1904 



FORESTRY AND IRRIGATION 



295 



saline conditions. It is expected that 

 the storage of the flood waters behind 

 the Tonto dam will have an important 

 effect in reducing the amount of salt in 

 the water used for irrigation. To as- 

 certain definitely this fact, a series of 

 periodical salt determinations will be 

 made in the river water at the dam, es- 

 pecially during flood periods. Careful 

 study will also be made of the evapora- 

 tion in the region of the dam in order 

 to discover what may be expected in 

 the \vay of concentration during the 

 periods of low water, or when the flow 

 from the reservoir is equal to or greater 

 than that contributed by the drainage 

 area. 



From rough preliminary calculations 

 it seems probable that with a reservoir 

 full of flood water containing only a 

 small proportion of salt it would require 

 many months of concentration by evapo- 

 ration and further contributions of 

 strongly saline water from the contrib- 

 uting basins to produce in the waters of 

 the reservoirs a salinity equal to that 

 now present in the stream. 



The waters of Tonto Creek and Verde 

 River are comparatively sweet, and the 

 degree of dilution which will be present 

 will have an important bearing upon the 

 water as it is distributed to the irrigated 

 lands in the Salt River Valley. Calcu- 

 lations in this direction will be made as 

 soon as data with reference to the flow 

 of these streams are collected. These 

 three features contribute the most im- 

 portant factors in determining the effect 

 of the salt in Salt River upon irrigated 

 crops. 



J- 



Public Lands Mr. Frederick V. Co- 

 Commission* ville, botanist of the 

 U. S. Department of 

 Agriculture, and Mr. Albert F. Potter, 

 grazing expert of the Bureau of For- 

 estry, are now in the southwest making 

 a careful study of the grazing interests 

 for the information of the Public Lands 

 Commission. 



Mr. Coville is giving special attention 

 to the grazing lease systems now being 

 applied to state, railway, and Indian 

 lands, with a view of determining 

 whether or not any of these systems 

 can be applied to the public lands. 



Along with this work, he is also study- 

 ing whether by some new system of man- 

 agement the condition of the ranges can 

 be improved. 



Mr. Potter's work deals more with 

 present methods of handling live stock 

 on the range and in securing informa- 

 tion in regard to the classification of 

 ranges that is, determining which 

 should be classified as summer and 

 winter ranges, as well as the further 

 division as to which are best suited for 

 cattle or sheep. His work is carried 

 on wholly with a view of determining 

 the more practical means for the control 

 of ranges generally, which is a subject 

 of prime importance to the grazing 

 interests, and one which the Public 

 Lands Commission is going into very 

 thoroughly. 



Remarkable 



Natural 



Dam. 



At Marble Falls, Texas, 

 Engineer Thomas U. 

 Taylor, of the U.S. Geo- 

 logical Survey, reports a 

 remarkable natural dam in the course of 

 the Colorado River. The formation of 

 limestone rocks has constructed a dam 

 where a fall of 1 2 feet has been utilized to 

 pump the water supply for the city. 



From the present lake level above the 

 falls to the head of the tail race there is 

 a fall of 16.4 feet; to the end of the tail 

 race, or to the tail-race pond, a fall of 19 

 feet ; to the pond under the highway 

 bridge, a fall of 21.60 feet. A small 

 outlay of money would increase the head 

 full} 7 5 feet without raising the crest of 

 the dam. From the lake under the 

 bridge to the bend in the river below 

 there is a fall of 12.80 feet, or a total 

 fall from the lake of 35. 40 feet, and to a 

 point 1.25 miles below the dam there is 

 a fall of 47 feet. 



There are two ways in which the 

 power could be materially increased : ( i ) 

 By excavating the tail race to the lake 

 under the bridge by cutting it down at 

 the head four and a half feet, which 

 would give an effective head of 21 feet; 

 (2) by raising the crest of the present 

 dam by the cheap construction of a dam 

 on the crest of the present natural dam 

 from 4 to 12 feet, giving a maximum 

 head of 33 feet. The minimum flow 

 found in recent years was 160 second- 



