CivilAche

 The Parshall Flume is a specially shaped open channel structure used to measure flow in unpressurized conduits and irrigation canals. By contracting the sidewalls and creating a drop in the flume invert, the structure forces flow from subcritical to supercritical, establishing critical depth near the crest. ​Under free-flow conditions, discharge (Q) depends solely on the water depth measured at an upstream gauge location $(H_a):$ $Q = C \cdot H_a^n$ ​Where $C$ and $n$ are empirical coefficients determined by throat width $W.$ For standard throat widths (e.g., W between $0.3\text{ m}$ and $2.4\text{ m}),$ $n$ $\approx 1.522 \cdot W^{0.026}.$ When downstream tailwater elevation rises such that the submergence ratio $(H_b / H_a)$ exceeds critical thresholds (0.6 for small flumes, 0.7 for larger flumes), flow becomes submerged, requiring a reduction factor correction: $Q_{submerged} = Q_{free} - Q_{correction}$ ​In major canal delivery networks and urban wastewater channels across Ind...

 Broad-crested weirs are robust discharge measurement structures installed across open channels. Flow over the flat crest accelerates to critical depth ($y_c$), where Froude number $Fr = 1,$ creating a unique relationship between upstream energy head (H) and discharge (Q). ​For a rectangular broad-crested weir of crest width b, the critical depth is $y_c = \frac{2}{3} \cdot H.$ Substituting $y_c$ into the critical flow equation ($Q = b \cdot \sqrt{g \cdot y_c^3}$) yields the ideal discharge relation: $$Q = C_d \cdot \left(\frac{2}{3}\right)^{3/2} \cdot \sqrt{g} \cdot b \cdot H^{3/2}$$ $$\approx 1.705 \cdot C_d \cdot b \cdot H^{3/2}$$ ​Where $C_d$ is the discharge coefficient accounting for boundary layer friction losses along the weir crest. ​In heavy sediment-laden canals across India, conventional sharp-crested weirs quickly trap silt, degrading measurement precision. ​Modern irrigation branch networks deploy self-cleaning broad-crested weirs equipped with non-contact ultrasonic ...