The waterways of Cochin-China communicate by means of natural or artificial channels (arroyos), facilitating transport and aiding in the uniform distribution of the inundation to which the country owes its fertility.
The lowlands of Tilsit are protected against inundation by dikes.
A portion of the stream of the Drin has found its way into the Boyana channel; the result has been a rise in the level of Lake Scutari and the inundation of the adjacent lowlands.
On the west the shore is perfectly flat, so that a slight rise in the water causes the inundation of a considerable area - a fact not without its influence on the estimates made at varying periods as to the size of the lake.
Centrifugal migration is usually a matter of compulsion; it may be necessitated by natural causes, such as a change of climate leading to the withering of pastures or destruction of agricultural land, to inundation, earthquake, pestilence or to an excess of population over means of support; or to artificial causes, such as the wholesale deportation of a conquered people; or to political or religious persecution.