Appendix, 165 



doors will close 2f hours after jElood, leaving ^k hours to high-water. 

 Again, 14 divided by 22, gives 0*63, which from the table gives the 

 time for opening again as 2 J hours after high-water, making the time 

 the doors would be shut as 5I hours each tide or iij in the day. 

 The drain must therefore be calculated to discharge the rainfall due 

 to 24 hours in 12^ hours. 



The figures in the table are based on the assumption that the out- 

 fall is on or near the sea, or an estuary, and that the ebb and flow both 

 last about 6 hours. If the sluice is situated some distance up a tidal 

 river, these figures will require modification, and the time determined 

 by observation of the tide at the particular locality where the sluice 

 situated. 



TABLE IX. 



To ascertain the height of the tide at any hour during the ebb and flood. 



Rule, — Multiply the range of the tide for the day by the constant 

 given in the table opposite the time required, the result will give the 

 height of the tide at that time. 



Example, — Required the height of a tide, the high-water level of 

 which rises 22 feet above low-water, at 2 J hours after high-water, or 

 the same time after flood. The constant for a falling tide opposite 

 2.30 is 0-63, which, multiplied by 22, gives 13*86 feet as the height 

 at 2 hours after high-water. For a rising tide the constant is 0-38, 

 which, multiplied by 22, gives %'z(> feet as the height above low- 

 water 2 J hours after flood. 



Falling Tide. Rising Tide. Constant for 6 Hours. 



Time after High Water. Time after Flood. Ebb and Flood 



H.M. H.M. 



o'oo 6*o I'oo 



0*30 5'30 0-96 



I'oo 5*00 0*92 



1-30 4*30 0-84 



2-00 4'oo 0*75 



2-30 3*30 0-63 



3-00 3*00 0*50 



3-30 2*30 0-38 



4*00 2*00 .. 0*26 



4-30 1*30 o-i6 



5*00 .. .. .. .. I'oo o'o8 



5*30 0-30 0-025 



