| Product(s): | StormCAD, CivilStorm, SewerGEMS, FlowMaster |
| Area: | Modeling |
Problem
How can a Sweeper inlet be modeled, and what are the considerations when setting the grate length and curb opening length input fields?
Background
A sweeper refers to a combination inlet where the curb opening length is longer than grate length. An on-grade sweeper inlet is typically installed with the excess curb opening length on the upstream side of the inlet.
Solution
In the OpenFlows software for a combination inlet on grade, the user should enter the grate length and the full curb opening length when inputting inlet data.
Sweeper Inlet On Grade
The following applies when the calculation option "Active Components for Combination Inlets on Grade" is set to "Grate and Curb":
- Since the interception capacity of a curb-opening inlet on grade is typically much smaller than that of a grate inlet, a conservative assumption is made where only the portion of the curb opening length in excess of the grate length is considered when computing inlet interception. Thus, the inlet capacity is computed as the sum of the flow intercepted by the curb opening upstream of the grate and the grate interception.
- The user should input the full curb opening length. The software will automatically subtract the grate length from the entered value when determining inlet capacity.
- For any curb opening length less than or equal to the grate length, only the grate is considered in the calculation.
Sweeper Inlet In Sag
In general, catalog inlet calculations use the HEC-22 standard. However there are many gray areas open for interpretation in the HEC-22 standard.
The in-sag inlet capacity is computed as the sum of the capacity of a combination inlet with equal grate and curb opening lengths, and the capacity of the curb opening in excess of the grate length. The calculation option “Active Components for Combination Inlets in Sag” should be set to “Grate and Curb”.
As for how those two parts are calculated – when in-sag, it solves either the weir equation (at low depths) or the orifice equation (at high depths), with weir length or clear open area based on the inlet parameters. (based on the incoming gutter flow, it solves for depth/head) There is also a weir/orifice factor in the calculations, so a gradual transition occurs between the low-depth weir flow and the high depth orifice flow.
Some additional details can be found in the documentation: https://docs.bentley.com/LiveContent/web/Bentley%20StormCAD%20SS5-v1/en/GUID-71437B8294D749129ECE3C109D13B605.html
The following applies when the calculation option "Active Components for Combination Inlets in Sag" is set to "Grate and Curb":
- The in-sag inlet capacity is computed as the sum of the capacity of a combination inlet with equal grate and curb opening lengths, and the capacity of the curb opening in excess of the grate length.
- The user should input the full curb opening length.