34 T^he Drainage of Fens and Low Lands. 



Taking the average of four sluices draining pure fen land 

 on the East Coast, with total width of openings varying 

 from 33 to 45 feet, and a mean width of 37 feet, the number 

 of acres to each foot of waterway is 1082. Allowing the 

 depth of water to be one-fifth of the width or 7*40 feet, and 

 that the water passes through with a velocity of i * 50 feet per 

 second, this nearly allows for the discharge of rainfall due to 

 quarter of an inch in 24 hours over the area drained. Of six 

 large sluices draining rivers and mixed fen and high land, 

 having openings varying from 74 feet and a mean of 55 feet^ 

 the number of acres to each foot of waterway is 2304. 

 Allowing the depth to be one-fifth of the width or 1 1 feet, it 

 would require a velocity of 2" 19 feet per second for sufficient 

 water to pass through to allow for a rainfall of a quarter of an 

 inch in 24 hours. The discharge, however, being due partly 

 to high land, the quantity of water passing through these 

 sluices is less than this quantity. 



Syphons. — Syphon pipes can be used for the discharge of 

 water from enclosed lands into the outfall instead of sluices, 

 but the cost of working them, and the loss of head required 

 to carry the water through, places them at a disadvantage as 

 compared with the ordinary sluices. 



When an accident occurred to the Middle Level sluice on the 

 River Ouse in 1862, it became necessary to place a solid dam 

 of a very substantial character across the drain, and in order 

 to afford means of discharging the water from the drain into 

 the river, syphons were erected under the direction of Sir 

 John Hawkshaw. 



The syphons erected at the Middle Level were 16 in number, 

 laid across the dam at an inclination of 2 to i on either side, 

 each end being terminated by a horizontal length containing 

 the upper and lower valves. The upper surface of the lower 

 pipes was laid I foot 6 inches below low water of spring tides, 

 and the top of the syphon was 20 feet above the same level. 

 The syphons were of cast iron i\ inch thick, 150 feet in total 



