#SEWER NETWORK DESIGN SOFTWARE HOW TO#
#SEWER NETWORK DESIGN SOFTWARE PLUS#

This linear regression makes use of the fact that the relationship between i and Оґ is typically of the form i = a/(Оґ + b), where a and b are constants. The portion of the Excel template shown at the right is a linear regression of storm duration, Оґ, vs the inverse of storm intensity, 1/i, using I-D-F data for the location of interest, to get an equation for storm intensity as a function of storm duration.

#SEWER NETWORK DESIGN SOFTWARE PLUS#

Sections of sewer pipe, the time of concentration is the inlet time to the first inlet plus pipe flow time to the inlet of the pipe section being designed, as given in column 7.Д¬olumn 8 is the calculated design rainfall intensity. For the first section of sewer pipe, the inlet time is the time of concentration. Column 3 is the inlet time from the farthest point in the drainage area. Column 3 is an estimate of the runoff coefficient. In this example, the manhole at 8th Street and Maple Avenue is assumed to be the uppermost part of this sewer line. Column 4 is the cumulative area draining to the downstream sections of sewer pipe. The column numbers given in the spreadsheet will be used to discuss the various parts of the spreadsheet calculations.Д¬olumns 1, 2, and 3 contain information from a map that is drawn to scale, like the one in the previous section and used for this example. The Excel spreadsheet template shown at the left contains the design calculations for a storm sewer line along Maple Avenue, from 8th Street to 4th Street, based on the manhole layout map shown in the previous section. Use of Excel Formulas in a Spreadsheet Template to Put it all Together This calculation is illustrated using Excel formulas in the Excel spreadsheet template presented in the next section, on page 2 of this article. The required minimum cover, the required pipe slope, and the ground surface elevations from a map like that shown at the left, are used to calculate the pipe invert elevations at each manhole. This will typically by specified by a state or local design code.

The design criterion that helps to determine the pipe invert depth (or elevation) at each manhole is a minimum required depth of cover above the sewer pipe for protection from freezing. Determining Pipe Invert Depths at Manholes

#SEWER NETWORK DESIGN SOFTWARE HOW TO#

to calculate the pipe diameter and slope is discussed and illustrated with an example in the article, вЂњ How to Use the Manning Equation for Storm Sewer Calculations.вЂќ The procedure is also illustrated in the spreadsheet template presented on page 2 of this article. The use of these design criteria and the Manning equation

The flow velocity in the sewer pipe must be greater than or equal to the design Vmin (usually 3 ft/s).

The pipe must be able to carry the design stormwater runoff rate.

The criteria used to calculate the design diameter and slope for a section of sewer pipe are as follows: Determination of design storm intensity is discussed in the article, вЂњ Calculating Design Rainfall Intensity for Use in the Rational Method.вЂќ The Manning Equation for Calculation of Pipe Diameter and Slope More details about the rational method and its use are given in the article, вЂњ The Rational Method for Calculation of Peak Storm Water Runoff Rate.вЂќ The most complicated part of rational method calculations is determination of the design rainfall intensity, which depends upon the design return period, the design storm duration, and the intensity-duration-frequency (IDF) relationship for the location of the storm sewer design. The design stormwater runoff rate to use for any stormwater drainage system design is typically calculated with the rational method equation, Q = CiA, where Q is the design stormwater runoff rate, C is the runoff coefficient (an estimate of the fraction of rainfall that becomes surface runoff), i is the design rainfall intensity, and A is the runoff area that drains to the section of sewer pipe being designed. The Rational Method for Calculation of Design Flow Rate An overview of typical design criteria and the overall hydraulic design procedure is available in the article, вЂњ Drain Storm Water with Good Storm Sewer Hydraulic Design.вЂќ Each of the steps is discussed briefly in the next several sections of this article and the spreadsheet template with the Excel formulas is then presented and discussed on page 2.

Finally, the pipe invert elevation at each manhole needs to be determined. The next step is calculation of the pipe diameter and slope for that section of storm sewer, using the Manning Equation. The first step in this stormwater drainage system design is using the rational method to determine the design stormwater runoff flow rate for a given section of storm sewer. The Excel template that can be downloaded from this article is useful for making the hydraulic portion of storm sewer design calculations between any pair of manholes.

Sewer network design software