234 THE BUTTES. 



SILT. 

 The amount of solid matter carried by a stream is a very serious 

 problem in connection with the construction of storage reservoirs 

 thereon. The most astonishing stories are told of volumes of sediment 

 carried by the rivers of Southern Arizona from their barren drainage 

 basins. It is said that when these floods first appear discharged off of 

 ranges that have been travelled by the large herds of cattle in quest of 

 grass, the soil, which is exposed to the direct action of the sun, being 

 exceeding light and dry is washed off in quantities that are enormous. 

 In order to determine the amount of silt in the Gila River at The 

 Buttes, the GeologicalSurvey has made observations by taking samples 

 of the water daily, and permitting the mud to settle in graduated tubes. 

 This amount of mud is then determined by reading its height upon the 

 graduations. The mud which is deposited has then been treated in the 

 case of numerous samples to a temperature of 212 degrees Fahrenheit, 

 and the final amount of solid matter determined by weight. Observa- 

 tions were continued from July 29, 1895, to December 31, of the same 

 year. Beginning on January 1, 1899, and continuing until July 31, 1899, 

 similar observations were made at the same station, the amount of mud 

 and solid matter being determined as previously. During the first 

 period the volume of water discharged at The Buttes was „60,523 acre- 

 feet, and it was found that this contained 37,984 acre-feet of mud in sus- 

 pension. This reduced to 7,704 acre-feet of solids. The average amount 

 of light sediment during this first period was 10% per cent, and the 

 amount of solids a little over 2 per cent. The total amount of water 

 discharged during the second period in 1899 was 118,981 acre-feet, which 

 containing 1.6 per cent of solids or 8 per cent of mud. Frequent ob- 

 servations were made, showing 20 per cent of mud in suspension during 

 the high stages of the stream, and in one instance 27 per cent, of mud 

 was observed. The average amount of mud for the twelve months' ob- 

 servation was 10 per cent, and the amount of solids 2 per cent. No 

 other stream in the United States is known to carry such a high per 

 cent, of mud sediment. This Is in striking contrast with the clear 

 streams of our northern forested basins. The water supply used for 

 domestic purposes from Cedar Creek, Washington, does not re- 

 quire filtering or settlement. 



The serious nature of this silt problem can readily be appreciated by 

 those who have studied the storage of water for irrigation. It is prob- 

 ably the gravest of all the engineering problems related thereto. For- 

 estry should assist greatly in removing dufRculties of this nature. 



