1142 
Journal of Agricultural Research 
Vol. V, No. 24 
and io, ii, and 30, it will be seen that for the i-foot weir at least the dis¬ 
charge through a box 32.5 feet long with sides set to the standard dimen¬ 
sions is within 1 per cent of the discharge obtained by placing 90° wings 
at the end of a similar box 20 feet long. The use of 45 0 wings will cause 
an error of about 2% per cent. Therefore the weir box for the new irriga¬ 
tion weir should be made with sides spaced 2 L at the plane of the weir 
and 2% L at 20 feet upstream from the weir, with the sides continuing at 
this angle until they meet the banks of the ditch or canal; or the box 
should be only 20 feet long with wings to connect the sides of the box 
with the canal banks, and these wings should form an angle of 90° with 
the axis of the weir box. The 90° wings (fig. 2) give a discharge about 1 
per cent greater than with the extended sides (fig. 4) for a head of 0.2 foot 
and about 1 per cent less for a head of 1 foot. 
Extending the sides of the weir box until they are the full size of the 
canal will give more accurate results, but this accuracy may not be re¬ 
quired, and the saving in cost of construction due to the shorter length 
of the weir box with wings may be more desirable than the 1 per cent 
of accuracy in measuring the water. Unless the canal bottom is easily 
eroded or scoured, it would not be necessary to extend the floor of the 
weir box beyond 20 feet, even if the sides of the box are extended. 
The comparatively high velocity of the water flowing through the weir 
box causes a wave action and generally disturbed condition of the water 
surface, which makes it quite impossible to determine the head h in the 
open weir box. Any stilling device placed in the weir would interfere 
with the action of the weir, and it is therefore necessary that a still box 
be placed outside the weir box and connected through the side of the 
weir box with one or more 1 -inch pipes located 6 feet from the plane of 
the weir. The pipe should be placed near the floor of the weir box to 
insure its being submerged for low heads, and care must be used to place 
the pipe normal to the side of the weir box, and not normal to the axis of 
the box. If the pipe is pointed downstream the velocity of the water in 
the weir box will cause a suction action which will make the water surface 
in the still box lower than that in the weir box. If the pipe is pointed 
upstream, there will be a velocity head added to the actual water level 
in the weir box, and the water in the still box will be higher than that in 
the weir box. Although no sand or silt will accumulate in the weir box, 
regardless of the amount carried by the stream, silt may be deposited in 
the still box and clog the connection pipe unless it is cleaned regularly. 
By making a deep still box, space will be provided for such silt accumula¬ 
tion and therefore less frequent cleaning will be required. The still box 
should have inside dimensions of at least 1 foot by or 2 feet, with such 
depth as is necessary. The head in the still box may be determined by 
means of a scale, a hook gauge, or an automatic registering gauge. 
The new irrigation weir may be constructed of lumber, but the design 
is such that it may be easily constructed of concrete. There would be 
