382 EXPERIMENT STATION EECOED. 



The remaining parts contain data similar to the above for other sections, as 

 follows: Parts II, South Atlantic coast and Eastern Gulf of Mexico Drainage 

 Basins; III, Ohio Iliver Basin; IV, St. I^wrence River Basin; and V, Hudson 

 Bay and Upper Mississippi River Drainage Basins. 



A method of determining' the daily discharge of rivers of variable slope, 

 M. R. and W. E. Hall and C. H. Pikkce ([/. .S'. Geo?. Harvey, Water-Huiyply 

 Paper 3J,5-E {191J,), pp. 11+53-65, figs. 2).— It is stated that the usual assump- 

 tion, when estimating the daily discharge of a stream by means of a discharge 

 rating curve, that the velocity and therefore the slope of the river surface 

 remain constant for the same gage height, is not always true, and that in many 

 streams, particularly those with very flat slopes, the variation in slope for the 

 same gage height becomes so large as to affect seriously the accuracy of the 

 method. Still greater variations are said to occur when flatness of slope is con- 

 joined with discharge into a body of water subject to large fluctuations of sur- 

 face elevation, as occurs in the lower Mississippi basin. For streams of this 

 nature it is proposed to base the estimate of daily discharge on both the gage 

 height and the slope determined for each day and at the time of each discharge 

 measurement and to adjust the discharge values on the assumption that for 

 the same gage height and conditions of channel the velocity will vary with the 

 square root of the slope. 



For this purpose the formula Q\=Qn-\ tt- i^ derived, in which Qi=actual 



V -are 

 discharge of a stream as determined by the current meter, i7i=the correspond- 

 ing difference in elevation of water surface between the two gages, and Qn= 

 a " normal " or theoretical value of the discharge for the " normal " or average 

 gage height difference Hn- 



" By means of discharge measurements the values of Qi may be determined 



for different gage heights ; -=- will be likely to vary with the different measure- 



-"« 

 ments and will be greater or less than unity according as the slope of the stream 



at the time of the measurement is greater or less than the average slope. The 



values ot Qn as determined from the expression Q„= /El w^^^' however, give 



a well-defined curve when plotted in the same way as tlie ordinary discharge 

 rating curve. The 'normal' discharge curv'e for ^^ having been determined, a 

 ' normal ' rating table is prepared from it in the ordinary way. To find the actual 

 discharge of the stream at any stage and for any slope the ' normal ' discharge 

 is taken from the ' normal ' rating table and multiplied by the proper value 



An example of the practical application of the method is given. 



The discharge of Yukon Iliver at Eagle, Alaska, E. A. Porter and R. W. 

 Davenport (f7. S. Geol. Survey, Water-Siipply Paper SJfS-F (1914), PP- 11+67- 

 77, pis. 2, figs. 2). — This paper describes the climatic conditions of the Yukon 

 River basin and reports the results of measurements of flow made by means of 

 floats. Observations made to determine the coefficient to be used in reducing 

 surface velocity to mean velocity showed this coeflicient to be 0.92. A com- 

 parison of run-off and precipitation in the basin indicates that the run-off was 

 approximately 65 per cent of the precipitation for the three years of observation. 



Profile surveys in Hood and Sandy Iliver basins, Oregon ( U. S. Geol. Sur- 

 vey, W<iter-Supp1y Paper 348 {1914), pp. S, pis. 6). — This reix»rt. prepared under 

 the direction of R. B. Marshall, describes the general features of the Hood and 

 Sandy River drainage basins and gives plans and profiles of these rivers and 

 some of their tributaries. 



