlike tho swamps, presented a solid foundation on which to dump spoil, and thus to build up and prepare a solid base for tho town. Tho low mud swamps and river alluvium greatly facilitated the dredging of the approach channels to both tho Atlantic and the Pacific locks.