18 EXPERIMENT STATION EECORD. 



Climatology of Venezuela (An. Estad. Venezuela, 1908, pp. 1-7, dgm. 1). — 

 Tables and a diagram are given which show the geographical position, altitude, 

 and mean annual temperature of the principal cities and towns of Venezuela ; 

 also the temperature, barometric pressure, and rainfall at Caracas during the 

 years 1904 to 1908. 



Ground-water supply and irrigation in the Rillito Valley, G. E. P. Smith 

 {Arizona Sta. Bui. 64, PP. 81-244, P^s. 5, figs. 58). — This is a report on an inves- 

 tigation undertaken to determine the possibility and practicability of reclaiming 

 small areas of land by the development and utilization of ground waters in the 

 arid valleys of southern Arizona. 



The studies here reported dealt with the origin, amount and .nine, character, 

 rate and magnitude of motion, and technical and economic questions relating to 

 the recovery of ground water in the Rillito Valley and the nearby portions of 

 the Santa Cruz Valley, which are considered typical arid valleys of southern 

 Arizona. 



" That small area projects can be successfully developed in the valleys of 

 southern Arizona by utilizing the ground vwater is the conclusion expressed in 

 this bulletin. Large irrigation projects commensurate with those of the United 

 States Reclamation Service in the Salt River Valley and on the Lower Colorado 

 are not to be found south of the Gila River. But numerous small areas, from a 

 few score of acres to ten thousand acres in extent, may be reclaimed. There 

 are ground-water supplies sufficient in amount; the economic considerations of 

 recovering these waters are not prohibitive." 



The bulletin describes the topography, geology, soils, and agricultural possi- 

 bilities of the Rillito Valley, the extent to which irrigation, particularly winter 

 irrigation, is already practiced, rainfall and surface water, underflow tests, logs 

 of test wells and other representative wells in the region, the water table, 

 ground-water supply, individual pumping plants, and a cooperative pumping 

 project. 



The rainfall of the Rillito watershed ranges from an average of 12 in. in the 

 valley to over 35 in. on the tops of the adjacent mountains, but practically all 

 of it is quickly lost by evaporation and it never affects the underlying water 

 table directly. There is little run-off from the valley into stream channels. 



" Of the greater rainfall on the mountains, a considerable percentage is dis- 

 charged from the mountain canyons. Records show greater average discharge 

 in winter than in summer. After issuing fx'om the rocky canyons onto the 

 valley fill, the stream flows rapidly diminish, being absorbed into the porous 

 gravel deposits, which are in some places of shallow depth and in other places 

 broad and deep, affording extensive storage capacity. The entire flow is usually 

 absorbed within a comparatively few miles. . . . 



" Studies of the water table prove that the ground waters of the Rillito Valley 

 are derived exclusively by seepage from the stream flows. . . . 



" The application of the electric method to the recent sands and gravels of the 

 Rillito near Fort Lowell has revealed the existence there of much higher under- 

 flow velocities than any others on record. 



"At the principal section tested . . . the high rate of movement is restricted 

 to the vicinity of the river and to shallow depths, so that despite the high 

 velocities, the quantity of underflow is not great." It is pointed out, however, 

 that small underflow ditches can be developed in this and similar situations if 

 conditions are favorable. 



" Bed rock, a dyke, a lava flow, consolidated gravels, a clay deposit, or other 

 ' accident of nature ' may furnish the favorable condition. Bends in the stream 

 course which cause it to descend along a ground-water contour produce favorable 

 locations for developing the underflow by gravity ditches. 



