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# Weir coefficient SI units

### Broad-crested Weir Coefficients - xpswmm/xpstorm Resource

HW r = the upstream depth, measured from the roadway crest to the water surface upstream of the weir drawdown, in m or ft. C d is determined from Figure 2, and other English unit research must be corrected by a factor of 0.552 [C d (SI) = 0.552 (C d English)] Figure 2 - English Discharge Coefficients for Roadway Overtoppin SI Units (1a) where L is the length of the lip over which the water flows, H is the head above the weir, and is the weir coefficient, tabulated almost always in English units, which leads to the 0.55 coefficient fo the SI form of the weir equation (Eq. 1b) Typically lateral broad-crested weir coefficients should be around 2.0 (US Units) or 1.0 (SI Units) which is much lower than weir coefficients used for inline structures. This blog post will be a detailed guide on how to choose the appropriate lateral weir coefficient and weir equation for your hydraulic model 8 WEIR EXPERIMENTS, COEFFICIENTS, AND FORMULAS. Weir section refers to the cross section of the overflowing stream in the plane of the weir crest. Crest contraction refers to the diminished cross section of the overflowing stream resulting from the upward curvature of the lower water filaments in passing the crest edge

For example, an inline, hydraulically efficient broad-crested weir might have a weir coefficient around 3.0 (US units) or 1.7 (SI Units). Turn that structure sideways (a lateral structure), and it will have a coefficient closer to 2.0 (US Units) or 1.1 (SI Units) Weirs. Weir is defined as a barrier over which the water flows in an open channel. The edge or surface over which the water flows is called the crest. The overflowing sheet of water is the nappe. If the nappe discharges into the air, the weir has free discharge. If the discharge is partly under water, the weir is submerged or drowned ### The RAS Solution: Weir Equations in HEC-RA

1. A.1. WEIRS A weir is a barrier in an open channel, over which water flows. A weir with a sharp upstream corner or edge such that the water springs clear of the crest is a sharp crested weir. All other weirs are classified as weirs not sharp crested. Weirs are to be evaluated using the following equation: Q = CLH 3/2 where: Q = Discharge in cf
2. Variation of the discharge coefficient with scale of weir.. 8. Discharge coefficients for broad-crested weirs with vertical upstream face^.. 9. Discharge coefficients for broad-crested weirs with upstream-face slope of 1/2:1... 10. Discharge coefficients for broad-crested weirs with upstream-face slope of 1:1.
3. Q = discharge over weir in ft 3 /s . C e = effective discharge coefficient . h 1 = head on the weir in ft . h 1e = h 1 + k h = angle of V-notch. The head correction factor, k h, is a function of (figure 7-6a). However, for fully contracted traditional 90-degree V-notch weirs, equation 7-6 and the rating table discussed later produce comparable.
4. Depending on the exact shape of the dam top, typical values range from 1.45 - 1.84 in SI units (2.63 - 3.33 in US Customary units). 1.10 to 1.66 in System International units (2.0 to 3.0 US..
5. Rectangular Weir Equation. The Kindsvater-Carter rectangular weir equation (ISO, 1980): The sum b+K b is called effective width and the sum h+K h is called effective head. The value for g is 9.8066 m/s 2 and K h =0.001 m. C e is a function of b/B and h/P, and K b is a function of b/B
6. Rectangular Contracted Weir. This calculates the water flow rate over a rectangular contracted weir. This weir has a rectangular opening where the sides are straight up and down. A contracted weir means that the ditch or canal leading up to the weir is wider than the weir opening itself. The water before the weir should be held in a relatively calm and smooth pool

Flow through a rectangular weir can be expressed in imperial units with the Francis formula q = 3.33 (b - 0.2 h) h3/2 (1b For S.I units the fully contracted rectangular weir equation is: Q = 1.84 (L - 0.2H)H3/2, where Q is the water flow rate in m3/sec, and H is in m. This weir equation is subject to the same conditions given above The broad-crested weir: Formulas: C = (2/3) 3/2 (g) 1/2. Q = CLH 3/2. INPUT DATA: Select: Hydraulic head H: Weir length L: INTERMEDIATE CALCS: Units selected: Gravitational acceleration g: Discharge coefficient C: OUTPUT: Discharge Q: Your request was processed at 12:50:21 am on August 4th, 2021 [ 210804 00:50:21 ].. Parameter Symbol US units SI units -------------------------------------------------------- Discharge coefficient Cw & Cws 3.33 1.84 Weir length L 6 ft 2 m Side slope S 1 ft/ft 1 m/m Head difference h 1.5 ft 0.5

• Broad-Crested Weir . The overtopping discharge coefficient C d is a function of the submergence using the equation: . The variables K t and C r are defined in the following figures, reproduced from the manual FHWA, HDS No.5, Hydraulic Design of Highway Culverts, 1985. The first two figures are used by Subsurface Utilities to derive the base weir coefficient Cr resulting from deep and shallow.
• The discharge coefficient for Cipoletti weirs is 3.367 (in English units), and it does not depend on L or P like it does for a rectangular weir. Though the discharge coefficient formulation is simpler than for rectangular weirs, its accuracy is not as good - about ±5% (USBR, 1997)
• The Cippoletti weir is a trapezoidal weir, having 1 horizontal to 4 vertical side slopes, as shown in figure. The purpose of the slope, on the sides, is to obtain an increased discharge through the triangular portions of the weir, which, otherwise would have been decreased due to end contractions in the case of rectangular weirs
• For rectangular weirs with a breadth of 15 feet and a H of 1 foot or more, the given value is 2.63 (1.45 for metric units). Trapezoidal shaped weirs generally have a larger coefficient with typical values ranging from 2.7 to 3.08 (1.49 to 1.70 for metric units)
• Generic Weir. Any other type of weirs can be modeled as generic weir using the following equation. where Q = discharge over weir (m3/s, ft3/s) h = head above weir crest (m, ft) L = crest length (m, ft) C = weir coefficient. The weir coefficient value depends on the weir type, and is the function of the head above the weir crest
• Broad crested weir equation. Equations to calculate flow rates are different for different weirs. For broad crested weir, the equation used is: q = C d × b × h 2 × (2g (h 1 - h 2)) 1/2. In this equation: C d is discharge coefficient ; b is the breadth of the weir; h 1 and h 2 are first and second head drops ; g is the gravitational acceleratio
• Clark's unit hydrography compared to Ponce's version: Correlation coefficient of a joint probability distribution: Storage volume of a detention basin: Blaney-Criddle: Penman: Penman-Monteith reference crop: Thornthwaite: Priestley-Taylor: Penman-Monteith ecosystems: Gumbel: Gumbel 2: Log Pearson: Log Pearson 2: TR-55 graphical: curve numbe ### Lateral Structure Weir Coefficients in HEC-RAS - Engineer

Weir discharge is provided by the general formula: where : Q = flow rate, in m 3 ·s -1 (or L·s -1 ), μ = weir discharge coefficient, L s = weir crest width, in m, h = water sheet height, in m (or cm), g = gravity acceleration in m·s -2, (9.81 in Paris). Additionally, P is used for the «height of the weir crest above the upstream. is the discharge coefficient usually ranging from 3.24 to 3.62 [1.80] to [2.20] for SI units H (m) is the head over the weir (from the weir crest to the upstream water surface) P (m) is the height of the weirplate B (m) is the width of the channel g is the acceleration of gravity Q = C. D. B H. 3/2. C. Francis obtained the coefficient of discharge from the same general set of experiments as those stated for the contracted rectangular weir. No extensive tests have been made to determine the applicability of these equations to weirs less than 4 ft in length. Similar to the contracted rectangular weir, heads less than 0.2 ft do not give accurate. Units used in this International Standard are SI units. 5 PRINCIPLE The discharge over thin-plate weirs is a function of the head on the weir, the size and shape of the discharge area, and an experimentally determined coefficient which takes into account the head on the weir, the geometrical proper

The Francis formula for the standard suppressed rectangular weir neglecting velocity of approach in in USCS units Q = 3.33LH3/2. in SI units Q = 1.857LH3/2 (3) and that including velocity of approach is in USCS units Q' = 3.33L [ (H + h)3/2 - h3/2] in SI units Q' = 1.837L [ (H + h)3/2 - h3/2] (4) In these formulas, the letters have the same. In SI units: Where Q is the discharge over weir (m 3 /sec), C d is the Coefficient of discharge, θis the angle of notch (degrees) and H is the head above bottom of notch (m). Example7.4: Determine discharge of 90 o V-notch having 30 cm head of flow. Solution: Discharge through V-notch Q=0.013 Note: These formulas are for savealls and general pipe flow, since there is no orifice coefficient included. 4. Weir water flows . TIP 0502-17 Papermaker's formulas / 4 Rectangular weir with end contractions English Units SI Units 3/2 d 2g L H 3 2 Q =C × × × � SI Units (continued) Select a double 0.6 m by 0.9 m grate. P effective = (0.5) (2) (0.6) + (1.8) P effective = 2.4 m Step 2. Check depth of flow at curb using The weir coefficient for a curb-opening inlet is less than the usual weir coefficient for several reasons, the most obvious of which is that depth measurements from.

### Lateral Structure Coefficients - Kleinschmid

The Flow Rate for a Broad-crested Weir calculator computes the flow rate of water (or similar liquids) over a weir that is characterized as broad (flat and wider than deep). Instructions: Choose units and enter the following: (b) Width of the weir (h1) First Head on the weir (h2) Second Head on the weir (Cd) Discharge Coefficient ii ACKNOWLEDGEMENTS This manual was prepared by Lewis A. RossmanEnvironmental Scientist Emeritus, U.S. , Environmental Protection Agency, Office of Research and Development, National Ris But it is generally agreed that lateral structure weir coefficients should be much lower than a similar inline configuration. For example, an inline, hydraulically efficient broad-crested weir might have a weir coefficient around 3.0 (US units) or 1.7 (SI Units)

Weir Valves Problem: Find the rate of flow of water through a 1½ unlined cast iron flanged valve, half open, with a pressure drop of one psi. Solution: From the 'Flanged End - Unlined' Weir Cv Table, the corresponding rate of flow is 42 gpm. Problem: Find the valve position of 2½ 'Glass Lined valv An associated question regarding the coefficients and how they are applied within SWMM. For weirs the coefficients are different systems of measure are different when comparing the metric or SI (meters - second) units and the English (feet - seconds) units. In the English units a sharp crested weir has a coefficient of about 3.2 while in the.

With the flow coefficients capacities of valves at different sizes, types and manufacturers can be compared. The flow coefficients are in general determined experimentally and express the. flow capacity in imperial units - GPM (US gallons per minute) that a valve will pass for a pressure drop of 1 lb/in 2 (psi) The flow factor - Kv - is also commonly used with capacity in SI-units partially contracted V-notch weirs. The coefficients given in Figures 5.9 and 5.10 for a V-notch sharp-crested weir can be expected to have an accuracy of the order of 1 .O% and of 1 .O% to 2.0% respectively, provided that the notch is constructed and installed with reasonable care and skil The Manning formula is an empirical formula estimating the average velocity of a liquid flowing in a conduit that does not completely enclose the liquid, i.e., open channel flow.However, this equation is also used for calculation of flow variables in case of flow in partially full conduits, as they also possess a free surface like that of open channel flow

### Weirs - Civil Engineering Portal - Biggest Civil

• Where: b is the lateral width of the weir 4. Example: Given the following values: 2 sec m g 9.81 b 2 m P 2 m H 0.35m s 3 m Q H 0.7539 The default units are SI (e.g., meters, kg, Newtons) sec 3 ft Q H 26.6254 The default SI units can be converted to english units by typing the apostrophe (') and entering a new unit type
• The effective weir coefficient, Ce, is a function of H/P and P/B, as shown in Figure 4 below. The curves in Figure 4 were plotted using values read from a similar set of curves in the Water Measurement Manual (ref. # 1). Using Excel curve fitting of the curves shown in Figure 4 (plotted on an Exce
• Measurement units and standards are different in different countries but to maintain a standard, SI units are mostly used when dealing with projects involving different countries or even different states. Small projects can be done with the locally used unit system but when the project is big, one standard unit system is to be used. [
• The coefficient for the weir is thus 1.705 x Cd which frequently has a value of 1.6. Note: The weir can be used for flow measurement using a single measurement of level upstream provided that a standing wave exists downstream of the weir. The condition at which the standing wave ceases is called the modular limit and is not investigated in this.
• g.

### USBR Water Measurement Manual - Chapter 7 - WEIRS, Section

There should be air (not trapped) underneath the water leaving the weir. The Length is the bottom width of the weir. The height is measured from the bottom of the weir opening to the top of the water level ponded behind the weir (not the water level right as it leaves the weir). Learn more about the units used on this page Discharge coefficient. Displayed when Weir type is set to Transverse, V-notch, Trapezoidal or Roadway, and the Variable discharge coefficient box is unchecked. The coefficient for flow through the central part of the weir. Typical values are: 3.33 US (1.84 SI) for sharp crested rectangular weirs Simple Broad-crested Weir Flow Calculator. Can you help me improve translations, program, or host these calculators? [Hide this line] Set units: m mm ft in [Hide this line] Inputs Weir length, l: X: Headwater height, h: X: Weir coefficient, Cw? X: Results Flow, Q (See notes) Flow, Q (See notes) X: Printable version (reload/refresh to restore. Weirs may be used to control the discharge, decrease the water slope in canals and to distribute water between canals for irrigation, etc. The objective of this research was to investigate the influence of using one opening or more in weirs on discharge coefficient (C d), the hydraulic jump characteristics and velocity distribution downstream of these structures

Broad crested weir flow rate calculations can be made with a rather simple equation if the weir height is great enough to cause critical flow over the weir crest. For a broad crested weir with less than critical velocity over the weir crest, the discharge coefficient will vary from 2.3 to 3.3 depending upon the breadth of the weir crest and the. Calculate discharge of a broad crested weir using simple broad-crested weir calculator. Variations in Head Ratio and Coefficient of Discharge for Broad-Crested Weirs. Ratio of actual head. Coefficient of to design head discharge. 0.20

### Dam Tops - United States Arm

• Discharge coefficient for flow through the central portion of the weir (for flow in CFS when using US units or CMS when using SI units). Typical values are: 3.33 US (1.84 SI) for sharp crested transverse weirs, 2.5 - 3.3 US (1.38 - 1.83 SI) for broad crested rectangular weirs, 2.4 - 2.8 US (1.35 - 1.55 SI) for V-notch (triangular) weirs: Flap Gat
• Sometime there is a need to correct for a weir plate cut at an incorrect angle. While other times the flows of a particular site don't match up well with the flow characteristics of the standard sizes of V-notch weirs. Regardless of the reason, there is a need to be able to calculate discharge equations for intermediate V-notches
• Brunner (2014) notes that side weir coefficients should be lower than the typical values used for transverse weirs, and suggests a range of 1.5 to 2.6 for weirs that model levees or roadways along natural channels. 6.3.4 Submerged Weir Flow As shown in Figure 6-6, submerged weir flow occurs when the water level on the downstream side of the.
• 0301 Dimensions and Units 0342.3 Sharp-crested Weirs Figure 52. Entrance loss coefficients for typical pipe entrance shapes.
• The Hazen-Williams equation is an empirical relationship which relates the flow of water in a pipe with the physical properties of the pipe and the pressure drop caused by friction. It is used in the design of water pipe systems such as fire sprinkler systems, water supply networks, and irrigation systems. It is named after Allen Hazen and Gardner Stewart Williams
• You can access both resources from the Help menu. For online help, click Help menu Contents. For the AutoCAD Civil 3D Hydraflow Hydrographs Extension User's Guide, click Help menu User's Guide (PDF). You can also open the online help from the application. Press F1 or click the Help button in any dialog box. Support and Sample File Location

A side weir is a flow diversion device, which is widely used in irrigation as a head regulator of distributaries and escapes. This paper presents a concept for an elementary discharge coefficient. It is available in either U.S. units or S.I. units. Read on for background information about a broad crested weir calculations spreadsheet. Background for a Broad Crested Weir Calculations Spreadsheet. Figure 1, below shows a longitudinal section of a broad crested weir with free flow over the weir. Figure 1 The broad-crested weir: Formulas: C = (2/3) 3/2 (g) 1/2. Q = CLH 3/2. INPUT DATA: Select: Hydraulic head H: Weir length L: INTERMEDIATE CALCS: Units selected: Gravitational acceleration g: Discharge coefficient C: OUTPUT: Discharge Q: Your request was processed at 07:24:05 pm on July 31st, 2021 [ 210731 19:24:05 ].. K = a units conversion coefficient, in which K = 0.0078 for traditional units and K = 0.0195 for SI units Anchor: #GOFMHFKF L = the channel flow length, in feet or meters as dictated by

6-ii (210-VI-NEH, August 2007) Part 654 National Engineering Handbook Chapter 6 Stream Hydraulics Tables Table 6-1 Froude numbers for types of hydraulic jumps 6-30 Table 6-2 Project dimensions by type and stage of project 6-35 Table 6-3 Scope of hydraulic analyses by project type 6-35 Figures Figure 6-1 Channel cross-sectional parameters 6- HEC-RAS is an integrated system of software, designed for interactive use in a multi-tasking, multi-user network environment. The system is comprised of a graphical user interface (GUI), separate hydraulic analysis components, dat More weirs widespread and commonly used is the weirs sharp with a notch of rectangular and triangular, which is often where the coefficient of discharge cd starts from 0.55 for the rectangular notch and 0.59 for the triangular notch, but these transactions are affected by viscosity and surface tension, roughness of the plate and weir.In this. The rational method is used around the world for peak flow estimation of small rural drainage basins and is the most widely used method for urban drainage design. The rational method equation is given below: Q - Peak flow (cfs or m^3/s). k - Conversion factor equal to 1.008 (SI) or .00278 (metric). C - Dimensionless runoff coefficient 1 : a fence or enclosure set in a waterway for taking fish. 2 : a dam in a stream or river to raise the water level or divert its flow. Weir. What are the types of Weir? Types of Weirs: Types of Weirs based on Shape of the Opening. Rectangular weir. Triangular weir. Trapezoidal weir. Types of Weirs based on Shape of the Crest. Sharp-crested weir

After measurement of actual mass flow rate, the coefficient of discharge can be determined. Units for Flow Measurement SI Unit for volume flow rate (volume/time): Cubic meters per second (m 3 /s) Other common units for volume flow rate. Litre per minute LPM): 1L/s = 10 3 cm 3 /s; Cubic centimetre per minute: 10 3 cm 3 /s = 10-3 m 3 / 4.1 Classification of the weirs Weirs can be divided up into fixed weirs and moveable weirs. Moveable weirs are always used when as constant a water level of the upstre-am water as possible is required and also when a particular damming height must not be exceeded in the highest of high waters. In the case of rivers with a high bed load-carryin The orifice equation describes the rate of flow of liquid through an orifice. The equation can be represented as: where Q = flow (cubic metres per second) = coefficient of discharge A = area of orifice (square metres) g = acceleration from gravity (9.81 m/s^2) h = head acting on the centreline (m) For a circular orifice, the equation becomes:Typical values for the coefficient of discharge are. Discharge coefficients were obtained for free-flow and submerged-flow conditions for both the overflow weir and notch. Riprap stability tests in the notch indicated that type C riprap (D50 minimum = Non-SI units of measurement used in this report can be converted to SI (metric) units as follows

### Rectangular Weir Discharge Calculator and Equation

Bitter about what? This mobile unit is an omphalocele a concern? Undies that leave the idea clearly. Is i less than that? Delightful blonde public flashing pussy outdoor. (602) 678-0072 Musher working with assistive technology? Sue must dig through fresh snow. Wood and rubber. Not amazingly efficient. Single use insulin after the romantic dinner Contracted horizontal weir Discharge coefficient Length of water Water above weir (crest) Discharge coefficient Weir length Number of contractions for 2 ˘ˇ British Units (ft) SI Units (m) 3 Contractions from both sides For standard contracted horizontal weir V-Notched weir. in which q is discharge per unit width; g = gravitational acceleration, and (h — w) = the pressure head on the weir. The discharge coefficient Q depends on the relative weir height (h - w)/h, and the crest shape, provided the effects of surface tension are excluded, (h - w) > 0.03 m

Figure 4.1 Dimensions of round-nose broad-crested weir and its abutments (adapted from British Standards Institution 1969) For water of ordinary temperatures, the discharge coefficient (cd) is a function of the upstream sill-referenced energy head (HI), and the length of the weir crest in the direction of flow (L) k = 1.49 for U.S. customary units and 1.0 for SI units S = slope of the energy line = S o for uniform flow n = Manning's roughness coefficient. Manning's Equation Manning's n-value is viewed as a roughness coefficient, but it is actually - Weirs and Flumes (critical controls) - Long prismatic channel (control reach). It doesn't matter how thick the weir is except where water flows over the weir through the V. The weir should be between 0.03 and 0.08 inches (0.8 to 2 mm) thick in the V. If the bulk of the weir is thicker than 0.08 inch, the downstream edge of the V can be chamfered at an angle greater than 45o (60o is recommended) to achieve the desired.

Pirate Ninja is a unit to measure power. It is defined as 1 kilowatt hour per sol, i.e., a Martian day. More specifically, 1 Pirate Ninja is equal to 40.6 Watts. Andy Weir, the author of The Martian, used the unit in his book a number of times. Also, the Curiosity rover team at the Jet Propulsion Lab uses the term Pirate Ninjas during. The width (weir length) is the same, so the crest height drops. By analogy with pipe flow - if you have 100 gpm flowing at 1 ft/sec you need a 6.4 pipe, but if your flow velocity is 6 ft/sec you only need a 2.6 pipe. In weir flow the numbers are not this extreme, but I think the principle holds. Katmar Software Engineering & Risk Analysis. Where C = weir coefficient (see table) L = weir length Detention Pond Size Estimation: Example for single design storm • The rectangular weir equation is: • Q o =3.2L w H w 1.5 Where q o = peak outflow discharge (cfs) L w = weir crest length (ft) H w = head over weir crest (ft) •H w and q o are computed as follows: H w = E max - weir. SIDE-WEIR ANALYSIS USING ELEMENTARY DISCHARGE COEFFICIENT By Prabhata K. Swamee, t Santosh K. Pathak, 2 and Masoud S. AlP ABSTRACT; A side weir is a flow diversion device, which is widely used in.

operate hydraulically like weirs at heads below 80 mm. Belled-ends on the outlets increases their capacity 75% at low heads. Border cablegation design equations, graphs and procedures are described. INTRODUCTION Cablegation is a semi-automated system for applying surface irrigation water (Kemper et al., 1981; Kemper et al., 1985; and Kemper et. To study the flow characteristics over a hump/weir. 4. K is a conversion factor which is 1 in SI units. n is the Manning coefficient (also called as resistance to flow). R is the hydraulic radius [L] S is the slope of the water surface or the linear hydraulic head loss. 2 1 3 2 aprons, broken-back culverts, outlet weir, and outlet drop followed by a weir. This edition is in both U.S. customary and System International (SI) units. A previous SI unit version of HEC 14 was published in 2000 as a part of the FHWA Hydraulics Library on CDROM, FHWA-IF-00-022

Weirs Computes hydraulic properties for six different weir types, including rectangular, v-notch, trapezoidal, circular, compound, and proportional. Automatically computes weir coefficients with user override. Computes by Known Q, Known Depth, or Q vs. Depth rating curves. Common user interfac Note: the weir coefficient should be specified differently in metric and US units (i.e. the coefficient is not dimensionless, due to the √g term implicit in the formulation). Equations Note that the unit modes for flow through a piping breach mirror those for the orifice unit, with ten added, i.e. Mode 12 for a piping breach is equivalent to. 82 Hwi = headwater depth upstream of a culvert relative to the culvert invert (or streambed for a buried-invert culvert) at the inlet [L] k = equivalent roughness height [L] ke = entrance loss coefficient ko = exit loss coefficient ks = pipe wall roughness height [L] K = coefficient for unsubmerged inlet control equations Kn = 1 for SI units. Navigation Weir jetties This report presents methodology for designing weir sand-bypassing systems. Jetties are generally shore-normal structures built at tidal inlets to fix the location of the inlet and associated navigation channel. In a weir-jetty system one or both jetties is constructed with a low weir section 50 , FOR

The coefficient f is the fluid friction factor and its value may be taken as 0.005 and 0.01 for clear and encrusted iron pipes respectively. For earthenware pipes, f may be taken as 0.0075. All other variables are in SI units, that is, meters and seconds. It is a common practice to place the pipe at the bed of the distributing channel t 19 Hazen-Williams 1920s Water flows with high Reynolds Number. Occasionally used - fire, irrigation & water distribution systems. Only for water within normal ambien The broad crested weir calculations spreadsheet being described here can calculate the flow rate over the weir for user specified values of the depth of flow upstream of the weir, y1, the length of the weir crest, L, (typically equal to the width of channel in which the broad crested weir is placed), and the value to be used for the weir. empirical coefficients and there is a need to obtain new accurate physical data to complement the existing evidence. In the present study, the discharge calibration of a large 90º V-notch thin plate weir was performed using an unsteady volume per time technique. The V-notch weir was initially closed by a fast-opening gate 1.49 is a units conversion factor. This coefficient is not needed (or is set equal to 1) for metric units. n is the Manning's roughness factor. This is a unitless value that represents the roughness factor of the conduit. More on the Manning n value below. A is the cross sectional area of the flow expressed in square feet. As noted above, the. Figure shows two common weirs, sharp-crested and broad-crested, assumed. In both cases the flow upstream is subcritical, accelerates to critical near the top of the weir, and spills over into a supercritical nappe. For both weirs the discharge q per unit width is proportional to g1/2H3/2 but with somewhat different coefficients Cd. 18