In storm sewer systems, inlets are the surface components that gather the ground runoff and convey it in the subsurface pipe network. The inlet capacities should be sufficient to intercept the flows that the sewer system can handle. In Carlson Hydrology Module, There are four types of inlets: Grate, Curb, Slotted and Combo. Inlets can be located on grade or in Sag locations. Inlets installed in sag points should be sized to capture the entire runoff approaching them. Inlets on grades may be designed to intercept either all or part of the runoff in the gutter. The longitudinal and cross slopes of the roadway, and the manning's n of the gutter influence the performance of an 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 library data file is stored in the ...\USER folder and is available for all projects.
From the Network > Sewer Network Libraries menu in the Hydrology Module, select Inlet Library to open the Inlet Library dialog. The dialog reads the library file and lists all inlets by their ID, type and profile. New button adds a new inlet, Edit button allows you to modify an existing inlet, and Delete button removes the highlighted inlet from the library. Load and SaveAs buttons allow you to load and save the inlet data.
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| Inlet Library Dialog |
When you create or edit an inlet, the New / Edit Inlet Dialog displays. On the General tab, you define the gutter and the inlet type and profile. In the Inlet ID box, type the inlet's ID. Choose the inlet type and profile.
A gutter is a section of pavement adjacent to the roadway, which conveys flow during a storm runoff event. When a grate inlet is used, its width can't exceed Gutter Width. 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 are depressed in relation to the adjacent pavement cross-slope. Therefore, the Local Depression should be entered when using a composite gutter.
You can either design or analyze the inlets. When the Design Inlet Length toggle is on, the inlet length is to be calculated based on the maximum allowable ponding width (spread) on the roadway and the interception efficiency. When the toggle is off, the spread and efficiency are to be computed. When the inlet is in a sag, the interception efficiency is always 100%.
Click on Symbol button to select a symbol for displaying the inlet in the plan view on the screen.
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| New / Edit Inlet |
The Grate Inlet tab allows you to create or edit a grate inlet. Grate inlets perform well on grade 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 easily clogging.
There are seven types of standardized grates, P-1-7/8 (P-50), P-1-7/8-4 (P-50x100), P-1-1/8 (P-30), Curved Vane, 45-deg Tilt Bar, 30-deg Tilt Bar and Reticuline. Please refer to HEC-22 for the details. You can also define your own type of grate by selecting Other in the Grate Type list. If you use a non-standard type of grate on grade, you must specify a splash-over velocity. Enter the grate dimensions in the Grate Length and Grate Width boxes. The grate width should not be greater than the gutter width.
If the grate inlet is in a sag, you need to enter the sag related parameters. A grate inlet in a sag operates as a weir at small ponding depths and like an orifice at large depths, which are dependent on the size of the grate. Clogging Ratio is the percent area of the inlet covered by debris. 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.
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| Grate Inlet |
The Curb Inlet tab allows you to create or edit a curb inlet. Curb inlets are less inclined to clog than are grate inlets, and have little interference to traffic operation. When placed on grade, their interception capacity decreases more significantly than that of grate inlets as the pavement longitudinal slope increases. So they are suitable for use in sags and relatively flat roadway.
In the Opening Length box, enter the curb opening length . When the curb inlet is in a sag, you need to specify the Throat Type of the inlet opening, the Opening Height, Weir and Orifice Coefficients. 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 greater than 1.4 times of the height. There are three curb throat types: Horizontal, Inclined and Vertical. Please refer to HEC-22 for details on throat types.
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| Curb Inlet |
Combo inlets consist a grate and a curb opening, and offer the advantages of both inlet types. The grate is usually the same length as the curb opening and placed alongside it, called equal length inlet. When the curb opening is longer than the grate, it becomes effective for intercepting trash and debris which may clog the grate. This is called sweeper inlet. In Inlet Library dialog, the Grate Inlet and Curb Inlet tabs together allow you to design a combo inlet.
The Slotted Inlet tab allows you to create or edit a slotted inlet. Slotted inlets are very effective in intercepting sheet flows due to their long lengths, and are suitable to placed 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 placed on the pavement and along the length of the gutter, and when the slot width is at least 1.75 in (45 mm), 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 depths are greater than 0.4 ft (0.12m). Refer to HEC-22 for more information.
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| Slotted Inlet |
Inlet Library dialog: Fill in values.
Pulldown Menu Location: Network
> Sewer Network Libraries > Inlet Library
Keyboard Command: inletlib
Prerequisite: None
File Name: \lsp\cntr_grd.arx