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Description

The CivilWeb pipe analysis spreadsheet includes a tool for calculating the flow and velocity at partial flows using Manning’s Equation. It also creates a graph so that the designer can ascertain many different values at a glance. Alternatively values for partially full pipe flow can be estimated from published charts such as the one below. Mar 29, 2011 The equations below are those used, together with the Manning equation and Q = VA, in the partially full pipe flow calculator (Excel spreadsheet) for flow depth more than pipe radius, as shown below. Θ = 2 arccos (r – h)/r A = πr 2 – K = πr 2 – r 2 (θ – sinθ)/2. P = 2πr – S = 2πr – rθ. Design Spreadsheet. Standard worksheet for design, construction, checkout of structures for water control. Table utilizing archived SCS Drainage Curve data for Maryland (based on EFH, Chapter 14: Drainage (archived)) Workbook used to compute grassed waterway dimensions based on permissible velocity criteria.

Gravity pipe flow of a partially filled pipe.

Hydraulic radius is calculated and all hydraulic properties of the pipe are calculated in a table.

Three charts are provided to highlight maximum and special conditions for hydsraulic radius (R), flow rate (Q) and velocity (V).

Manning's n, hydraulic radius, slope and velocity can also be calculated for existing conditions.

GRAVITY PIPE FLOW - PARTIALLY FILLED PIPE

BY MANNING'S EQUATION

References:

Gravity Flow in Pipes - The Manning Formula, William C. Dunn PE

Manning Equations, Robert Pitt & Shirley Clark

Validation:

Worked through book examples & hand calculations.

Some variables in manning's equations have interesting properties

shown in the table & Charts on the Calcs sheet, providing a method

of self validation. Place cursor on dots on the charts to get values.

Calcs Sheet:

Determine the hydraulic radius based on water depth in pipe.

Input is US or SI; use the units of your choice, the rest are

converted automatically.

Output is in US & SI units.

A Table based on percent of water depth points out some

interesting properties of hydraulic radius, flow rate and

velocity.

Charts show visually the properties of hydraulic radius,

flow rate, and velocity plotted against percent of water

depth in the pipe.

Find Depth of Flow -- Q, n, S, r Known. Enter n, S and r. Take a guess at d.

Keep incrementing or decrementing d until Q = known value. You have found

d.

n-Value Sheet:

Provides a Table of Manning's cofficient n.

Slopes Sheet:

Explains visually how slopes are determined.

n,R,S,V Sheet:

Helps to solve for n, R, S, V for existing conditions.

Provides calculations to determine pipe diameter with

known design requirements of Q, Vallowable, Smin, and n.

Calculation Reference
Gravity Pipe Flow
Piping Calculations
Manning's Equation

Calculation Preview

08 Sep 2017

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Mr. Tony, can you please re-load this 'Gravity flow calc' excel file in dropbox again. Thanks in advance.

Try downloading again. Everything worked when the calcs were accepted.
Here's a link to my Dropbox. I'll leave it there for a week.
https://www.dropbox.com/s/70pdp7huy5xdz0f/Gravity%20Pipe%20Flow%20-%20Mannings%20Eqn.xlsm?dl=0

Manning 27s Equation Excel Spreadsheet Example

The worksheet downloaded fine but it seems none of the equations are in the calc cells. Am I missing something?

A great debut calculation Tony I have awarded a free 6 month XLC Pro subscription by way of thanks.

Excel Free Download

Where to Find Partially Full Pipe Flow Calculator Spreadsheets

To obtain Excel spreadsheets for partially full pipe flow calculations, click here to visit our spreadsheet store for partially full pipe flow calculator spreadsheets. Read on for information about Excel spreadsheets that can be used as a partially full pipe flow calculator.

The Manning equation can be used for flow in a pipe that is partially full, because the flow will be due to gravity rather than pressure. the Manning equation [Q = (1.49/n)A(R^2/3)(S^1/2) for (U.S. units) or Q = (1.0/n)A(R^2/3)(S^1/2) for (S.I. units)] applies if the flow is uniform flow For background on the Manning equation and open channel flow and the conditions for uniform flow, see the article, “Manning Equation/Open Channel Flow Calculations with Excel Spreadsheets.”

Direct use of the Manning equation as a partially full pipe flow calculator, isn’t easy, however, because of the rather complicated set of equations for the area of flow and wetted perimeter for partially full pipe flow. There is no simple equation for hydraulic radius as a function of flow depth and pipe diameter. As a result graphs of Q/Q_full and V/V_full vs y/D, like the one shown at the left are commonly used for partially full pipe flow calculations. The parameters, Q and V in this graph are flow rate an velocity at a flow depth of y in a pipe of diameter D. Q_fulland V_full can be conveniently calculated using the Manning equation, because the hydraulic radius for a circular pipe flowing full is simply D/4.

With the use of Excel formulas in an Excel spreadsheet, however, the rather inconvenient equations for area and wetted perimeter in partially full pipe flow become much easier to work with. The calculations are complicated a bit by the need to consider the Manning roughness coefficient to be variable with depth of flow as discussed in the next section.

Is the Manning Roughness Coefficient Variable for Partially Full Pipe Flow Calculations?

Using the geometric/trigonometric equations discussed in the next couple of sections, it is relatively easy to calculate the cross-sectional area, wetted perimeter, and hydraulic radius for partially full pipe flow with any specified pipe diameter and depth of flow. If the pipe slope and Manning roughness coefficient are known, then it should be easy to calculate flow rate and velocity for the given depth of flow using the Manning Equation [Q = (1.49/n)A(R^2/3)(S^1/2)], right? No, wrong! As long ago as the middle of the twentieth century, it had been observed that measured flow rates in partially full pipe flow aren’t the same as those calculated as just described. In a 1946 journal article (ref #1 below), T. R. Camp presented a method for improving the agreement between measured and calculated values for partially full pipe flow. The method developed by Camp consisted of using a variation in Manning roughness coefficient with depth of flow as shown in the graph above.

Although this variation in Manning roughness due to depth of flow doesn’t make sense intuitively, it does work. It is well to keep in mind that the Manning equation is an empirical equation, derived by correlating experimental results, rather than being theoretically derived. The Manning equation was developed for flow in open channels with rectangular, trapezoidal, and similar cross-sections. It works very well for those applications using a constant value for the Manning roughness coefficient, n. Better agreement with experimental measurements is obtained for partially full pipe flow, however, by using the variation in Manning roughness coefficient developed by Camp and shown in the diagram above.

The graph developed by Camp and shown above appears in several publications of the American Society of Civil Engineers, the Water Pollution Control Federation, and the Water Environment Federation from 1969 through 1992, as well as in many environmental engineering textbooks (see reference list at the end of this article). You should beware, however that there are several online calculators and websites with equations for making partially full pipe flow calculations using the Manning equation with constant Manning roughness coefficient, n. The equations and Excel spreadsheets presented and discussed in this article use the variation in n that was developed by T.R. Camp.

Excel Spreadsheet/Partially Full Pipe Flow Calculator for Pipe Less than Half Full

The parameters used in partially full pipe flow calculations with the pipe less than half full are shown in the diagram at the right. K is the circular segment area; S is the circular segment arc length; h is the circular segment height; r is the radius of the pipe; and θ is the central angle.

The equations below are those used, together with the Manning equation and Q = VA, in the partially full pipe flow calculato

Manning%27s Equation Excel Spreadsheet