2 BULLETIN 115, U. S. DEPARTMENT OF AGRICULTURE. 
Since the bulletin is prepared for engineers and others who are 
familiar with gates and gate structures, it does not attempt to treat 
the subject fully, but merely gives examples of structures which 
serve the purpose for which they are intended better than many 
others in common use. Local conditions control many features of 
gate structures, and the descriptions given relate to existing struc- 
tures in actual use, which it is believed will prove suggestive and can 
be readily adapted to other conditions by local engineers and ditch 
owners. 
MATERIALS USED. 
A few years ago most of the structures in American canals were 
of wood, but more recently concrete, both plain and reinforced, has 
come into common use. Wood has the advantages of cheapness and 
ease of handling and the disadvantage of rapid depreciation. Con- 
crete has the advantage of permanence, but is costly. In determin- 
ing which to use, these points must be taken into consideration. 
The most prominent facts in connection with recent irrigation de- 
velopment under both public and private agencies have been the 
high cost of water rights and the inability of settlers to make the 
payments required. In view of these facts there is much to be said in 
favor of the cheaper wooden structures for original construction 
with a view to their replacement with more permanent structures of 
concrete as the wood decays. This will lessen first cost and bring 
the heavier cost after the lands have been put under cultivation and 
the expenses incident to the establishment of new farms have been 
met. The use of wood has the further advantage that any mistakes 
in either the type of structures or their location are not so costly. It 
frequently happens that structures are found to be placed too high 
or too low, or to be too small or not of the best type for the purpose 
to be served. A few years' experience in their operation will demon- 
strate these facts, after which permanent structures may be put in 
with an assurance that they are what is needed. 
Another condition to be taken into consideration in determining 
the material to be used for structures is the damage which is likely 
to be done in case of failure. If the failure of a structure will result 
in great damage to the canal system, or to crops or other property 
below, only the most nearly permanent construction should be used.j 
If ,i on the other hand, failure will mean merely the replacement of the 
structure itself, cheaper construction may be used. 
Probably the best practice is to make combined wood and concrete 
structures, using concrete for the parts which are inaccessible 
and not easily replaced and wood for the accessible parts which 
can be replaced easily. Local conditions affecting the relative prices 
of wood and concrete will also help to determine which material 
should be used. 
