Name: weir flow rates and channel depth
Uploaded: 2025-03-26T15:05:26.000Z
Duration: 1 min 26 s
Channel: JoVE

Water flows in a rectangular channel with flow rates between minimum and maximum values. The weir head is set one meter above the channel bottom.The objective is to measure the flow depth for three types of weirs: rectangular sharp-crested, triangular sharp-crested, and broad-crested under minimum flow rate conditions.For the rectangular sharp-crested weir, the flow rate depends on the weir coefficient, channel width, gravitational acceleration, and fluid depth.Setting the weir head to one meter simplifies the equation, and the depth for the minimum flow rate is calculated.The triangular sharp-crested weir’s flow rate depends on the weir coefficient, gravitational acceleration, fluid depth, and notch angle.After substituting values, the equation is expressed in terms of depth; for the given minimum flow rate, the depth is calculated.For the broad-crested weir, the flow rate depends on the weir coefficient, channel width, gravitational acceleration, and fluid depth. With a one-meter weir head, it simplifies to a depth function, determining the minimum flow depth.Among the weirs discussed, the triangular sharp-crested weir results in the maximum flow depth.

weir: problem solving

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 rate depends on the weir coefficient, the channel width, gravitational acceleration, and the fluid depth. When the weir head is fixed, the equation simplifies by reducing the variables to channel width and depth. This configuration allows the flow rate to be plotted against depth for visualizing the relationship between flow depth and discharge.The triangular sharp-crested weir, or V-notch weir, incorporates an additional parameter, the notch angle, which directly affects the flow rate equation. This weir is particularly suited for low-flow conditions and is governed by the relationship where the discharge is proportional to the product of the tangent of half the notch angle, the square root of gravitational acceleration, and the fluid depth raised to the power of five over two. The discharge coefficient is typically obtained from standard references or experimental data. By plotting the discharge coefficient against depth, the weir's performance can be analyzed over varying flow conditions. This weir is highly sensitive to changes in the notch angle and is especially effective in measuring small flow rates accurately.For the broad-crested weir, the flow rate is influenced by the discharge coefficient, channel width, gravitational acceleration, and fluid depth. When the weir head is fixed, the equation simplifies to a function of depth alone. This type of weir is robust for higher flow rates but requires careful design to satisfy constraints on block length and head-to-depth ratios.Comparing the flow rate versus depth across these weir types allows for the evaluation of their efficiency and accuracy under different conditions, aiding in the selection of the optimal design for the specified flow range.

Weir: Problem Solving

Water flow in open channels is often measured using hydraulic structures such as weirs, which allow precise calculation of discharge. In a rectangular ...

Education

JoVE Core

Civil Engineering

Unit 1

Open Channel Flow

KEY TERMS AND CONCEPTS

weir flow rates and channel depth

Weirs are hydraulic structures used to measure water flow in open channels. In a rectangular channel, they help calculate discharge, or the volume of water passing a point each second. The weir head is held at a fixed height above the channel bottom, which makes the math easier and lets students compare depth with flow rate.

Three weir types are used in this setting: rectangular sharp-crested, triangular sharp-crested, and broad-crested. The rectangular sharp-crested weir depends on the weir coefficient, channel width, gravitational acceleration, and fluid depth. When the weir head stays fixed, the equation becomes simpler and the flow rate can be plotted against depth to show how discharge changes.

The triangular sharp-crested weir is also called a V-notch weir. It adds notch angle as an extra factor in the flow equation. This design works well for low-flow conditions because it is very sensitive to small changes in depth. The discharge is proportional to the tangent of half the notch angle, the square root of gravitational acceleration, and the fluid depth raised to the five-halves power. The discharge coefficient usually comes from standard references or experimental data, and plotting it against depth helps show performance over different flow conditions.

The broad-crested weir is influenced by the discharge coefficient, channel width, gravitational acceleration, and fluid depth. With a fixed weir head, its equation also reduces to a function of depth alone. This type is sturdy for higher flow rates, but its design must meet limits on block length and head-to-depth ratios. Comparing flow rate versus depth for all three weirs helps show their efficiency and accuracy and supports choosing the best design for a given flow range.

Weir Flow Rates and Channel Depth

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Weirs are hydraulic structures used to measure water flow in open channels. In a rectangular channel, they help calculate discharge, or the volume of water passing a point each second. The weir head is held at a fixed height above the channel bottom, which makes the math easier and lets students compare depth with flow rate. Three weir types are used in this setting: rectangular sharp-crested, triangular sharp-crested, and broad-crested. The rectangular sharp-crested weir depends on the weir...

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key terms and concepts

Compare rectangular, V-notch, and broad-crested weirs in open channels. Learn how depth, angle, and design affect discharge and flow measurement.

Weir Flow Rates and Channel Depth | JoVE K12

JoVE Core Civil Engineering offers a foundational exploration of essential construction materials such as bricks, stones, steel, wood, and concrete, along with fluid mechanics topics like flow over immersed bodies, open channel flow, and dimensional modeling. It also covers key surveying concepts, including leveling, traverse adjustments, curve design, topographic mapping, and geospatial technologies (GPS & GIS). Science-in-action videos showcase laboratory research on materials, fluids, and surveying practices in real-world engineering systems.

civil engineering

Weir Flow Rates and Channel Depth

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