20 The Drainage of Fens and Low Lands, 



the whole of which was removed and carried back to the 

 outfall when the winter floods came. 



Allowing Y^ as an amount that would be carried by a 

 stream without overloading, this would be equal to about 

 0*09 lb. in every cubic foot of water.* Taking a main drain 

 having 30 feet bottom, with slopes of 2 to I, depth of water 

 8*0, velocity I J mile an hour, the quantity of earthy matter 

 carried in suspension would be 117 tons an hour, as follows : — 



The area is 368 feet, velocity 132 feet per minute ; 



368 K 132 X *09 X 60 ^ , 



~ = 117*1 tons an hour. 



2240 ' 



Allowing ten hours for a working day, 1171 tons of earth, if 

 loosened and broken up in the form of mud, would be carried 

 away by the water. 



Machines used for Dredging, Scouring, etc.— As a 

 practical illustration of the working of this system the 

 dredger employed by the Deeping Fen Trustees, hereafter 

 described, was employed in cleaning out the Vernatts drain, 

 which receives the water pumped from Deeping Fen, in 

 Lincolnshire, containing 30,000 acres. The velocity of the 

 stream, where the dredger was at work, varied according 

 to the state of the tide in the river Welland, being very 

 sluggish at high water, and increasing to about i;^ mile an 

 hour at low water. The boat was employed on a section 170 

 chains in length, for eleven weeks, and during this time the 

 whole of the weeds and mud accumulated, together with a 

 portion of the bottom of the drain, consisting of clay, in places 

 veiy hard, was broken up by the dredger, and transported by 

 the water free and clear, not only of the drain itself, but also 

 of the channel of the river, and deposited in the estuary ten 



* Allowing 7ocx> grains in i lb. avoirdupois, and that a gallon of water weighs 

 10 lbs., this would give 70,000 grains in a gallon. Taking the proportion of 

 T^ would give 100 grains of earthy matter to a gallon of water. Or taking the 



62* 1 



cubic foot of water at 62*5 lbs., and the same proportion would give — = 



= 0*08928 &c. lb. in a cubic foot of water. 



