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HISTORY OF ENGINEERING.

Book I.

The marshes increasing in breadth and height have a greater surface of water upon them,hut not an increased depth; and yet, there is more water requiring a passage to the seathan before; for as long as the depth of water is considerable upon these salt marshes, thewater makes its way to sea, by settling gradually, and passes off, in the nearest directionover the marsh surfaces, without having any need for the gullies and creeks as drain. Thelast foot in depth, over the whole surface, is what produces the scour, in the several gullies;and this is increased to a great degree, in consequence of the water having retreated fromthe gullies, and allowing the lull force of their draining off to operate upon theirchannel.

Whilst the neap tides were suffered to cover the surface of the marshes, the scour wouldbe on the increase, and the harbour improved ; but as soon as this scour was diminished,the gullies would become choked up, and the harbour in proportion injured.

The elevation of the surface of the salt marshes, from the fresh deposit of mud at everytime they were overflowed, would not stop at the neap tides, but would gradually risehigher and higher towards the high water of spring tides, until they became so high thatno embankments were necessary; and the same effect would happen in all the creeks andgullies, which would elevate their beds in the same proportion. The surface of themarshes, rising higher and higher from the neap to the spring tide mark, they became lessoverflowed, and the gullies, not having so much water down them, would grow lesscapacious; the creeks would suffer from the same cause, and eventually the main channel.'The tide water, however, at the same time flowing in through the creeks and gullies tothe several extremities of its branches, must flow back the same way, and their extremitieswould be the first to silt up ; this progress continuing, and there being no natural tendencyat work as a remedy, it alone could be changed by employing human ingenuity anti labour.The harbour of Wells was kept open by the reflow of the tidal water, or, as it is called, theback water ; and whatever has cut off or diminished this has been a detriment to thescour, and to the maintenance of the channel.

When a backwater, assisted by a large freshwater river, makes its way through moveablesands, its direction will be that where there is the greatest declivity ; and if that happensto be in the shortest direction, it has no natural tendency to gain a longer course, winchwould necessarily lessen its force; and wherever we find water flowing in a course that isnot the shortest, we may conclude that it has a more speedy descent in that directionthan in any other, and thus it is that many streams have a meandering course. “ Thebar at the mouth of the harbour appears not to have been noticed by Smeaton , as ofmuch importance to the hindrance of the navigation, nor did he fancy that it formed anyinjury to the entrance for the shipping. Between Hunstanton and Weybourne on thiscoast are numerous low dunes or hills 50 or 60 feet in height, which are formed along theshore, and arc composed of blown sand; these in the course of time are united into a solidand compact mass by the roots of the Marram, or Arundo arenaria ; and such is the presentset of the tides along this shore, that the harbour is now securely defended by these naturalbarriers.

“ The harbours of Wells , Clay, and many others, are defended from all encroachments bythe ocean, by such deposits which have entirely altered the contour of the coast.

“ King s Lynn Harbour was a place of importance at the time of the Norman conquest .It is situated on the Great Ouse river, where its breadth is very considerable ; the town sison the eastern bank, at a distance of about 10 miles from the ocean, and four small riversor fleets divide it into several parts.

“ Mr. John Smeaton , who reported upon the state and improvement of this river harbour,in the year 1767, found that the course of the Ouse was in as good a condition as it had beendescribed in former accounts, and that there was no material cause of complaint. A barhad formed itself on the upper mouth of the west channel, and the current at low water wasconfined to the east channel, which was proportionally improved in consequence; nature, inspite of all the objections made to the contrary, had taken this course, and Smeaton was notwilling to propose any thing which should counteract her intentions.

“ It had been suggested some years before to build two jetties, to prevent too much swellrunning into the harbour, which should serve also to remove the bar forming in the eastchannel; but Smeaton was of opinion, that where a channel must be maintained through avast mass of sand, capable of shifting by winds, seas, currents, and other powers, the moredirectly the waters make their passage out to sea the better. Any check given to theindraught of the raging tides, which was complained of, would also check the moderate ones,and the greater the efflux, which in some measure depends upon the influx, the better thechannel would be made and maintained. Too great tides may be a partial evil, though afault on the right side, and in this, as well as in many affairs of human life, the judgmentconsists in choosing the least of two evils.

“ It was not wise to affect the indraught of the tides, or to diminish the quantity of freshwater coming down the river from above, but to leave nature to do what was required; for