8 



through the sea-dyke 32 feet long and 47 inches wide. 

 In the more modern farms the sides and floor are of 

 concrete, but in the older forms (figs. 1 to 4) the framework 

 is built up entirely of fir planking supported by piles. 

 Twenty-one feet from the seaward extremity two narrow 

 sluice shutters are fitted sliding up and down in a grooved 

 framework and actuated either by a screw adjustment or 

 by the leverage of a crowbar. From this point the floor 

 of the sluice slopes gently downwards towards each 

 extremity so that its level at the seaward end is 

 depressed 4 inches and that at the inner end 2 inches 

 below the level at the sluice gates. The floor of the 

 sluice is arranged so as to be from 3 to 4 feet below the 

 mean level of the entrance ponds and about 2 feet above 

 the bottom of the wintering ponds. Each extremity of 

 the sluice (S. and S.S. text fig. 1) is furnished with a 



32 FT. 6 IN 



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CONCRETE WALL 



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CONCRETE WALL 



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Fig. 1. — Plan of sluice to show general design and dimensions. 



S.G. Sluice gate provided with two shutters ; 

 S.S. Seaward wire net screen ; S. Inner screen. 

 S.N. Indicates position of frame of sleeve-net. 



moveable wooden frame sliding in vertical grooves cut 

 in the side walls. Over each frame is nailed a screen of 

 strong wire netting of small mesh so that when in place in 

 its grooves it furnishes an effectual barrier to the passage 

 of all but very small objects. The overall dimensions of 

 these frames are 6 feet 9 inches by 4 feet 1 inch. Eight 

 feet behind the sluice gates and 2 feet in front of the 

 screen at the inner end of the sluice is another pair of 

 grooves accommodating a third frame. This instead of 

 being covered with wire netting as are the other two has 

 the mouth of a long tapering cotton net, the manche, 



