BUEEAU OF PUBLIC EOADS. 499 



conclusion from a theoretical standpoint, few satisfactory demonstra- 

 tions based upon long-continued records have been made. The 

 record kept by the bureau this year ^vill therefore add an important 

 contribution to the existing data on this subject. By the use of the 

 soil thermograph a continuous record was kept for one year beginning 

 May 1, 1921. on a tile-drained tract and on an adjoining undrained 

 tract, on the college farm at Athens. Ga. The results showed that 

 at a depth of 18 inches below the surface the average temperature 

 of the drained soil was nearly 2° higher than that of undrained soil 

 at the same depth. A similar record is now being kept at Athens 

 and also on the experimental farm at Summerville. vS. C. for a depth 

 of 12 inches. 



The amount of run-off from agiicultural land and the flow of water 

 under various conditions afford a field for research on which many 

 times the funds available for such work might be expended with 

 profit. Run-off is the very basis of drainage design. The success 

 or failure of the system hinges on the decision as to how much water 

 must be carried and how it shall be carried. This applies as well to 

 the tile system installed by the individual farmer as to the great 

 dredged ditches and floodways designed in connection with com- 

 munity projects affecting hundreds of landowners. The Little River 

 drainage district in southeast Missouri, one of the largest in the coun- 

 try, affords unique opportunity for the study of the flow of water in 

 floodways and determination of run-off from the drainage area. The 

 floodway consists of parallel levees, some 1,200 feet apart, built to 

 carry the hill water directly across the flat, intervening country to the 

 Mississippi River. The spring of 1922 afforded an exceptional chance 

 to study the flow in this floodway as affected by high stages of the 

 Mississippi, and the bureau was fortunate to be able to take advantage 

 of the opportunity. Before terminating this investigation it is hoped 

 that a chance will be afforded to study the floodway under conditions 

 of simultaneous high run-off from the hill land and low stage of the 

 Mississippi. The complete data, when secured, will fill a gap in 

 engineering knowledge necessary for the proper design of similar 

 projects. 



Other surface run-off data were collected through the keeping of 

 continuous stage readings on certain streams in Alabama and North 

 Carolina, the channels of wliich have been so gauged that the discharge 

 at various stages is known. Continuous record of discharges from tue 

 systems were kept in conjunction with records of rainfall and tem- 

 perature on the college farm at Athens. Ga., on the State experimental 

 farm at Summerville, S. C, and in Pitt County, N. C. These data 

 will be invaluable in the future design of large and small systems to 

 operate under similar conditions. 



The investigation of the durability of tile under soil conditions 

 existing in certain counties in southwestern Minnesota was continued. 

 The cooperation given by the Minnesota department of agriculture 

 and the State department of drainage and waters has aflorded oppor- 

 tunity to extend the scope of the work so as not only to aim at defining 

 the areas where the use of concrete tile— as at present manufactured — 

 is not advisable, but also to carry on research that it is hoped will lead 

 to the commercial production of concrete tile that will be highly 

 resistant to the action of soil alkalis. In the summer of 1921 a labora- 

 tor}' to be devoted to this work was established at the University of 



