At any lateral structure HEC-RAS has the ability to model lateral weirs, gated spillways, culverts, diversion rating curves, and an outlet time series. The user can set up a single lateral weir, a weir and separate set of gates, a weir and group of culverts, or any combination of weir, gates, culverts, rating curves, and a time series outlet. The gated spillways can have either radial gates (often called tainter gates), vertical lift gates (sluice gates), overflow gates (open to the air or with a covered top), or user defined gate curves. The spillway crest of the gates can be modeled as either an ogee shape, broad crested weir, or sharp crested weir shapes. The culverts can be any of the available shapes from the standard HEC-RAS culvert capability. The diversion rating curve can be used alone, or in conjunction with the other hydraulic outlet types. The rating curve can be used to represent an entire structure or a particular outlet that could not be modeled with HEC-RAS. Lateral structures can be connected to storage areas, 2D Flow Areas, or another river reach.

The lateral structure option can also be used to model a levee. In general, the user should end their cross sections at the inside top of the levee, and then use the lateral structure option to represent the top of the levee along the stream. The area behind the levee could be represented with either a 2D Flow Area, storage area (or combination of interconnected storage areas), or another river reach. Water that goes above the levee will be modeled as weir flow. The user also has the option to evaluate levee breaching.
HEC-RAS now has the option to have georeferenced lateral structures. Under the menu item labeled GIS Tools, there is now a table option called Lateral Structure Centerlines Table. User can use the Measure Tool to draw a line that would represent the lateral structure geospatial X and Y coordinates, then paste those coordinates into the Lateral Structure Centerline Table (This is optional). If a user inserts geospatial coordinates for a lateral structure, not only will it be drawn geospatially correct, but HEC-RAS will figure out how elements (1D cross sections and 2D Face Points) are connected to the lateral structure based on its spatial location.

If you put in a Geospatial centerline for a lateral structure, the length of the lateral structure weir/embankment stationing must be within 0.5% of the length of the centerline put in (i.e. they need to be consistent with each other in terms of length).

This section of the User's manual will describe how to enter the data for lateral weirs, gated spillways, culverts, lateral rating curves, and outlet time series. For information on general modeling guidelines and the hydraulic computations of lateral weirs, gated spillways, and culverts, please see Chapter 8 of the HEC-RAS Hydraulic Reference manual. To find out how to view specific results for a lateral structure, see Chapter 9 of this User's manual.