98 IRRIGATION PRACTICE 



historical rivers, a large number of which are partially 

 diverted for irrigation purposes. (Figs. 18, 19.) 



69. Seasonal variation of suspended matter. The 

 suspended matter carried by a river varies in quantity 

 from month to month. This is well shown in the follow- 

 ing table, constructed from the records of the Green 

 River, at Jensen, Utah, during the years 1905 and 1906. 



SUSPENDED MATTER CARRIED BY THE GREEN RIVER, AT JENSEN, 

 UTAH, EACH MONTH DURING THE YEAR 1905-06. 



(In parts per million) 



April 2,278 October 666 



May 917 November 79 



June 415 December 64 



July 91 January 17 



August 613 February 28 



September 4,749 March 3,170 



In March and April, during the time of the heavy 

 spring rains, the loads of sediment were very large; as 

 also in September and October, when the fall rains 

 occurred. During the summer months of June, July and 

 August, when only occasional showers fell, the suspended 

 matter was low; and in November, December, January 

 and February, when the ground was largely covered with 

 snow, it was even smaller. 



During the seasons of the year when the lands around 

 the headwaters of the rivers are not covered with snow 

 and ice, the quantity of suspended matter carried by a 

 river varies directly with the time and quantity of pre- 

 cipitation. A sudden flood will render the river turbid 

 with suspended matter, and the longer seasonal floods of 

 spring and fall are characterized by long periods of muddy 

 water. In a part of the western United States where the 

 growing season is rainless, the water is clearer during the 



