62 BULLETIN 376, U. S. DEPARTMENT OF AGEICULTURE. 



Throughout approximately the last 100 feet of wood pipe ending at 

 a, Plate IX, tapering staves are inserted in the pipe until an elliptical 

 section 12 feet wide and 9 feet high is reached at a. The area has been 

 increased so gradually up to 84.82 square feet that, it is computed, 

 3.99 feet of velocity head have been recovered, the velocity meanwhile 

 being reduced to 11 .8 feet per second. Between b and c the transition 

 section changes from an elliptical to a rectangular shape 13| feet wide 

 by 10.6 feet high, with an area of 153.12 square feet. In this transi- 

 tion section the vertical walls and flat floor and roof begin at b with 

 zero width, increasing to full width at c, the corners being rounded 

 out in the concrete. The velocity is further diminished to 6.54 feet 

 per second and the computations show an additional velocity head 

 of 1.51 feet recovered. At the upper end of the canal leading from 

 the structure the velocity is further reduced to 2.10 feet per second by 

 enlarging the section, the additional recovered velocity head being 

 computed as 0.59 feet. Thus of the 6.14 feet devoted at the inlet end 

 to increasing the velocity, the computations show the recovery of all 

 but the 0.05 foot, which is due to the difference in velocities in the 

 channels above and below the structure. However, even with care- 

 fully designed transition sections the computations show an aggregate 

 of 1.80 feet devoted to "entry head" at the various changes in cross 

 section. 



The outlet structure of the Similkameen Siphon of the West Okano- 

 gan Irrigation District, Washington, is also designed with a view to 

 conservation of velocity head. This structure (B, PI. IX) consists 

 of a 46-inch stave pipe tapered in a length of 12 feet to a diameter of 

 57.5 inches, the pipe then discharging into a wooden flume. The 

 most noticeable feature of the structure is the use of guide wings 

 extending into the flume. These prevent a sudden enlargement of 

 the cross section at the end of the pipe and tend to recover the veloc- 

 ity head. The floor of the flume is extended into the pipe to the point 

 where the taper section begins, thus preventing contraction and con- 

 sequent loss of head due to extension of the segment of the pipe below 

 the floor line at the bulkhead. No attempt is made to secure water- 

 tightness in these guide wings, but the water is allowed to enter 

 between the wings and the flume proper so that no pressure may be 

 brought against the light wings. All tightness is secured at the bulk- 

 head and in the flume proper. 



Where a change is made in the size of pipe a long taper transition 

 section is usuaJlj installed. In the Altmar pipe (No. 51) the diameter 

 is changed from 12 to 11 feet. This change is so gradual that it can 

 hardly be detected by the eye. In a similar way the Mabton pressure 

 pipe (Nos. 43, 45, and 46) is reduced from 55f inches to 48| inches. 

 Where changes in sectional area are made in this manner probably 



