Weir Flow Equation
Weir Flow Equation - Related Videos
07:15
Parameterizing V-notch Weir Equations for Flow Monitoring in a Drainage Control Structure
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2025
This protocol describes methods for obtaining weir flow equation coefficients for a V-notch weir within a drainage control structure using (1) a laboratory calibration procedure and (2) an online tool, the "Weir Flow Equation Coefficients Calculator", developed by the authors. These methods apply to flows contained within the V-notch and overtopping flows.
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Weir
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2025
A weir is a hydraulic structure designed to partially obstruct an open channel, enabling precise control and measurement of water flow. By forcing water to flow over or through it, a weir allows for accurate determination of discharge rates, making it an essential tool in water resource management. These structures are extensively used in regulating river flows, irrigation systems, and flood control channels.Types of Weirs and Their FeaturesWeirs are categorized primarily into sharp-crested and...
01:26
Weir: Problem Solving
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2025
Water flow in open channels is often measured using hydraulic structures such as weirs, which allow precise calculation of discharge. In a rectangular channel, flow rates are measured using three types of weirs: rectangular sharp-crested, triangular sharp-crested, and broad-crested. The weir head is set at a fixed height above the channel bottom, simplifying calculations and enabling the relationship between depth and flow rate to be analyzed.For the rectangular sharp-crested weir, the flow...
01:30
Bernoulli's Equation for Flow Along a Streamline
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2025
Bernoulli's equation relates the energy conservation in a fluid moving along a streamline. The equation applies to incompressible and inviscid fluids under steady flow. For such a flow, Newton's second law is applied to a small fluid element, which experiences forces due to pressure differences, gravity, and velocity variations. The force balance leads to the following form of Bernoulli's equation: Here, P is the pressure, ρ is the density of the fluid, v is velocity, g denotes the...
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Bernoulli's Equation for Flow Normal to a Streamline
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2025
Bernoulli's equation for flow normal to a streamline explains how pressure varies across curved streamlines due to the outward centrifugal forces induced by the fluid's curvature. The pressure is higher on the inner side of the curve, near the center of curvature, and decreases outward to balance these centrifugal forces. The pressure difference depends on the fluid's velocity and radius of curvature. The pressure variation is minimal in flows with nearly straight streamlines. However, the...
FAQs
For a common sharp-crested weir, discharge rises approximately with the upstream head raised to the three-halves power. Consequently, a change in head does not produce a simple one-to-one change in flow: the calculated discharge responds nonlinearly. This relationship makes precise upstream water-level measurement especially important when the equation is used for streamflow or environmental monitoring.
The calculation requires the weir’s geometry, crest length, upstream head, and discharge coefficient. Geometry and crest length describe the structure through which water passes, while the coefficient accounts for the discharge relationship used in the selected equation. Omitting or misrepresenting any of these inputs can weaken the resulting flow estimate, so the physical structure and measured conditions must match the calculation.
Accurate results depend on appropriate weir conditions, calibration, and careful head measurements. These requirements connect the mathematical estimate to the actual monitoring structure and water level. If head is measured poorly or the setup is not appropriate, the calculated discharge may not represent the flow being observed, limiting its value for environmental assessment.
First, identify a suitable weir and document its geometry and crest length. Next, measure the upstream head carefully and select the relevant discharge coefficient. Apply the equation using these measured and structural values, then use calibration to check whether the calculated discharge represents the observed setup. This workflow supports more reliable streamflow and monitoring results.
They support streamflow measurement, irrigation and drainage regulation, wastewater treatment outfall assessment, and the design of hydrological monitoring structures. In each case, the equation converts observed water-level and structure information into a discharge estimate. This helps engineers monitor or manage water movement in distinct environmental and infrastructure settings.
If upstream head changes, the estimated discharge should change according to the three-halves relationship for the common sharp-crested form. Results should therefore be interpreted alongside the structure’s geometry, crest length, coefficient, and current weir conditions rather than from water level alone. This is particularly relevant when monitoring streams or wastewater outfalls over time.