In storm sewer systems, inlets are the surface components that gather the ground runoff and convey the flow to a subsurface storm sewer network. The inlet capacities should be sufficient to intercept the flows that the sewer system can handle. Inlets can be located "on-grade" or in sag locations. Inlets located "on-grade" may be designed to intercept either all or part of the runoff in the gutter whereas inlets that are installed in sag points should be sized to capture the entire runoff approaching them. The longitudinal and cross-slope of the roadway along with the Manning's "n" value of the gutter influence the performance of the inlet. These parameters can be obtained automatically in the watershed modeling of the sewer network design. The details of the inlet design procedures can be found in the HEC-22 Manual.
The Inlet Library command allows you to make, edit and store
inlets. The working Inlet library data file is stored (by default)
in the %AppData%\Carlson
Software\...\User\Inlet.dta file and is available across
all Carlson Software projects.
The Custom Properties function defines additional fields for each inlet. Values for these fields can be entered into the Inlet Library. Then these fields are available in the Report Sewer Network command.
When you create or edit an inlet, the New/Edit Inlet dialog box displays (shown below).
Inlet ID: Indicate the name of the inlet.
Inlet Type: Indicate the type of inlet:
Profile: Indicate whether the inlet is located in a sag portion of a vertical curve or "on grade."
Gutter Parameters: A gutter is a section of pavement adjacent to the roadway, which conveys flow during a storm runoff event. Gutters can have uniform and composite sections. A uniform gutter has the same cross-slope value as the cross-slope of the roadway adjacent to the gutter. A composite gutter section is depressed in relation to the adjacent pavement cross-slope. Therefore, the Gutter Depression should be entered when using a Composite gutter. The Local Depression is the depression for curb inlets that are off the gutter section.
Design Inlet Length: When enabled, the inlet length is calculated based on Design Constraints of the maximum allowable ponding width (spread) on the roadway and the interception efficiency. When disabled, the spread and efficiency are computed. When the inlet is at a sag location, the interception efficiency is always 100%.
Symbol Name: Click on Symbol button to select a symbol for displaying the inlet in the plan view on the screen.
When either the Grate or Combo inlet type is specified, the controls on the Grate Inlet tab are enabled allowing you to create or edit the Grate details. Grate inlets perform well on grades where clogging with debris is not a problem. Their capacity decreases as the pavement longitudinal slope increases. Grate inlets are not generally recommended for use in sag locations because of their tendency to clog. There are seven types of standardized grates:
P-1-7/8 (P-50), P-1-1/8 (P-30), 45d Tilt Bar, Reticuline, P-1-7/8-4 (P-50x100), Curved Vane, 30d Tilt Bar
Please refer to HEC-22 for additional details. You can also define your own type of grate by selecting Other in the Grate Type list. If you use a non-standard grate on grade, you must specify a splash-over velocity. Enter the grate dimensions in the Grate Length and Grate Width boxes. When a grate inlet is used, its width can't exceed the Gutter Width.
If the grate inlet is in a sag location, sag-related parameters need to be specified. A grate inlet in a sag operates as a weir at small ponding depths and like an orifice at large depths and these are dependent on the size of the grate. The Clogging Ratio is the percent area of the inlet covered by debris whereas the Opening Ratio is the ratio of the open area to the total area, which can be obtained from HEC-22. You need to specify the Opening Ratio if you use a non-standard grate.
When either the Curb or Combo inlet type is specified, the controls on the Curb Inlet tab are enabled allowing you to create or edit the curb inlet. Curb inlets are less inclined to clog than are grate inlets and have little interference on traffic operation. When placed "on grade," their interception capacity decreases more significantly than that of Grate Inlets as the pavement longitudinal slope increases. As such, Curb Inlets are suitable for use in sag locations or on relatively flat roadways.
When the Curb Inlet is located in a sag, you need to specify the Throat Type:
Please refer to HEC-22 for details on throat types. Additional parameters including the Opening Height, Weir and Orifice Coefficients must also be specified. A curb inlet in a sag behaves as a weir when the depth of water ponding at the curb is less than or equal to the height of the curb opening and like an orifice when ponding depth is greater than 1.4 times the height.
When a Slotted inlet type is specified, the controls on the Slotted Inlet tab are enabled allowing you create or edit a Slotted inlet. Slotted inlets are very effective in intercepting sheet flows due to their long lengths and are suitable to place on roadways. They are very sensitive to clogging and therefore not recommended for use in sags and other locations where debris loadings are considerable. When the slot width is at least 1.75 inches (45 mm) and placed on the pavement along the length of the gutter, the slotted inlet operates similarly to a Curb Inlet.
When installed in a sag, Slotted Inlets perform as weirs to depths up to 0.2 ft (0.06m) and like orifices when the depth is greater than 0.4 ft (0.12m). Refer to HEC-22 for more information.
When the Combo inlet type is specified, the controls on the Grate Inlet tab and Curb Inlet tab are enabled and offer the advantages of both inlet types. The grate is usually the same length as the curb opening and placed alongside it; also called an Equal Length inlet. When the curb opening is longer than the grate, it effectively intercepts trash and debris which may clog the grate and is otherwise known as a Sweeper Inlet.
When a Ditch inlet type is specified, the controls on the Ditch Inlet tab are enabled allowing you create or edit a Ditch inlet. Ditch inlets are typically placed only in sag locations making their capture efficiency 100%. Care should be taken when utilizing Ditch inlets such that the opening does not create a dangerous traffic hazard. In addition to specifying the Bottom Width of the Ditch Inlet, also specify the Left and Right Side ratios as an H:1 ratio.
The Calculation tab allows you to determine how the active inlet will perform against the following parameters:
Flow to Inlet: Specify an assumed amount of flow that will be traveling to the inlet.
Longitudinal Slope: Specify the slope that leads into the inlet.
Pavement Cross Slope: Specify the slope of the pavement that abuts the inlet.
Manning's n: Indicate the Manning's n value for the pavement that abuts the inlet or click the Library to retrieve the Manning's n value from the Pavement Manning's n Library.
Intercepted Flow: The amount of flow that is intercepted by the inlet is reported.
Bypass Flow: The amount of flow (if any) that by-passes the inlet is reported.
Gutter Spread: The gutter spread (distance from the curb to the outermost edge of the flow of water) is reported.
Water Depth: The water depth in the gutter is reported.
The working Pavement Manning's n library data file is stored (by default) in the %AppData%\Carlson Software\...\User\Paven.dta file and is available across all Carlson Software projects. Selecting a desired pavement value and clicking the OK button returns the selected Manning's n value back to the Calculation tab.
Clicking the New or Edit button allows a new pavement type and it's corresponding Manning's n value to be specified.
Type of Pavement: Indicate the desired type of pavement.
Manning's n Value: Indicate the Manning's n value associated with the pavement type.
Pulldown Menu Location(s):
Network > Sewer Network
Libraries
Keyboard Command: inletlib
Prerequisite: None