from the Removal of London Bridge. 23 



by opening the upper part of the river will prevent it from 

 rising so high as it now does near the bridge, and that there- 

 fore not only is there a probability of no greater elevation oc- 

 curring there than at present, but that it will, in similar cir- 

 cumstances, be lower below bridge — consequently that no 

 danger can arise above. To this I reply, that when it is high 

 water at the Nore, we have it, v/ithin two hours, high water at 

 London Bridge, at the distance of forty miles ; so that the 

 high water passes up at the rate of twenty miles per hour: so 

 much more rapidly than any known velocity of tJie river, that 

 its effects are not to be accounted for by the fiov.ing of the cur- 

 rent merely, as may be supposed the case in filling up the 

 pond to Teddington through the arches of London Bridge. 



In this last case we have levelled along the banks of the 

 river, and find, after correcting the marks expressing Trinity 

 datum, that the lowest surface of high water is between Put- 

 ney and Kew ; that it rises about one foot to Teddington, and 

 nearly as much at London Docks : but this is liable to con- ' 

 siderable variation. The rise in the upper part of the river 

 pond may be easily accounted for by the accumulation of the 

 fresh waters of the river over and above what is tidal water. 

 The fall from London tov/ards Putney seems to show that the 

 tide has not time, through the contracted passage, to fill up 

 the pond above bridge to the lower level. 



From London Bridge to Blackwall the high water seems, 

 from the observations, to be level : the quantity of water re- 

 quired to fill up this difference of level is, after all, so 

 small, that with an unobstructed waterway it would evidendy 

 make no difference worthy of notice in the level of the tide 

 below bridge, even were it subtracted from the mass that lies 

 between London Bridge and the Nore. Whereas consider- 

 ing the great rapidity with which the lower part of the river 

 is filled by die tide, it is clear that an unobstructed tide would 

 fill up this trifling increase in at least as little time as the pre- 

 sent period. 



But to render this a matter of calculation: we find the 

 average breadth of tide-water at the Nore to be 3^ miles ; at 

 Gravesend half a mile, the distance being 18 miles; which, at 

 6000 feet per geographical mile, with 15 feet of tide, gives from 

 the Nore to Gravesend 17,000 millions cubic feet of tide- 

 water: at London Bridge, taking die breadth at 1000 feet and 

 3000 at Gravesend, we have in 24 miles, and with the same 

 depth, 4320 million of cubic feet, or l-4th additional tide-wa- 

 ter. There run at |M-esent through London Bridge, between 

 the lowest ebbs anil high water of ordinary sjn-iiigs (or 14-feet 

 tides) above bridge, 582 millions cubic feet (582,342,710}; 



and 



