RURAL ENGINEERING. 883 



which is based on the straight-line formuhi for rectangular notches, gives dis- 

 charge values for the 1-, 1.5-, 2-, 3-, and 4-ft. Cipolletti notches that agree 

 within a maximum of 1 per cent with the curves plotted from the experimental 

 data, the divergences at all but a few points being 0.5 per cent or less. The 

 formula for the 0.5-foot notch is g=1.566JI''^-f 0.56iJ'". The Cipolletti type 

 of notch does not give discharges as nearly proportional to the length of crest 

 as does the rectangular type, consequently, . . . the rectangular-notch weir is 

 to be preferred. 



" The general formuhi for discharges through triangular notches of from 

 28° 4' to 90°, and probably up to 109°, is 



/„- 0.0195 \ 

 Q=(0.025-f 2.462 S)H{^-^—so?n, ) 



where E is the head in feet and S the slope of the sides. Triangular notches 

 having side slopes greater than about 1:4 (109°) are impractical, as the 

 nappe adheres. The 90° triangular notch is the most practical triangular notch 

 and should be used in preference to either rectangular or Cipolletti notches 

 for discharges up to approximately 3 cu. ft. per second. The approximate 

 formula Q=2A9H^'^^ will give discharge values for 90° notches which agree 

 very closely with the value obtained with the general formula for triangular 

 notches. 



" The crest and sides of a weir notch need not be knife-edged. They are suf- 

 ficiently sharp if the upstream corner of the edges is a distinct angle of 90° or 

 less and the thickness of the edges is not so great that the water will- adhere 

 to them. The head should be measured upstream from the weir a distance of 

 at least 4H, or sidewise from the end of the crest in the plane of weir a dis- 

 tance of at least 2H. 



" The distances required for full contractions with rectangular and Cipolletti 

 notches are approximately 211, but an additional cross-sectional area of the 

 weir box is required to reduce the velocity of approach. 



" With end contractions equal to 2_ff and a bottom contraction equal to SH, 

 or end contractions equal to 3-ff and a bottom contraction equal to 2H, the 

 mean velocities of approach are about J ft. per second, and the discharges 

 with medium to high heads do not agree more closely than approximately 1 per 

 cent with the discharges computed by the formulas. The average ratio of the 

 cross-sectional area of the weir box to the cross-sectional area of the notch re- 

 quired to give discharges within 1 per cent of the values obtained with the 

 formula is greater than 7 and is probably near 15. 



" In order to make the results comparable with those for rectangular notches, 

 the end contractions for trapezoidal notches should be measured from about 

 the middle point of the side of the notch, rather than from the end of the crest. 

 A notch which would give discharges proportional to the lengths of the notches 

 would probably have curved sides, the slope decreasing with the head. 



" For all practical purposes, discharges through rectangular and Cipolletti 

 notches are not alfected until the notch is submerged to a depth equal to one- 

 tenth the head upstream from the weir. Submergence equal to one-eighth the 

 head upstream from the notch decreases the discharge approximately 2 per 

 cent, that equal to one-fourth approximately 6 per cent, and that equal to one- 

 third approximately 9 per cent." 



Notes on the duty of water, J. W. Beaedsley (Cornell Civ. Engin., 24 {1916), 

 No. 4' PP- 153-160, figs. 2). — It is the purpose of this paper "to indicate some 

 of the questions arising in a determination of the area to be developed under 

 a given water supply, with special reference to conditions existing along the 

 relatively dry coastal plains on the south side of Porto Rico. . . . 



