Some field instruments provide FlowWorks with flow in addition to depth and velocity. However, some instruments are unable to calculate flow on their own. In such a case, you can use FACE to create a Channel that compiles virtual flow values based on depth and velocity data.
The process for compiling flow data using Circle is twofold:

Start by creating a Calculated Channel. Once complete, you will need to proceed to step 2 (which is discussed in this topic). The image below shows Channel setup for this example. Notice how we set this Channel to be expressed in Million Gallons per Day (MGD):
 Configure a FACE formula calculation using Circle, that references both depth and velocity Channels, applies the Circle formula, and compiles the resulting virtual flow data in this Calculated Channel (read below).
Important: These instructions are a continuation from the topic, "Creating a Calculated Channel". From step one, it is assumed that you are back at the Configure Sites Page, after having completed setup of a new Calculated Channel.
To configure FACE with the Circle calculation:
 Starting from the Configure Sites page, locate the "Flow_MGD" Calculated Channel you just created. First find the Site that the Channel resides in, then choose the Channel.
 Click . This will direct you to the respective page, where summarizing information on the Calculated Channel is displayed.
 Click . This will take you to the page where you will configure the calculation. This page has three distinct sections  the following steps take you through each part, beginning from the top of the page.
 Provide a Calculation Name and Description (both are optional).
 For Calculation Type, select Formula. The bottom of the page will update with dropdown lists to allow you to define the source channel and interval length.
 Ignore Start Date and End Date. We want this Channel to calculate Flow for all past, present, and future data.
 Choose the Source Components. In this example, we need to select two. For Source Component 1, begin by locating the Site that the depth Channel resides in; then choose the Channel. Next, click to add a new line for Source Component 2. Locate the Site that the velocity Channel resides in; then choose the Channel.
 Redefine the Variable Names. By default, the process has assigned "A" to the depth measurement, and "B" to velocity. You could proceed to use these variable names, however it is good practice to use something that is more likely to make sense later in time. Thus, in this example, we will assign depth with variable "D"; and velocity with variable "V".

Define the formula in the Define Equation box, using the variable names assigned to your source components.
We are going to use the Circle function which when given the diameter of a pipe and the depth of the material in that pipe, will return the area crosssection of the pipe occupied by the material. The syntax of this function is: Circle(Depth, Diameter)
So if we take this value and multiply it by the velocity, we get flow.
If we go back to just a plot of the Depth and the Velocity from our Site, we see that our measurements for Depth are in inches and the Velocity we are measuring is in feet/second:
The conversions needed will be to move the result of the Circle function (which makes no conversions – feed it inches and you get squareinches, feed it feet and you get squarefeet) from squareinches to squarefeet: 0.006944 squarefeet per squareinch.
And to move cubicfeet per second into gallons per day: 0.646316889697 (cubicfeet/per second) * (seconds / day) (milliongallons / cubicfeet).
When we take the result from the Circle function, multiply that by the velocity and then by our two conversion factors, we get: Circle(Depth, Pipe diameter) * Velocity * 0.006944 *0.646316889697 or Circle(Depth, Pipe diameter) * Velocity * 0.004488 = MGD
Thus, in the Define Equation box we will type: Circle(D,17.5)*V*0.004488
Important: The author of this topic is not trained in any way that should be taken as an expert in hydrodynamics. Thus you should use your own constants or prove to yourself that the conversions represented here are valid and more than just looking good.
 Optionally, you can add this Calculated Channel to other Sites under Advanced Options. For this example, we will omit this.
 Click . You will be directed back to the View Calculated Channels page, where the new calculation will appear in a list:
You can use the calculated Flow channel in any of FlowWorks' tools. If we were to graph this new Channel alongside its two source Channels, the resulting graph will look something like this:
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