1172 
sub-laterals and branches of sub-laterals 
may be necessary in order to convey 
water to the lands to be irrigated. When 
it reaches the land, it is generally dis- 
charged at the highest point to be ir- 
rigated, and from there carried in pipes, 
or small ditches for distribution. 
The irrigation system if seen on a 
map would resemble somewhat a river 
with its tributaries reversed. The tribu- 
taries of a stream flow from the higher 
lands in rivulets creeks and streams 
into the main channel. The irrigation 
system flows from the main channel and 
branches into smaller ones as the water 
is conveyed to the lands to be irrigated, 
which lands must be lower than the in- 
take of the canal, in order that there 
may be a gravity flow. 
How to Conduct Water to Land 
What is the best method of conduct- 
ing water to the lands? It is general- 
ly conceded that while as an initial cost 
ENCYCLOPEDIA OF PRACTICAL HORTICULTURE 
the open ditch system is cheaper, never- 
theless in the end it is more expensive, 
and that there is considerable loss on 
account of evaporation and seepage. Just 
how much this loss is, depends largely 
upon the soil, amount of sunshine, wind, 
and the intensity of heat. 
Measurements to Ascertain Loss 
In the canals of Colorado, California, 
Utab, Washington and Wyoming, care- 
ful measurements have been made which 
indicate that the losses range from al- 
most nothing in some of the best and 
most favorably situated canals, to 50 per 
cent in canals built in porous soils. Pip- 
ing is not always practical, but where it 
can be used it is best, especially in those 
sections of the country where water is 
scarce. The economy which could be ef- 
fected by the use of piping in the dis- 
tribution systems is illustrated by the 
following table compiled by the pipe com- 
panies: 
Canals carrying 100 eu. it per second, or more, loss per mile.... ........ 1% to 5% 
Canals carrying 50 to 100 ecu. £t. per second, loss per mile......... eee nee 3% to 8% 
Canals carrying 25 to 50 cu. ft. per second, loss per mile............0.06- T% to 14% 
Canals carrying 15 to 25 cu. ft. per second, "loss per mile ........506. 12.10% to 18% 
Canals carrying 5 to 15 cu. ft. per second, loss per mile.......... cee eee 16 » tO 27% 
Canals carrying 2to 5 cu. ft. per second, loss per mile... ............02 20% to 40% 
The preceding percentages of loss are 
general averages and may vary in differ- 
ent localities according to climatic and 
soil conditions; but it will be noted that 
the losses rise very rapidly as the volume 
decreases. Hence the smaller the ditch 
the greater the loss. The greatest econ- 
omy is therefore secured in those cases 
where the pipe would of necessity be 
small, say from 4 to 12 inches in diam- 
eter. These losses are wholly prevent- 
able, and aS water becomes more valu- 
able and the cost of delivery greater, pre- 
vention will pay. On many irrigated dis- 
tricts the slope of the land is too great 
for ditches unless stop-boxes or drop- 
boxes are provided. In many cases lands 
4nch pipe: 
Slope 1 in Be discharges 0.6 sec. 
Slope 1 in 50, discharges 0.88 sec. 
6-inch pipe 
Siope 1 in 30, discharges 1.5. sec, 
uns o in ay , discharges 1.0 see. 
' neh 
* ft. 
. ft. 
Slope 1 in 50, discharges 4.6 sec. ft 
Slope 1 in 100, discharges 3.2 sec. ft. 
ft. 
ft. 
ft. 
ft. 
and crops below the ditch are damaged 
by breaks due to washing where the 
Slope is too great. 
Capacity of Pipes 
It may be interesting to note the rela- 
tive carrying capacity of several typical 
sizes of ditches compared to those sizes 
of wood pipe which, on various gradients 
or slopes, will carry approximately the 
same quantity of water as the ditches 
given—the ditches being assumed to be 
built on that gradient which will not in- 
duce an excessive velocity. It should be 
borne in mind that much greater veloc- 
ities are permissible in pipes than in 
ditches. 
saeees Ditch requires 1.0 ft. bottom width 
neces Ditch requires 20 ft. bottom width 
Ditch requires 2.5 ft. bottom width 
eee eee Ditch requires 3.0 ft. bottom width 
