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

RELATION OF DIFFERENT FACTORS TO ENGINEERING. 13 water-containing capacity. Then, too, the rainfall is so heavy that the ground is soon saturated and the percentage of run-off becomes high. The streams on their way to the ocean pass through three general stages of size and activity. In the first stage the stream is small and flows swiftly down the gradient of a steep valley, carrying along bits of soil and rock from the surface over which it passes. In the second stage the stream is less swift but much larger, having been reinforced by many smaller influents. Because of its greater volume its carrying capacity is greater, and bowlders, cobbles, and gravel are rolled along its bottom, grinding each other as they go, and thus manufacturing finer and more easily transported material. The third and last stage is that in which the stream flows through a wider, flat, and almost base-leveled valley, on the last course of its oceanward journey. The water now moves with comparative slow- ness, hence can carry only the finest sediments and is forced to deposit part of its load. The wide lower part of a stream valley is generally called a flood plain, for it is flooded during very high water and receives a small building-up increment of sediment from each flood. The heaviest deposition of sediment is along the line where the river overflows its banks, because the current is materially slowed down along this line. The ground is therefore built up higher near the river bank, and in this way what arc termed 11 natural levees ” are formed. The finer sediment is often held in suspension until the river current is checked when it reaches the sea. The sediment then, if not carried away by tidal currents, falls to the bottom at or near the river mouth to form bars or shoals. relation of streams to canal construction. The streams of the Canal Zone have a most vital relation to the canal, because they furnish the water to fill the dammed-in part of the waterway between the locks (see PL IV). Without the streams only a sea-levél canal would be possible. The damming of the streams originated Gatun Lake and caused the backwater to fill Culebra Cut to navigable depth. The waste water from Gatun Lake will operate an immense hydroelectric plant which is to supply the whole Canal Zone with light and electric power, and is to bo used to electrify the Panama Railroad. In the building of the railroad, roads, etc., and in some of the concrete construction and other work incidental to canal construction, it was found that gravel served the purpose almost as well as crushed rock and was much cheaper. The general method by which streams roll rock fragments and bowlders along their bottom in their swifter upper courses and gradu- ally grind them into gravel, and how they deposit the gravel whero their velocity slows down, somewhat and carry the finer silts down to