324 Mr Taylor, Tides in the Bristol Channel 



increase even approximately uniformly. For this reason the mouth 

 ot tJie channel has been taken at section A. 



Straight lines were next drawn in figs. 2 and 3 to represent the 

 best values to take for the uniform rates of increase in breadth 

 and depth of the channel. These are shown as dotted lines there. 

 Ihe values of A and h^ in equation 3 were taken in this way as 

 a^o = 80 nautical miles, h^ = 25 fathoms. Since the period of the 

 semi-^diurnal tide is 124 hours, a = 2../12.4. From these data k is 

 found to be -0118 (miles)-i. 



If the rise and fall of tide is known at one point of the channel 

 equation 4 enables us to find it at all other points. In order to 

 compare the theoretical and observed increase in tide due to the 

 contracting walls of the channel, the simplest method appears to 



^.il"" TA i^.''T^ '''^ ^^^ ^^^^ °f *i^^ ^t ^^^ i^^outh of the 

 Jiristol Channel to determine the constant K, in equation 4, and 

 then to apply equation 4 to calculate theoretically the tides at 

 places up the channel at which tidal measurements have been made 



ihe rise and fall of tide at the time of spring tides has been 

 measured at a number of places on the shores of the Bristol Channel 

 These are shown on the sketch chart (fig. 1) by means of numbers 

 placed against the names of the places in question* 



ihe rise and fall of tide at section A has been taken as 27 feet 



npfcTr "l ^^ ^??'^'' ^^ ^S""" ^'^^ ^^^ measured tides in the 

 r^^eighbourhood. Using this figure the theoretical rise and fall of 



drawn''^.Pp'S caMated for all values of x, and a curve has been 

 drawn (see fig. 4) to show the relationship between them On 

 Poking at this curve it will be seen that in the range with which 

 we are concerned the curve is very nearly a straight fine. 



on the .kptrf wf ' S ^^*^ .di«*^^ces, X, for the places shown 

 on the sketch chart (fig. 1) are given in columns 3 and 2 of Table II 

 ihey are represented by means of the dots in fig. 4. It will be seen 

 tidtt'.r^'''?'''* ^'*\''^. ^^' theoretical tides and the observed 

 ir^ T^ -f^'^' '^''''^ ^^°'^^ i^^^ed than one might have ex- 

 iCe'r Irt "of A' 'T'^^f'^ '^^^ ^^^ ^se and fall of tide in the 

 deSri" . tt''''^\ ''/' ^'^^*' «^ ^^^^ greater than the 



dep h at low water The calculated tides at the places mentioned in 

 iable II are taken from the curve (fig. 4), and are given in column 4. 

 in tide dl fn .lf^'''^f ' *.^' predicted with the observed increase 

 fror^ thp fi. contracting channel, 27 feet has been subtracted 



areJlltTJ ''" "^f «f cjl^n^ns 3 and 4 of Table II. The results 

 are given m columns 5 and 6. 



theorvofh'dp!/''''^ f'"' '''^^*' *^^* *^^ "^^^1 hydrodynamical 



abnormal t^^^^^^^ 



abnormally high tides which exist at the head of the Bristol Channel. 



