586 EXPERIMENT STATION RECORD. 



ditioiis which, as a rule, are most favorable for the life of the wood. Corrosion 

 is greatly accelerated by the presence of alkali In the soil. . . . Under such 

 conditions the bands almost invariably fail at the bottom of the pipe. . . . 



" With so many influences affecting the life of wood pipe no attempt should 

 be made to strike an average of durability except in cases where attending con- 

 ditions are kn(nvn to be the same. Where pipes are fully exposed and supported 

 free from all contact with the soil the conditions are much less variable than 

 otherwise, and a life of at least twenty years may be quite reasonably expected 

 for either fir or redwood if properly maintained. If placed in the ground or in 

 contact with the soil, the life of wood pipe may, under very favorable conditions, 

 be much greater than twenty years, otherwise it may be a great deal less. In 

 contact with soil the durability is nearly always a matter of some uncertainty." 



Irrigation investigations, G. E. P. Smith and A. L. Engee (Arizona Sta. 

 Rpt., 1913, pp. 280-285). — Further experiments with reinforced concrete caisson 

 curbs (E. S. R., 29, p. 484) demonstrated their effectiveness for developing 

 shallow wells. 



Measurements of the surface flow of Sabino Canyon in the vicinity of Tucson 

 from 1904 to 1912 indicate that the available supply is sufficiently large, but that 

 *' the remarkable disparity between the discharges of such years as 1904 and 

 1910 and those of 1905 and 1907, together with the fact that there is a tendency 

 for several lean years to come together, necessitates much greater storage 

 capacity for a reservoir project than would be the case if the rainfall, and hence 

 the run-off, were more evenly distributed." 



Experiments as to the necessary slope of the land in border irigation indicated 

 that " under ordinary conditions it is best to run the borders down the steepest 

 slope, or nearly so, and thus reduce the cost of grading the land to a minimum, 

 and then to adjust the width and length of the lands to the head of water. 

 The effects of silts in river irrigating waters must be considered, inasmuch as 

 these silts tend to settle out at the head ends of the lands, making those ends 

 more impervious to water than the lower ends. These deposits, also, produce 

 a slope lengthwise of the land. The tightening effect of the silt blanket must 

 be counteracted so far as possible by the various methods of cultivation in use. 

 The amount of desirable slope is influenced further by the kind of crop, alfalfa 

 requiring more than crops which are irrigated between rows. But with clear 

 or moderately clear water lands should never be graded entirely level." 



Relations between physical constitution of soils and the distribution of 

 irrigation waters, A. MiJNTZ and E. Lain^ (Min. Agr. [France], Ann. For^ts, 

 Hydraul. [etc.]. No. U (1912), pp. 1-130, pis. 7, figs. 9).— In continuation of 

 previous studies on the relation of the physical properties of the soil to irri- 

 gation (E. S. R., 24, p. 522) the authors extended their investigations to include 

 the module, and time, method, and amount of irrigation most favorable to 

 crops, with particular reference to the design of irrigation works. 



The permeability of the soils used in the experiments varied from an infiltra- 

 tion of 0.5 to 60 cm. (0.2 to 23.4 in.) per hour. In the module experiments 

 it was found that for the less permeable soils the module should be such that 

 the flow through the diversion gate is about 0.3 liters per second per meter 

 of width of the irrigated parcel. For soils of average permeability this should 

 be from 1^ to 2 liters per second and for extremely permeable soils should exceed 

 liters per second per meter of width of the irrigated parcel. It is also con- 

 cluded in this connection that the improper choice of module is one of the main 

 causes of failure in irrigation. 



Irrigation experiments with hay crops showed that the most economical 

 amount for an irrigation is an amount just sufficient to reach the extremities 



