Situation: Advances in HEC-RAS now allow for improved simulation of overbanks using 2D Flow Areas. Coupled 1D/2D models where 1D cross-sections represent the bank-to-bank cross-section data and 2D flow areas represent overbank areas has greatly improved the accuracy and robustness of HEC-RAS models. This is particularly the case in flat, urban areas with significant overbank […]
HEC-RAS has the ability to simulate flow at hydraulic controls in a variety of ways. Bridges, culverts, inline structures, lateral structures, and SA/2D area connections can all act as hydraulic controls. Effectively, they break up the conservation equations used between cross sections in a 1D reach and/or cells in a 2D area with empirically derived […]
HEC-RAS allows for four different gate types that will compute the stage-discharge relationship of that gate for you based on the physical size/shape of the gate and a few empirical coefficients: Sluice Gates, Radial Gates, Overflow Gates (closed top) and Overflow Gates (open air). However, sometimes the built-in gate types don’t quite fit the gate […]
Lateral structures can be used in HEC-RAS to transfer flow from a river/reach to a storage area, or to another river/reach. With the coming release of HEC-RAS with 2D capabilities (estimated beta release January/February 2014), you’ll be able to hook a river/reach to a 2-D area using a lateral structure. Although its primary function in […]
I am working on a dam breach project where I’m trying to simplify a complicated model with dozens of tributaries and storage areas. In the process, I’m converting a few tributaries into storage areas (which are surrounded by other storage areas). For example, I want to convert the reach below (from 5.43 to 0.55) to […]
This is a great presentation put together by Mr. Steven Piper of the Hydrologic Engineering Center that discusses in detail the use of “Rules” at inline structures. Dr. Michael Gee forwarded this presentation to me after seeing some discussion on the forum about the use of Rules for inline structures. Thanks for the suggestion Dr. […]
Though it’s not very common, it is possible to get negative flows over inline structures for unsteady flow simulations. It’s much more likely you’ll see negative flows over a lateral structure though. Negative flows are simply discharges in your model going the opposite direction than what you have defined as the downstream direction (or primary […]
One of the limitations of HEC-RAS is that it is a one-dimensional model. Simply put, RAS assumes all flow moves along a singular dimension. For a given cross section, all of the flow is assumed to move either downstream, or all of it moves upstream, along the singular dimension (which can be defined as a […]
Our office ran into an unusual modeling situation recently. Here is a description of the situation: The project is a dam breach model, and the spillway for the dam diverts water to an adjacent basin. The spillway is actually more like a canal (the spillway reach) that runs about a mile until it empties into the adjacent […]
An off-channel storage area in HEC-RAS can be a very useful way to simulate flooding in interior areas, adjacent ponds and lakes, urban areas next to rivers, green storage, or just about any area that you expect to flood but will be better represented as ponded water versus actively conveying water. Connecting rivers to off-channel […]