784 



EEPORT — 1903. 



Taking account of continuous falls of six Lours' duration or longer, there were 

 ninety-one occasions with a total duration of 822 hours, a total fall of 99-99 inches, 

 and an average rate of -122 inch per hour. 



Taking account of falls exceeding -50 inch in amount, there were eighty-six 

 occasions with a total duration of 70o| hours, a total fall of 109-47 inches, and an 

 average rate of -156 inch per hour. 



The maximum rate at which i inch or more of rain fell during the eighteen 

 months in question was* 560 inch per hour, a total of 1-40 inch falling in two and 

 a half hours from 8 to ]0.30 p.m. on September 21, 1899. This is a trifling 

 rate compared with the fall of from 2 to .3 inches in an hour, which may occur 

 in a thunderstorm in any of the drier parts of the country ; and even if attention 

 is confined to falls of one hour only, no instance occurred of a rate equal to 

 •7C> inch per hour. The peculiarity of the Seathwaite rainfall seems to be its long 

 duration and comparatively small rate of fall. The longest and heaviest shower 

 in the period considered was nineteen and a quarter hours, during which .3-59 inches 

 of rain fell, at an average rate of -186 inch per hour. 



The duration of rainfall during daylight (sunrise to sunset) and during dark- 

 ness (sunset to sunrise) was calculated for the year 1900, with the result : — 



This shows that the duration of rainfall in daylight and darkness was practi- 

 cally identical, but that there was a very slightly greater intensity in the night 

 than during the day. _ , , ,. 



It is very desirable to extend the use of recording rain-gauges, and to be of 

 much value the scale should be open enough to give exact readings, preferably 

 giving a separate record strip for each day. 



8. On the Tidal Regime of the River Mersey. 

 By James N.. Shoolbred, B.A., M.Inst.C.E. 



Since the last meeting of the British Association at Southport in 1883, twenty 

 years ago, many circumstances have occurred to change tlie tidal regime of the 

 River Mersey. Of these the principal are :— (1) the removal by dredging of the top 

 of the bar (to a depth of seventeen feet) which closes the seaward extremities to 

 the river in the estuary : (2) the rectification of the sides of the channel within 

 the river, due to the construction of the dock and other walls, on both sides of the 

 river, but principally on the Bootle shore of the Lancashire side. 



In the upper portion of the tidal river the Manchester Ship Canal has also, 

 probably, contributed somewhat to changes in the tidal regime ; though to what 

 extent is a matter of dispute. 



The two first-named causes have undoubtedly produced very considerable 

 effects by the freer passage for the ingress and the outlet of the tidal water, 

 due to the partial removal of the impeding wall formed by the bar, and by the 

 readier flow and ebb of the tidal stream, afforded by the smooth faces of the 

 walls at the more recently constructed Northern Docks and elsewhere. 



The result of the dredging operations, alone, has been to provide throughout the 

 entire distance, from the bar throughout the Queen's Channel, and right up to the 

 landing stage, a central waterway having a depth of twenty-seven feet at low 

 water of the lowest spring tides ; while at high -water of the same tides there is a 

 depth of fifty-eight feet. This has entailed, during the period 1890-1902, the 

 dredging of 29 million tons of sand at the bar, of 46 millions in the estuary chan- 

 nels and of 10 millions in the river itself, making a total of 85 million ton§. 



