inundations, has almost wholly obviated that source of apprehension. Between the beginning of the fifteenth century and the year 1761, thirty-one destructive floods of the Arno are recorded; between 1761, when the principal streams of the Val di Chiana were diverted into that river, and 1835, not one.[382] _Improvements in the Tuscan Maremme._ In the improvements of the Tuscan Maremma, more formidable difficulties have been encountered. The territory to be reclaimed was more extensive; the salubrious places of retreat for laborers and inspectors were more remote; the courses of the rivers to be controlled were longer and their natural inclination less rapid; some of them, rising in wooded regions, transported comparatively little earthy matter,[383] and above all, A like example is observed in the Anapus near Syracuse, which, below the junction of its two branches, is narrower, though swifter than either of them, and such cases are by no means unfrequent. The immediate effect of the confluence of two rivers upon the current below depends upon local circumstances, and especially upon the angle of incidence. If the two nearly coincide in direction, so as to include a small angle, the joint current will have a greater velocity than the slower confluent, perhaps even than either of them. If the two rivers run in transverse, still more if they flow in more or less opposite directions, the velocity of the principal branch will be retarded both above and below the junction, and at high water it may even set back the current of the affluent. On the other hand, the diversion of a considerable branch from a river retards its velocity below the point of separation, and here a deposit of earth in its channel immediately begins, which has a tendency to turn the whole stream into the new bed. "Theory and the authority of all hydrographical writers combine to show that the channels of rivers undergo an elevation of bed below a canal of diversion."--Letter of FOSSOMBRONI, in SALVAGNOLI, _Raccolta di Documenti_, p. 32. See the early authorities and discussions on the principle stated in the text, in FRISI, _Del modo di regolare i Fiumi e i Torrenti_, libro iii, capit. i. the coast, which is a recent deposit of the waters, is little elevated above the sea, and admits into its lagoons and the mouths of its rivers floods of salt water with every western wind, every rising tide.[384]