The Isthmus of Suez Question

by Ferdinand de Lesseps

It is exactly the same with the waves of the sea; every fluid molecule placed at the surface of the billow experiences an oscillatory movement nearly vertical, so that if a body floating on the surface of a wave is watched it will be seen to remain in the same place, sometimes in the hollow of the wave, sometimes on its summit, and if at length it changes its place, that depends upon other circumstances, such as the force of the wind or the direction of the currents.

This oscillatory movement which is perceived on the surface of the sea, is necessarily developed to a certain depth, which will be greater in proportion as the undulations are stronger at the surface. This fact has been confirmed by experiment; it has been ascertained in effect that the agitation of the sea caused by the wind, is communicated to a certain depth, variable according to the wind, according to the sea, and the places where the observations were made, and that beyond that depth the sea is perfectly calm. Thus it may be admitted as an observed and well proved fact, that the waves require a certain depth for their free developement; if an obstacle is presented to this developement, there will be a forcible re-action of the wave against this obstacle which will be carried off, if it is moveable, and will enter into the system of the wave. This action of the waves against the deeps is what is called the ground swell.

This established, it has already been seen that the coast of the sea, as well as the projecting capes, resign to the sea every year a certain amount of earthy and rocky matters. These matters are removed by the waves which break upon the shore, the soft portions are quickly disintegrated by this powerful action, and form muddy sand and mud, and the hard portions are rounded into pebbles the size of which is diminished more and more by the prolonged action of the force which set them in motion and which reduces them to sand; but in proportion as these matters arrive at a sufficient degree of tenuity, they become susceptible of submitting to the transporting force of the waves and currents, and quit the place where they were formed.

This transporting force depends both upon the height of the tides and the direction of the winds, as well as their intensity, combined with that of the currents which are observed in all seas. So that while considerable masses of matter are set in motion along the shores, the rivers, especially those which traverse a great extent of country, transport as far as their mouths only muddy matters, so light that they are carried to a distance, and afterwards deposited in the depths of the sea. This is remarkably the case with the Nile, whose waters at the time of the inundation are distinguished by their colour for more than ten leagues into the sea. All the deposits and accretions of the river up to 20 kilom. above its mouth are muddy, while all the banks which are at its mouth are composed of sand alone.

Thus, all the impediments of the mouth of the Nile evidently emanate from the sea. To demonstrate it by still farther evidence, we will repeat the reasoning of the engineer M. Bonniceau relative to the alluvium of the river Mersey, in his excellent work upon the navigation of tidal rivers: “If the deposits emanated from the elevated lands in a sensible degree, the quantities deposited from time to time ought to be proportional to the quantity of rain that falls at the same epochs, because the same amount of matters descending from the elevated lands and transported by the river, ought to be partly regulated by the quantity of water that carries them; but it is a fact well ascertained, that the accumulations of sand which exist in the vicinity of the mouth are greater in proportion as the waters of the river are less abundant, while on the contrary at the time of the increase, when the Nile contains nearly 0 met. 008 of matter in suspension, the sand banks are removed and thrown back far off into the sea.”

It is said that Alexander the Great was determined in his choice of the situation for the port of Alexandria by the consideration of the winds and littoral currents which carry eastward the matters held in suspension by the Nile, and thus cover the coast with sand. If this theory were true, no alluvium ought to be perceived westward of the mouth of the river. Now all the coast from Tripoli as far as El Aritch is covered with sand banks, which frequently form downs, and these downs are found at the present time transported several leagues into the interior of the lands westward of the Rosetta mouth.

The port of Alexandria itself has not escaped the action of the ground swell, for a sand bank has been formed which occupies a good third of the total superfice of the roadstead. Happily for the port the accumulation of sand appears to have been arrested long ago, or rather its increase has become imperceptible.

The roadstead of Alexandria owes its depth to the disposition of its sides in respect to the winds and currents. It is like the roadstead of Algiers, which is everywhere very deep, while the neighbouring ports have sand banks. It cannot be said that these sand banks are owing to the presence of rivers, which do not exist in the whole extent of the coast of Barbary, for the few land streams that are scattered along the shore cannot be called by that name.