Name: designing trapezoidal irrigation channels
Uploaded: 2025-03-26T15:04:50.000Z
Duration: 1 min 27 s
Channel: JoVE

K12 Standards

Virginia  Standards of Learning

HIgh School

Earth Science

ES.8

ES.8.d

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

Design Example: Design of an Irrigation Channel

تقوم إدارة الري بتصميم قناة شبه منحرفة غير مبطنة لتوصيل 5.66 متر مكعب في الثانية من المياه لمشروع زراعي. تتميز القناة بمنحدر لطيف يبلغ 0.0008 وهي مبنية بنسبة انحدار جانبي من 2 أفقي إلى 1 رأسي لضمان الاستقرار. يؤخذ معامل خشونة مانينغ على أنه 0.025 ، وهو ما يمثل المقاومة الطبيعية لمادة القناة الترابية غير المبطنة. مع تثبيت عرض القناة عند 3 أمتار ، يتم حساب العمق المطلوب لتحقيق معدل التدفق المطلوب. تستخدم صيغة مانينغ لتحديد عمق التدفق من خلال ربط سرعة التدفق بمنحدر القناة والخشونة ونصف القطر الهيدروليكي. يتم حساب نصف القطر الهيدروليكي بقسمة مساحة المقطع العرضي على المحيط المبلل ، مما يدعم ظروف التدفق المنتظم المطلوبة. ينتج عن حل معادلة مانينغ بهذه المعلمات عمق مطلوب يبلغ 1.15 متر ، مما يوفر مساحة مقطع عرضي تبلغ 6.09 متر مربع. يحافظ هذا التصميم على متطلبات تصريف القناة ، مما يدعم توصيل المياه بكفاءة مع سرعة تدفق متوازنة لمنع التآكل وضمان الاستقرار.

مثال على التصميم: تصميم قناة الري

تستخدم القنوات شبه المنحرفة على نطاق واسع في أنظمة الري نظرا لفعاليتها من حيث التكلفة وكفاءتها في نقل المياه. تتميز القنوات شبه المنحرفة بقاع مسطح وجوانب مائلة ، مما يجعلها مستقرة وأسهل في البناء مقارنة بالأشكال الأخرى. يتم تحديد العرض السفلي ونسبة الانحدار الجانبي بناء على سعة التدفق المطلوبة وظروف الموقع. يتم الحفاظ على المنحدر الجانبي لطيفا للقنوات غير المبطنة لمنع تآكل التربة. تشمل المعلمات الهيدروليكية في تصميم القناة معدل التدفق (Q) ونصف القطر الهيدروليكي (R h ) ومنحدر القناة (S o ). يلعب نصف القطر الهيدروليكي دورا مهما في تحديد سرعة التدفق ومقاومته ويتم تقديمه بواسطة: <figure class="image image-style-align-center image_resized" style="display:table;margin-left:auto;margin-right:auto;width:9.56%;"> <img style="aspect-ratio:170/150;" src="https://cloudfront.jove.com/files/ftp_upload/18090/18102_Equation_1_editor_18090.svg" alt="18102_Equation_1.svg"> </figure> يتم اختيار المنحدر الطولي بناء على ظروف التضاريس لضمان قوة جاذبية كافية لحركة المياه دون التسبب في تآكل مفرط. معادلة مانينغ هي أداة أساسية تستخدم في تصميم القناة لحساب سرعة التدفق والتفريغ. يربط معلمات التدفق على النحو التالي:<figure class="image image-style-align-center image_resized" style="display:table;margin-left:auto;margin-right:auto;width:14.53%;"><img style="aspect-ratio:299/150;" src="https://cloudfront.jove.com/files/ftp_upload/18090/18102_Equation_2_editor_18090.svg" alt="18102_Equation_2.svg"></figure> هنا ، n هو معامل خشونة مانينغ ، الذي يمثل المقاومة التي يقدمها سطح القناة. بالنسبة للقنوات غير المبطنة ، عادة ما تمثل n المواد الطبيعية مثل التربة أو العشب. قيمة k هي واحدة إذا تم استخدام وحدات النظام الدولي للوحدات. تتضمن عملية التصميم اختيار الأبعاد المناسبة وحل معادلة مانينغ بشكل متكرر لتحديد عمق التدفق المطلوب. هذا يضمن أن القناة تلبي متطلبات التفريغ مع الحفاظ على سرعة تقلل من التآكل والترسيب. من خلال الموازنة الدقيقة بين العوامل الهندسية والهيدروليكية ، توفر القنوات شبه المنحرفة حلا فعالا ومستداما لتوصيل المياه في أنظمة إدارة المياه الزراعية وغيرها.

Trapezoidal channels are widely used in irrigation systems due to their cost-effectiveness and efficiency in conveying water. Trapezoidal channels feature ...

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

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 prevent soil erosion.

Channel design also uses key hydraulic parameters. These include flow rate, often written as Q, hydraulic radius, written as Rh, and channel slope, written as So. The hydraulic radius affects flow velocity and resistance. The longitudinal slope is chosen from the terrain so water can move by gravity without causing too much erosion.

Manning’s equation is a basic tool for calculating flow velocity and discharge in the channel. It uses Manning’s roughness coefficient, n, to represent how much resistance the channel surface creates. In unlined channels, this roughness often comes from natural materials such as soil or grass. When SI units are used, the value of k is 1.

The design process brings these geometric and hydraulic factors together. The designer selects dimensions and then solves Manning’s equation again and again to find the required flow depth. This helps the channel carry the needed discharge while keeping the velocity low enough to reduce erosion and deposition. Trapezoidal channels therefore provide an efficient and sustainable way to deliver water in agricultural and other water-management systems.

Designing Trapezoidal Irrigation Channels

designing-trapezoidal-irrigation-channels

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

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...

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

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

Learn how trapezoidal irrigation channels are sized using flow rate, hydraulic radius, slope, and Manning’s equation to reduce erosion and meet discharge needs.

Designing Trapezoidal Irrigation Channels | JoVE K12

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Designing Trapezoidal Irrigation Channels

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