484 Twenty-e;ighth Annual Report 



nite policy of building farmsteads on the margins of the bottom- 

 land should be adopted and all newcomers should be warned 

 against building residences on ground subject to injury by river 

 floods. It is possible that better river control by reservoirs on the 

 Gila and its tributaries will reduce the menace in the future and 

 levee protection will be possible to i limited extent. 



WELL DRILLING AND DEVELOPMENT 



Considerable time has been spent during the past year accumu- 

 lating data on the drilling and perforating of wells and more par- 

 ticularly on the development of the wells after perforating. This 

 has been done with a view to early publication. 



EVAPORATION AND DUTY OF WATER 



For several years this department lias desired to undertake 

 special investigations to study the relationship between the evapo- 

 ration-rate and the duty of water. Although evaporation records 

 are common and have been kept at various times in many places, 

 yet the mass of data thus accumulated is almost worthless for com- 

 parative purposes, because of the absence of standardization in 

 equipment and method, and because as a rule no contemporary 

 observations have been made of other climatic factors. Clearly, it 

 was the province of the United States Weather Bureau to control 

 such standardization, and in 1915, as soon as the Bureau had made, 

 tentative plans for a standard evaporation pan, this office had sev- 

 eral of them built. Later, when Congress made appropriation for 

 twenty-five Class A evaporation stations, three of them were ob- 

 tained for Arizona under cooperative arrangement. This station 

 selected the sites and furnished the pans and standard enclosures. 

 The Weather Bureau furnished hook gages, rain gages, and maxi- 

 mum and minimum thermometers. The observers are paid by this 

 station. 



The purpose being to test the hypothesis that water re<|uire- 

 ments of plants are proportional to the evaporation-rates, three 

 locations were chosen widely separated in climatic conditions. They 

 are Yuma, the Salt River Valley, and near Willcox. The altitudes 

 above sea level are 127 feet, 1225 feet, and 4200 feet, respectively. 

 Approximately similar soil conditions were ^ound in tb.c three 

 places, and in each place the evaporation pan and other instruments 



