How can a user model a sidewalk trench drain in StormCAD / CivilStorm / SewerGEMS?
If the sidewalk trench drains act as a slot inlet that runs down the middle of the sidewalk, and the cement slopes down toward the slot on both sides, you should be able to use a slot inlet type. For the “gutter type”, you can pick “v-shaped” and define the slopes on each side. The gutters between the catch basins would represent the length of sidewalk between the individual slots.
If the slot or grate runs down the whole length of the sidewalk you may need to break it into multiple sections, with a catch basin and subsurface conduit between (and respective segment of catchment draining to it).
For a very long length of this, you can use the Element Property Inferencing tool (see Help) to automatically create manholes at a set interval between the upstream and downstream manhole, then use the Batch Morph tool to morph them into catch-basins. Also to simplify the task of assigning catchments to each segment of the inlet, consider using the catch-basin flow input fields, such as the External CA/External Tc, which can be added to the catch-basin flex-table and global edited.
For additional information on slot drains, please see Stormwater Conveyance Modeling and Design book offered on Bentley's website.