This is a greatpresentation 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. Gee!  Mr. Piper kindly provided permission for me to post this to RASModel.com.  This presentation is also available to download at:

https://www.dropbox.com/s/8q8lagd5e91w6uo/AdvancedRules.pdf

Enjoy!

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 only an overview. 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 operating procedures for determining and controlling the releases from reservoirs and other types of hydraulic structures can be quite complex. HEC-RAS allows flexibility in modeling and controlling the operations of hydraulic structures through the use of rules. The rules can be used to operate the height of the gate openings. Alternately, the rules can directly control (or constrain) the flow despite the gate openings (or even without gates at all). 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). Rule operations in HEC-RAS are available for inline hydraulic structures, lateral hydraulic structures, and storage area connections.
Rules for controlling hydraulic structures can be entered after an inline structure, lateral structure, or storage area connection has been added to the project. From the Unsteady Flow Data editor, add or select the given structure and then click on the Rules button. This will bring up the Gate Rule Operation editor (as shown in the next slide). 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.

The Open and Close Rate controls how fast the gates can move. 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/or Close Rate can be left blank, which means the gate can move to any new setting in a single time step.
The Max and Min Opening will constrain the maximum and minimum gate opening settings. 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. If the Max is left blank, then the gate maximum opening is limited only by the height of the gate. If the Min is left blank, then the minimum opening is fully closed (i.e. 0.0).
The Initial Opening provides the first setting for the gate. This opening height will be used during the initial backwater computation. The gate will be left at this setting until it is changed by a rule operation. The Initial Opening is required for all gate groups, if any, in the hydraulic structure and may not be left blank.
In this example, row 7 is getting the wsel at the dam. Row 13 is checking to see if it is 0600 hours. If it is, then rows 17 and 22 are executed. Row 17 computes a new gate opening elevation for the drop gates. The new elevation is 3.5 feet below the wsel at the dam. Row 22 converts the elevation into an actual gate opening and tells the program to use the new gate opening. The final result is that at 0600 hours the drop gates are adjusted to have 3.5 feet of head on them.
To enter or edit the rule operations, click the Enter/Edit Rule Operations button.

Operation Types:

Comment. Provides a user entered line of text (for documentation only).

New Variable.  Allows the user to create a variable and give it a custom name.

Get Simulation Value. A variable is set equal to a given value in the simulation, such as the flow at a cross section or the time of day.

Set Operation Parameter. Changes the operation of the hydraulic structure, for example, adjusting the gate height or setting a maximum discharge.

Branch (If/Else). Controls which operations are executed on the basis of an If-Then test (e.g., do different gate operation checks based on seasonal considerations).

Math. Performs math operations such as summing flows or averaging water surfaces.

Table. This operation allows the user to enter a table and perform table lookups to get a value.

A group of rules for one hydraulic structure is referred to as a rule set. At the start of each time step, each rule set is evaluated to check for changes to the operation of the given hydraulic structure. Rule operations are performed from the first (top) rule to the last (bottom) rule. By default, each rule operation is evaluated once. However, branching operations (If/Then/Else, etc) can cause some rule operations to be skipped. No looping or jumping to prior rule operations is allowed. That is (during a given time step), a rule operation may not be performed more than once.
Note: A rule set is only called once during a time step, even if the program iterates during that given time step. (Whatever rules are “in force” at the start of the time step will apply during all of the iterations).
The Get Simulation Value operation provides information about the current state of the model.
In the above example, the wsel at a cross section just upstream of the dam is being retrieved and stored in a variable named “WSEL at dam.”
There are currently seven categories of simulation variables. These are Time, Solution, Cross Section, Inline Structure, Lateral Structure, Storage Areas, and Storage Area Connectors. Clicking on the “+” will expand the list for that category.
For all the variables under Time, the user can select to use the time at the beginning of the time step (default), the end of the time step, or the previous time step.
For the remaining [non-time] variables, the user can select the current value, the value from the previous time, or a “look back” value.

Clicking the Math operation button creates a math operation as shown. The result of the math operation can be assigned to either a new variable or an existing variable.
The math operation itself is composed of up to four different “expressions.” Each expression that is defined will return a real number. Expressions should be defined from left to right. So if a math operation is composed of two expressions, the left two expressions should be defined
and the right two expressions should be left as “[not set]” (i.e. they should be left blank). If more than one expression is defined, then the user must choose an algebraic connector from the drop down menu between them. The choices are: addition, subtraction, multiplication, and division.

In order to use a variable in an expression, or store the result into an existing variable, the user selects the variable with a pull down menu, as shown.
In row 129, there is a two part If/Then. In the first part, the rule operation is checking to see if “Canal Dam Vol since midnight” is greater than or equal to “Canal Dam Vol Diversion.” In the second part, it is checking to see if “Green Dam 4 Hour Ave Flow” is less than 10. Since the two different parts are connected with an “Or,” if either part is true, the expression will be true and rules 134, 135, and 136 will be executed. In more understandable terms, there is a check to see if the maximum amount of water has been diverted, or if the four hour running average flow at Green dam is below 10 cfs. If either is true, then all of the gates will be fully shut (and no more flow will be diverted for the rest of the day).

To control a given aspect of he hydraulic structure, a Set Operational Param rule operation is used. In the example above, rule 63 is setting the “gate flow desired” to the [previously calculated] value of “Flow New.” This will cause the RAS program to adjust the gate settings in order to get the desired flow. (The actual computed flow may be slightly different due to convergence tolerances and changing water surface elevations.)
There are a number of different operational parameters that can be set. In addition to setting the gate opening height or having RAS compute the height to get a desired flow, the user can: set a maximum flow, set a minimum flow, fix a given flow, etc.

In this simple example, a rule set that is attached to a lateral structure is being used to divert flow from the main river. The diversion is based both on the amount of flow going through a downstream dam and the time of day.

After getting the time of day and the flow at the inline structure, the actual diversion is determined from a lookup table as shown above. So, for instance, if the time is 12 (i.e. 1200) and the flow through the dam is 10,000 cfs, then 1000 cfs will be diverted.

In this example, the user has selected to interpolate. So if, for example, the flow was 11000 at

12 hours, then the flow diverted would be 1100 cfs. Instead, the user could have selected “nearest index value” which would have resulted in 1000 cfs being diverted for a main river flow of 11000. This option could be useful, for instance, if the lookup table was being used to set gate openings that can only be opened in discrete amounts.

Note that in row 13, the flow diversion (‘Flow to Divert’) has been set as a “Total Flow (Fixed)”. This means that the flow being diverted by this lateral structure is being entirely controlled by the rules (and the value from the lookup table). There are no gates and no hydraulic computations (e.g. computed flow over a weir).

In this, and following, slides, the gate control will be switched from elevation control to a rule set that has the same basic functionality.

The gate opening rates, maximum, minimum and initial gate opening are entered.
Next, the <Enter /Edit Rule Operation> button is clicked.

The first rule that is needed is the water surface elevation immediately upstream of the inline structure.
Clicking the <Get Sim Value> button, as shown, will start the creation of the first rule.

On the left, beneath where it says “Assign Result”, a descriptive variable name should be entered (in this case, WSEL).
Under Simulation Value, the Cross Section tab should be expanded and WS Elevation chosen.

Next, the river station just upstream of the inline structure is selected from the pull down menu.

On the right, the default “Value at current time step” should be left as-is. This gets the water
surface at the start of the timestep. Other choices would get a previous water surface or a
lookback/time-averaged water surface.

The next step is to add a rule that checks to see if the water surface is high enough that the gates need opening.
Clicking on the <Branch (If/Else)> button, will start the second rule. The If test compares the value of two different “Expressions”. Clicking on <Edit> underneath the Expression on the left will bring up the Edit Rule Expression editor as shown. Clicking on the Variable pull down menu will show all of the variables in the rule data set. In this case there is only one. Selecting the variable WSEL (which is created by rule 1), allows the value of the water surface to be compared to the second expression. Since the water surface is the desired item, the rest of the fields are left blank. (If it was desired, the Variable could be multiplied by a Coefficient, raised to an Exponent, and/or a Constant added.

For this If test, the check is to see if the water surface is greater than 6.0 feet. Between the two Expression buttons, there is a pull down menu that is used to select the “>” (greater than) operator.
The right Expression is clicked and the number 6 is entered in the Constant field.

The next rule is to set the gate opening height when the water surface is above 6.0 feet.
Clicking the <Set Operational Param> button will display the menu on the lower left and the
Gate.Opening operation is selected. Under Select Gate Group, the Left Group is selected.
The gate opening is set to 10.0 feet using the expression editor.

Every If rule must have a corresponding End If. Click the <Branch> button, which initially creates an If rule. Change this rule to an End If by the selecting the End If radial button as shown.

Another conditional must be created to close the gates when the water surface gets low enough.
The quickest and easiest way to do this is by making a copy of the existing rules (that open the gates), and then editing the copy.
Highlight rules 2 through 4 by clicking on rule 2 and then pressing the down arrow while holding the shift key (shift + down arrow).

Next, click on the Copy button, then move the cursor below row 4 (as if a new rule was to be made using one of the standard Insert New Operation) and then click on the Paste button.
The keyboard shortcuts Ct+X and Ctrl+V, can be used instead of clicking on the copy and paste keys.

Copying existing rules using the Ctrl+X and Ctrl+V shortcuts (and then editing the copy) can save a lot of time and effort.

The next step is to edit the just copied rules.

The 6 needs to be changed to a 4 (in the If rule), the operand needs to be changed from a greater than to a lesser than, and the gate opening value needs to be changed from 10 to 2.

Finally, it is a good idea to click on the <Check Rule Set> button. RAS will check for any basic errors in the rule data set. (For instance, if there is a If rule that does not have a corresponding End If.) If the Check Rule is not performed at this stage, RAS will still perform the check at run time. Errors will generate a message for the user about the problem. The Check Rule button is
a short cut that allows the user to identify problems while the Operation Rule editor is still open.

In addition to If/Then, the rules also allow for If/Then/Else and If/Then/ElseIf/Else type constructions (as well as nested If/Then statements).

In the above example, the gate opening will be set to 10 if the WSEL is greater than 6.0 feet. Otherwise, the opening will be set to 6 feet if the WSEL is above 5.0 feet. Finally, it will be set to 2 feet if the WSEL is less than 4.0 feet.

If the WSEL is less than or equal to 5 feet, but greater than or equal to 4 feet, the gate opening will not be changed.

Deciphering (aka debugging) what a complicated rule set is actually doing can be tricky. RAS has a text based output file referred to as the Detailed Log. The operation of each rule in a rule set can be examined on a timestep by timestep basis from this log.
The log output is turned on as shown above.

Every rule that is executed will be shown—as will the result of that rule. The output shown above is taken from the previous rule data set that opens the gate when the WSEL is greater than
6.0 feet.
Rule 1 is executed and the variable WSEL is set to the water surface which is around 6.01 feet.  Rule 2 is executed and this rule is True because the value of the first expression (~6.01) is
greater than the second expression (6.0).  Rule 3 is executed and the gate opening for the Left Group is set to 10 feet. No other rules are executed for this rule data set (for this time step).  Use the find function to locate when things happen. For instance, the string “0002 True” was searched on to find this location in the log file.

Note: having detailed (debug level) output for the rule data set directly available within the
GUI is already on the RAS “wish list”.

The canal data set (which is included as one of the sample data sets when RAS is installed) provides a good example of the sophisticated operations that are possible with the advanced rule capability.
In this data set, the rules are being used to allow RAS to model a reservoir and a water supply canal in Florida. The Florida water district has a complicated operating agreement that it must conform with.
A reservoir has been modeled as a series of cross sections. A water supply canal leaves the side of the reservoir. This has been modeled with a junction and an inline structure (shown above and red circle) on the diversion canal. The main dam on the reservoir is further downstream (and is not shown on the above graphic).
The flat terrain (river gages suffer backwater effects far upstream of the dam) and the large groundwater flows make measuring inflows to the reservoir difficult. Instead, the inflow to the reservoir is assumed to be equal to the outflow (the outflow from the main dam plus the outflow through the water diversion canal).
The water district’s allowable diversion is based on the previous day’s outflow (midnight to midnight). Additionally, the water district is not allowed to divert water when the outflow from the main dam is too low. (The flow at the main dam is reduced when the reservoir drops too low—so, the water district is, indirectly, prevented from making diversions when the reservoir water surface is low.)

Rules 3 through 5 create three variables. New variables are most often created with a Math or Get Sim Value operation. However, it is sometimes convinent to have the variable creation be its own rule. Note: the Initial Value = 0 sets the variable equal to 0.0 at the very start of the simulation (the very first time the rule set is called for the first timestep). Afterwards, the variable will keep its value between time steps (e.g., if it equal “5” at the end of the first time the rules set is called, it will equal “5” at the start of the next time). To set it equal to 0.0 at the start of each time step, a Math operation should be used.
Rule 10 gets the length of the time step with a Get Simulation rule. A math operation is then used to compute the length of the time step in seconds.
Rules 16 and 17 get the outflow from the main dam and the diversion canal.
Rules 20 and 21 add the volume of outflow (for this time step) to the current volume. The
“current volume” is the volume of outflow since midnight.

Rules 26 and 27 get the day of the month at the beginning of the time step and the end of the timestep. If the data set is using 15 minute time steps, at some point the beginning of the timestep will be at 11:45pm and the end of the timestep will be at 12:00am. When that happens, the beginning day of month will not equal the end. Beginning might be 5 and ending 6, or beginning could be 31 (or 30 or 28) and the end will be 1 (the first of next month).
Note: The rules use a 24 hour clock, so in the above example, the timestep would actually be at
23:45 and 00:00.

Rule 31 checks to see if it is midnight. When the timestep starts and ends on different days, it is midnight.
Rule 39 computes the total average outflow for the previous 24 hours (in cfs). Rules 42 and 43 zero out the volume variables for use for the next day.
The methodology for determining the allowable diversion is based on the amount of outflow. No diversion when the flow is less than 100 cfs (rule 47). 10% of the previous days flow when the flow is between 100 and 150. A sliding scale (from 10% to 30%) when the flow is between
150 and 215. 30% for flows between 215 and 1000 and a maximum of 300 cfs (for flows over
1000).

Up to four separate expressions can be combined into a single Math operation.

Rule 69 converts the allowable diversion from cfs to a daily volume.
The gates are adjusted at midnight and are left in place until the allowable diversion has taken place. The gate flows are computed so that the diversion will take approximately 20 hours. (If the flow was based on a 24 hour diversion and the gate flow was slightly less than assumed, then the gates would either have to be adjusted or the full, allowable diversion would not take place).
Rule 77 computes the 20 hour flow on a MGD basis.

The inline structure has three different gate groups (that are used in normal operations). The gates are overflow (drop) gates.
For each gate group, the water district has a table that shows the amount of head that should be on that gate group for a given flow.
Rule 80 computes the amount of head needed on gate group #1 using the lookup table (shown above). The value that goes into the lookup table (input) is determined by the expression editor. In this case it is the “Canal Dam 20 hour MGD” variable (which the first part of the name can just be seen left of the lookup table). The result of the lookup (output) is stored in a new variable, “Head Opening #1”.

The head on the drop gate is the upstream water surface minus the gate opening height minus
the invert elevation of the gate. Rearranging, gives the gate opening to be equal to the head plus the invert minus the upstream water surface as computed in rule 100.
Rule 100 computes the desired gate opening.
Rule 105 actually sets the gate opening to the value that was computed by rule 100.
The computation for the gate opening involves two different variables (Head and WSEL), which meant that two different “Expressions” had to be used. The Set Gate Opening command only has a one Expression. So a Math operation was used (which can have up to 4 different variables/expression) in rule 100.

There are two different triggers for shutting the gates:
One trigger is the first part of rule 129. It checks to see if the allowable volume of water has been diverted. If it has, then rules 134-136 make sure all the gates are closed.
The other trigger is based on the outflow from Green dam. When the flow at Green dam is below 10 cfs, the water district must stop diverting water. (This only happens at low reservoir levels.) However, it is possible for the reported flow at Green dam to briefly drop below 10 cfs, either because of a switch in gate operations or because of a “missing value” from the remote data operation. To accommodate this, the water district does not have to stop the diversion until the average flow over 4 hours has dropped below 10 cfs.
Rule 124 computes a running, 4 hour average of the flow from Green dam. Looking at the lower right of the above screen shot, the Lookback period is from 4 hours ago to the current times step (0 hours ago).
The second part of rule 129 checks if this 4 hour average is below 10 cfs. If it is, all of the gates are closed.

The rules between an If/Then and it corresponding End If can be collapsed and/or expanded. This is done by clicking on the “+/-” to the left of the row number. This option can make viewing complicated data sets easier. (The rules are still active.) All of the rules that are involved in the once daily computations (at midnight) have been collapsed, above.

Written by Daniela Todesco | WEST Consultants

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 a storage area. We happen to have the topographic data used to generate the original model (although we don’t have the original geodatabase), so we’re good to go.

In order to do that, we need to delineate the storage area polygon, define new storage area connections, and generate lateral structures. The new “reach” (now a storage area) will look like the one below.

Now we need station-elevation data for storage area connections and lateral structures. Easy, right? Well, not so fast. HEC-GeoRAS seems to have some issues exporting data when you take an existing project and try to modify shapefiles and extract data for only a portion of the entire model. It is especially difficult if you’re not the one who built the model in the first place. The shortcut is to think outside GeoRAS and obtain simple 3D station-elevation points directly from a TIN or grid for the storage area or structures you need. The bad part about that is that extracting tools in ArcGIS doesn’t really have an option to limit the number of points that are generated, and you end up with thousands of points that you can’t really use in HEC-RAS (the limit for cross section points, storage area connection weir/embankment points, and lateral structure weir points is 500). For example, in the connection called 83Coal in the figure above, I end up with over 2300 points. I’m stuck. Or so I thought…

It turns out that RAS automatically “expands” its Station Elevation table to store however many points you need. In my case, 2339…

HEC-RAS will still give you an error if you try to run the model with this data (the limit of 500 points still stands for computations!), but a simple click of the “Filter” button you see in the figure above solves the problem. Voila! Hope you liked this new (for me) discovery.

Written by Daniela Todesco, P.E.  |  WEST Consultants

Copyright © The RAS Solution 2014.  All rights reserved.

If you have built enough HEC-RAS models, you’ve probably discovered that having data in different vertical datums is a bit of a pain. RAS lets you adjust the vertical datum of individual cross sections (under “Geometric Data”, “Cross Section”, “Options”, “Adjust Elevations”) or portions of the model (“Geometric Data”, “Tools”, “Datum Adjustment”). However, I have to confess this: datum adjustments are always a little bit puzzling to me. I need pen and paper and a little numbering conversion to make sure that I’m doing things right when moving from one vertical datum to the next. And I recently had a “eureka” moment when I finally realized that the sentence “NAVD88 is higher than NGVD29 (for most of the locations we work on)” is actually wrong. Let me step back a moment and I’ll explain why.

The two most common vertical datums used in the U.S. are the North American Vertical Datum of 1988 (NAVD88) and the National Geodetic Vertical Datum of 1929 (NGVD29). NOAA’s VERTCON program can be used to compute the conversion factors from one datum to the other.

Tidal datums are, in general, confusing. Vertical elevations can refer to NAVD88, the station datum, Mean High Water, Mean Low Water, Mean Range of Tide, and a variety of other datums. In recent years, NOAA has been updating its reference tables with excellent graphs showing how the different datums relate to each other (like the one below for Astoria, OR - http://tidesandcurrents.noaa.gov/datums.html?id=9439040 -, where all elevations presented are related to the station datum, which is the Columbia River Datum or CRD).

Let’s say that you download data in the Astoria station datum and you want to convert the data in NAVD88. Since the NAVD88 datum is 2.02 ft above the station datum, you need to subtract 2.02 ft from the station datum to obtain elevations in NAVD88. Or, to make it easier to remember, if the data you obtain is in datum X and you want to convert it to datum Y, you need to ADD the vertical distance between the two datums if X is ABOVE Y (or SUBTRACT if X is below Y). In our case, X is the Astoria station datum, Y is NAVD88, X is below Y, and you subtract 2.02 ft to the Astoria datum to obtain elevations in NAVD88 (the distance between the two). Makes sense, right? This also explains why for most locations on the West Coast USA, the elevation in NAVD88 of a certain location is always higher than the elevation in NGVD29 of the same location (that’s because the NGVD29 datum is actually above the NAVD88 datum). For example, in Astoria, you need to subtract 3.4 ft to elevations in NAVD88 to obtain elevations in NGVD29.

Now, to confuse things even more, gage locations along the Columbia River follow an intrinsic datum that actually changes as you move upstream from the river’s mouth. For example, at Astoria, the station datum is BELOW NGVD29, while at Vancouver, the station datum is ABOVE NGVD29 (see graph below, at http://www.thsoa.org/hy05/09_1.pdf).

The USGS sent us a nice graph (see below) that helped me clear things up when reading datum-related station description information. This one is for the Columbia River at Vancouver gage in WA. The short station description reads: “Datum of gage: 1.82 ft above NGVD29”. The long version reads: “Datum of gage is Columbia River Datum (add 1.82 ft to correct to NGVD29)”. Remember: X is the station datum, Y is NGVD 29, X is ABOVE Y, so you need to add the distance to go from X to Y. To add something more to this graph, I would say that in CRD, the 0 of the NGVD29 datum is 1.82 ft below the 0 of the CDR datum, which reflects the previous graph. Hope this helps!

Written by Christopher Goodell, P.E., D.WRE  |  WEST Consultants

Copyright © The RAS Solution 2014.  All rights reserved.

As RAS model development is done more and more through GIS, using the HEC-GeoRAS extension, cross section point filtering is becoming a standard part of the HEC-RAS model development exercise.  It’s not too uncommon for a model created in GIS to have multiple hundreds of cross section station elevation points.  This is normally not a problem, as long as you don’t exceed 500 points (the maximum allowed for any cross section in HEC-RAS.  However, do an interpolation with bounding cross sections that have more than 255 points each, and you will have interpolated sections with more than 500 points.  Try to run that model and HEC-RAS will give you a message like this:

Fortunately, this is easily remedied.  Simply use the Cross Section Points Filter tool located in the Tools menu item in the Geometry schematic:

In this tool, you can filter a single cross section, or do multiple cross sections together.  For a single cross section, either go to the cross section indicated in the error message, or scroll through the river station dropdown box until you find one with more than 500 points.

Once you’ve selected your cross section(s), you have a number of different ways to filter.  Near and Colinear filtering will remove points that are either very close to another point, or that are in line with other points.  You just provide the tolerances (tell RAS how close is too close, etc.) . Once you enter the tolerance values, press the “Filter Points on Selected XS”, and check to see if you removed enough points to get below 500.  If not, you’ll have to tighten your tolerances.  This can take a little bit of trial and error as you figure out what tolerance levels will remove enough points. 

My preferred method for filtering is to use the “Minimum Area Change” method.

Here, all you do is enter in the desired number of cross section points you wish to have in the cross section (500 or less), and then HEC-RAS will remove points until it gets to that number.  No trial and error necessary.  BUT, you do not have control on which points are removed.  HEC-RAS uses a built-in scheme to remove points while minimizing the change in cross section area.  At first I was a bit reluctant to use this feature, thinking that it might drastically alter the shape of my cross section.  However, when comparing the original and filtered cross sections, I’ve never noticed a visual difference.  The “minimum area change” scheme that is used by HEC-RAS does a very good job at preserving the shape and hydraulic characteristics.  Give it a try next time you need to filter. 

Written by Christopher Goodell, P.E., D.WRE  |  WEST Consultants

Copyright © The RAS Solution 2014.  All rights reserved.

So you want to control HEC-RAS from a external program.  Perhaps, you have a lot of plans to run and want to run in batch mode.  Maybe you wish to run HEC-RAS, evaluate the results, make some changes, and rerun HEC-RAS-all automatically, on its own, while you’re at home with the family.  The good news is it can be done.  The bad news is there is really no documentation on how to do this. However I will be publishing a book on this topic this year, so keep checking back for more information on that.

In the meantime, here’s a quick way to open HEC-RAS, select the plan you want to run, and then run it, all through Visual Basic for Applications in Excel.  If you have HEC-RAS, and you have Excel, you can do this. 

To begin, open Excel and enter the VBA Environment by pressing Alt-F11 or by clicking on the Visual Basic button under the DEVELOPER tab. If the DEVELOPER tab is not already present in your list of menu items, you can add it by accessing the Excel Options under the File menu item and selecting Customize Ribbon. Check the box next to the Developer tab so that it shows up on in your list of menu items. The DEVELOPER tab provides quick access to the VBA Code Editor as well as a host of other programming options and tools. The VBA editor will look like this when it’s opened for the first time.

Visual Basic for Applications Editor.

If a module doesn’t already exist, add one by clicking INSERT…Module from the Visual Basic Editor. A new module will be added and the space to the right of the window will be ready for programming code. You can change the name of the module if you like in the properties window (see figure below).

Visual Basic for Applications Editor with a New Module.

Before you can begin accessing the RAS Dynamic Link Library (RAS DLL), it must be added as a reference. In the Visual Basic for Applications window, select Tools…References from the menu items. A window that lists all of the available reference libraries will come up as shown in the “Add Reference” window. Look for the HEC River Analysis System reference and check the box next to it.

Add Reference Window.

If you don’t see a reference for HEC River Analysis System, you need to install HEC-RAS on your computer. If you have multiple versions of HEC-RAS installed on your computer, you’ll see multiple entries for HEC River Analysis System. Make sure to check the one for the version of HEC-RAS you wish to use.

Now that you’ve added the RAS DLL as a reference, you have access to it’s library of commands that can control HEC-RAS.  Click on the module (Module 1) and type the following code:

Now, it should open and run whatever project you have listed in cell C4 on your Excel Sheet. 

Next, you might want to explore the RC.Plan_SetCurrent() subroutine and a Do-Loop block in your code to run through multiple plans in batch mode. 

Have Fun!

Written by Christopher Goodell, P.E., D.WRE  |  WEST Consultants

Copyright © The RAS Solution 2014.  All rights reserved.

I don’t think you’ll find this anywhere in the manuals, but HEC-RAS has a very convenient tool for measuring lengths and slopes in the Geometry window and just about any graphical plot.  It only works in the geometry window if your RAS model is georeferenced, as it measures distances based on coordinates.  However, in the graphical plots, it works great whether your model is georeferenced or not. 

While in the Geometry window or any graphical plot, push and hold the Ctrl key on your keyboard.  You’ll see your cursor change from a pointer to a crosshair with a measuring square like this:

While keeping the Ctrl key pressed, mouse click and move the measuring tool.  You’ll see a line drawn on the plot. 

When you release the Ctrl key, you’ll see a window pop up with the line length, as well as the x direction length (dx) and the y direction length (dy).  dy/dx gives you the slope of the line.  This is very useful for getting river bed slopes for using the normal depth boundary condition or for calculating n values using Jarrett’s equation.  You’ll notice that Polygon Area is also provided.  This works if you click multiple times in the plot, making a polygon.  This is useful if you’re interested in measuring surface area of a storage area in the geometry window. 

You’ll notice that Polygon Area is also provided.  This works if you click multiple times in the plot, making a polygon.  This is useful if you’re interested in measuring surface area of a storage area in the geometry window.  Just be sure to keep the Ctrl key depressed while making your “clicks” to define the polygon. 

Written by Christopher Goodell, P.E., D.WRE  |  WEST Consultants

Copyright © The RAS Solution 2014.  All rights reserved.

Another simple, yet very convenient tool not found discussed in the manuals is the ability to zoom in on one of the axes of a graphical plot.  This is especially useful when trying to determine if you’ve captured the true peak discharge in a steeply rising hydrograph.  Take the following example: an unsteady flow dam breach output flow hydrograph.

Here we have a steeply rising flow hydrograph from a breach at the inline structure that appears to have a peak discharge of about 35,000 cfs.  To visually inspect whether or not this hydrograph captures the true peak, we can zoom in on the x axis by clicking and dragging a “bar” on the axis itself.  Simply place your cursor just below the x axis line, on the axis labels (in this plot, the time, in hours), then click and drag a red bar bracketing the portion of the hydrograph you wish to zoom in to.

Once you release the mouse button, the plot zooms in only on the x axis, in effect “spreading” out the hydrograph so that the peak is more apparent.  Notice that the full range of discharges still appear in the plot, we’ve simply truncated the time window to a more visually convenient range. 

Now notice we can see that because the hydrograph output interval is set too coarse (in this case every 10 minutes), we miss out on the true peak of the discharge hydrograph.  It happens somewhere between 1950 hours and 2000 hours.  By rerunning the model with a smaller hydrograph output interval, we can capture a better representation of the true peak discharge.  In the next figure, the discharge hydrograph is shown for the same location with a 2 minute hydrograph output interval.

After zooming in again on the x axis, we can see that we have a much better representation of the true peak of the discharge hydrograph, which is closer to 42,000 cfs, versus the 35,000 cfs shown in the first simulation:

The axis zooming feature works on any plot (input or output) and you can zoom on either the x or y axis.  So next time you’re evaluating hydrographs, or simply wish to have a better view of a curve in any of the plots, give the axis zooming feature a try.

Written by Christopher Goodell, P.E., D.WRE  |  WEST Consultants

Copyright © The RAS Solution 2014.  All rights reserved.

I’m starting a new series called “Exploring HEC-RAS”.  Each post will discuss a feature in the menu items, starting with the Tools menu item in the Geometry Schematic.  Today’s topic is “XS Interpolation Within a Reach”.

There are two options for interpolating cross sections in HEC-RAS:  “Within a Reach…”, let’s call this Option A, and “Between 2 XS’s…”, Option B.  First, let’s briefly review why you may need to interpolate cross sections in HEC-RAS.  Cross Sections should be selected early on in your project to adequately define changes in geometry, roughness, bed slope, and discharge.  Also, cross sections are needed to properly define the expansion and contraction zones around bridges, culverts, and inline structures.  Additional cross sections are needed in areas of rapidly varying flow and/or significant grade breaks to avoid overestimation of energy loss (http://hecrasmodel.blogspot.com/2010/01/another-reason-for-interpolated-cross.html).  There’s also that pesky warning message that seems to always pop up:    

Each of these warning messages suggest that more cross sections will provide a better solution.  Finally, in unsteady flow modeling, there’s a relationship between cross section spacing, wave speed, and computational time step that minimizes errors and numerical instabilities (Courant Condition).  Interpolating cross sections is a quick and convenient way to satisfy this relationship. 

The first interpolation method, Option A, is called Interpolation “Within a Reach…”.  This is also called “blind” interpolation, because you cannot see nor control how HEC-RAS interpolates new cross sections.  They are interpolated based on the internal interpolation scheme, with no user interaction, except for entering a maximum spacing value.   This method is good for testing whether the spacing of cross sections will help produce a more numerically stable simulation.  You can choose to interpolate over an entire river/reach, or a segment of a reach, based on your selection of the Upstream River Station and Downstream River Station. 

Here you can see there’s a single input box for the Maximum Distance between XS’s.  RAS will then determine the number of interpolated cross sections necessary between each set of original cross sections so that the main channel reach lengths never exceed that maximum distance.  There are a couple of other options to be aware of in this window:  Cut Line GIS Coordinates allows you to control whether HEC-RAS interpolates the cut line coordinates of the original cross sections, or simply displays the interpolated cross sections as perpendicular segments along the reach centerline.  Whatever you select here will have no bearing on the computations, but will only change how the cross sections are displayed in the geometry schematic.  If you have a georeferenced project with adequate initial spacing, the first option should display the interpolated cross sections just fine.  However, if you have a very sinuous river and the original cross sections are spaced too coarsely, the interpolated cross sections may not follow the stream centerline very well, sometimes resulting in interpolated cross sections laying off center or completely away from the stream centerline (see below). 

In this case, to better display the layout of the interpolated cross sections, select the “Generate for display as perpendicular segments…” option.  This will lay the interpolated cross sections centered on their bank stations and perpendicular to the stream centerline.

Notice how the interpolated cross sections now follow the stream centerline.  However, be aware that these new interpolated cross sections are NOT georeferenced.  If you will be mapping your results on inundation maps, it would be better to cut new original cross sections around the bend section of the reach and use the “Linearly Interpolate cut lines…” option. 

The dropdown box “Decimal Places in interpolated Sta/Elev” simply directs HEC-RAS to how many decimal places to carry out the station elevation points for the interpolated cross sections.  The default is 2 and is generally left alone.  One case where you may want more precision in the decimal places is with extremely shallow reaches, where the resulting bed profile may look “stair stepped” due to rounding off of the channel invert point.  Adding more precision will help to smooth this out. 

A word of warning about Interpolation Option A, “Within a Reach…”.  The interpolated cross sections under this method are generated by built-in interpolation routines, that simply linearly interpolate station elevation points based on their proportional stationing within a subsection.  You have no control over the interpolation.  As such, it is very important that before you use these interpolated cross sections for your final RAS model, you verify that they accurately describe the geometry of the reach.  If important geometric features are not captured or are improperly defined, you’ll want to get real cross sections, or interpolate using Option B, “Between 2 XS’s”.  It is advised that blind interpolation (Option A) only be used to test the numerical adequacy of the cross section spacing.  More on Option B in the next post.  Stay tuned. 

Written by Christopher Goodell, P.E., D.WRE  |  WEST Consultants
Copyright © The RAS Solution 2014.  All rights reserved.

A few testers have discovered a dll conflict when trying to open the new 5.0 beta version of HEC-RAS.  The following message appears:

This happens if you’ve installed the HDF5 Viewer as described in the new “Combined 1D and 2D Modeling with HEC-RAS” document on page 115. 

HDF5 is a new file format used by HEC-RAS to store 2D output as well as some 1D output (in addition to the standard output files and dss files).  The HDF5 file contains more output information than is currently available in the HEC-RAS graphics and tables, such as velocity information for cell faces and face points.  The HDF5 Viewer is currently the only way for users to access the 2D velocity output. 

The issue is resolved by uninstalling the HDF5 Viewer.  HEC will be posting an updated install soon that corrects this problem. 

Written by Christopher Goodell, P.E., D.WRE  |  WEST Consultants
Copyright © The RAS Solution 2014.  All rights reserved.

To my international HEC-RAS user friends.  It’s time again to remind everyone that you need to have your Region and Language Windows settings set to English (United States), particularly if you are running unsteady HEC-RAS models.  If you live somewhere other than the USA, and you get an error message relating to the “time” data, or “date” inputs, it’s a good bet that you need to change your region and language settings.

Hi HEC-RAS users.  HEC is extremely busy dealing with bugs and questions at the moment.  They’re currently working mostly to fulfill their obligations for technical support to the Corps of Engineers only.  If you are trying out the new version 5.0 beta, and you discover a bug, or if you simply have a comment or suggestion, please post them to The RAS Solution Forum.  I’ve agreed to collect, filter, and screen bug reports and comments and periodically send to HEC.  You can get to the forum and two new sub-forums: “HEC-RAS Version 5.0 Bugs”, and “HEC-RAS Version 5.0 Suggestions/Comments”, by following this link or by clinking the “The RAS Solution Forum” button up above. 

http://hecrasmodel.blogspot.com/p/hec-ras-bloggery-forum.html

Please post in the appropriate folder and keep the comments civil and constructive.  If you have a bug report, please post in the “bugs” folder and include as much information as is practical, but still keep it as brief as possible.  If you discover a “work-around” in the meantime, please included that as well. 

Also, don’t forget to get the latest version of HEC-RAS 5.0 beta here:

http://hecrasmodel.blogspot.com/2014/06/update-to-hec-ras-50-beta.html

Thanks-

Chris G.

@RASModel

Written by Christopher Goodell, P.E., D.WRE  |  WEST Consultants

Copyright © The RAS Solution 2014.  All rights reserved.

Critical depth is an important hydraulic parameter when evaluating hydraulic modeling results.  As we know from our college hydraulics 101 class, water flowing at depths less than critical depth is supercritical and water flowing at depths greater than critical depth is subcritical.  Supercritical flow is characterized by relatively shallow depths and high velocities.  Subcritical flow is characterized by relatively deep depths and slower velocities.  The forces dominating the movement of supercritical flow are inertial, while the forces dominating the movement of subcritical flow are gravitational.  The flow regime (subcritical or supercritical) a particular cross section, or series of cross sections is in, can be determined by the Froude Number,

, where F = Froude Number, V = Velocity, g = gravitational constant, and d = depth.

A Froude Number greater than 1 indicates supercritical flow, a Froude Number less than 1 indicates subcritical.  A Froude Number = 1 is considered “critical” and possesses the minimum amount of specific energy (potential energy plus kinematic energy, per unit mass).  This is considered an unstable condition in nature and is very rare.  If you ever get a Froude Number = 1 in your results, most likely, there is a problem with the computations (i.e. in steady flow, RAS could not come up with a valid solution, so it defaults to critical depth). 

For those of you who have run steady flow HEC-RAS models, you know that there are three flow regime options for computing a steady flow run:  subcritical, supercritical, and mixed flow (both sub and supercritical).  If you select RAS to run in subcritical, and somewhere in your system RAS is not able to compute a valid subcritical answer, then it defaults to critical depth and moves on.  If you select RAS to run in supercritical, and somewhere in your system RAS is not able to compute a valid supercritical answer, then it also defaults to critical depth and moves on.  If you select mixed flow, RAS will compute both a subcritical and supercritical profile and anywhere there is a valid solution for both regimes, RAS will select the one that has the higher specific force value.  If, in mixed flow, there are any cross sections that “default to critical depth”, that means there was a problem with RAS obtaining a solution.  Usually, this means your cross section spacing is too far apart, you are in an area of rapidly varied flow (with not enough cross sections), or just bad input data. 

In unsteady flow, contrary to intuition, checking the “Mixed Flow” box in the unsteady flow analysis window does NOT tell RAS to evaluate both sub and supercritical solutions.  This is done anyway in unsteady flow-whether “Mixed Flow Regime” is checked or not.  Let me repeat:  HEC-RAS can compute solutions in both subcritical and supercritical in unsteady flow regardless of whether “Mixed Flow Regime” is checked or not.  Checking the “Mixed Flow Regime” box in the unsteady flow analysis window simply uses a stabilizing scheme for situations near critical depth and with large changes in velocity with respect to time (the local acceleration term in the St. Venant Equation).  This is described further in http://hecrasmodel.blogspot.com/2011/04/mixed-flow-regime-options-lpi-method.html.  

It’s very helpful to understand the solution you’ve obtained after running RAS by viewing the water surface profile plot with the “critical depth” variable turned on.  This allows you to gage how close you are to critical depth, and more importantly, allows you to quickly evaluate if your solution has defaulted to critical depth anywhere, indicating a problem with the solution.  The critical depth variable can be turned on in any of the graphical plots by selecting Options…Variables.  Then check the box next to Critical Depth Elevation. 

When you do this, RAS will plot critical depth, but ONLY at certain locations.  Notice the plot from the Single Bridge HEC-RAS example data set.  Critical depth (in red) is only plotted downstream of the bridge, and at a couple of cross sections upstream of the bridge.  That is because RAS will only compute critical depth if your answer is supercritical, close to critical depth, or RAS is not able to come up with a valid solution (defaulting to critical depth) and at the boundaries. 

If you would like HEC-RAS to compute critical depth everywhere for you, go to the steady flow analysis window, and select Options…Critical Depth Output Option. 

Then check the box next to “Critical Always Calculated.