Parliamentary plans on these lines approved of by James Walker, Consulting Engineer to the Trustees, were submitted to and sanctioned by Parliament in 1840; but so inadequate was the appreciation of the depth required, that 20 ft. at high water neap tides was recommended by Logan as the extreme depth of the river and harbour, and a clause in the Act empowering the deepening to proceed until every part thereof shall have attained at least a depth of 17 ft. at high water neap tides.
The depth in the harbour of Glasgow at the present time is from 25 ft. to 29 ft, and in the river from 27 ft. to 29 ft. at high water neaps, high water springs being about 2 ft. higher. The average tidal range of spring tides at Glasgow is 11 ft. 2 in., and at Port Glasgow 10 ft.; and of neaps at Glasgow 9 ft. 2 in., and at Port Glasgow 8 ft. 3 in.
While jetties and training walls, or parallel dykes, performed a useful part in the early improvement of the river, it is to persistent dredging that the enormous increase in the magnitude of the river since 1840 is due.
The early dredging was performed by large rakes, or porcupine ploughs, as they were called, because they were provided with strong iron teeth, wrought by hand capstans, which drew the material from the bed of the river on to the banks.
Hand-wrought, and subsequently horse-wrought, dredges, with small buckets on a ladder, succeeded the plough, and in 1824 the first steam dredger was started on the river. It dredged, however, only to 10 ft 6 in. Now several of the dredges employed can work in 35 ft. depth of water.
Mr. Deas, the engineer to the Clyde Trust, has stated[55] that it is due to the application of steam power to dredges, and the subsequent adoption of steam hopper barges for carrying the dredged material to the sea, that the rapid enlargement not only of the Clyde and the Harbour of Glasgow, but of the Tyne, the Tees, and several other similar rivers in recent years are due. But for the introduction of the latter, it would have been physically, financially, and otherwise impossible to have disposed, within so limited a time, of the enormous quantities of material which have been dredged from these various rivers and harbours.
Up till 1862, all the material dredged from the river Clyde and harbour of Glasgow was loaded on punts holding eight cubic yards, and deposited on the alveus or foreshores, or the low-lying land adjoining the river. Many acres were thus reclaimed, to the great gain of the riparian proprietors, to whom the Trustees required to hand over the ground free of cost. The adoption of steam hopper barges, holding from 240 to 320 cubic yards each, removed these obstacles, and enabled the deepening, widening, and straightening of the river and harbour to be proceeded with more rapidly, without seriously obstructing the navigation with steam tugs and trains of punts. The result has been that while in 1861 the total quantity dredged and deposited on land was 593,176 cubic yards, the total quantity dredged in 1887 was 1,319,344 cubic yards, only 64,000 cubic yards of which was deposited on land. The total quantity dredged during the forty-two years ending 1888 amounted to 32,027,834 cubic yards, the quantity in the first twenty-one years being 9,091,544 cubic yards, and in the last twenty-one years, 22,936,290 cubic yards.
In 1755, the Clyde at Glasgow was only 15 in. deep at low water, and 3 ft 8 in. at high water, while the depth at Marlinford, three miles below the harbour, was 18 in., and at Erskine, or Kilpatrick Sands, about eight miles below, and at Dumbuck Ford, ten miles below, only 2 ft. at low water. In 1781, the depth at Dumbuck Ford was 14 ft. at low water; it is now 20 ft. In 1806, Telford reports that on February 14th of that year the Harmony, of Liverpool, came up with ordinary spring tide, drawing 8 ft. 6 in. of water; but up till 1812, the river from the harbour downwards to Bowling was so shallow, that the Comet required to leave Glasgow and Greenock, respectively, at or near high water to prevent it grounding in the river. Now, vessels drawing 23 and 24 ft. of water pass up the river almost daily. The Clyde Trust, who are charged with the control of the river, had expended thereon, up to the middle of 1887, upwards of eleven and a half millions sterling, and had, besides, contracted a debt of over four and a half millions. The accompanying diagram will show the depths of the channel in Glasgow harbour at different dates, but the whole of the river has been dredged constantly from that city down to Port Glasgow, a distance of nearly twenty miles, and the bed of the river between these points is now virtually level throughout.
Depth of the Clyde at Different Periods.