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See also: river of central See also: Italy
.
It traverses the Tuscan Apennines—in which it rises at a point some 12 M
.
N. of Pieve See also: San Stefano, 416o ft. above sealevel—in a series of picturesque ravines, skirts the west See also: foot of the See also: Sabine Mountains in a broad shallow valley, then crosses the See also: Roman Campagna, cutting its way through See also: Rome, and finally enters the Tyrrhenian (Mediterranean) See also: Sea by two arms at See also: Ostia and Fiumicino, the latter artificial
.
Its See also: principal tributaries are the Paglia, the Nera and the Anio or Teverone, and it is generally navigable by boats up to the confluence of the Nera, a distance of 104 m., though, owing to the rapidity of the current, there is very little navigation above Rome
.
The See also: total length of the river is 240 m., of which 21 M. lie between Rome and the sea
.
This latter portion of the river's course is tortuous, but in spite of this, and although the See also: depth varies from only 7 to 20 ft., and in ,'places at low See also: water does not exceed 4 ft., it is nevertheless navigated by vessels up to 18o tons See also: burden and proposals have been made to embank and dredge it so as to increase this depth to 8 ft. at least, or to build a See also: ship canal up to Rome
.
The See also: area of the See also: Tiber See also: basin is 6845 sq. m
.
The stream is heavily charged with sediment, and from that circumstance got its See also: ancient epithet of flavus (tawny)
.
It does not, however, See also: form a See also: delta proportionate to the See also: volume of its water, owing to a strong sea current flowing northwards close to the See also: shore, to the sudden sinking of the sea to a See also: great depth immediately off the mouth of the river, and possibly also to the permanent subsidence of the See also: Italian See also: coast from the Tiber mouth southwards to Terracina
.
Still it has advanced at each mouth about 2 M. since Roman times, while the effect of the sediment it brings down is seen on the See also: north-west almost as far as Palo (anc
.
See also: Alsium), and on the See also: south-See also: east beyond Tor See also: Paterno (see See also: LAURENTINA VIA) in the gradual advance of the coast
.
The See also: rate of advance at Fiumicino is estimated at 13 ft. per annum
.
From Rome to the sea the fall is only 6.5.: See also: I000
.
The arm which reaches the sea at Fiumicino is a canal, dug by See also: Claudius and improved by Trajan (see See also: PORTUS), which partially silted up in the See also: middle ages, and was reopened for navigation by See also: Paul V. in 1612, 22 M. long, 8o-13o ft. wide, and with a minimum depth of 5 ft
.
The See also: lower course of the Tiber has been from the earliest ages subject to frequent and severe inundations; of more See also: recent ones, those of 1598, 1870 and 1900 have been especially destructive, but since the See also: year 1876 the See also: municipality of Rome, assisted by the Italian See also: Government, has taken steps to check, and possibly to prevent these calamities within the city by constructing embankments of See also: stone, resting on caissons, for a total distance (counting in both sides of the river) of 6
See also: miles
.
The See also: flood of 1900 carried away about 4 m. of the new See also: embankment on the right See also: bank of the right arm opposite the See also: island owing to the faulty planning of the course of the river at that point, which threw the whole of the water into the right arm, and except in flood See also: time, See also: left the left arm dry—a fault which has since been corrected
.
In the prehistoric See also: period the mouth of the Tiber must have been situated at the point where the hills which follow it on each See also: side cease, about 12 in. below Rome
.
On the right bank they are of pliocene See also: gravel, on the left of tufa; and on the latter, on a cliff above the river (the ancient Puilia saxa) stood Ficana (marked by the farmhouse of Dragoncello), which is said to have owed its origin to Ancus Martius
.
Beyond these hills the low coast See also: belt formed by the solid See also: matter brought down by the river begins; and on each side of the mouth in the flat ground were See also: salt marshes (see OSTIA, PORTUS)
.
The flood of 1900, when the river both above and below Rome extended over the whole width of its valley, from See also: hill to hill, and over most of the low ground at its mouth, gave an idea of the conditions which must have existed in prehistoric days
.
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