2 BULLETIN 115, r. S. DEPARTMENT OF AGEICULTURE. 



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. 

 If .1 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 inaccessibh 

 and not easily replaced and wood for the accessible parts whicl 

 can be replaced easity. Local conditions affecting the relative price 

 of wood and concrete will also help to determine which materia 

 should be used. 



