The Neenah Foundry Company (Neenah, Wisconsin - http://www.nfco.com) produces an extensive range of storm water inlets/catch basins, commonly referred to as 'Neenah grates'.

These Neenah grates are not currently included in the default Bentley SewerGEMS Engineering Libraries, but in Bentley SewerGEMS it is quite straightforward for users to add them as required.

To Model a Neenah Grate for On Grade Inlets

1. Click the Components > Catalog> Inlet Catalog.
2. In the Inlets Catalog dialog, click New. Type a name for the new inlet.
   Note: We suggest using the Neenah catalog number, and the transverse and longitudinal slopes that the curve capacity values will correspond too). Unlike the in HEC-22 calculations, there is no general relationship available for Neenah grate capacity versus longitudinal slope, so each Neenah grate is entered in Bentley SewerGEMS as a Kerb Channel Depth vs. Captured Flow curve which is specific to a particular transverse and longitudinal slope.
3. Next click Inlet Type and select Kerb Channel Depth vs. Captured Flow. Enter the below ground Structure Width and Structure Length.
4. Now refer to the Neenah technical information to find the K value associated with this grate (for the appropriate transverse and longitudinal slopes).
5. For this example, for a longitudinal slope of 2% and a tranverse slope of 5%, use a K value of 16. Then a depth versus captured flow relationship can be determined using the equation:

   

6. Now this relationship can be copied and pasted into the Kerb Channel Depth vs. Captured Flow area of the Inlet editor. To do this, copy the data to the windows clipboard, then in Bentley SewerGEMS , select the top right cell in Kerb Channel Depth vs. Captured Flow grid and press Ctrl+V to paste.
   Note: Make sure the units used in the Inlet editor match the units used in determining the Depth vs. Captured Flow relationship.

This inlet is now set up and ready to use in the current Bentley SewerGEMS model. To make it available for use in other models, click on the Synchronization Options button and select Export to Library.

To Model a Neenah Grate for In Sag Inlets

For rectangular grates in sag, it is generally possible to enter a Neenah grate as a standard Grate Inlet Type.

However, please note that the Bentley SewerGEMS uses the HEC-22 methodology for computing capacity, which does not always produce capacities that correspond to capacities given by Neenah Foundary (since some discharge coefficients are slightly different).

The designer should verify that they are satisfied with the calculated capacity in these cases.

For non-rectangular grates, the designer should compute, or request from Neenah Foundry, a Kerb Channel Depth vs. Captured Flow relationship for the grate and then enter that in Bentley SewerGEMS using a procedure similar to the procedure outlined for Inlets On Grade above.

Note that the capacities of grate inlets in sag are not a function of the transverse of longitudinal slopes, so one Kerb Channel Depth vs. Captured Flow curve per grate is sufficient for all transverse and longitudinal slopes.