The navigable mileage of the Alabama rivers is 2000 m., but obstructions often prevent the formation of a continuous route, notably the "Muscle Shoals" of the Tennessee, extending from a point io m.
Its level varies with the obstructions formed by ice, falling as much as 28 ft.
On account of the rapid fall of its tributaries, the union of so many of them with the main stream near its middle course and the obstructions to the flow of the water in the lower course, the Passaic is subject to disastrous floods.
Among the miscellaneous powers of an urban council with respect to streets may be mentioned the power to widen or improve, and certain powers incorporated from the Towns Improvement Clauses Act 1847, with respect to naming streets, numbering houses, improving the line of streets, removing obstructions, providing protection in respect of ruinous or dangerous buildings, and requiring precautions to be taken during the construction and repair of sewers, streets and houses.
These relate to obstructions Hackney and nuisances in streets, fires, places of public resort, hackney carriages and public bathing.
Precisely the same thing happens in the actual crust of the earth, except that, in the formations usually met with, the strata are so irregularly permeable that no such uniform percolation occurs, and most of the water, instead of oozing out near the sea-level, meets with obstructions which cause it to issue, sometimes below the sea-level and sometimes above it, in the form of concentrated springs.
The formation of the second class of bodies is a great loss to the gas manufacturer, as, with the exception of the trace of benzene carried with the gas as vapour, these products are not only useless in the gas, but one of them, naphthalene, is a serious trouble, because any trace carried forward by the gas condenses with sudden changes of temperature, and causes obstructions in the service pipes, whilst their presence in the tar means the loss of a very large proportion of the illuminating constituents of the gas.
The principal obstructions between Old Moldova and Turnu Severin were the Stenka Rapids, the Kozla Dojke Rapids, the Greben section and the Iron Gates.
Below these obstructions the Kebbi to its junction with the Benue has a depth of not less than 6 ft.
A still more important expedition was that of Lieutenant Hourst, who, starting from Timbuktu in January 1896, navigated the Niger from that point to its mouth, executing a careful survey of the river and the various obstructions to navigation.
From 1904 onwards the French undertook works on the Niger between Bamako - whence there is railway communication with the Senegal - and Ansongo with a view to deepening the channel and removing obstructions to navigation.
Similarly the obstructions offered to water communication by interruption through land or shallows are overcome by cutting canals or dredging out channels.
The experiment was so far successful that, with incredible difficulty, the two vessels did actually reach Meskene, but the result of the expedition was to show that practically the river could not be used as a high-road of commerce, the continuous rapids and falls during the low season, caused mainly by the artificial obstructions of the irrigating dams, being insurmountable by ordinary steam power, and the aid of hundreds of hands being thus required to drag the vessels up the stream at those points by main force.
Wide at large ones - and they should be as free as possible from obstructions, such as pillars supporting the roof.
The improvement of waterways in the interior of the empire was not neglected, the Babylonian canal system was repaired, the obstructions in the Tigris removed.
Many of the Atlantic coast rivers would afford excellent port facilities if obstructions were removed from their mouths.
The French philosopher, therefore, regarded these obstructions as the effects of friction.
The pope goes on to say that he found it too difficult, on account of the length and obstructions of the way, to send any one (of ecclesiastical position?) a latere, but he would despatch Philip to communicate instruction to him.
The morainic belts and other obstructions in the drift plains hem in the waters in the intervening basins and create what are called " glacial lakes," var y ing in diameter from a few yards to several miles.
This weir retains the river above it at half-tide level, in order to cover the mud-banks which had been bared at low tide between Richmond and Teddington by the lowering of the low-water level, owing to the removal of various obstructions in the river below.
He says on Free the one hand, " not only as a man, but as a British subject I pray for the flourishing commerce of Germany, Spain, Italy and even France itself," and condemns " the numerous bars, obstructions and imposts which all nations of Europe, and none more than England, have put upon trade."
Though now pierced by road and railway, they stood in former times as a barrier of mountain and jungle between northern and southern India, and formed one of the main obstructions to welding the whole into an empire.
Unfortunately, the obstructions thrown in the way of this settlement by the Persian commissioner, the untoward appearance at Bampur of an unexpected body of Kalatis, and the absence of definite instructions marred the fulfilment of the programme sketched out; but a line of boundary was proposed, which wa~ afterwards accepted by the litigants.
The bed of the great river maintains a fairly constant position between its extreme banks, but the channels within that bed are so constantly shifting as to require close supervision on the part of the navigation authorities; so much detritus is carried down as to form a perpetually changing series of obstructions to steamer traffic.
The opening up of the wide thoroughfare of Chambers Street, on the site of College Wynd and Brown and Argyll Squares, cleared the precincts of unsightly obstructions and unsavoury neighbours.
Besides, it was declared a free imperial port in 1719, and was therefore released from the obstructions to trade contained in the hampering legislation of the period.
Complaints of the obstructions in it are not uncommon, and John Taylor, the Water Poet (1580-1653), in a poem commemorating a voyage from Oxford to London, bewails the difficulties he found on the passage.
But as Mariotte observed similar obstructions even in glass pipes where no transverse currents could exist, the cause assigned by Guglielmini seemed destitute of foundation.
At the same time the ancient graveyards round the city were swept smooth and levelled; obstructions were demolished, outworks constructed, and the defences generally renovated.