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

يتدفق الماء في قناة مستطيلة بمعدلات تدفق بين القيم الدنيا والقصوى. يتم تعيين رأس السد بمقدار متر واحد فوق قاع القناة. الهدف هو قياس عمق التدفق لثلاثة أنواع من السدود: مستطيلة متوجة حادة ، مثلثة متوجة حادة ، وعريضة القمة في ظل ظروف الحد الأدنى لمعدل التدفق. بالنسبة للسد المستطيل ذو القمة الحادة ، يعتمد معدل التدفق على معامل السد وعرض القناة وتسارع الجاذبية وعمق السائل. يؤدي ضبط رأس السد على متر واحد إلى تبسيط المعادلة ، ويتم حساب عمق الحد الأدنى لمعدل التدفق. يعتمد معدل تدفق السد الثلاثي المتوج الحاد على معامل السد وتسارع الجاذبية وعمق السائل وزاوية الشق. بعد استبدال القيم ، يتم التعبير عن المعادلة من حيث العمق ؛ بالنسبة للحد الأدنى لمعدل التدفق المحدد ، يتم حساب العمق. بالنسبة للسد عريض القمة ، يعتمد معدل التدفق على معامل السد وعرض القناة وتسارع الجاذبية وعمق السائل. مع رأس سد بطول متر واحد ، فإنه يبسط إلى وظيفة العمق ، ويحدد الحد الأدنى لعمق التدفق. من بين السدود التي تمت مناقشتها ، ينتج عن السد الثلاثي المتوج الحاد أقصى عمق للتدفق.

السد: حل المشكلات

Weir: Problem Solving

غالبا ما يتم قياس تدفق المياه في القنوات المفتوحة باستخدام الهياكل الهيدروليكية مثل السدود ، والتي تسمح بحساب التصريف بدقة. في قناة مستطيلة ، يتم قياس معدلات التدفق باستخدام ثلاثة أنواع من السدود: مستطيلة متوجة حادة ، مثلثة متوجة حادة ، وعريضة القمة. يتم تعيين رأس السد على ارتفاع ثابت فوق قاع القناة ، مما يبسط العمليات الحسابية ويتيح تحليل العلاقة بين العمق ومعدل التدفق. بالنسبة للسد المستطيل المتوج ، يعتمد معدل التدفق على معامل السد وعرض القناة وتسارع الجاذبية وعمق السائل. عندما يكون رأس السد ثابتا ، يتم تبسيط المعادلة عن طريق تقليل المتغيرات إلى عرض القناة وعمقها. يسمح هذا التكوين برسم معدل التدفق مقابل العمق لتصور العلاقة بين عمق التدفق والتفريغ. يشتمل السد الثلاثي المتوج ، أو السد V-notch ، على معلمة إضافية ، زاوية الشق ، والتي تؤثر بشكل مباشر على معادلة معدل التدفق. هذا السد مناسب بشكل خاص لظروف التدفق المنخفض وتحكمه العلاقة التي يتناسب فيها التفريغ مع ناتج ظل نصف زاوية الشق ، والجذر التربيعي لتسارع الجاذبية ، وعمق السائل المرفوع إلى قوة خمسة على اثنين. عادة ما يتم الحصول على معامل التفريغ من المراجع القياسية أو البيانات التجريبية. من خلال رسم معامل التفريغ مقابل العمق ، يمكن تحليل أداء السد على ظروف تدفق مختلفة. هذا السد حساس للغاية للتغيرات في زاوية الشق وهو فعال بشكل خاص في قياس معدلات التدفق الصغيرة بدقة. بالنسبة للسد العريض ، يتأثر معدل التدفق بمعامل التفريغ وعرض القناة وتسارع الجاذبية وعمق السائل. عندما يتم إصلاح رأس السد ، يتم تبسيط المعادلة إلى دالة العمق وحدها. هذا النوع من السد قوي لمعدلات التدفق الأعلى ولكنه يتطلب تصميما دقيقا لتلبية القيود المفروضة على طول الكتلة ونسب الرأس إلى العمق. تسمح مقارنة معدل التدفق مقابل العمق عبر أنواع السدود هذه بتقييم كفاءتها ودقتها في ظل ظروف مختلفة ، مما يساعد في اختيار التصميم الأمثل لنطاق التدفق المحدد.

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

الهندسة المدنية

Unit 1

الوحدة الأولى

Open Channel Flow

الجريان في القنوات المفتوحة

KEY TERMS AND CONCEPTS

المصطلحات والمفاهيم الأساسية

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

energy considerations in open channel flow

energy-considerations-in-open-channel-flow

Flow Depth and Energy in Open Channels

Open channel flow involves water moving with a free surface exposed to the air. Rivers, canals, and artificial channels are common examples. In these systems, gravity and surface effects shape the flow more than the behavior seen in closed pipes. Energy analysis helps explain how depth, velocity, and slope work together. Specific energy combines the potential energy from water depth and the kinetic energy from flow speed. For a given discharge, or flow rate, there are often two possible depths...

uniform depth channel flow

Channel Slope and Flow Balance

Uniform depth channel flow keeps the water depth steady along an open channel. This idea is often used for irrigation canals and is also a useful approximation for rivers. The channel bottom slope must match the energy slope. That balance offsets the gravity energy lost to shear stress at the boundary, so the depth does not change along the channel length. In a constant cross-section channel, uniform flow means the depth and velocity stay consistent. Two key measures are the flow area and the...

uniform depth channel flow: problem solving

uniform-depth-channel-flow-problem-solving

Calculating Trapezoidal Channel Flow Rate

Calculating trapezoidal channel flow rate starts with the channel shape and the depth of flow. For a trapezoidal channel, identify the bottom width, side slope, and flow depth first. These values define the cross-section used in the calculation. Next, find the cross-sectional area for the flowing water. Use the depth of flow, the bottom width, and the side slope angle to determine area. Then calculate the wetted perimeter, which includes the bottom width and the sloped side lengths that touch...

gradually varying flow

Open Channel Depth Changes in GVF

Gradually varying flow in open channels describes water depth that changes slowly along a channel. The depth adjusts over distance as gravity, shear forces, and energy needs stay in balance. This creates a low rate of change in the water surface. Gradually varying flow is common in natural streams, rivers, and canals. In these settings, the depth shifts little by little over long distances. The slope of the channel bed, compared with the energy slope, helps determine how the flow behaves. A...

 rapidly varying flow

Hydraulic Jumps in Open Channels

Rapidly varying flow in open channels describes a sudden change in water depth over a short distance. The depth can change so quickly that the rate of change with distance is close to one. These flows are difficult to analyze exactly because they are transient and multi-dimensional. Approximate solutions with simplified models still give useful insight into how they behave. A common example is the hydraulic jump. In a hydraulic jump, fast and shallow water changes quickly into slower, deeper...

hydraulic jump

Flow Regimes and Energy in Hydraulic Jumps

Hydraulic jumps happen in open channels when fast, shallow water changes into slower, deeper water. This sudden rise in depth depends on the upstream Froude number, which compares flow speed to wave speed. A hydraulic jump can form only when the upstream flow is supercritical, with Fr greater than 1. If Fr is less than 1, the flow is already subcritical, and a jump cannot form. That is because the jump would require a negative head loss, which is not possible under thermodynamic principles.

hydraulic jump: problem solving

Hydraulic Jump in a Rectangular Channel

Hydraulic jump in a rectangular channel shows how flow speed and water depth change when a gate closes downstream. The jump travels upstream at 2 meters per second, so that wave speed is part of the calculation. The initial channel flow speed is 6 meters per second. To find the water depths on each side of the jump, first calculate the effective upstream velocity. This combines the flow moving through the channel with the upstream-moving wave. Next, identify the flow velocities before and...

weir

Weir Flow Measurement and Control

A weir is a hydraulic structure that partly blocks an open channel and helps control water flow. It also makes it possible to measure discharge, which is the amount of water moving past a point in a given time. Because of this, weirs are important in water resource management. Weirs are used in river flow regulation, irrigation systems, and flood control channels. They guide water to flow over or through the structure, which lets engineers estimate flow rates more accurately. This makes them...

weir: problem solving

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...

underflow gates

Irrigation Canal Gate Flow Control

Underflow gates control water flow in irrigation canals. They help manage discharge so water moves where and when it is needed. The main underflow gate types are vertical gates, radial gates, and drum gates. Vertical gates move up and down. They create a free-flowing water jet. Radial gates pivot to regulate flow, and drum gates rotate for fine adjustments. Each design supports effective flow management in different canal settings. Downstream conditions change how water passes through an...

design example: design of an irrigation channel

design-example-design-of-an-irrigation-channel

Designing Trapezoidal Irrigation Channels

Trapezoidal irrigation channels are a common choice for moving water in farms and other water systems. Their flat bottom and sloping sides make them stable and easier to build than many other channel shapes. They are also cost-effective and efficient for carrying water. The channel size depends on the needed flow capacity and the site conditions. Designers choose the bottom width and the side slope ratio to match those demands. For unlined channels, the side slope is kept gentle to help...

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 provides a foundational exploration of essential construction materials in civil engineering, focusing on bricks, stones, steel, wood, and concrete through easy-to-understand animated videos. This collection covers the properties, manufacturing processes, and practical applications of these materials. Additionally, the accompanied science-in-action videos demonstrate the research experiments performed in laboratories.

civil engineering

Weir Flow Rates and Channel Depth

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