The Initial Opening is required for all gate groups, if any, in the hydraulic structure and may not be left blank. The gate will be left at this setting until it is changed by a rule operation. This opening height will be used during the initial backwater computation. The Initial Opening provides the first setting for the gate. If the Min is left blank, then the minimum opening is fully closed (i.e. If the Max is left blank, then the gate maximum opening is limited only by the height of the gate. Building on the previous example of opening the gate one additional foot, if the gate was at 3.5 feet and the maximum was set to 4 feet (even though the gate was 6 feet tall), over a five minute period, the gate would open to 4 feet and then stop. The Max and Min Opening will constrain the maximum and minimum gate opening settings. The Open and/or Close Rate can be left blank, which means the gate can move to any new setting in a single time step.
So if, for example, a rule operation required the gate to open one additional foot and the gate opening rate was 0.1 ft/min and the user had selected a one minute time step, it would take ten time steps for the gate to reach the new opening height. The Open and Close Rate controls how fast the gates can move. In the Gate Parameters table at the top of the editor, some initial information can be entered for any gate groups that are in the hydraulic structure. This will bring up the Gate Rule Operation editor (as shown in the next slide). From the Unsteady Flow Data editor, add or select the given structure and then click on the Rules button. Rules for controlling hydraulic structures can be entered after an inline structure, lateral structure, or storage area connection has been added to the project. Rule operations in HEC-RAS are available for inline hydraulic structures, lateral hydraulic structures, and storage area connections. Examples of variables that could be used to control releases from a hydraulic structure are: current flows and water surfaces at the structure, current flows and stages at downstream or upstream cross section locations, time considerations (winter, morning, etc), and/or previously computed values (accumulated outflows, running averages, etc). Alternately, the rules can directly control (or constrain) the flow despite the gate openings (or even without gates at all). The rules can be used to operate the height of the gate openings. HEC-RAS allows flexibility in modeling and controlling the operations of hydraulic structures through the use of rules. The operating procedures for determining and controlling the releases from reservoirs and other types of hydraulic structures can be quite complex. To get a working knowledge of the rule capability in RAS, it is recommended that the user read the detailed documentation in the User’s Manual. The advanced rules allow sophisticated control of hydraulic structures (inline structures, lateral structures, storage area connectors, and, in the next RAS version, pumps).
This presentation is also available to download at: Piper kindly provided permission for me to post this to. Michael Gee forwarded this presentation to me after seeing some discussion on the forum about the use of Rules for inline structures.
Steven Piper of the Hydrologic Engineering Center that discusses in detail the use of “Rules” at inline structures.
This is a great presentation put together by Mr.