Next, give a description for the lateral structure in the Description box and then define where its headwater position is. You can place the lateral structure in either of the overbanks (left or right side) or adjacent to either bank station (left or right).
The plan data Optimization button is just a shortcut to the plan file to quickly define whether or not you want to optimize the flow split over the lateral structure during the initial conditions run. Typically you will want to optimize this if you have flow over the lateral structure at the beginning of the simulation. If your initial conditions are below the lateral structure, leave this off. The Breach button is a shortcut to the breach editor, if you want to breach this lateral structure during the simulation.
The “Tailwater Connection” is really the subject of this post-this is how you connect the river to the storage area. Make sure you select “Storage Area” as your Type and then go choose the storage area you want to connect to by clicking the “Set SA” button. Alternatively you could connect a lateral structure to another river/reach or you could connect it to nothing (send the flow over/through the lateral structure out of the system).
There’s still work to be done to define the Weir/Embankment (if not already done), but the Storage area and the river are now connected via the lateral structure. If you want to make sure you are connected, look at the points of the lateral structure on the geometry schematic. If you see thin black lines connecting the end of the lateral structure to the storage area, then you know RAS recognizes them as being connected (sometimes you have so zoom in close to see the “connection lines”).
If you are having difficulty connecting lateral structures to rivers and/or storage areas, I highly encourage you to open up this example in HEC-RAS and have a look around. Normally you will find the example projects in C:\Program Files\HEC\HEC-RAS\4.1.0\Example Projects.
The “4.1.0” might be different if you’re using a different version of HEC-RAS. If you don’t see the example projects here, go to the Help menu item on the main HEC-RAS window and select “Install Example Projects…”