Question

A Cipolletti weir discharges water with the head of water over the crest being 250 mm. If the head due to velocity of approach is 0.01 m, What will be the excess percentage of flow, when corrected for velocity of approach as compared to when not so corrected?

• A. 3.2%
• B. 4.2%
• C. 5.3%
• D. 6.3%

Answer 1

The correct option is C 5.3%

Discharge when approach velocity is neglected

$Q=\frac{2}{3}{C}_{d}L\sqrt{2g}{H}^{3/2}$

If velocity of approach, $V_a$ is to be taken into consideration

$Q_a=\frac{2}{3}{C}_{d}L\sqrt{2g}[{(H+h_a)}^{3/2}-h_a^{3/2}]$
Excess percentage of flow

$=\left(\frac{Q_a-Q}{Q}\right)\times 100$

$=(\frac{Q_a}{Q}-1)\times 100$

$=[\frac{{(0.25+0.01)}^{3/2}-{0.01}^{3/2}}{{\left(0.25\right)}^{3/2}}-1]\times 100$

$=5.3\%$