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THE CIVIL ENGINEER AND ARCHITECT'S JOURNAL. 



71 



were very minute ; but to be fully understood require the expla- 

 natory maps and sections accompanying Mr. Webster's book. We 

 shall, howe\er, attempt to give an abstract of Mr. Rendel' 

 evidence in the House of Lords : — 



" The estuary of the Dee, and the estuary of the Mersey, and the character 

 of the two rivers are manifestly wholly different — their forms are different. 

 They are ditferent in this respect ; the Dee is for the whole extent of it a 

 shallow estuary ; the Mersey, from the contraction at its mouth, has an ex- 

 ceedingly deep channel opposite Liverpool, containing an enormous mass of 

 water, but immediately that it widens out in the same form as the Dee, it 

 loses its depth and becomes a shallow estuary ; therefore, suppose the tide 

 to come up, as I describe it with reference to the large chart, as at present 

 — and nothing in our works can prevent that, for the worlis are within the 

 gorge — it conies up in a large body, presenting to all intents and purposes, 

 the head of a werlge, and it gradually tapers out, losing its solid and com- 

 pact form as it advances up the estuary. It is manifest that if we can make 

 that wedge into a uniform column, as we shall do by these works, we shall 

 perfect the efficiency of the channel after these works are made ; the part 

 outside Seaconibe is perfectly untouched ; we do nothing to that. Then, 

 in order to ascertain precisely the whole economy of this tidal action in the 

 estuary, and to satisfy my own mind, and in order to give evidence before 

 jour Lordships, I had tidal observations taken at Formby, which is, in fact, 

 the headland on the Lancashire shore ; observations were siuiul'.aneously 

 taken at Prince's dock, \\hich is the narrow part of the gorge of the estuary ; 

 also at New Brighton, Fiddler's Ferry, and Warrington Bridge, so that I 

 have been able to trace the relative heights and the relative times of high 

 water of the same tides at all those points, and I have done it at spring 

 and at neap tides. The results I will give from the diagrams I have 

 before me. 



The width of the river at Egremont — the point which corresponds with 

 the north end of the Liverpool docks — at high water, is 4,030 feet; the 

 sectional area of the channel at that point at high water spring tides is 

 236,449 square feet. At Seacombe, only 3,000 feet within that point, the 

 width is reduced to 3,000 feet, and the sectional area to 184,622 feet ; it is 

 altogether a gorge at that point ; it is completely the gorge of the estuary, 

 which has been defined by the works of the dock trustees on the one side 

 and the natural rock of Seacombe on the other. At Wallasey Pool the 

 width is 6,040, it will be reiluced by building the wall to assimilate with 

 the other sections, namely to 3,350 feet. At Woodside pier, the width is 

 3,500 feet, therefore the tftect of the wall is to make the shores parallel, 

 and consequently to takeoff this great width which Wallasey Pool occasions. 

 That wall, when made, v\ill in my opinion, improve the channel and course 

 of the river ; it will directly accomplish that object, and one immediate 

 result likely to follow is the taking away of Pluckington Bank formed by 

 the tide setting into Wallasey Pool and occasioning an eddy. The consequent 

 good effect will be, that the quantity of water at the least, if not more, 

 which now goes into Wallasey Pool, would go up into the estuary, and by 

 going up into the estuary it must necessarily be of greatly more value to the 

 maintenance of the estuary and the scouring power of the river than 

 passing into the pool. There will be nearly 300 feet greater width opposite 

 our works than at Seacombe. The minimum section of the river being at 

 Seacombe, the next smallest section is at Woodside, and the next at 

 Tranmere. The sections at Seacombe and Woodside will continue the 

 smallest sections after the works are completed. If Pluckington Bank be 

 swept away, it will make a difference greatly in favour of the narrows as 

 they exist at present ; it will make a larger section, and improve the estuary 

 above. After Tranmere, the estuary becomes very wide; after you get 

 above the bulb the bottle commences. 



This section is the profile of the river ; it is on an exaggerated scale as to 

 height compared with length. Here is the Victoria Car, then the Crosby 

 Channel fall into this enormous cavity ; here we have Seacombe, which is 

 the narrowest part of the river ; the bed rises up again opposite Gaiston to 

 the level of low water. The river has excavated for itself within these 

 narrows, within which it has been confined, a channel quite down to the rock 

 in this particular place. The greatest depth at Egremont at low water 

 spring tides is 67 feet. The greatest depth at Seacombe, which is deter- 

 mined by the rock, for it is scoured down to the rock, is 52 feet; the 

 greatest depth opposite Wallasey Pool is 62 feet ; opposite Woodside the 

 greatest depth is 64 ft. 7 in., this is at low water spring tides. At Tran- 

 mere, we get 61 ft. 4 in. according to our soundings. It would appear that 

 except in hollows in the rocks the sand has been scoured down to the rock, 

 but as the current passes in and becomes impaired in efficiency by those hol- 

 lows or irregularities on the shore, there are parts where banks have begun 

 to accumulate, and it is only in certain parts that we can detect rocks by the 

 plummet. The Mersey presents the character of a deep narrow channel 

 supplying the estuary above ; it presents tne character of a narrow artificial 

 gorge supplying a shallow e.\tensive estuary. 



According to the observations I have made there can be no doubt that the 

 supply of water into the estuary above, depends upon the momentum 

 generated in those narrows. The bulb at Wallasey Pool detracts from the 

 momentum. The straightening the wall in the manner described would im- 

 prove the current and increase the momentum, inasmuch as the present ir- 

 regular shores make irregular currents; those irregular currents act upon 

 each other and impair the general effect. If they can be made direct they 

 are made more efficient, and consequently they will send a larger body of 



water up into the estuary, or at all events they will send that water up into 

 the estuary which now runs into Wallasey Pool. 1 am as great an enemy as 

 any one to the general question of abstracting water from estuaries, but 

 there is pecuHarity in this case which takes it out of the general class of 

 causes of the abstraction of water from estuaries. 



To ascertain the strength of the currents, I had accurate observations 

 (with watches adjusted) at Egremont, Seacombe, Wallasey, Woodside, and 

 Tranmere, and having a fleet of boats and a steamer to attend us, we put 

 down floats, so far submerged that the wind could have no effect upon 

 them, in the centre of the stream and on either side, far enough from the 

 shore to feel the strength of the current, and the floats were observed as 

 they passed each of the lines of the sections at the above places. The 

 distances were great enough to give as accurate a result as could be ob- 

 tained by any experiment of the kind, none of them being less than 2,600 

 feet, and the greater part from that to 3,000. The mean velocity of the 

 tide upon the flood from Egremont to Seacombe was 6173 feet per second, 

 from Seacombe to Wallasey it was 7'211 feet per second; which expresses 

 this, that the tide heaps up on the seaward side at Seacombe Point faster 

 than that section can pass it through, so that it runs faster to relieve itself 

 on the inside cf the Seacombe Point than it does from Egremont to Sea- 

 combe. You have that increased velocity by the increased head outside 

 Seacombe. From that section to the section at Woodside, the velocity is 

 reduced to 5'891 feet per second. That arises from the current being im- 

 paired by passing into the bulb ; it has, in fact, the efTect of cross currents 

 and eddies, as 1 have described. From Woodside to Tranmere the velocity 

 is 5-33 feet per second. The ebbs are the very reverse. It will be observed 

 that on the flood the tide was strongest from Seacombe to Wallasey Pool; 

 upon the ebb, the strongest current is from Seacombe to Egremont ; there 

 the velocity of the ebb tide was 6';03 feet per second ; the velocity of the 

 ebb from Wallasey to Seacombe was 6'139, and from Woodside to Wallasey 

 5-49. These are ordinary spring tides. Tlie velocity of the ebb from Tran- 

 mere to Woodside was 5-54 feet per second, which proves that the water is 

 heaped up by the tide at Seacombe Point faster than it is vented ; anything 

 \\hich can be done to improve the channel of the estuary between those 

 narrows and the upper narrows must necessarily tend to vent that quantity 

 of water with greater facility. Those were the results of actual observation, 

 the theoretical results on a comparison of the sectious agreeing with them 

 as nearly as can be expected. 



The object of these tidal sections is to show how the tides flowed on the 

 days of observation. At the time stated it was high water at Formby, 

 which is quite at the mouth of the estuary. At the same time, if you carry 

 on your eye to the Prince's dock you find that the tide is heaping up, 

 actually rising up, at the Prince's dock. Then if you go on to EUesmere 

 Port, you find that the tide is still rising; although at the time it is rising 

 there it has fallen at sea; and so, all the way on to Uuiicorn and Fiddler's 

 Ferry ; and you get the profile at all the points by the diflerent lines laid 

 down here, which in words is this : that inasmuch as the tide had by flowing 

 into the estuary .attained a velocity in passing through these narrows at 

 Liverpool, its own acquired velocity or momentum carried it forward, and 

 heaped it up in the estuary according to all these lines, for it would be im- 

 possible if that were not the case to account for the fact, that the tide does 

 so rise; and it is just this — 1 will suppose the fluid to be a solid ; if a solid 

 has acquired a given velocity, we know perfectly well in mechanics that 

 unless some force interposes to stop the velocity of the body it will be 

 carried on ; and it is precisely so in this case, the water flows on by the im- 

 pulse that it has received at that narrow gorge, and it rises above its level. 

 If the elevation were due to nothing more than statical pressure, which is 

 merely the pressure of the head without the velocity, it would terminate 

 its course, for there is no law of nature to make it go further. What 

 would be the state of things in an estuary like the Dee, would be deter- 

 mined by the form of the shore and other questions, but here you have the 

 peculiarity so strongly marked, that you cannot mistake the cause. The 

 effect there would be, that as the mouth of theDee is wider than its head, it 

 would receive a larger wave than would be due to the upper part of the 

 Dee, and, therefore, if it had acquired suflncient velocity, the water would 

 accumulate up the Dee to a certain extent ; but inasmuch as the extent to 

 which it would accumulate is due to the velocity of the stream, it could not 

 attain the same head in the upper part of the Dee as it does in the Mersey; 

 it depends on the velocity. 1 should say this, that inasmuch as the profile 

 represented is that which is due to the statical pressure (which is no- 

 thing more than liead without force or velocity) ; all that is above that 

 must be due to impetus : for we see here in the Mersey what we see in 

 every river, and what we see in the Dee : instead of the narrow part being 

 at the top, the narrow part in the Mersey is at the mouth ; therefore, so far 

 as is due to momentum, if you could make the Mersey and the Dee at all 

 agree, it would follow, that you would in the Dee have an enormous heaping 

 up compared with what you have in the Mersey. If you could by any pos- 

 sibility give to the water entering the Dee the same velocity as the water 

 entering the Mersey, keeping the section the same, it would heap up here 

 quite in the same way as it does in the Severn ; but it cannot have that 

 velocity, because there is not the same cause to excite it, namely, the con- 

 traction. 



For determining how much the tide has risen up the estuary above its 

 level at the gorge, 1 lake the level at Prince's Basin, which is in the gorge. 

 I will take the tide on the 1st of June, which was a spring tide. Suppose 

 we start with the tide at high water at Prince's dock, which is in the gorge 



