Volume 3 No.4, Spring 2000

ISSN# 1523-9926


Software Tool
Open Channel Flow Calculations

Ratan Kumar
Dept. of Engineering Technology
University of North Texas
Denton, TX 76203


This paper discusses a software tool that performs analysis for Open Channel Flow. The tool tries to automate a typical discussion on this subject that is normally presented in several undergraduate Fluid Mechanics textbooks. The software does not try to duplicate the pedagogical contents of the textbook but tries to automate the equations and other pertinent numerical needs. The subject is relevant to both the Mechanical/Manufacturing and Civil Engineering technology students. An attempt has been made to present the varied computational activities in an integrated manner.



The topic of Open Channel Flow occupies an important section in undergraduate Fluid Mechanics Course. There are several textbooks1, 2 that do a wonderful job in explaining this subject that is taught to Mechanical, Civil and Manufacturing Engineering technology students. To supplement the theory there are some software that automate the equations that are presented during the discussion. However  most of the software, try to focus on the flow of fluid in the pipe during fluid flow analysis. There are some specialised software for performing open-channel flow analysis but its scope is limited to certain industrial sections and cannot be used for academic purpose. To cater to the educational need some modules have been developed in commercially available mathematical3, 4 and spreadsheet5 packages. However there are certain constraints associated with these modules like: a) the user needs to have access to the software that loads these modules, b) the user needs to be familiar with the software’s environment, c) the user has to refer to textbooks/manuals for entering data from tables and charts.

Keeping the above limitations in mind the author has designed and developed a software that can be quite useful for the students. The software can be thought of as a calculator or a toolbox for open-channel flow calculations. The user interface has been so designed that there is very little to no learning time involved. The theme of this software is very different from other educational software available in this area: it has been designed as a quick solver. The software acts like a black box and shields the user from selecting the equations. Also no programming is required to tie up the equations to values obtained from tables and chart. As a result the software works like a calculator and comes in handy when the students wants to check his/her calculation or arrive at a result quickly.



As has been discussed ahead the software is designed like a specialized calculator for open-channel flow. To help in this activity, the following features are embedded in the program to aid the end user:

a)     items are grouped together in a logical and numbered manner. For example if the task is to find the channel section property, the user performs the activity by following the numerically arranged steps. First a channel section is selected from a drop-down list box. Next values are provided to the known parameters associated with the channel. The user also selects the type of units and automatically the standard units are displayed. An image box is present to clarify the terms associated with the selected section. Finally by clicking the solve button, results are obtained for the section area, hydraulic diameter and hydraulic depth. To summarize, the user starts from item number one and goes down executing the next items one by one till the final result is obtained. Figure 1 gives a typical layout for performing an activity. 

 Figure 1. Screen for uniform-flow calculation

b)     the user input box has been specially designed to accommodate not only a single numerical data but mathematical expression as well. This means that one can either enter a number like “1” or enter a mathematical expression like “cos (0), 10^0, (4^2-tan(45°)-13) etc.” each of which is read in by the text box as having the value unity. The ability to enter expression becomes useful in a variety of way: a) the user does not need a calculator to convert an expression into a single value and then input it into the text box, b) the input boxes can recognize several special mathematical functions that comes in handy for technical computation. For example, while calculating the volumetric flow rate for uniform flow as seen in Figure 1, the value for known term hydraulic diameter is entered as the product of two quantities. The input box can also directly handle special mathematical term like “pi”.


Figure 2. User interface for Channel Section calculations

c)     Several of the terms have tooltip help for term explanation. This comes in useful when the definition of the term is needed quickly. Figure 2 shows the tooltip help associated with the term hydraulic diameter. Also as has been discussed ahead, a picture is provided to elucidate any further explanation.



The software is designed to keep the major topics of interest as clickable buttons and which in turn is arranged vertically on the left-hand side. The topics are:

·        Introduction to Open Channel Flow

·        Channel Section Property

·        Uniform Flow

·        Critical Flow

·        Varied Flow

·        Hydraulic Jump

·        Weirs

·        Roughness Coefficient

It will not be possible to discuss all the topics and their functionalities, but the salient features for some of them are discussed below.

Channel Section Property: In this section, the user can perform analysis to find out the area, hydraulic diameter and hydraulic depth for the open channel section. The selection combo box (item 1) contains eleven different sections (rectangle, trapezoid, triangle, circle, parabola, trough with round bottom, round-cornered rectangle, rounded-bottom triangle, asymmetric triangle, quadrilateral with one vertical side and rectangle of great width) that can be handled. The parameters associated with each appear automatically in section 3, once the selection for the channel is made.

Uniform Flow: This section does not limit itself to the calculation of flow velocity or the volume flow. It handles all parameters that are involved during the analysis of open channel flow for flow that is uniform in nature. The parameters that are involved in the analysis are: flow velocity, volumetric flow, fluid depth, the bed slope, hydraulic diameter, manning coefficient and the friction factor. Once the unknown term is selected on the left side (in section 1), section 3 gets populated with other terms whose values are needed for calculation. The type of unit is selected next and by clicking the solve button the unknown parameter is immediately calculated. As has been discussed ahead, numerical expressions can be entered into the text boxes for quick calculation.

Weirs: Weirs are built across an open channel to raise the fluid level or to measure it. They are perhaps the oldest and still the most useful of the hydraulic structures. The section on weirs handles eight different kinds: Sharp-crested weir in rectangular channel, rectangular-notch thin-plate weir, triangular-notch thin plate weir, proportional sutro- notch thin plate weir, long-base rectangular weir, long-based round nosed weir, semicircular weir and hydrofoil shaped weir. Once the type of weir is selected, and the proper values are entered for the calculation, the discharge of the fluid through the weir gets computed. An image box displays the selected weir and explains the different terms involved during calculation.



This paper describes a software that addresses the pedagogical issues associated with open channel flow calculations. It is to be noted that there are mathematical software that provide a limited add-on capability for performing similar type exercises. The discussed software, on the other hand, is a standalone and customized application that just handles open-channel flow analysis. It cogently glues together a multitude of analytical and textual issues associated with a open-channel in a user-friendly windows environment. The software is designed to serve as a toolbox for calculation purpose. The topics in the software are judiciously segmented to include the most common subjects that are covered in the open-channel flow chapter of fluid mechanics textbooks. The software serves as a supplementary tool to these textual contents and is able to provide information on the fly and at the same time help in the computation of several associated mathematical problems. To accomplish a quick and efficient numerical solution, special text boxes are provided. The text boxes have a special feature in that they can accept not only a unique numerical value but a mathematical expression as well. Throughout the software there is help available via tooltip, term definition and pertinent images. Tables that are normally found in textbooks are provided with automated features as seen in Figure 3.


Figure 3. Screen showing the roughness coefficient values


1. R.L.Mott, "Applied Fluid Mechanics", 4th edition, Prentice Hall, NJ
2. Simon L.A.,"Hydraulics", 4th edition, Prentice Hall, NJ.
3.  TK Solver, Universal Technical Systems, Inc., Rockford, IL.
4. MathCad, MathSoft Inc., Cambridge, MA.
5.  Microsoft Excel, Microsoft Corporation, WA.

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