19171 RURAL ENGINEERING. 283 



depends upon the velocity and wetted cross-sectional area at two points in the 

 flume, and two gage readings, therefore, are necessary." 



From the experimental data the formula for discharge through the V-notch 

 Venturi flume is as follows : 



Q=6.68H62[(Hd-0.14Ho+0.02)2+0.01Ha+0.56]^/ ^ _ H ft* 



(2§+na)^Ha^ 



'i,- 



In this formula Q=thc discharge in eecond-feet; Ha=the head at the gage in the 

 upstream section; H5=the head at the throat section; and H(j=no — H5. 



" The discharge through the Venturi flume with trapezoidal cross section, 

 having side slopes of 1 : 1 in a plane normal to the axis of the flume and with 

 a bottom throat width of 6 in., is represented by the following equation, which 

 was derived in a manner similar to that given for the V-uotch Venturi flume: 



Q_r [(Hd-0.Q9Ha-0.005)H0-001Ha+0.274] -1 q+H6)H6 



V. 





" The Venturi flume is not an exact measuring device, but it is thought to 

 be sufficiently accurate to meet usual practical needs, especially such as are 

 encountered in irrigation practice in the West. Although experiments have 

 been made only on the smaller sizes of Venturi flumes, it seems reasonable to 

 expect that structures built according to the general plans will be applicable 

 to the measurement of streams of considerable size with an accuracy com- 

 patible with field requirements. The Venturi flume seems to fulfill the condi- 

 tions of being free of trouble from sand, silt, or floating trash ; requires little 

 loss of head for making the measurement ; is a structure that is simple to 

 build, easy to operate, and has a comparatively low cost ; and is free from 

 error in measurement due to aquatic growth or other changes in the channel, 

 provided the floor of the flume is not below the grade of the channel." 



Investigations of irrigation pumping' plants, H. E. Mukdock {Montana Sta. 

 Bui. 115 (1911), pp. 125-l.'i8, figs. 6). — Field and laboratory tests of pumping 

 outfits, consisting of various combinations of engines and pumps for different 

 heads, are reported. The results of the laboratory tests are sunmiarized in 

 the following table: 



