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, 
