11 



Normal annual precipitation at stations alonr/ Platte River and trihutaries. 



Station. 



'Altitude. P^*- 



South Platte: 



Longs Peak 



Moraine, Colo 



Cheesman . _ 



Denver 



Laporte . _ 



Fort Collins - - 



G-reeley 



Fort Morgan - 



North Platte, Nebr. 

 North Platte: 



Saratoga, Wyo 



Laramie, Wyo 



Alcova, Wyo 



Fort Laramie, Wyo. 



Gering, Nebr _ _ 



Bridgeport, Nebr . . . 



North Platte, Nebr . 

 Platte: 



Lexingrton 



Kearney 



Grand Island 



Fremont 



Plattsmouth 



Feet. 



8,600 

 7,900 

 (), 7«2 

 .5. 2<)1 

 .5.(J»;i) 

 4,if.l4 



4,b:j7 



4,000 

 2,821 



Inches. 

 IB. 47 

 Iti.'.W 

 U.W 

 14. 49 

 15.29 

 14.08 

 11.92 

 11.74 

 18.27 



14.08 

 9.8.5 

 9.44 

 11.19 

 15.00 

 16.09 

 18.27 



22.09 

 26. 89 

 28. .57 

 :^), 76 

 32. 60 



The facts given in the table are shown graphical!}' in the diagrams 

 (figs. 1 and 2). In these diagrams the horizontal scale represents 

 distance in miles; the vertical scale represents altitude and depth of 

 precipitation. In each curve the altitude steadily diminishes, while 

 the precipitation is high in the extreme altitudes, drops down near 

 the base of the mountains, then gradually increases to the east, the 

 decrease in altitude and the increase in precipitation being remark- 

 ably uniform from the base of the mountains east. Throughout a 

 large portion of the area the rainfall is insufficient for the needs of 

 maximum crops. 



A common assumption is that irrigation is necessary for successful 

 agriculture where the annual rainfall is less than 20 inches. In a 

 general way the assumption is borne out by agricultural practice 

 along the Platte. Laporte is just at the foot of the mountains, 

 and no agriculture is attempted without irrigation. North Platte 

 is at the other edge of the distinctly arid zone, and there many farms 

 are regularly irrigated except during years when the rainfall is 

 al)Ove normal, although some are " dry farmed." At Lexington, 

 where the rainfall is just over the 20-inch mark, a canal covers a 

 large area of farm land, but only a part of the farmers use water, 

 and the canal management is carrying on a cami)aign of education 

 to demonstrate to the people the benefits of irrigation. At Kearney, 

 where the rainfall is a little greater, a large canal was constructed, 

 but is not regularly used for irrigation. Irrigation is practiced all 

 along the North Platte, and at none of the stations on that stream 

 does the rainfall equal 20 inches. In general, then, the distinctly 



