1841.] 



THE CIVIL ENGINEER AND ARCHITECT'S JOURNAL 





PAPERS ON HARBOURS AND RIVERS. 



Reporl on tie. tiavigalion of the Forth. Dij Robert Stevenson Sf Sons, 

 Civil Engineers. 



Prefatory A'oto— Having been called upon, by the magistrates of 

 Stirling, to revise, with a view to its being printed, the following 

 Report, which was made as far back as 1828, we have done so with 

 much care. It affords us great satisfaction to be enabled to state, that 

 the views contained in the Report have derived additional confirma- 

 tion from our past experience, more especially in the case of the 

 River Tay, whose navigation was formerly obstructed by obstacles 

 \\-hich, although composed of different materials, closely resemble, in 

 their position and extent, those which at present hinder the advance- 

 ment of the tiade of the Forth. By the partial removal of the various 

 fords, the depth of water in the Tay, at spring tides, has been increased 

 from 11 feet 9 inches to 10 feet; and the works, which are not yet 

 completed, have occupied little more than two years. The hardness 

 of the materials which compose the Fords of the Forth may render 

 their removal more tedious; but it ought not to be forgotten, that it, 

 at the same time, ensures greater permanency in the form of the ex- 

 cavated channel. It is therefore with increased confidence that we 

 repeat the recommendations of the Report of 1828. 



Robert Stevenson & Sons. 



Edinburgh, Dec. 10, ]_&3S. 



The Firth and River Forth are navigable for the largest class of 

 mercbSnt vessels, as high as the port of Alloa; and in spring tides, 

 vessels drawing 9 feet water may proceed to Stirling, lying lui miles 

 above Alloa, while those drawing 7k feet water, may reach the mills 

 of Craigforth, 5 miles above Stirling. The improvement of the navi- 

 gation between Alloa and Stirling, has long been regarded as a desir- 

 able object, and was brought under the notice of the Reporter by the 

 magistrates of Stirling, in the month of November, 182.5, when it was 

 proposed to petition Parliament for leave to bring in a bill for this 

 measure. * * * 



Above Alloa the river becomes very circuitous. By the navigation 

 the distance from thence to Stirling is 10^- miles, while in a direct 

 line it measures only 5 miles. It has been proposed to render the 

 navigation of this part of the river more direct, by cutting through 

 the links, or peninsular necks of land, for which the track of this river 

 is so remarkable. This would shorten the navigable track ; but it 

 would have a direct tendency to deteriorate the navigation below, as 

 a great volume of the tidal water, wdiich at present passes over and 

 scours the lower banks four times in the twenty-four hours, would be 

 cut off and diverted from its course. The cutting of the links and 

 straightening the river would also, in a material degree, interfere with 

 the vested rights of the proprietors of the banks, by depriving some 

 of the benefit of a water communication, and destroying the valuable 

 salmon fisheries of others. This plan, therefore, though worthy of 

 consideration, is, upon the whole, judged inexpedient in the existing 

 state of things. The Reporter proposes to improve the present chan- 

 nel of the river by deepening it, and removing part of the numerous 

 obstructions called Fords, and he therefore now proceeds to describe 

 in detail each of these obstructions, and the works which are con- 

 sidered necessary for their removal. 



Between Alloa and Stirling there are seven principal fords, or 

 shallow parts of the river, which form so many obstructions to the 

 navigation. It is not believed that incumbrances of a similar geo- 

 logical structure are to be met with in almost any other river in the 

 kingdom. The Firths of Tay, Moray, Clyde, Solway, and the Rivers 

 Alersey, Severn, Thames, and Humber, have their peculiar tides and 

 difficulties, both in the form of rocks and sand banks, but none of these 

 channels are impeded by successive chains of imbedded stones and 

 rocks, appearing at low water, like those called the Fords of Stirling. 

 Various hypotheses have been started to account for the existence of 

 these fords. Some have supposed them to be artificial, arising from 

 stones having been thrown into the shallowest parts of the river at an 

 early period, to render it fordable for cattle. But from the minute 

 examination which the progress of this survey has enabled the reporter 

 to make, he has no hesitation in stating, that they are natural barriers 

 of rock traversing the valley of the Forth, and are what geologists 

 term whi7i-di/kes, which, from the continued scouring of the bed of the 

 river, have assumed the irregular appearance now presented by them 

 at low water. Similar formations of whin or gieenstone rock occur 

 on the southern face of the Abbey Craig, and also on the northern side 

 of Stirling Castle. The fords, like the cliffs at these places, consist of 

 stones, varying in size from a cubic foot to a cubic yard, imbedded in 

 a matrix of friable rock. The joint effect of the crooked channel of 

 the river, and the obstructions caused by the fords, produces a great 



retardation in the velocity of the flood, which, in the upper parts of 

 the river, is very sensibly less than that of the flood in the Firth, and 

 travels at the rate of only one mile in five minutes. Although this 

 retardation may be considered to be in part due to the operation of 

 the river current, yet it is obvious, from its languor, that this cannot 

 be the principal cause, and it is therefore to be sought for chiefly in 

 the obstructions offered by the fords. On the days of new and full 

 moon, it is high water at Alloa Pier at four hours and forty minutes ; 

 at Tullibody Pier at five hours and ten minutes; at Povvis Hole at five 

 hours and ten minutes; and at five hours and ten minutes at Stirling 

 Shore or Quay. The consequence is, that the tide does not attain its 

 maximum height at these three last places, until it has been ebb tide 

 for half an hour at Alloa. It appears further, from this train of obser- 

 vation, that the perpendicular rise of spring tides at Alloa, is about 

 19 ft. 4 in.; at Tullibody, llU feet; at Powis Hole, 12 feet; and at 

 Stirling, 7 ft. 8 in. ; while the corresponding rise of neap tides at these 

 stations is respectively Hi feet, llA feet, 7 feet, and 3 feet. There 

 being, therefore, a rise of 19 ft. 4 in. in spring tides at Alloa, and only 

 7 ft. S in. at Stirling, the available depth at that place is less than it 

 would have been had there been no rise on the bed of the river, by 11 

 ft. 8 in. Before leaving the subject of the tides, it may be proper to 

 remark, that the maxinuun point of high water at Alloa Pier is 4 

 inches above the level of the high water at Tullibody Pier, wliile it is 

 2 inches lower at Powis Hole, and 3i inches higher at Stirling Shore. 

 The great object, tlierefore to which the reporter would direct the 

 exertions of the Magistrates of Stirling, as Conservators of the Navi- 

 gation of the Forth, is to the removal of the Fords, which are the chief 

 obstructions to the free passage of the tide waters. The advantage of 

 deepening the bottom in the upper reaches of the river is obvious, as 

 the natural effect of such a change is to permit the tide to flow over 

 the lowered ridges at an earlier period of the tide, and thus to allow 

 high water to take place sooner, before the tide below may have fallen 

 to any considerable extent; while, at the same time, an increased 

 depth is obtained. Vessels may then start from AUoa earlier in the 

 flood-tide, and reach the shallowest parts of the river, near Stirling, at 

 the top of high water. In this view of the method of improving this 

 part of the navigation, it is very satisfactory to know, that a navigable 

 track through the whole of these obstructions may be formed at a 

 comparatively small expense, by the common and simple process of 

 blasting with gunpowder, and the use of flats or lighters fitted with 

 cranes and other apparatus. The Reporter will now describe, in de- 

 tail, the extent of the operations he considers necessary at the different 

 fords. 



On the reach between Alloa and Throsk, he proposes that a buoy, 

 provided with suitable moorings, should be laid down at the seaward 

 extremity of the bank, on the eastern side of Alloa Island, about a 

 quarter of a mile above Alloa Pier. This buoy will be useful as a 

 direction for avoiding an extensive spit of sand, on either side of that 

 island. On its western side a perch or beacon is to be erected as a 

 further guide for that channel. 



The commencement of Throsk Ford is about a mile and a quarter 

 above Alloa Pier. The channel on this ford is very shallow, and when 

 the river is in its state of summer water, it dries nearly all the way 

 across ; but as this part of the river has the advantage of a perpendi- 

 cular rise of about 18 feet in spring tides, and 134 feet in neap tides, 

 the navigation is comparatively little impeded.' On referring to the 

 plan and longitudinal section of the river, it will be seen, by the parts 

 coloured red, that little excavation is proposed here. A buoy, liow- 

 ever, is intended to be moored in a central position to show the deepest 

 water, and, as a farther direction, a perch is to be erected on the star- 

 board hand. This perch will also serve to point out the proper chan- 

 nel for passing Tullibody Island. 



Cambus Ford is about a mile and a quarter above Throsk. The 

 bottom of the channel towards the lower end of this ford consists of 

 large stones and roots of trees, and in its upper part, large boulder 

 stones appear above the surface at low water. The rise of tide at 

 this ford is 164 feet in spring tides, and llA feet in neap tides. The 

 navigable channel to be cleared measures about 500 yards in length, 

 and 30 yards in breadth at the bottom. An average cutting of one 

 foot in depth will give about 20 feet at high water of spring tides at 

 this place. A perch is to be erected on the larboard hand, opposite 

 Tullibody Yare or Pier, and another on the starboard hand, to the 

 westward of the Mouth of the Devon. By this means vessels will be 

 enabled to avoid the foul ground at the bank on the opposite side of 

 the river. The track of Cambiis Ford is so obvious, that it is not 

 considered necessary to moor a buoy to point out the deepest channel. 

 Badneath Ford is about three quarters of a mile above Cambus. Its 

 bottom consists of two irregular lines of boulder stones, crossing the 

 bed of the river with numerous detached masses of the same descrip- 

 tion. From the winding direction of the channel at this place, the 



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