20 BULLETIN 304, U. S. DEPARTMENT OF AGRICULTURE. 



liberal dimensions. If the outer end of the sluiceway is not below 

 low-water line of the river, the bottom of the channel through which 

 the water will flow beyond the end of the pipe should be protected 

 from washing out by riprap, paving, or a concrete floor carried to a 

 safe distance. Where feasible, this protection should extend below 

 low-water line. 



The sluiceway should be sufficient in size to discharge in 24 hours 

 such an amount of water as would cover the whole drainage area 

 one-fourth inch deep. In making this calculation the velocity of the 

 water through the sluiceway should not be assumed to be greater 

 than 5 feet per second. The sluiceway openings should be low 

 enough so that their highest point will be at about the line at which 

 it is desired to maintain the water level within the district. Their 

 interior surfaces should be as smooth as possible in order to reduce 

 the friction which retards the flowing water. If the entrance to the 

 pipes is made well rounded, their maximum discharging capacity will 

 be considerably increased. Automatic outward-opening flap valves 

 may be put on the outer end of the pipes, but in important cases there 

 should be also a place where the pipe may be closed by stop planks 

 or by a gate valve if the automatic valve should get out of order. 1 

 On large sluices hand-operated gates of standard construction are 

 much preferable to the automatic type, as they are positive in their 

 action and not likely to get out of order. An excellent sluice with 

 four compartments and four gates is shown in figure 1 of Plate III. 



DESIGN OF PUMPING PLANT. 



NECESSARY CAPACITY OF PUMPING MACHINERY. 



Before discussing in detail the conditions determining the size 

 needed for a pumping plant it will be illuminating to describe the 

 general method of operation of such a plant in the latitude of Illinois. 

 In the late summer and fall, since the precipitation is slight and is 

 more than balanced by evaporation, the pumps are not run. During 

 the winter storms are more frequent and evaporation is small, so that 

 gradually the ground becomes completely saturated and the ditches 

 full. Some districts pump occasionally throughout the whole winter; 

 others start the pumps at some date in the spring and operate them 

 continuously night and day for several days to remove the large 

 accumulation of water stored up during the winter months. Gradually 

 the water level in the ditches is lowered, and when the desired mini- 

 mum is reached the machinery is stopped during the night. The 

 water will rise in the ditches perhaps 2 or 3 feet during the night. 

 When the pumps start up in the morning the water level at the 

 pumping plant quickly drops a foot or more and then more slowly for 

 the rest of the day. At points some distance away the effect of 



i U. S. Dept. Agr., Office Expt. Stas. Bui. 158, Separate 9, Report of Drainage Investigations for 1904. 



