476 ANNUAL REPORTS OF DEPARTMENT OF AGRICULTURE, 



uniform methods of testing throughout the country. With this pur- 

 pose in view representatives of the bureau, during the j^ear, visited 

 32 of the 68 laboratories engaged in this work and conferred in each 

 case with the engineer in charge of the laboratory relative to methods 

 of testing and material control. 



As a further means of control over methods employed in testing 

 road materials, a system of check testing was inaugurated at the 

 beginning of the past fiscal year, whereby duplicate samples of ma- 

 terials were to be submitted to the bureau and to the State or other 

 laboratory engaged in the routine testing. One hundred and eighty 

 such check tests were made during the year. 



At the beginning of the fiscal year the bureau's division of tests 

 discontinued all routine supervision over material control on Federal- 

 aid work other than as outlined above. This supervision was con- 

 centrated in the various district offices under the immediate jurisdic- 

 tion in each case of a materials engineer designated by the district 

 engineer for the purpose. In order to train the materials engineers 

 in the details of the work which they were to perform, they were 

 called to the Washington office in February and given a course in 

 materials testing, the results of which have been reflected in the in- 

 creased attention given material matters in connection with the con- 

 struction of Federal-aid roads. 



FARM DRAINAGE INVESTIGATIONS. 



One of the outstanding drainage investigations conducted during 

 the fiscal year 1923 was that relating to the flow of water through 

 pipe culverts at the hydraulic laboratory of the State University of 

 Iowa, at Iowa City, where exceptional facilities are available for such 

 work. During the year vitrified clay, corrugated metal, and concrete 

 pipe culverts 30 feet long with diameters of 12, 18, 24, and 30 inches 

 were tested, the work being done in cooperation with the Stat e^ Uni- 

 versity of Iowa. The coefficient of roughness n in the Kutter 

 formula, for concrete pipe ranges from 0.012 for the 12-inch size to 

 0.013 for the 30-inch size, for vitrified clay pipe from 0.010 for the 

 12-inch size to 0.013 for the 30-inch size, and for corrugated metal 

 pipe from 0.019 for the 12-inch size to 0.023 for the 30-inch size. 

 Some of the results obtained are highly important from the stand- 

 point of practical construction and already have been made use of 

 in connection with the design of culverts 'for Federal-aid projecih. 

 The results obtained also bear directly upon the design and ca- 

 pacities of pumping plants, tide gates, sluice gates, and tile drains, 

 and the application of the results in designing and constructing such 

 improvements will materially reduce the cost of such structures. 



The results with concrete, vitrified clay, and corrugated metal 

 pipe culverts 30 feet long with straight end- wall entrances and 

 varving in diameter from 12 inches to 30 inches show that a 12-inch 

 vitrified-clay pipe culvert with beveled lips upstream will carry 

 about 65 per cent, an 18-inch clay pipe culvert about 50 per cent, 

 a 24-inch clay pipe culvert about 40 per cent, and a 30-inch clay 

 pipe culvert about 30 per cent more water than corrugated metal 

 pipe culverts of similar sizes, while a 12-inch concrete pipe with 

 beveled lip end upstream will carry about 49 per cent more water, 

 an 18-inch concrete pipe about 40 per cent, a 24-inch concrete pipe 

 about 36 per cent, and a 30-inch concrete pipe about 32 per cent 

 more water than corrugated metal pipes of the respective sizes. 



