The purpose of the Quick-2 Mailing List is to provide up-to-date information about Quick-2 software, tutorials, and other related topics pertinent to the Federal Emergency Management Agency (FEMA) and the National Flood Insurance Program (NFIP).

This month we will examine the channel capacity of a circular channel. For this analysis we will determine the channel capacity of three different types of concrete channels. They will include a concrete culvert that is straight and free of debris, a concrete culvert with bends and some debris, and a storm sewer. We will then look at the rating curve to determine the maximum discharge of the channel and at what depth this occurs.

In doing this, we will use Quick-2 to do the following:

  • Determine the discharge using the circular channel capacity method
  • View rating curves to determine maximum flow of each pipe
  • View the detailed input/output data

Concrete Culvert, Straight and Free of Debris

Manning's n-value .011
Channel Slope .0044 ft/ft
Diameter 36 in
Depth 3 ft

Concrete Culvert, with Bends and Some Debris

Manning's n-vlaue .013
Channel Slope .0039 ft/ft
Diameter 36 in
Depth 3 ft

Concrete Storm Sewer

Manning's n-value .015
Channel Slope .0053 ft/ft
Diameter 72 in
Depth 6 ft

To Determine the Channel Capacity Using Quick-2 Circular Channel Capacity:

  1. Create a new file and save it as a Quick-2 file type (.qk2)
  2. Click 'Method' and select 'Channel Capacity' and then 'Circular'
    [Hit 'Enter' after each step below]
  3. Enter '1' for the cross-section number
  4. Enter the manning's n-value from the data above
  5. Enter the Slope from the data above
  6. Enter the Diameter from the data above
  7. Enter the Depth from the data above

When all the data is entered, the 'Compute' button will have a box around the word 'compute.' To compute the Discharge, either click on 'Compute' or hit enter.

The results are displayed on the right side of the screen in the 'Output' section. The computed Discharge for cross section 1 is 52.3 (cfs).

Next click on 'New X-Sec' and enter '2' for the next calculation. Go through steps 4, 5, 6, and 7 entering the data for the concrete culvert with bends and some debris. When data is entered hit the 'Compute' button for the 'Discharge'. The calculated discharge for cross section 2 is 41.7 cfs.

Follow the same steps to enter the data for the Storm Sewer and call it cross section 3. The calculated discharge is 267.2 cfs.

The rating curve data can be viewed by clicking on 'View' and 'Rating Curve Data'. This screen will contain data for all three of the cross sections. To print a copy of the data go to 'File' and 'Print'. To complete this exercise we will be using the rating curve data. When we look at the rating curve data we will see three columns for each cross section. The first column labeled CWSEL is the computed water surface elevation for the cross section. The second column labeled Q(CFS) is the total discharge for the cross section. And the third labeled Area (Sq Ft) is the total area within the cross section below the water surface elevation. Note if you have any questions as to any variables in the program you can go to the toolbar and click on 'Help', 'Contents' then 'Overview of Quick 2' and 'Definition of Variables'. Beginning with cross section 1 we can see from the rating curve data that the maximum flow of 56 cfs occurs between a depth of 2.7 and 2.85 feet. Looking at cross section 2 the maximum discharge is 45 cfs and occurs at a depth of 2.85 feet. Cross section 3 reaches a maximum discharge of 287 cfs at a depth of 5.7 feet. We can see that regardless of the type of culvert maximum discharge occurs at about 95% full flow.

Next we will take a look at the Rating Curve and Cross Section Plot for cross section 1. Go to 'View' and 'X Sect Plot' to view the cross section. At the bottom of the graph click on 'Curve Now !' and the rating curve will be plotted on the same graph. As we look at the graph we can see that the rating curve tails back in and to the left. This is because the maximum flow in the pipe actually occurs at approximately 95% full flow. As the pipe flows above 95% the increase in friction loss will reduce the amount of discharge. We can print a copy of the graph for each cross section. Simply click on the 'Print' button at the bottom of the screen.

Last we can also view a detailed copy of the input/output data to have for our file. Go to the tool bar at the top of the screen and click on 'View' and 'Detailed Input/Output'. This is a print out of all the cross sections and the data used. This is a simple way to view all the data from our exercise. To print a copy go to 'File' and 'Print'.

View the archive page for all Flood Hazard Mapping listservs.

Last Modified: Monday, 25-Jun-2007 11:57:20 EDT