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NOROINNAM

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Originally appearing in Volume V23, Page 384 of the 1911 Encyclopedia Britannica.
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NOROINNAM . IRINIRNAVIN. WNIMIN. _ See also:

J1.4>a sae!~JIOJ. snit sits. $$$$$ ACC PAW See also:ORAN& aa~naN ^See also:AAl+__------ A.H.W. 1001. 14. $4. See also:a4. 'r I-1°. NOO O 10 10 80 A l.W. 1103.

1 . , 1 40 1 1 1 , 1 so 1 1 i 37141013. the fresh-See also:

water See also:discharge, generally forms the navigable- channel, which is scoured out during floods. Narrowing the See also:river between the bends to bring the two channels together would unduly restrict the tidal flow; and in a river like the See also:Hugh dependent on the tidal influx for the See also:maintenance of its See also:depth for two-thirds of the See also:year, and with channels changing with the wet and dry seasons, so that deepening by dredging in the turbid river could not be permanent, training See also:works below See also:low water to bring the ebb-See also:tide current into the See also:flood-tide channel, which latter must not be obstructed at all, offer, aided by dredging, the best prospects of improvement. The See also:average See also:rate of enlargement adopted for the trained channel of the Nervion, in proportion to its length, is I in 75 between See also:Bilbao and its mouth, and I in 71 for the See also:Weser from See also:Bremen to See also:Bremer-haven; and these ratios correspond very nearly tothe enlargement of the regulated channel of the See also:Clyde from See also:Glasgow to See also:Dumbarton of i in 83, and of the See also:Tyne from See also:Newcastle to its mouth of r in 75. Accordingly, a rate of enlargement comprised between I in 70 and I in 80 for the regulated or trained channel of the See also:lower portion of a tidal river with a fairly level. See also:bed may be expected to give satisfactory results. Works at the Outlet of Tidal See also:Rivers.—Tidal rivers flowing straight into the See also:sea, without expanding into an See also:estuary, are subject to the obstruction of a See also:bar formed by the heaping-up See also:action of the waves and See also:drift along the See also:coast, especially when the fresh-water discharge is small; and the scour of the. currents is generally concentrated and extended across the See also:beach by parallel jetties for lowering the bar, as at the outlets of the See also:Maas (See also:figs. 11 and 12) and of the Nervion (figs. 19 and 20). In the latter See also:case, however, the trained outlet was still liable to be obstructed by drift during See also:north-See also:westerly storms in the See also:Bay of See also:Biscay; and, except in the case of large rivers, the jetties have to be placed too See also:close together, if the scour is to be adequate, to See also:form an easily accessible entrance on an exposed coast. Accordingly, a See also:harbour has been formed in the small bay into which the Nervion flows by two converging breakwaters, which provides a sheltered approach to the river and protects the outlet from drift (fig. 19), and a similar See also:provision has been made at See also:Sunderland for the mouth of the See also:Wear; whilst the See also:Tynemouth piers formed See also:part of the See also:original See also:design for the improvement of the Tyne, under shelter of which the bar has been removed. by dredging (fig.

17). Training Works through Sandy Estuaries.—Many tidal rivers flow through bays, estuaries or arms of the sea before reaching the open sea, as, for instance, the See also:

Mersey through See also:Liverpool Bay, the See also:Tees through its enclosed bay, the Liffey through See also:Dublin Bay, the See also:Thames, the Ribble, the See also:Dee, the See also:Shannon, the See also:Seine, the See also:Scheldt, the Weser and the See also:Elbe through their respective estuaries, the See also:Yorkshire See also:Ouse and See also:Trent through the See also:Humber estuary, the See also:Garonne and See also:Dordogne through the See also:Gironde estuary, and the Clyde, the See also:Tay, the See also:Severn and the St See also:Lawrence through friths or arms of the sea. These estuaries vary greatly in their tidal range, the distance inland of the ports to which they give See also:access, and the facilities they offer for See also:navigation. Some possess a very ample depth in their See also:outer portion, though they generally become shallow towards their upper end; but dredging often suffices to remedy their deficiencies and to extend their deep-water channel. Thus the St Lawrence, which possesses an ample depth from the See also:Atlantic up to See also:Quebec, has been rendered accessible for sea-going vessels up to See also:Montreal by a moderate amount of dredging; whilst dredging has been resorted to in parts of the Thames and Humber estuaries, and on the Elbe a little below See also:Hamburg, to See also:pro-vide for the increasing See also:draught of vessels; and the Mersey bar in Liverpool Bay, about 11 m. seawards of the actual mouth of the river, has been lowered by suction dredging from a depth of about 9 ft. down to about 27 ft. below low water of equinoctial See also:spring tides, to admit Atlantic liners at any See also:state of the tide. Some estuaries, however, are so encumbered by See also:sand See also:banks that their rivers can only form shallow, shifting channels through them to the sea; and these channels require to be guided or fixed by See also:longitudinal training walls, consisting of mounds of See also:rubble See also:stone, See also:chalk, slag or fascines, in See also:order to form sufficiently deep See also:stable channels to be available for navigation. The difficulty in such works is to See also:fix the wandering channel adequately, and to deepen it \MIl1 NOI1N11°iOro11Nrt $U N* See also:AIN. sufficiently by the scour produced between the training walls, without placing these walls so close together and raising them so high as to. check the tidal influx and produce See also:accretion behind them, thereby materially reducing the See also:volume of tidal water entering and flowing out of the estuary at each tide. The high training works in the Dee estuary, carried out in the 18th See also:century with the See also:object of See also:land reclamation, unduly narrowed the channel, and led it towards one See also:side of the estuary; and though they effectually fixed the navigation channel, they produced very little increase in its depth, but caused a very large amount of sand to accumulate in the estuary beyond, owing to the See also:great reduction in tidal volume by the reclamations, and diminished considerably the channel through the lower estuary in width and depth without checking its wanderings.' The training of the channel of the Ribble through its estuary below See also:Preston, for improving its depth and rendering it stable, was begun in 1839, and has been gradually extended at intervals; but the works have not yet been carried out to deep water, and a, shifting, shallow channel still exists through the sand banks, between the end of the training walls and the open sea. The high training walls adopted along the upper part of the channel enabled the upper end of the estuary on both sides to be tide (figs. 25 and 26). The channel, however, was made too narrow between See also:Aizier and Berville and was subsequently enlarged, and large tracts of land were reclaimed in the upper estuary.

The reduction in tidal capacity by the reclamations, together with the fixing and undue • restriction in width of the channel, occasioned very large accretions at the back of the lower portions of the training walls and at the sides of the estuary beyond them, and an See also:

extension of the sand banks seawards. Moreover, the channel has always remained shallow and unstable beyond the ends of the training walls down to deep water near the mouth of the estuary.' Conclusions about Training ,. Works in Estuaries.—Experience has proved that training works through sandy estuaries, by stopping the wanderings of the navigable channel, produce an increase in its depth, and, consequently, in the tidal scour for maintaining it. This scour, however, being concentrated in the trained channel, is withdrawn from the sides of the estuary, which in its natural See also:condition is stirred up periodically by the wandering channel; and, therefore, accretion takes See also:place in the parts of the estuary; from which the tidal scour and fresh-water discharge have been permanently diverted, especially where an abundance of sand from outside, put in suspension by the action of the prevalent cAUOEBEC.

End of Article: NOROINNAM

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