A submerged rectangular weir is a hydraulic structure used for flow measurement. It consists of a rectangular notch submerged in water, with the downstream water level higher than the weir crest. Flow rate is calculated using the submerged weir equation, accounting for submergence effects. It’s suitable for high flow rates but can be sensitive to submergence conditions.
Submerged Rectangular Weir Calculator
Flow Rate: cubic meters per second (m³/s)
| Parameter | Description |
|---|---|
| Weir Type | Submerged Rectangular Weir |
| Crest Shape | Rectangular |
| Purpose | Flow measurement and control |
| Weir Crest Length (L) | Length of the weir crest, typically in meters |
| Head of Water Over Weir (H) | Depth of water over the weir crest, in meters |
| Submergence Ratio | Ratio of downstream water level to weir crest height |
| Flow Conditions | Completely submerged flow |
| Flow Equation | Q ≈ 2.49 * L * H^1.5 (Weir Equation) |
| Coefficient of Discharge (Cd) | Typically around 0.61 (for free flow) |
| Flow Measurement Accuracy | Affected by submergence and flow conditions |
| Advantages | Suitable for high flow rates, versatility |
| Disadvantages | Sensitivity to submergence, limited accuracy under certain conditions |
| Maintenance | Periodic cleaning and inspection required |
| Applications | Commonly used in open channels, industrial and environmental monitoring, water control systems |
| Note | Accuracy may vary depending on submergence, flow regime, and weir design |
| Reference | Weir Handbook, Hydraulic Engineering Manuals |
FAQs
What is the formula for a rectangular weir? The formula for the flow rate (Q) over a rectangular weir is approximately:
Q ≈ 2.49 * L * H^1.5
Where: Q = Flow rate (cubic meters per second) L = Length of the weir (meters) H = Head of water over the weir (meters)
What is the submergence of a weir? Submergence is the depth of water over the top of the weir. It is denoted by the letter “H” in the weir formula.
What is the formula for the weir equation? The formula for the weir equation is approximately:
Q ≈ 2.49 * L * H^1.5
How do you calculate water flow over a weir? To calculate water flow over a weir, you can use the weir formula mentioned above, where you need to know the length of the weir (L) and the head of water over the weir (H). Plug these values into the formula to estimate the flow rate (Q).
What is the head of water over a rectangular weir is 38cm? If the head of water (H) over a rectangular weir is 38 cm, you can use the formula to estimate the flow rate (Q) based on this value.
What is the coefficient of discharge for a rectangular weir? The coefficient of discharge (Cd) for a rectangular weir is approximately 0.61.
What is the equation for submerged flow? The equation for submerged flow in a rectangular weir is the same as for free flow, as mentioned earlier: Q ≈ 2.49 * L * H^1.5.
Is a weir drowned or submerged? When the water level upstream of a weir is higher than the crest of the weir, the weir is considered submerged or drowned. In this condition, the flow is different from free flow over the weir.
How do you size a weir? To size a weir, you need to consider factors like the expected flow rate, the head of water, and the desired accuracy of measurements. Typically, engineers use standard formulas like the one mentioned above to determine the appropriate length and dimensions of the weir.
What is rectangular weir? A rectangular weir is a type of flow measurement structure used to determine the flow rate of liquid (usually water) in open channels. It consists of a rectangular-shaped notch or opening over which water flows.
How does a rectangular weir work? A rectangular weir works by allowing liquid to flow over its notch or crest. The height of the liquid (head) over the weir crest and the length of the weir are used in formulas to estimate the flow rate accurately.
What is the depth of water flowing over the weir called? The depth of water flowing over the weir is called the head (H) of water.
What is the formula for flow rate through a valve? The formula for flow rate through a valve depends on various factors like valve type, size, and pressure drop. The most common formula used is the valve flow coefficient (Cv) formula, which relates flow rate to valve characteristics. Cv ≈ Q / √(ΔP).
How accurate is Weir equation? The Weir equation provides a reasonably accurate estimate of flow rate over a weir when certain assumptions are met. However, its accuracy can vary depending on factors such as the shape of the weir, submergence, and flow conditions. For precise measurements, other methods or technologies may be more accurate.
What is the overflowing sheet of water on a weir? The overflowing sheet of water on a weir is the flow of liquid (usually water) that passes over the weir crest, forming a thin sheet or stream of flowing water.
What is main reading required in calculation for rectangular weir? The main readings required for calculations involving a rectangular weir are the length of the weir (L) and the head of water over the weir (H).
What is the maximum head for a weir? The maximum head for a weir is typically determined by the design and purpose of the weir. There is no fixed maximum head for all weirs, as it depends on the specific application and engineering requirements.
Does the length of the weir affect the discharge coefficient? Yes, the length of the weir (L) can affect the discharge coefficient (Cd) to some extent. The Cd value may vary slightly with changes in the weir’s length, but it is primarily influenced by the weir’s geometry and flow conditions.
What is weir depth and discharge? Weir depth refers to the depth of water flowing over the weir crest (head), denoted as “H” in the weir equation. Discharge is the flow rate of water passing over the weir, represented as “Q” in the equation.
What is the difference between rectangular notch and rectangular weir? A rectangular notch and a rectangular weir are similar in that they both are used for flow measurement. However, the key difference is that a weir has a solid crest or edge, while a notch has an open or notched crest.
What is the most efficient weir design? The efficiency of a weir design depends on the specific application and requirements. There is no universally most efficient design, as efficiency can vary depending on factors like flow conditions, submergence, and desired accuracy.
Which weir is more efficient? The efficiency of a weir design depends on the specific parameters and conditions. Rectangular weirs are commonly used and can be efficient for various applications, but other types of weirs, such as V-notch weirs or trapezoidal weirs, may be more efficient for specific flow measurement tasks.
Why triangular weir is preferred over rectangular weir? A triangular weir is preferred over a rectangular weir in some cases because it provides a more accurate measurement of flow for certain flow conditions. The V-notch in a triangular weir allows for better flow rate estimation at lower heads compared to a rectangular weir.
What is the difference between free flow and submerged flow? Free flow occurs when the water level downstream of a structure (like a weir) is lower than the crest of the structure, allowing the liquid to flow freely over it. Submerged flow occurs when the downstream water level is higher than the crest, causing the structure to be submerged, and the flow behavior is different.
What are the flow conditions for weirs? The flow conditions for weirs can vary, but they are typically used in open channels to measure flow rates. Weirs are designed to handle free flow, partially submerged flow, or completely submerged flow, depending on the specific application and design.
What is the effect of submergence on the flow? Submergence affects the flow rate over a weir by altering the flow behavior. In submerged flow, the flow rate is influenced by the water level upstream and downstream of the weir, and the weir equation differs from that of free flow.
Where should a weir be placed? A weir should be strategically placed in an open channel or watercourse where flow measurement or control is needed. The location should be chosen based on engineering considerations, such as flow characteristics and measurement accuracy requirements.
How should a weir be constructed? Weirs are typically constructed with durable materials like concrete or metal to withstand water flow. They should be designed with specific geometry and dimensions based on the desired flow measurement or control objectives.
What are the advantages of a rectangular weir? Advantages of a rectangular weir include simplicity, ease of construction, and versatility for various flow measurement applications. They are also commonly used and well-understood in hydraulic engineering.
Why is the rectangular weir important? Rectangular weirs are important in hydraulic engineering because they provide a straightforward method for measuring and controlling flow rates in open channels, which is crucial for various industrial, agricultural, and environmental applications.
What is the most commonly used weir? The most commonly used weir types include rectangular weirs, V-notch weirs, and trapezoidal weirs. The choice of which one to use depends on the specific requirements of the application.
What is the length of a rectangular weir? The length of a rectangular weir can vary depending on the specific design and application. It can range from a few centimeters to several meters, depending on the desired flow measurement accuracy and conditions.
What is the difference between a weir and a spillway? A weir and a spillway are both hydraulic structures used to control and manage the flow of water, but they serve different purposes. A weir is primarily used for flow measurement or control, while a spillway is designed to safely discharge excess water from a reservoir or dam to prevent overtopping and flooding.
What is the difference between a barrage and a weir? A barrage and a weir are both hydraulic structures used to control water flow, but they have different purposes and functions. A barrage is typically a larger and more complex structure designed to impound water, while a weir is primarily used for flow measurement or control.
What is the flowing of water from height called? The flowing of water from a height is commonly referred to as a waterfall or cascade.
What is the easiest way to calculate flow rate? The easiest way to calculate flow rate depends on the specific situation. For simple cases, you can use the basic formula: Flow rate (Q) = Volume / Time. In more complex situations, specialized equations and instruments may be required.
What is the maximum velocity through a valve? The maximum velocity through a valve depends on the valve’s design, size, and purpose. Valves are often rated for specific maximum velocities to ensure proper operation and prevent damage.
What is the difference between CV and flow of a valve? CV (Flow Coefficient) is a measure of a valve’s flow capacity under specific conditions, while the flow rate of a valve refers to the actual volume or rate of fluid passing through the valve.
What is the approach velocity of a weir? The approach velocity of a weir refers to the velocity of the water as it approaches the weir crest. It can affect the accuracy of flow measurement and needs to be considered in weir design.
What is the effective length of a weir? The effective length of a weir is the portion of the weir crest where flow measurement or control is considered. It is typically measured in meters or feet and is relevant for calculating flow rates.
What is the flow equation for a rectangular weir? The flow equation for a rectangular weir is approximately: Q ≈ 2.49 * L * H^1.5, where Q is the flow rate, L is the length of the weir, and H is the head of water over the weir.
What is the simplified Weir equation? The simplified weir equation is the formula used to estimate flow rate over a weir, typically in a rectangular weir. It is an approximation that simplifies complex fluid dynamics. The equation is: Q ≈ 2.49 * L * H^1.5.
How is weir overflow rate calculated? Weir overflow rate is calculated by dividing the flow rate (Q) over the weir by the length of the weir (L). It is often used to assess the rate of flow per unit width of the weir.
Is the surplus water in weir allowed to flow over? Yes, surplus water in a weir is allowed to flow over the weir crest, which is how weirs function to measure or control flow rates.
What is maximum submergence ratio weir? The maximum submergence ratio for a weir refers to the point at which the downstream water level rises so high that it submerges the entire weir. Beyond this point, the weir may no longer accurately measure flow.
How high can a submersible pump lift water? The maximum height (head) to which a submersible pump can lift water depends on the pump’s design and capacity. Some submersible pumps are capable of lifting water to several hundred meters or more.
What is the CD of rectangular weir? The coefficient of discharge (Cd) for a rectangular weir is approximately 0.61.
What is the flow coefficient of a weir? The flow coefficient is not typically used to describe weirs. Instead, the coefficient of discharge (Cd) is commonly used to characterize the flow behavior over a weir.
What is the discharge over a rectangular weir directly related to? The discharge over a rectangular weir is directly related to the head of water over the weir (H) and the length of the weir (L), as described in the weir equation: Q ≈ 2.49 * L * H^1.5.
What is flow through submerged weir? Flow through a submerged weir occurs when the water level downstream of the weir is higher than the weir crest, causing the weir to be submerged. The flow behavior is different from free flow, and calculations need to consider the submerged conditions.
What does the coefficient of discharge tell us? The coefficient of discharge (Cd) tells us how efficiently a weir or similar flow measurement device allows water to pass over it. It accounts for losses and variations in flow behavior.
What is the formula for the discharge of water? The formula for the discharge of water over a weir is approximately: Q ≈ 2.49 * L * H^1.5, where Q is the discharge, L is the length of the weir, and H is the head of water over the weir.
What is the difference between flow coefficient and discharge coefficient? The flow coefficient (Cv) and discharge coefficient (Cd) are different terms used in fluid dynamics. Cv is often used for valves and represents the flow capacity, while Cd is used for weirs and other flow measurement devices, indicating how efficiently they allow flow.
Which is better V-notch or rectangular notch? The choice between a V-notch and a rectangular notch depends on the specific flow measurement requirements. A V-notch weir is often preferred for measuring low flow rates or for applications where high accuracy is needed at lower heads. A rectangular notch may be more suitable for higher flow rates.
In what situations would a rectangular weir be more appropriate to use than the V-notch weir? A rectangular weir may be more appropriate than a V-notch weir in situations where the flow rates are relatively high, and a broad range of flow conditions needs to be measured with reasonable accuracy. Rectangular weirs are versatile and can handle a wide range of flow rates.
How accurate is a rectangular weir? The accuracy of a rectangular weir depends on various factors, including the design, submergence, and flow conditions. In many cases, rectangular weirs provide reasonably accurate flow measurements when properly designed and operated. However, for highly accurate measurements, other specialized flow measurement methods may be preferred.
What are some disadvantages of a weir? Some disadvantages of weirs include limitations in handling extremely high flow rates, sensitivity to submergence conditions, and the need for periodic maintenance and cleaning to ensure accurate measurements. Additionally, weirs may not be suitable for all flow measurement applications.
Do weirs slow down water? Weirs can slow down the flow of water as it passes over the crest, causing a temporary reduction in velocity. However, their primary purpose is not to slow down water but to measure or control its flow.
What is the most efficient weir design? Efficiency in weir design depends on the specific application and goals. There is no one-size-fits-all “most efficient” design, as efficiency can vary based on factors like flow rates, accuracy requirements, and hydraulic conditions.
What is the best weir shape? The best weir shape depends on the flow conditions and measurement accuracy requirements. Common weir shapes include rectangular, V-notch, and trapezoidal. The choice of shape should align with the specific needs of the application.
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