1 4 The Drainage of Fens and Low Lands. 



South Bullock Pumping Station, which is about 12 miles 

 above the junction of this river with the Humber, in July 

 1887, previous to the cutting of the weeds, the mean inclina- 

 tion in the surface at low water was at the rate of 0*63 feet 

 per mile. After the weeds were cut between these stations and 

 in the river below, this was reduced to 0*15 feet per mile, the 

 water standing at Hempholme Lock, at low water, 2 • 84 feet 

 lower after all the weeds were cut than it did before the 

 cutting commenced. The lowering of the level and the de- 

 crease in the rate of inclination was progressive as the 

 cutting went on. The difference was not so great at the 

 lower station, as the weeds below this were not so thick, and 

 the river more affected by tidal influence ; but there the low- 

 water level was depressed i"09 feet by the removal of the 

 weeds. This alteration was considered to be due almost 

 entirely to the removal of the weeds. 



Inclination in the Surface of Water.— Every inch 

 of fall being of value in flat districts the area of the drain is so 

 proportioned that the surface inclination of the water in the 

 drain is reduced to as low a rate as is compatible to the efficient 

 discharge of the water. Dubuat considered that the eighth of 

 an inch in a mile would cause a sensible movement in a canal. 

 The inclination of main tidal rivers through flat districts, 

 when properly trained, varies from 3 to 1 2 inches in a mile, 

 and should not under ordinary conditions exceed 6 inches. 

 Large tidal channels, when undisturbed by floods, flow 

 with an inclination as small as i inch in a mile. Main 

 arterial drains in well-drained flat districts flow with an 

 inclination of from i^ to 3 inches per mile. The Middle 

 Level drain, when the .syphons were at work, had a surface 

 inclination, over 15 miles at the lower end, of i\ inch 

 per mile. The main drain in Deeping Fen, Lincolnshire, 

 discharges the full quantity required to keep both the 

 pumping engines at work, with an inclination of 8 inches 

 in 12 miles, or at the rate of i\ inch per mile. The Black 

 Sluice drain in the same county, in floods, has an inclination of 



