Tuesday, December 28, 2010

How to Create a Hotstart File in HEC-RAS for Dam Breach Analysis

Written by Aaron A. Lee   | WEST Consultants
Copyright © RASModel.com. 2010. All rights reserved.
While running unsteady flow simulations in HEC-RAS instabilities may occur when transitioning from the automatically created initial condition file to the first computed time step. These instabilities can be caused by mixed flow conditions, flow splits, or poorly defined initial conditions. A hotstart is another option available for defining initial conditions for the project model. This article presents one technique for setting up a hotstart run to help with initial conditions problems and to troubleshoot problem areas in your project model.

This is done by creating a new plan, using a flow file with a constant discharge as the upstream boundary, and a stage hydrograph as the downstream boundary over a 24 hour period. Typically 24 hours is long enough, but you may find that a longer hotstart period is required. The downstream boundary water surface elevation is defined artificially high, and over the simulation it is gradually reduced until it reaches the true starting depth for your project model. At this point the hotstart file will be written by HEC-RAS. In HEC-RAS lingo, the term “hotstart file” is used interchangeably with “Restart File” and “Initial Conditions file”.

STEP 1. Create a new flow file by opening the current unsteady flow file and navigate to File, Save As, and name it “hotstart”. Once saved, change the upstream boundary condition by selecting Flow Hydrograph under the Boundary Conditions tab. Change the discharge to a constant flow equal to that of the first timestep for the 24-hr period. In this example, shown in Figure 1, the entire Flow column should be modified to contain 155 for the full 24-hr simulation.

image

Select Stage Hydrograph as the downstream boundary condition. The beginning stage should start at an artificially high elevation - somewhere near the invert of the upstream-most cross section. The final elevation at the end of the 24-hr simulation should be equal to the starting downstream water surface elevation of the project plan. Once these values are added into the Stage column, use the Interpolate Missing Values button to add the missing elevations.

The elevation at each time interval should gradually decrease. This makes it easier for the modeler to observe problems as they occur, and where they happen in the model. For this example, the starting elevation is 820 ft and the final elevation is 637.25 ft. This is shown in Figure 2. Save the “hotstart” flow file.

image STEP 2. Navigate to the Unsteady Flow Analysis window and save as a new plan named “hotstart plan”. Name the short ID as “hotstart”. This will create a new plan that will be used to define the initial conditions for the project plan. Under the Unsteady Flow Analysis window select the Ending Date and Time to 24 hours after the Starting Date and Time (or whatever time frame you want to use-just be sure it is consistent with the hotstart flow hydrograph and stage hydrograph you created in Step 1).

STEP 3. The next step is to set up the model so that the hotstart file will be written. Under the Unsteady Flow Analysis window navigate to Options, then Output Options. Figure 3 shows this window.

image

Check the boxes that write the initial conditions file at the Fixed Reference of the hotstart simulation ending date and time. At the end of the specified simulation time (24 hours) HEC-RAS will automatically write the initial condition file. The final step is to ensure that the hotstart plan is using the correct geometry file, and the created “hotstart” flow file. Once the plan is completed and saved, compute the Hotstart simulation.

STEP 4. The profile plot should be reviewed for problems with the hotstart model. This will indicate areas that may cause problems in your project model. Over the course of the hotstart simulation, as the water surface drops into place along your bed profile, look for hints of instabilities. If you hotstart simulation crashes, you’ll know exactly where to investigate-the intersection between the artificially high horizontal pool and the bed profile at the time of the crash. To use the hotstart file as your initial conditions, go to the Unsteady Flow editor of your project plan. Click on the “Use a Restart File” box and browse for the initial conditions file. This file will have an extension that indicates that hotstart plan number that created it, the simulation time (day-month-year) when it was created, and .rst. In this example, it should look like:

Workshop4.p03.10NOV2006.rst

*Warning-If you make a change to the geometry in your project model, you’ll have to re-run your hotstart simulation. However, once everything is set up, this is very easy to do. Simply open the hotstart plan and run it. Then open the project plan and run it.

Friday, October 22, 2010

Some useful debugging tools

Written by Chris Goodell, P.E., D. WRE | WEST Consultants
Copyright © RASModel.com. 2010. All rights reserved.

Recently I’ve had some real difficult models to set up and run. Some real beasts. And some of these take hours to run. As you can imagine, when one of these models is crashing, strategies for effectively diagnosing and fixing errors become very important. You don’t want to “chase” problems in models with 2 hour run times. You’ll never get your model stable. You need to be able to diagnose the problem and come up with a confident fix, while minimizing the time spent running the model to “try out” possible fixes.

Here’s a real useful tool that has recently been added to HEC-RAS.

image

In the Runtime Computational Options, you have the option to “disregard” Lateral Structures, Storage Area Connections, Breaches, and Pumps in the computations. Let’s say you turn off lateral structures, rerun your model and it runs fine.

image

Then you know that there is a problem with one or more of your lateral structures. Simple diagnosing tool-but very effective.



Also, I’ve been using the Computation Level Output a lot. By checking this box on the Unsteady Flow Analysis window, you are able to look at some select output parameters at every computational time step interval. These parameters include water surface elevation, flow, and lateral inflow. You can view two types of plots: a spatial plot and a time series plot, by going to the “View” menu item on the main RAS window.

image

The first two are very useful, and at a computation interval level, can show you things that just won’t show up on the detailed output profile plots. However, the ability to monitor lateral inflow, graphically, and at the computation interval level, is a powerful way to determine when and how much discharge is entering a given reach laterally (via lateral structures from other reaches or storage areas).

image This is a common source of errors that can lead to instabilities in complex HEC-RAS models, and aside from this plot, I don’t know of another way to graphically see this.

Thursday, August 19, 2010

How to use a Storage Area to define a Reservoir.

Written by Chris Goodell, P.E., D. WRE | WEST Consultants
Copyright © RASModel.com. 2010. All rights reserved.

It’s a little confusing, and not really directly covered in the manuals anywhere. But I get this question a lot. “How do use a Storage Area to define my reservoir in RAS?” First of all, make sure using a Storage Area and level pool routing is an appropriate way to model your reservoir. This is even more important if you are modeling a dam breach on this reservoir. Check this post first to make sure it’s okay.

Once you’re happy with the level pool assumption, draw in (or import)your downstream reach in the geometric editor. Then add in your cross sections. Next, place your inline structure (dam) at the upstream end of the reach. You’ll need to place two dummy cross sections upstream of your inline structure (and downstream of your storage area). These can be copies of the cross section downstream of the dam, but should be as close as possible to the upstream toe of the dam and close enough to each other to minimize the associated volume (relative to the reservoir’s total volume). Next draw (or import) your storage area upstream of the inline structure and it’s two dummy cross sections. It’s not uncommon to have the two cross sections reside within the storage area’s boundaries. That’s okay and it doesn’t affect the computations either way.

To make RAS recognize the connection between the upper dummy cross section and the storage area, you have to “move” the upper end point of the reach inside the storage area. To do this, go to Edit…Move Object, in the main geometry window.

image

Once in “move” mode, click and drag the upstream end point inside the storage area. RAS should then automatically recognize the connection. Make sure to uncheck “Move Object” in the menu once you’re finished. It should look something like this when done:image

Make sure you provide some outlet flow, or your dam will overtop at the beginning of the simulation. This can be done by coding in gates, or by providing pilot flow. If you’re providing pilot flow, you must enter in an “Internal R.S. Initial Stage” for one of the dummy cross sections to set up your starting pool elevation. This is set in the Options menu item in the Unsteady Flow Editor.

image

Wednesday, August 18, 2010

Stability Issues with Storage Areas

Written by Chris Goodell, P.E., D. WRE | WEST Consultants
Copyright © RASModel.com. 2010. All rights reserved.

Storage Areas in unsteady RAS are notoriously stable. That’s why we like to use them. Get the water out of the 1-d St. Venant unstable environment, into the 0-d stable continuity environment. However, I recently discovered a problem with storage areas that could cause your model to go unstable, or at least chug along slowly at max iterations.

Storage Areas in RAS are defined solely by a storage-elevation curve. That’s another reason we like them…they’re easy to code in. A typical storage-elevation curve looks like this:

image

Notice how is rises fairly quickly in stage from its minimum elevation then starts to level off as the added volume per ft of stage becomes larger and larger.

Now, if you have a storage volume curve that rises too quickly, it could pose problems.

image

Because the storage area is handled with the continuity equation, this is typically not an issue by itself. However, when these storage areas are connected with a reach (and they typically are) in the “quickly rising” range of elevations (here in the example between elevations 4388 and 4393), then we might violate my number one rule of unsteady flow RAS modeling-Changes should happen gradually-changes in discharge, changes in stage, changes in flow area, etc. etc ,whatever. In this case we are changing the stage in the storage area which is causing a quick change in flow over the connecting lateral structure and a quick change in stage in the adjacent cross section(s).

Solution: Looking at this steeply rising storage area curve , we can guess that the quickly rising portion of the curve might represent some small ditches or creeks, or even some small pits within the storage area. Is it critical to represent these features in the model, especially if we’re most interested in the high flow portion of the simulation? Also, will it make that much difference to remove these features? Probably not. We should keep the invert or minimum elevation point, incase any connecting cross sections have inverts at that elevation, but if we remove the 2nd and 3rd points from the curve, it doesn’t drastically change the look of the curve, and it just might stabilize this area.

image

How to spot this problem: While you’re running your model, if it gets caught on maximum iterations at a storage area, or if it bounces between a storage area and an adjacent part of a reach, then this could be the problem. Also, if you’re maxing on iterations at a cross section or range of cross sections that is adjacent to a lateral structure, and the elevation of the reported error suggests you are overtopping that lateral structure, make sure that the connecting storage area doesn’t have a steeply rising storage elevation curve.

Here’s an example:

Maximum iterations of 20 at: RS WSEL ERROR

03JAN2010 09:50:38 River Upper 34454.76 4423.88 0.055

03JAN2010 09:51:00 River Upper 34602.8* 4424.34 0.027

03JAN2010 09:51:08 River Upper 34602.8* 4424.39 0.048

03JAN2010 09:51:23 SA Area47 4392.44 0.052

03JAN2010 09:51:30 River Upper 34602.8* 4424.34 0.026

03JAN2010 09:51:38 River Upper 34602.8* 4424.39 0.047

03JAN2010 09:51:53 SA Area47 4392.66 0.058

03JAN2010 09:52:00 River Upper 34454.76 4423.93 0.028

03JAN2010 09:52:08 River Upper 34602.8* 4424.39 0.048

03JAN2010 09:52:23 SA Area47 4392.91 0.065

03JAN2010 09:52:30 River Upper 34454.76 4423.93 0.027

03JAN2010 09:52:38 River Upper 34602.8* 4424.40 0.048

03JAN2010 09:52:53 SA Area47 4393.19 0.073

03JAN2010 09:53:00 River Upper 34454.76 4423.94 0.030

03JAN2010 09:53:08 River Upper 34602.8* 4424.40 0.050

03JAN2010 09:53:23 SA Area47 4393.50 0.080

03JAN2010 09:53:30 SA Area47 4393.58 0.083

03JAN2010 09:53:38 River Upper 34602.8* 4424.40 0.051

03JAN2010 09:53:53 River Upper 34602.8* 4424.38 0.022

03JAN2010 09:54:00 River Upper 34454.76 4423.94 0.023

03JAN2010 09:54:08 River Upper 34602.8* 4424.41 0.050

03JAN2010 09:54:30 River Upper 34454.76 4423.96 0.037

Notice how the errors are bouncing between Storage Area 47 and a specific part of the reach “River Upper”. If we check storage area 47, sure enough, its storage elevation curve rises very quickly, and could probably be adjusted to removed the stability issue in the range of stages shown in the computation message log (about 4392 to 4393 ft).

image

Tuesday, July 13, 2010

Cross Section Points Filter

Written by Chris Goodell, P.E., D. WRE | WEST Consultants
Copyright © RASModel.com. 2010. All rights reserved.

Now that a lot of us use GIS to generate our cross sections, this is becoming a much more “used” feature in RAS: The Cross Section Points Filter. RAS allows a maximum of 500 station-elevation points in any given cross section. It is very common for one or more cross sections cut in GIS to come in with a LOT of station elevation points. And then, if you interpolate cross sections (interpolated cross sections have more-or-less double the station elevation points as their bounding sections) you’ll have even more points. Exceeding 500 points in a cross section is very easy to do.

RAS offers a few ways to filter out points. There is the “Near and Co-linear” filter. This allows you to specify a tolerance for points that are very close to each other, and points that are in a straight, or nearly straight line. RAS will then remove points that are within the tolerance level (i.e., if you have three points in a perfectly straight line, there is no need to include the middle point in your geometry-unless it happens to be a bank station or n-value break point, in which case RAS will preserve it).

However, my preference normally is to use the “Minimum Area Change” option. RAS will remove points sequentially in an effort to minimize the area change of the cross section. You, as the user, simply specify the number of points you want RAS to filter to, and all the work is done for you. This is a much more convenient way to filter points-and much faster, but be aware that you have a lot less control over how the points are filtered. If you have a lot more than 500 points to begin with, it is a good idea to compare the “before” and “after” cross sections to make sure the new cross section preserves the true geometry. In my experience RAS does a great job at filtering using the Minimize Area Change option.

If RAS tells me there are a lot of cross sections that need to be filtered, I’ll use the “Multiple Locations” tab to get them all done at once. Select all the cross sections in your geometry (even the ones that don’t exceed 500 points) and RAS will only filter the cross sections that need filtering.

image

Thursday, June 24, 2010

Contraction and Expansion Losses for Unsteady Flow

Written by Chris Goodell, P.E., D. WRE | WEST Consultants
Copyright © RASModel.com. 2010. All rights reserved.

Since unsteady flow was introduced in HEC-RAS years ago, the contraction and expansion loss coefficients were not used, because losses due to contraction and expansion were automatically approximated in the conservation of momentum equation. Since steady flow RAS does not use the momentum equation for backwater computations, we had to approximate the contraction and expansion losses using those loss coefficients that you see for every cross section in the cross section editor. When switching to unsteady flow, you could leave those coefficients in every cross section; RAS just won’t use them.

image

In the latest version of RAS (version 4.1), the release notes indicate that RAS may not be capturing all of the C&E losses in unsteady flow, particularly at sharp contractions and expansion. And therefore, unsteady contraction and expansion loss coefficients can now be used.

From the 4.1 Release notes:, “In general, contraction and expansion losses are not used in unsteady flow, and therefore the default coefficients are 0.0. Forces due to contractions and expansions are handled in the momentum equation through pressure force differences. However, because HEC-RAS is a one-dimensional unsteady flow model, the one-dimensional momentum equation does not always capture all of the forces action on the flow field at a sharp contraction and/or expansion zone. In order to better approximate the forces acting on the water, and the resulting water surface elevation, at a contraction and/or expansion, the user can enter empirical contraction and expansion coefficients for unsteady flow modeling. These coefficients will be multiplied by a change in velocity head, just like in steady flow modeling, but the resulting energy loss gets converted to an equivalent force for placement into the momentum equation.”

Notice that there is a new table for entering unsteady flow contraction and expansion losses.

image

So the obvious question is, “what values do we use for unsteady flow contraction and expansion coefficients?” Are they the same as their steady flow counterparts? Also, when do we want to use them?

Any suggestions out there???

Thursday, April 29, 2010

Probabilistic Methods for Dam Breach Modeling

Written by Chris Goodell, P.E., D. WRE | WEST Consultants
Copyright © RASModel.com. 2010. All rights reserved.

I would appreciate any feedback from you all on this topic. It's something I've been thinking about for a while now. My biggest concern with the current practice of dam breach modeling is the overwhelming uncertainty associated with dam breach parameters. Not only the ultimate breach shape and development time, but things like the initiation mechanism of the breach, the discharge coefficients (both weir and orifice), and the progression rate. The deterministic approach we use leaves a bit to be desired in my opinion. Sensitivity analyses have shown that the breach outflow hydrograph can easily vary by 100% or more, based on the set of parameters used. I've been considering ways to generate a breach outflow hydrograph based on probabilistic methods. The idea being instead of providing our "best conservative guess" for the breach hydrograph, we can produce a 95% (or whatever percent) conditional non-exceedance hydrograph based on both overall peak discharge and also timing. Meaning, this is the dam breach hydrograph that will not be exceeded in peak value 95% of the time, given a dam failure for a given failure mechanism (overtopping or piping). This is done by assigning probablity distribution functions to each breach parameter, then run a Monte Carlo simulation using random assignments (within the minimum and maximum bounds and following the prescribed distribution function) for each breach parameter. Then we can plug the resulting 95% hydrograph (or the associated set of breach parameters to create that hydrograph) into our HEC-RAS unsteady flow model and resume our deterministic approach. At least we have taken the deterministic selection of breach parameters out of the analysis. I suppose at some time, the entire model could be approached with probabilistic methods, but first things first. In fact, HEC is currently working on implementing Monte Carlo simulation capabilities into HEC-RAS for a future release.

I wonder if any state Dam Safety office is ready for this type of analysis for preparing inundation maps for emergency action plans. I think it makes more sense.

Tuesday, March 30, 2010

Dynamic versus Level Pool Reservoir Drawdown for Dam Breach Modeling

Written by Chris Goodell, P.E., D. WRE | WEST Consultants
Copyright © RASModel.com. 2010. All rights reserved.

This is a summary from a paper (Goodell,Christopher;Wahlin, Brian. “Dynamic and Level Pool Reservoir Drawdown: A Practical Comparison for Dam Breach Modeling.” 33rd IAHR Congress Proceedings, Vancouver Canada, 2009) on level pool versus dynamic reservoir drawdown for dam breach modeling. In RAS you can define your reservoir with a series of cross sections (which uses dynamic routing) or a storage area (which uses level pool routing). Dynamic routing is generally assumed to be more accurate, but the size and shape of a reservoir can sometimes make level pool reservoir adequate.

A key component to dam breach modeling is the reservoir drawdown. This has a significant impact on the magnitude and shape of the breach outflow hydrograph, and ultimately the extent of flood inundation in the downstream reach. Drawdown of the reservoir can be modeled with the precise and physically correct dynamic routing method, which uses the full St. Venant equations of Conservation of Mass and Conservation of Momentum. However, this requires detailed bathymetric data for the reservoir, which is frequently very difficult and expensive to obtain for existing reservoirs. Furthermore, dynamic routing is complex and prone to numeric instabilities. A level pool drawdown is a more simplistic, numerically stable approach that can be used successfully under certain circumstances and requires only a simple stage-storage curve for the reservoir.

Two primary characteristics emerge as indicators of a given reservoir’s ability to be described by a level pool analysis. The Compactness Factor, Fc, is simply the ratio of the dam height (H) to the reservoir length (L). The longer and shallower the reservoir, the lower the Compactness Factor and the more the reservoir acts like a river during its drawdown. Thus dynamic routing would be more appropriate in this situation. Short, relatively deep reservoirs are more compact, have a larger Fc value, and can be adequately described using a level pool analysis.

The Translation Factor, Ft, describes the relationship between the speed of the breach development and the ability of the reservoir to supply water to replace the water leaving through the breach. The easier the reservoir can deliver water to the breach, the more it can be described by a level pool analysis. Fast breach developments and long reservoirs are more appropriate to be modeled by dynamic routing. The Translation Factor is computed as:

Ft = ct/L

Where: c = shallow water wave celerity =clip_image002.

d = representative reservoir depth.

and t = time.

A third parameter can be used to help graphically display the results of the various simulations. The Drawdown Number, Dn, is defined as the product of the Translation Factor and the Compactness Factor.

clip_image002




It becomes apparent that for high Drawdown Numbers, the level pool analysis produces results very close to dynamic routing. By enveloping the data points, a 5% threshold Drawdown Number is shown to be 0.41. That means that a reservoir with a Drawdown Number of 0.41 or greater will produce peak outflow results within 5% of a dynamic routing simulation. The 10% threshold Drawdown Number of 0.24 is also indicated on the plot.

You can see the full paper in the referenced proceedings. Also, the Hbox software has an automated utility for determining the appropriateness of level pool reservoir drawdown based on thd Drawdown Number analysis.

Wednesday, March 24, 2010

Dam Breach Modeling Q & A

Written by Chris Goodell, P.E., D. WRE | WEST Consultants
Copyright © RASModel.com. 2010. All rights reserved.

Some questions and answers related to dam breach modeling in HEC-RAS…

Question. The Sunny Day model has a consistent water surface elevation from the very start of the model – it only decreases once the breach occurs. How is HEC-RAS setting this starting WSEL?

Answer. You define the starting water surface elevation either by equalizing the flow from your outlet works with the reservoir inflow, or by setting an initial conditions water surface elevation in your flow editor and a pilot flow through the dam equal to the reservoir inflow at the beginning of the simulation.

Question. My breach models show a dramatic decrease in max Q from the cross-section immediately downstream of the dam to the end of the model. I know that HEC-RAS has an inherent storage routine that attenuates the flow throughout the model but is it reasonable to have a result that shows a beginning max Q of 12,370 cfs and an ending Q of 275 cfs (the reach is approx. 3.8 miles long with a slope of 0.02 ft/ft upstream and 0.001 ft/ft downstream)? This is an arroyo about 800-900 ft. wide, Manning’s at .055.

Answer. I would be skeptical of those results. Perhaps there is an error somewhere in the simulation, or you have a lot of flow leaving the system. Sometimes, if your model is not properly constructed, you can develop a large “wall of water” in profile view. A lot of times this is due to poorly defined HTAB parameters. This will create an artificial pool of water behind the wall, which will drastically attenuate your flood wave. Look in the profile plot and animate through your simulation. If you see an unexplainable wall of water backing up flow, that would be the cause.

Question. My models are stable but still have inherent errors (max iterations) and critical depth defaults to varying degrees. Does this have a significant effect on the model results? Changing parameters at this point to reduce inherent errors most likely will cause instability.

Answer. Max iterations are not necessarily a problem as long as the associated errors are small and it is not causing visible instabilities or obvious errors in your results. I try to get rid of all max iterations where possible. If not possible, I try to get the errors below 0.1 ft as much as I can (my own rule of thumb). RAS does not typically default to critical depth in unsteady flow (like it does in steady flow). But it sounds like you have areas that have flow close to critical depth. This can cause instability problems. If you believe flow should be close to critical depth in these locations, try turning on the Mixed Flow option and adjusting your LPI factor. If you do not believe flow should be near critical in these locations (most of the time in natural streams you should not see critical or supercritical flow), then you may be underestimating your Manning’s n values. Manning’s n values for the front end of dam breach flood waves and steep reaches are frequently underestimated. Check Jarrett’s equation if in a steep reach. Your reach slope of 2% is quite high. An n value of 0.055 is possibly too low during the low flow period preceding the dam breach flood.

Question. Does the number of vertices defining a cross section matter, in another words, does the model run better with cross sections that have fewer vertices but still accurately define the section, vs. similar sections that have many redundant vertices?


Answer. Better definition is usually advantageous. RAS does not like to have long horizontal portions of cross sections which is common for coarsely-defined cross sections. It can cause numerical problems. These days, having the maximum number of points in a cross section (500) typically does not noticeably slow down computation speed. I recommend getting as much detail as you can in your cross sections.

Tuesday, March 23, 2010

Bridge on a Spillway

Written by Chris Goodell, P.E., D. WRE | WEST Consultants
Copyright © RASModel.com. 2010. All rights reserved.

I just got an interesting question. How do I model a bridge that has a spillway just downstream of it? Here’s an example of what I’m talking about:

water flowing over the spillway at the Bitan Bridge, Xindian, 8 Aug 2007

As I see it, there are a three ways to approach this. You could go conventional, and model both a bridge and an inline weir and try to squeeze in a couple of cross sections in between. This is probably the easiest, but not always possible if the bridge is on top of, or very close to the weir.

Another approach is to model the bridge as a bridge, and the weir with a series of closely spaced cross sections. This can be problematic if you have a high drop over the spillway with low tailwater elevations. And the cross sections will have to be very tightly spaced, to prevent over-estimation of energy loss over the weir. This is not recommended for vertical drop structures.

A third approach would be to model both the bridge and the weir together as an inline structure. The bridge opening can be simulated using a gate (or series of gates). The space between the gates simulates the piers. The gate invert is the top of the weir. The gate height then simulates the distance from the top of the weir to the bottom chord of the bridge. The upper chord of the bridge can be entered in as the top of dam. Make sure to leave the gate wide open for the entire simulation. Also, a nice advantage is that each gate can have it’s own weir discharge coefficient.

image

Any other suggestions out there?

Friday, March 12, 2010

Adding Help Files and References to RAS

Written by Chris Goodell, P.E., D. WRE | WEST Consultants
Copyright © RASModel.com. 2010. All rights reserved.

Everyone has their favorite references that they go to for help and guidance when developing hydraulic models. It could be the n-value table in Chow, or Tony Wahl’s Breach Parameter paper, or simply specific exerts in the RAS manuals. Whatever your preference, HEC has provided a very convenient way to easily access reference documents while in the HEC-RAS environment. You simply copy the document and paste it into the \Program Files\HEC-RAS\4.1.0 folder. You have to change the name so that the file begins with “RasHelp_”. That is how RAS recognizes it as a help document. Then when you open RAS, under the Help menu, you’ll see your custom documents listed for easy access. Notice that I have Appendix B of the RAS Hydraulic Reference Manual, a summary of Breach Parameter equations, and a Sediment Gradation Table in the Help menu.

image

image

Monday, March 8, 2010

Earthquake in Chile. February 27, 2010

Written by Chris Goodell, P.E., D. WRE | WEST Consultants
Copyright © RASModel.com. 2010. All rights reserved.

I know this is an HEC-RAS blog, but I decided to bend the rules a little and post a recap of my experience during the earthquake in Chile last weekend. Hope you find it interesting...

Early Saturday morning, February 27th, around 3:30 am, a massive earthquake rocked south central Chile. The epicenter was just off the coast of Chile’s second largest city, Concepcion. I was in Santiago at the time, approximately 300 miles north of Concepcion, with plans to fly to Concepcion on Sunday to teach a class at the University there. I had just arrived in Santiago Friday morning, February 26th, and spent the day site-seeing and getting used to my “meager” accommodations. Actually, the room is quite nice, for the price and it has a kitchenette. However, the wireless internet was not working in my room. Friday night, I had a great time at dinner with old friends of mine, who are residents of Santiago, Patricio and Macarena Banados. Dinner traditionally happens very late in Chile, and I returned to my hotel around 12:30 am. I was very tired from the overnight flight and the time difference, so I fell asleep very quickly while watching BBC (the only English language channel on the TV).

At about 3:30 am, local Chilean time, I woke up to a rumble. I was lying in bed and it began to shake a little. Living on the west coast, I’ve felt a few earthquakes in the past. There was one in Portland, while I was on spring break from college in 1993. Like the Chilean one, it too abruptly woke me up. However, the Portland earthquake was more of a novelty. I believe it was about a 5.6 on the Richter scale. I woke up, wobbled over to my window and stood there watching for anything to happen while my parent’s house shook a little. It lasted about 30 seconds, if I recall. The Chilean earthquake was a lot different.

Though it woke me up with a little mild shaking, this earthquake quickly began to grow in intensity. Within (probably) about 10 seconds, my entire room was violently shaking. Outside my window, which I had left open before going to bed, I could hear loud cracking and popping sounds over the background rumbling and of car and building alarms that began to sound. It was so violent, that I quickly decided that this was not another “Portland” earthquake. My first thoughts were that I was on the 14th floor of an apartment building, and I’m in Chile-both of which scared me to death. At that point all I could think about was to get as far away from the edge of the building as I could. While I could see the dark outline of the hanging lamp in the kitchenette swinging back and forth, and I could hear stuff toppling over in my room, I made my way to the door. I have to admit that at this time I briefly paused and considered getting dressed first (I was only in my boxer shorts), but I don’t think I could have even put clothes on with the shaking that was happening. Furthermore, it was very dark in my room, since the power was already off. So I decided to put aside my modesty and get out.

Quickly panic set in as I realized that my door was locked. And this was not a matter of twisting the latch, like a typical American hotel room door. This door is the kind that is locked with a key from the inside. To make it worse, there were two locks (of course I had set both of them before going to bed), two different keys, it was dark, and one of the locks had to be “giggled just right” to unlatch. The exercise of finding the keys, and fumbling around with the locks (it’s hard to put a key into a lock, when the lock doesn’t stay in the same place!), felt like it took forever, all while I’m expecting the building I’m in to collapse around me. FINALLY, I got the door opened, briefly thought about locking it behind me (but didn’t) and stumbled through the hallway. I knew from structural engineering class in college that a central “core” elevator shaft is frequently the strongest part of the building. Not sure if that applies in Chile, but that’s where I headed. I made it to the elevator, put my hands on either side of the elevator doorway, took a wide stance, and braced myself. I figured I would never make it down 14 flights of stairs with the kind of shaking I was feeling, so I decided to wait it out on my floor at the elevator. This is when I put my head down and started praying. “Please, God…make this stop.” Over and over. It felt like another 30 to 40 seconds that I was at the elevator bracing myself, before the earthquake finally subsided. All told, the earthquake lasted anywhere from 90 seconds to 2 minutes (I’ve heard both reported).

Even though the earth stopped shaking, my body was trembling uncontrollably. My legs felt like noodles, my hands were shaking, and my heart was beating out of my chest. That was when I realized I had to get out of this building. I didn’t know if there had been serious structural damage, or broken gas lines. Either way, I wanted to get out. So I ran back to my room, happy that no one on my floor had come out to see the half-naked gringo running around, opened the door and frantically looked for clothes to throw on. With my shorts and shirt on, I grabbed my shoes, jacket, phones, and computer bag and left.

This time, when I left the room, people started to emerge from their rooms. I ran down the hall towards the stairwell. As I passed the elevator, it opened up and a Chilean man came out. I was thinking “what the &#$*% are you doing in the elevator?” If I knew how to say that in Spanish, I probably would have. But instead I ran by. The elevator must have been running on backup power. He said something to me in Spanish as I ran by that I think was “Where are you going?” I yelled back, “A bajo!” Apparently, even with my short response, he could tell from my accent that I was a foreigner, so he ran after me telling me in English to stop and come back. So I stopped. The guy seemed like he knew what to do. He asked me “are you scared?” “YES, I’m scared. I’m getting out of here.” Then he told me I should come with him. To my astonishment, he said it was better to take the elevator down. I said “Really?!?!” My mixed tone of sarcasm and confusion didn’t faze him and He said “Yes yes yes. Come on.” So I did. Thinking about that now, what an idiotic thing to do! Fortunately we made it to the bottom floor without incident. On the way down, the Chilean man could tell I was very scared and was nice enough to reassure me that everything was okay. He kept saying over and over, “This is not Haiti. This is not Haiti.” You see, the small, impoverished country of Haiti had just experienced a devastating earthquake a few weeks before, where their cities and towns were left in ruin. “We have earthquakes here a lot. Our buildings are strong.” It was reassuring.

Nevertheless, my immediate goal was to get outside and as far away from the building as possible. I was taken aback that just about everyone was standing in the lobby or just outside the lobby door on the sidewalk. I got to the sidewalk outside the lobby and put on my socks, shoes, and jacket, then crossed the busy 4 lane street to the other side. There were only 3 other people (out of hundreds) who decided to cross the street-all were Asian. I found it very odd that all of the locals had no problem standing at the base of this 21-story high rise.
At this point I tried to make some phone calls. Not surprisingly, the phones system was completely jammed and I couldn’t get a call out to my family. After redialing what must have been 100 times, I finally got my wife, Wendy’s cell phone, but it went to voice mail. By now, it was almost 4:00 a.m. in Chile, and 11:00 p.m. in Portland. I figured everyone had gone to sleep already, knowing nothing of what was going on in Chile. So I left a brief message, saying there was an earthquake, and I was okay. I found this out later, but Wendy did get the message that night and stayed up all night watching the news and trying to call me back. I spent the next hour or so trying to make phone calls to no avail. My cell phone battery was getting very low, so without power to recharge it, I decided to wait until the next day to try calling again, so that I could preserve whatever battery power I had left.

In total, I probably spent a couple of hours outside-standing, sitting, pacing, and praying. Occasionally I would check back in the lobby to see if I could find anything out, but could find no one who spoke English. The lobby was packed with people, some of whom were already making beds for themselves on the floor. At about 6:00, I went back in the lobby again, and noticed that some people were heading back up the stairs. So, I weighed my options. I could remain outside, tired, uncomfortable, and helpless, or go back to my room and try to sleep. The building looked okay from the outside. No cracks or visible damage anywhere. My sleepiness took control and I walked the 14 flights of stairs back to my room. With my iPhone’s Flashlight app (that was a lifesaver!), I managed to get my room prepped for a quick escape in case of any large aftershocks, and fell asleep on my bed, with all my clothes on. I must have lain there for a half-hour or so, still completely wired from the adrenalin, but then fell asleep. Speaking of iphones, I’m still angry at myself for not having my iPhone at the ready, for video recording impending after-shocks.

Sure enough, I was woken at 7:30 am to a big aftershock and a chorus of car alarms. Nothing like the original earthquake, but still much bigger than the Portland earthquake and enough for me to jump out of my bed and run to the door. As I made my way to the door, I noticed the hanging lamp in the kitchen swinging back and forth again. By the time I got the door opened, the aftershock had ended. I took a quick peek outside (by now it was light outside), and seeing no damage, decided to stay in my room. While I was looking outside, I saw some kids playing in a room in the other wing of the building. They seemed to be enjoying the excitement. That somehow, made me feel better. By now, despite the lack of sleep and jetlag, I was fully awake. Now that there was daylight outside, I could see the effects the earthquake had on my room. To my astonishment, it was in very good shape. No visible cracks anywhere. My toiletry items had all fallen off the sink, and some kitchen items had fallen onto the floor, but the room was just fine. (Note, as I’m typing, at 1:40 pm on February 28th, another small aftershock occurs. That makes 7 aftershocks now that I’ve felt so far. I’m sure many more that I didn’t feel. There is a tennis club across the street from my hotel that has an alarm that goes off with the larger aftershocks. It has reliably been going off just before I feel the shaking. It’s nice to have warning.). At this time, the engineer in me took over, and I decided to have a walk around the hotel, to survey the damage. I started on my floor, and worked my way upstairs to the roof, where there is a patio and two pools. On my floor there was not too much damage. Some drywall had crumbled and fallen to the floor around the doors, and some tiles had popped off, but otherwise, nothing much. On the roof, there was much more damage, but still surprisingly little, given the violence of the initial earthquake. No one else was up there. (note, another small aftershock as I type and accompanying tennis club alarm. I can also hear some chimes jingling around-1:45 pm, February 28th). There is a water heater room on the roof and the door was open. Inside the water heater room, entire sections of sheetrock from the roof had come down. Also, ashtray cans on the patio were toppled, and tiles had popped off walls. Next to the pools, there was a lot of standing water in low areas on the patio, where apparently water had sloshed out of the pool the night before. All of the filter caps, that are common around the perimeter of pools, had popped off during the quake, and some had slid (or floated) across the patio as much as 10 feet. I’m assuming the wave action in the pool pushed the filter caps out from the inside. As I was surveying the pool and patio, the second aftershock happened. This one was imperceptible to me, but I knew it was happening because out of nowhere, the pool started making waves, and the air was completely still. The water in the pool was previously glassy smooth, and then there were some small waves. I took video of this with my iPhone. As I glanced around the skyline of Santiago (360 degree view from the roof), I was surprised to see that from my vantage point, there was no damage I could see. All of the buildings that were there the previous day, were still there. Even the older ones.

After the rooftop survey, I decided to take a walk around the Bellavista neighborhood near my hotel. During this walk, I was able to see a lot of damage. Most of the damage was on building facades, or roof tiles sliding off. The first significant damage I saw was a Subway sandwich shop, where the top 10 feet of the facade had crumbled to the sidewalk below. There was a massive pile of bricks and stucco. I couldn’t help but wonder if someone had been below during the quake. They would not have survived. As I continued to walk, many buildings had roof and facade damage, and many windows had popped out and shattered on the ground below. But surprisingly, all of the buildings in this very old neighborhood were still standing, many with no perceptible damage to the exterior at all.

Shortly after I got back to my hotel, around 12:00 noon, the power came back on. So I charged my phone while watching the BBC to see what was going on. This was when I learned that the epicenter was just off the coast of Concepcion and there was significant damage there. Many buildings had collapsed, some were still on fire, a bridge had fallen into the Rio Bio Bio, and reportedly, up to 70 people had died. As I type, the updated death toll is over 700 and I’m very concerned for my friends and their family who live in Concepcion. I still cannot get a phone call through to them. All of Concepcion is cut off. I also learned that the airports in Santiago and Concepcion were both closed indefinitely, and the road to Concepcion was shut down due to collapsed bridges. It looks like I won’t be making it to class. It was also fascinating to see on the news how the entire Pacific ring was bracing for tsunamis. Concepcion itself, being on the sea, was rocked by a big tsunami, shortly after the quake. There was a lot of concern that Hawaii was going to get hit with a large tsunami, but by the time it eventually got to Hawaii, it was rather uneventful. Currently, as I watch the news, seismologists say the earthquake was an 8.8 on the Richter scale at its epicenter near Concepcion, and an 8.0 in Santiago. I am stunned to hear this. An 8.0 is about 400 times stronger than the 5.6 I felt in Portland years ago. It’s amazing that more damage did not happen in Santiago. Hats off to Chilean structural engineers! There were a few more aftershocks while back in my room. The smaller ones are hard to tell if it’s really an aftershock, or just my own perception. So with the swimming pool as my inspiration, I set up a make-shift “earthquake-ometer”: a glass of water. Filled to the top so that any spilled water would tell me if there had been any aftershocks while outside.

With phone charged, I later I walked to the Providencia neighborhood, where there was much more damage. Given that, it’s interesting that Providencia is a newer neighborhood than Bellavista. A church dome was completely destroyed, a modern office building had a deck that had partially collapsed around its 30th floor, and panes of glass had popped out of buildings all over the place. On my way to the Providencia neighborhood, I walked through the parks that line the Rio Mapocho. All thoughout the parks are 10-ft high lamps capped with three lights each-there must be thousands of them. The lights have (had) glass domes on them. Almost every single lamp I walked by had 1 to 3 of the domes shattered on the ground below. While eating lunch in Providencia (at one of only a few restaurants that was open), I felt the third aftershock. The waiters appeared to be having a good time watching “the concerned gringo”.
On my way back to my hotel, while still in Providencia, I was finally able to get through to my wife on my rented mobile phone. What a relief that was, especially when I found out that she had indeed received my message the night before telling her I was okay. She gave me some details about what she was hearing on the news at home.

After spending some more time in my hotel room, and no internet to use, I decided to head out to the Plaza de Armas for a wireless hotspot walkaround with my iPhone. While walking through the Ahumada pedestrian mall, I found an unrestricted wireless connection and was finally able to get on the internet. People must have thought me a gringo loco, since I was pacing around, back and forth, trying to maximize the wireless signal strength. I took care of some email, tried to Skype with my wife (to no avail), and spent some time on Facebook. Though Wendy had let everyone know I was okay, it was good to be connected again to the world, so I could check in.
Well, with the Santiago airport closed indefinitely, and the class almost surely cancelled, my plan is to wait around Santiago until I can get a flight out. My friends Patricio and Macarena have no power or water at their home, so I’m going to stay at the hotel here and make the best of it. Fortunately, I was able to extend my stay without any problem. Now, if they could only get around to fixing the wireless internet connection.

RAS 4.1

HEC-RAS version 4.1 is officially on the grid!!!

Sunday, February 28, 2010

Earthquake in Chile!

Wow. That was scary! I was on my way to Concepcion to teach an HEC-RAS class for some students at the Universidad de Concepcion. Fortunately I decided to spend a few days in Santiago, before going to Conocepcion. I was on the 14th floor of the hotel, and had the fright of my life. The news has said the earthquake was an 8.0 Richter in Santiago. Wow! But everything is okay and I finally got internet back in my hotel room. Now I just have to wait for the airport to open so that I can get out of here. Needless to say, the class in Concepcion is cancelled. I'm very sad to see what has happened in Conce, and really hope that my friends and colleagues there are all okay.

Wednesday, February 24, 2010

Wind-induced waves in reservoirs.

Written by Chris Goodell, P.E., D. WRE | WEST Consultants
Copyright © RASModel.com. 2010. All rights reserved.

Though HEC-RAS has no function for computing wave heights, its a fairly simply procedure that can be done external to RAS and incorporated into your design, or breach assumptions.

There are equations for wave heights and run up as a function of wind speed, reservoir depth, and fetch length. You simply gather some historical wind data that you can assign probabilities to. Assign a wind direction (to be conservative, you can assume the longest fetch length, unless the wind never blows that way), then compute wave heights and run up for different frequencies of wind magnitudes. Which frequency you design to (100-year, 50-year, etc) is up to you and your client.

Here’s a good place to start:

http://140.194.76.129/publications/eng-manuals/em1110-2-1420/c-15.pdf

Here are some other interesting links that might lead to additional information:

http://wave.oregonstate.edu/

http://www.wldelft.nl/cons/area/wds/im/wave-dynamic-structure.pdf

Monday, February 8, 2010

Hydraulics Toolbox

Written by Chris Goodell, P.E., D. WRE | WEST Consultants
Copyright © RASModel.com. 2010. All rights reserved.

I don't want to use this blog as a platform to sell stuff, but I find this software very useful when doing RAS models. So much so, that I thought I'd post it just for anyone's information. The software is called "Hbox" which is short for Hydraulics Toolbox.






If you have any questions about Hbox, or want to try a demo version, send me an email...

Tuesday, January 26, 2010

Lateral Structure flows into Multiple Cross Sections

Written by Chris Goodell, P.E., D. WRE | WEST Consultants
Copyright © RASModel.com. 2010. All rights reserved.

Not sure if this will be changed for the soon-to-be-released version 4.1, but for now, the option to drop flow from a lateral structure into multiple cross sections is a little awkward.

First thing you do is specify that you want to drop your lateral flows into cross sections. Then set your upstream TW river station (the downstream one will be greyed out).

image

Then, go to the Weir/Embankment editor for your lateral structure. At the bottom left, you'll see weir stationing reference. Select TW flow goes: "over multiple XS's". Then on the right hand side you'll see a table for specifying weir stationing for your TW cross sections.

image

Friday, January 22, 2010

Release Notes for Version 4.1

Just heard that HEC-RAS Version 4.1 is due out in about 1 week. I thought I’d take this opportunity to post the Version 4.1 Release Notes to give you all a sneak peak of what’s to come. Check the HEC website in the next week or so for the official software release.

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Hydrologic Engineering Center

River Analysis System
HEC-RAS
Release Notes
Version 4.1
January 2010
Approved for Public Release – Distribution Unlimited

Introduction
Version 4.1 of the River Analysis System (HEC-RAS) is now available. This version supersedes version 4.0, which was released in March of 2008 to the general public, and all previous versions. Several new simulation features have been added to the program since that time. Version 4.1 of HEC-RAS includes the following new features:
1.
Hydrologic Routing Reaches Within an Unsteady Flow Model Run
2.
New Flow Data And Boundary Conditions Editor for Unsteady Flow
3.
Contraction/Expansion losses for Unsteady Flow
4.
Minor Losses for Unsteady Flow
5.
New Junction Hydraulics Option for Unsteady Flow
6.
Groundwater Leakage for Storage Areas
7.
Water Quality Modeling Enhancements
8.
Sediment Transport Modeling Enhancements
9.
New RAS Mapper Floodplain Delineation Capabilities
10.
User’s Manuals and Help System
Other minor enhancements were also added. The development team has also continued careful and systematic testing of the program since the last release. The results of that testing in combination with reports from users has allowed the identification and repair of various problems. Some minor problems that did not affect results but caused problems in the program interface have been repaired without being specifically documented.
Installation
The installation program and all documentation are available on the HEC website at http://www.hec.usace.army.mil/ . This new release is installed independently of any previous versions of the program. Users may have the new version and previous versions of HEC-RAS software installed simultaneously for parallel use or testing. This new version is fully compatible with projects developed in any previous version of the program. However, once a project has been opened in Version 4.1 and saved, it may not be possible to open it with an older version of the software and reproduce the old results.

The new installation package is designed to be easy to use. It will take you through the steps of selecting a directory for the program files and making other settings. Use the following steps to install the program on the Microsoft Windows® operating system:
1. Download the installation package from the HEC website to a temporary folder on the computer. If the software was provided to you on a CD-ROM or other media, insert it in the appropriate drive.
2.
Run the installation program. In Windows Explorer, double-click the icon for the installation program. You must have administrator privileges to run the installer.
3.
Follow the on-screen prompts to install the program.
New Capabilities
Hydrologic Routing Reaches within an Unsteady Flow Model Run
This option allows the user to define portions of a model to be routed with a hydrologic routing technique instead of using the full unsteady flow equations. The software will simultaneously solve the unsteady flow equations and the hydrologic routing reaches each time step. This option is very useful when encountering portions of the model that are very steep, and full unsteady flow routing is either unstable or not possible at all. Currently the only hydrologic routing method available is Modified Puls routing. This option only works as part of an unsteady flow model, and is ignored when using a geometry file in steady flow mode.
For details on how to use the Hydrologic Routing Option within an Unsteady flow mode, please review Chapter 6 of the User’s Manual.
New Flow Data And Boundary Conditions Editor for Unsteady Flow
The Unsteady Flow Data Editor was modified to be more flexible, as well as add the capability to attach more than one inflow hydrograph to a storage area. The Boundary conditions Tab, and how boundary conditions locations are established has changed.
For details on how to use the new Unsteady Flow Boundary Conditions editor, please review the section on Flow Data in Chapter 8 of the User’s Manual.
Contraction/Expansion losses for Unsteady Flow
In general, contraction and expansion losses are not used in unsteady flow, and therefore the default coefficients are 0.0. Forces due to contractions and expansions are handled in the momentum equation through pressure force differences. However, because HEC-RAS is a one-dimensional unsteady flow model, the one-dimensional momentum equation does not always capture all of the forces acting on the flow field at a sharp contraction and/or expansion zone. In order to better approximate the forces acting on the water, and the resulting water surface elevation, at a contraction and/or expansion, the user can enter empirical contraction and expansion coefficients for unsteady flow modeling. These coefficients will be multiplied by a change in velocity head, just like in steady flow modeling, but the resulting energy loss gets converted to an equivalent force for placement into the momentum equation.
For details on how to use the contraction and expansion losses option for unsteady flow modeling in HEC-RAS, please review Chapter 6 of the User’s Manual.


Minor Losses for Unsteady Flow
Minor losses due to bends, junctions, etc… can be added to both the steady flow and the unsteady flow solution. Minor losses are computed by the user entering a K loss coefficient at a specific cross section. The K loss coefficient can vary from 0.0 to 1.0. This loss coefficient gets multiplied by the velocity head at that specific cross section in order to compute the minor energy loss. This energy loss is added to the energy equation for steady flow computations. For unsteady flow computations, the energy loss is converted to an equivalent force and inserted into the momentum equation. In both cases the energy loss is assumed to act as a force in the upstream direction to decrease flow velocity and increase stage.
For details on how to use the minor losses option in HEC-RAS, please review Chapter 6 of the User’s Manual.
New Junction Hydraulics Option for Unsteady Flow
For unsteady flow there are two options for modeling the hydraulics at a junction. The default option makes some simplifying assumptions for the hydraulics at a junction. If the junction is a normal flow combining junction, then all cross sections that bound the junction are given the same water surface each time step, based on the computed water surface at the downstream side of the junction. If the junction is a flow split, the water surfaces at the junction are based on the computed water surface at the upstream side of the junction. This simplifying assumption requires users to place cross sections fairly close together around a junction, depending on the slope of the stream. If cross sections are too far apart, model stability problems can arise from the forced water surfaces at all cross sections that bound the junction.
A new junction hydraulics option called the Energy Balance Method has been added for unsteady flow modeling. When this option is turned on, an energy balance is performed across the junction in order to compute the water surfaces, rather than forcing them to all be the same. This is a very useful option for medium to steep streams, or where junction reach lengths are fairly lengthy.
For details on how to use the new junction hydraulics option in HEC-RAS, please review the section on Junctions in Chapter 6 of the User’s Manual.
Groundwater Leakage for Storage Areas
A groundwater Interflow boundary condition could already be applied to a river reach in HEC-RAS, but now it can be applied to a storage area. Groundwater can come into a reach or storage area, and surface water can leave a reach or storage area, depending on the water surface head. The stage of the groundwater reservoir is assumed to be independent of the interflow from the river, and must be entered manually or read from DSS. The groundwater interflow is similar to a uniform lateral inflow in that the user enters an upstream and a downstream river station, in which the flow passes back and forth. The groundwater interflow option can also be linked directly to a storage area, for modeling groundwater exchange with ponded areas. The computed flow is proportional to the head between the river (or storage area) and the groundwater reservoir. The computation of the interflow is based on Darcy’s equation. The user is required to enter Darcy’s groundwater loss coefficient (hydraulic conductivity, in feet/hr), a time series of stages for the groundwater aquifer, and the distance between the river and the location of the user entered groundwater aquifer stages (this is used to obtain a gradient for Darcy’s equation).
For details on how to use the Ground Water Interflow Options for river reaches or storage areas in HEC-RAS, please review the boundary conditions section of Chapter 8 of the User’s Manual.
Water Quality Modeling Enhancements
Dispersion coefficients could already be assigned to individual water quality cells. This approach works well for relatively uniform cross sections because variations in the dispersion face area product are also small. However, when channel geometry is non-uniform, particularly in locations where a steep drop in channel geometry occurs, a corresponding discontinuity in the dispersion face area product leads to a solution with minor instability. Because these discontinuities are enhanced by unsteady flow, in some situations it may become desirable for the model to compute the dispersion coefficient each time step, as a function of velocity and channel geometry. This computation option is now available in the Water Quality Data menu under Dispersion Coefficients.
A constant temperature option has been added. The water quality simulation window now contains a control that allows user override of energy budget computations with a user entered constant water temperature. It is possible to run the nutrient simulation model (NSM) with the temperature override in place; however, this is not advised. Although the energy budget override option overrides computation of water temperature, all meteorological inputs are still required and algae will still respond to variations in solar radiation. The constant temperature option is provided primarily for testing purposes and for simple BOD-DO studies.

Water quality now supports reverse flow. If a negative velocity is encountered at the downstream boundary, the water quality model automatically adds boundary conditions for all enabled constituents.
For more information on Water Quality Modeling in HEC-RAS, see Chapter 19 of the User’s manual.
Sediment Transport Modeling Enhancements
Calibration parameters for several of the sediment transport equations have been exposed. Critical shear or transport parameters, coefficients and exponents of four transport equations can be edited to calibrate transport. Coefficients should only be altered within a reasonable range that can be defended based on physical processes. The Wong and Parker correction to the MPM equation can also be selected.
Pass through nodes have been added to the program particularly for bend or pool cross sections. Cross sections identified as pass through nodes will transport 100% of the sediment that enters the associated control volume, keeping the node from aggrading or degrading.
Finally, the settling depth parameter can be edited by grain size. Each grain class is assumed to be uniformly mixed over a vertical fraction of the water column for settling computations. Previously these fractions were hard wired to the grain classes, sometimes resulting in unrealistic settling depths when users changed the default grain classes. The settling depth can now be edited in the user defined grain classes editor.
For details on how to use the Sediment Transport Modeling Capabilities in HEC-RAS, please review Chapter 17 of the User’s Manual.


New RAS Mapper Floodplain Delineation Capabilities
HEC-RAS has introduced the new capability to perform inundation mapping of water surface profile results. Using the HEC-RAS geometry and computed water surface profile, inundation depth and boundary datasets area created by the RAS Mapper. In order to use the RAS Mapper for delineation, you must have a terrain model in the binary raster floating-point format (.flt). The resultant depth grid is stored in the .flt format while the boundary dataset is store in ESRI’s Shapefile format for use with geospatial software.
For details on how to use the RAS Mapper Floodplain Delineation Capabilities in HEC-RAS, please review Chapter 20 of the User’s Manual.


HEC-RAS Manuals and Help System
The HEC-RAS User’s Manuals has been completely updated for the 4.1.0 software release. All of the chapters have received updated text and graphics. New information has been added to several of the Chapters Additionally, the help system has been updated to reflect the software 6
changes. The new help system directly uses the users manual PDF file. The software still has context sensitive help, in that, while on any editor if you select the help menu option or press the F1 key, a help window will appear with the correct section of the manual displayed.


Problems Repaired
The following is a list of bugs that were found in version 4.0 and fixed for version 4.1:
1. Sediment: When using the Exner Active method, the time-series external sediment load was being double counted. Exner5 works correctly.
2.
Unsteady (preprocessor bridge/culvert curves). The GeomPreprocessor was sometimes computing a critical depth that is right at the elevation of the ineffective flow areas when it should be getting a critical depth that is just slightly above the ineffective flow areas. This causes it to have a higher velocity head and a critical energy that is too high. If the pressure/weir solution is below this "incorrect" critical energy, it may be inappropriately discarded. This problem most frequently showed up in a "jump" in the bridge curves where the solution incorrectly goes from pressure/weir to energy only.
3.
Unsteady (Dam/Levee Breach). There was a bug when the side slopes of a breach (dam or levee) was set to vertical (slope = 0). The post processor was not showing the Q Breach flow and the breach might be lowering the entire weir to the bottom elevation of the breach (instead of just the rectangle).
4.
Unsteady (time slicing). There was a potential output bug with any data set that had time slicing turned on (either from the time slicing editor or from the hydrograph editor using the max change in hydrograph flow without reducing the time step). This bug caused the DSS output for storage areas and internal boundaries (weirs, gate openings, etc.) to be incorrectly "stretched out" in time.
5.
Steady (Manning’s n). The weighted Manning's n total was not being computed correctly.
6.
Sediment: The reported mass capacity was not being computed correctly. For Exner5, the mass capacity was not taking into account any silt or clay sizes. For both Exner5 and the active layer method, the capacity was based on the conditions at the start of the sediment computation interval. The reported capacity is now an average of the capacity over the sediment computation interval (i.e. an average of the capacity at each bed exchange increment). This was only an error for output.
7.
Sediment: One of the options for the Exner Active method is to make the thickness of the active layer equal to d90. The program was only computing this depth at the start of each computation loop--it was not 7
8.
Steady: The cumulative volume amounts were being reset to zero at culverts and inline weirs, this has been fixed.
9.
Steady and Unsteady: When a storage connector has a culvert that has entirely supercritical flow, a bug could occasionally be triggered that causes RAS to crash.
10
. Steady (Ice): There was a bug with the ice computations (both for dynamic ice jams and ice cover) that could cause the steady.exe program to lock up. This only happened when a main channel bank station is at the end of a cross section.
11.
Steady (culvert): For the Conspan culvert, the Manning's n bottom option was being ignored if the depth of fill was set to zero. This has been fixed so that the optional Manning's n of the bottom will be included in the computations even when the bottom fill is set to zero.
12.
Steady (bridge): For bridges with class B momentum flow, the momentum answer was occasionally being disregarded. This has now been fixed.
13.
Steady and Unsteady (Pump): At the start of a profile (or start of an unsteady run), when the pump trigger water surface is between the water surface on and water surface off elevation, the pump could be either on or off. The bias-on flag, on the pump editor, allows the user to select whether the pump should on (box checked) or off (box unchecked). There was a bug in version 4.0 that sometimes the pump would incorrectly start out as on, even though the bias-on flag was not checked.
14.
Steady (lateral structure): The optional angle term for a Hager type of lateral weir was not being used.
15.
Unsteady (storage connectors): When the water surface for the two connected storage areas were at the exactly the same stage, the program would sometimes crash or go unstable.
16.
Unsteady (time slicing): The time slicing option would sometimes cause the post processor to crash (the DSS/hydrograph output was ok).
17.
Steady (Ice): A cross section that has ice and the water surface was above the top of the cross section (the cross section is "extended"), had a bug that could cause the flow area in the overbank to be ignored.
18.
Unsteady (Storage Areas): The preprocessor could crash with a memory bug if a project had more than 500 storage areas.
19.
Steady (lateral structure): Multiple cross sections on the tailwater side did not have appropriate run time checking for possible user entered data errors.
8
20.
Steady (lateral structure): There was a bug if the user tried to specify cross section intersections on the tailwater side, but not the headwater side (i.e. the head waterside was set to default).
21.
Steady (encroachments): For the encroachment output tables, the change in water surface elevation just upstream of multiple openings was incorrect.
22.
Unsteady: The volume accounting (that is reported in the computation log file) was not correct for lateral structures (the sign was reversed). This was causing a larger reported volume error, and percent error, than was actually the case.
23.
Unsteady: The volume accounting (that is reported in the computation log file) was not correct for groundwater (the sign was reversed). This was causing a larger reported volume error, and percent error, than was actually the case.
24.
Unsteady (advanced rules): The "fixed gate flow" (for both inline and lateral structures) had a bug that was causing the flow to be ignored when the gate opening was set to zero feet. The fixed flow for the new version is now being used even if the gate opening is set to zero.
25.
Unsteady (advanced rules): When the advanced rule procedure was getting a simulation value, for instance the current water surface in a storage area, it was not getting the proper value (it was getting an "assumed" value not the final computed value). This would generally only be a minor difference (eg, a few hundredths of a foot).
26.
Unsteady (advanced rules): For inline structures, the advanced rules (such as flow minimum) was not working correctly for negative (ie, reverse) flow.
27.
Unsteady (advanced rules): For advanced rules for a lateral structure, the "structure flow additional" was not actually being added in to the flow.
28.
GeomPreprocessor (multiple opening): The geometric preprocessor had a bug that could cause an unrealistically high critical depth. This would then cause the internal boundary curves to be too high and the unsteady water surface results to be too high.
29.
Steady (Froude number): The alpha velocity coefficient was added to the computation of the froude number.
30.
GeomPreprocessor (internal boundary curves): Bridges (or culverts) that have multiple blocked ineffective flow areas could cause problems with the internal boundary curves.
31.
Unsteady (I.B. stage/flow): The internal boundary (force a known stage and/or flow at an interior cross section) had a bug that could cause the known stage/flow to be applied further downstream than the user specified.
32.
Steady (multiple critical depth): When the program computed multiple critical depths, the critical depth that gets selected has been modified. Where it used to select the lowest valid water surface, it will disregard the lowest water surface if it has an unreasonably high energy.
33.
Steady (weir flow): Prior to version 4.1.0, weir flow for bridges was based on computing weir flow over the upstream road section. The program is now checking to see if the downstream road section is more constricted. Whichever section will constrict the flow the most is then used as the controlling section.
34.
Unsteady (critical flow): The option to reduce the time step based on changes in the flow hydrograph ("critical" boundary condition) was not working for a lateral inflow hydrograph.
35.
Unsteady (Dam and Levee Breach): The breach was not growing during the very first time step after the breach should have started. This "missed" growth was then being added to the very last breach time step growth (so it would essentially have a double growth on the last time step).
36.
Steady (lateral structure/flow optimization): If a lateral structure that was being flow optimized also had multiple cross sections on the tailwater side, flow was not being transferred to the tailwater side (the flow was going out of the system).
37.
Import Station Elevation Data - Version 4.0.0 attempted to filter colinear points and introduced a bug that sometimes did not import the last point.
38.
The menu item on the Geometric schematic editor: "GIS Tools/GIS Cut Lines/Adjust Cut Line Lengths to Match XS Lengths" loads an editor that allows users to automatically adjust the lengths of cross sections to match cut line lengths or cut line lengths to match the cross section length. This dialog did not have a mode to leave user specified cross sections alone, if the option was selected, then all cross sections in the selected reach were adjusted. A "none" option has been added so that users can leave some cross sections without adjustment.
39.
The unsteady flow editor in version 4.0.0 has a new button that plots all the inflow boundary conditions on one plot. The axis for this plot was off by a factor of 24 (hours were plotted as days). This problem has been fixed.
40.
The DSS file viewer would crash when reading a DSS file that had no data. Fixed in 4.1.0
41.
Exporting GIS data with no output profiles selected caused the program to crash.
42.
Exporting GIS data could cause the program to crash if there were different number of profiles selected for export previously than now currently exist. 10
43.
The culvert editor for Box culverts Chart #9 had only one scale (#2), but was actually using scale #1. This has been fixed and both scale #1 and scale #2 are now available.
44.
Background Image Files in Geometry Editor: There was a problem storing references to background image files if they were not stored on the same drive.
45.
The summary of errors warning and notes would produce an inaccurate list of errors for multiple openings with culverts in them.
46.
Node Specific Output Table: In the node specific output table with the table in the inline weir mode, the program would display an error message if you picked a reach without an inline weir.
47.
Vertical Variation of Manning’s n: There was a problem with allocating enough space in the computation engine when the XS above an inline weir used the vertical variation in Manning's n.
48.
Pump stations can now copy data from one station to another.
49.
Profile Plot with Lateral Culvert Structures: Plotting filled in culverts on lateral structures did not position the blocked graphic on the profile plot correctly.
50.
Exporting GIS bounding polygon was incorrect when some of the XS's were not found in the output file. A message has been added warning users when specific XS's were not found in the output when generating the GIS export file.


The following is a list of bugs that were found in version 4.0 Beta and fixed for version 4.0.0:
1. Pressure Flow at a Bridge. For pressure flow at a bridge, where the downstream inside cross section iis the most constrictive opening, the program was not checking for supercritical flow at the cross section just downstream of the bridge.
2.
Storage Areas. There was a limit of 500 storage areas. This is now unlimited, in that it is dynamically dimensioned when you execute the program.
3.
Rules Boundary Conditions Editor. The application of Rules to a storage area connections did not work. This has now been made functional in version 4.0.
4.
Rules Boundary Conditions Editor. There was a maximum of 20 rule operations that performed a Get or Set operation. If the rules set used more than 20 of these type of operations, the 21’s and subsequent did not function correctly. This was fixed for version 4.0, and there is now no limit on the number of this type of operation. 11
5.
Rules Boundary Conditions Editor. Not all of the Rule "Set Variables" operations, for instance the Operation called “Structure.Flow Maximum”, were working properly. These were fixed for the final release version.
6.
Permanent Ineffective Flow Areas. For unsteady flow, permanent ineffective flow areas were not always working properly when the wsel was higher than the ineffective flow elevation. On accession the program computed incorrect hydraulic variables for the area above the permanent ineffective flow area. This was fixed.
7.
Mixed Flow Option for Unsteady Flow. With the Mixed flow option on, Unsteady flow computations would occasionally "lockup" if there was a bridge or culvert in the model.
8.
Levee Breaches. For a levee breach, when output was computed in the post processor, the amount of flow going over the levee was being reported incorrectly. The [DSS] hydrograph output flow was correct.
9.
No. of Hydrograph Output Locations. The number of Hydrograph output locations (for unsteady flow) was still limited to 800 locations maximum. This has been made unlimited, in that it is dynamically allocated. The user is only limited by the amount of RAM on their computer.
10. Unsteady Flow Start time Problem. If the user entered starting time (unsteady flow) was not a multiple of the Hydrograph Output interval and the Detailed Output interval, the program would report incorrect results at various time steps. For example, if the Hydrograph Output Interval is every 5 minutes, the time window can start at 0100 or 0105, but not 0101.
11.
Ground Water Flow. Groundwater flow was being computed incorrectly due to a mistake in the units (i.e. the Darcy coefficient was not being used with consistent units between the interface and the computational engine).
12.
Critical Depth Computation. There was a computational error with in the computation of critical depth in conjunction with a cross section that contained Blocked Obstructs.
13.
Encroachments at Multiple Opening Bridges/Culverts. For a multiple opening bridge with encroachments, there was a bug if the upstream cross section and the downstream cross section did not "line up" (did not use the same starting stationing).
14.
Manning’s N Computation with Lidded Cross Sections. For a cross section with a lid, if the lid did not cross over the entire channel, the composite Manning's n computation was incorrect.
15.
Velocity Distribution Plot/Table with ICE. The flow/velocity distribution plot and table for a cross section that has ice was not reporting the regions with ice only correctly.
16.
Cumulative Volume Output. The reported flow volume computations at structures (bridge, culvert, inline, etc.) have been made more accurate. This is an output change only. These volumes are not used during the hydraulic computations.
17.
Ineffective Flow Areas in Unsteady Flow. If both overbanks have ineffective flow areas all the way up to or inside of the channel (that is, there is no "active" flow area in either overbank) then the ineffective storage was being ignored during the unsteady flow computations. This was a very series problem, as it would not allow water to go out into storage, and thus not allow for hydrograph attenuation. This was fixed. Any model that has ineffective flow areas inside of or right up against both banks of the channel, with no active overbank area, should be run with the new program to see the significance of this mistake.
18.
Internal Stage/Flow Boundary Condition. While this boundary condition type has been available for a while, it was not very flexible, and had limited use. This boundary condition type has been made more flexible and can be used at any internal cross section to force stages or flows, and it can also be used just upstream of an inline structure to force the stage upstream of the structure or the flow coming out of the structure.
19.
Bridge Piers. A bridge pier that was only defined on the upstream or downstream side of the bridge was not being handled correctly.
20.
Simultaneous Unsteady Flow Runs. Trying to run multiple RAS unsteady flow data sets at the same time in the same directory was causing a run time error. The program uses a set of scratch files when it runs, if the files are in the same directory, both runs are trying to read and write to the same scratch files.
21.
Gate Operations with Restart Files. If a data set had a restart file, the program would not use the gate controls from the current plan (for instance, the water surface elevations to open or close the gates). Instead, it was incorrectly using the gate controls from the plan that was used to create the restart file.
22.
Hydrograph Output Interval. There was a problem if the Hydrograph Output Interval was set to Monthly.
23.
Lateral Structure Connected to Multiple Cross sections. For a lateral structure that is connected to multiple cross sections on the tailwater side, various bugs have been fixed.
24.
Lateral Structure Connection. For a lateral structure, setting the tailwater connection type to “Out of the System” sometimes caused a run time error.
25.
Negative Flow Through Piping Failure. A piping failure breach (for a dam/levee failure) was not allowing negative flow, once the tailwater became higher than the headwater. If the breach fully collapsed, this was not an issue.
26.
ICE at Bridges. Ice computations at bridges had a bug when the ice in the overbanks was a different thickness than the ice in the channel.
27.
Storage Area Connections. For storage area connections, the geometry preprocessor was ignoring the [optional] user entered maximum flow.
28.
Pump Override Rules. For advanced pump rules, the override based on time was not always working correctly.
29.
Detailed Log Output. If the Write Detailed Log Output for Debugging was checked, but the starting time was left blank, then the detailed output didn't always start at the correct time (blank should start at the initial starting time). The ending time being left blank was also causing problems.
30.
Minor Losses with k values. For minor losses, "K loss" (Steady Flow data under Set Internal Changes in WS and EG), the program was using velocity (k * v) instead of velocity head (k * v^2/2g) to compute the losses.
31.
Restart File. For a data set using a restart file, after loading the restart file the program was incorrectly performing one "warm up" time step. This could cause a minor difference in the results and it was also causing occasional output problems with the post processor.
32.
Bridge Culvert Editor. The menu Option for "Class B Defaults" (was called "Momentum Class B Defaults", but was renamed because it applies to energy bridge computations as well.
33.
Batch Mode Computations. Run Batch mode was made to work with quasi unsteady flow plans, in addition to the current steady flow and unsteady flow plans.
34.
Regional Language Settings. The program was modified to run regional language settings other than English (Decimal point still needs to be the delimiter).
35.
Plan comparison on profile plot. If more than one plan was selected for comparison, and one of them had no output profiles (had not yet been run), then clicked on the "Profiles" button to drop down the list of available profiles, caused the program to generated an exception and crashed.
36.
Debug Report. The option to create a Debug Report (Compress current plan files) from the main HEC-RAS windows File menu did not include restart files. This option has been fixed so that it now includes the restart file in the debug report compressed file.
37.
Internal Boundary Curves. The error checking for the program limited the number of points on the free flow curve to 80, when the actual limit is 100.
38.
Bridge Skew Option. The Bridge Skew option, when used with a multiple opening, was not properly handled and caused the program to crash.
39.
Flow Multiplier for Hydrographs. Unsteady flow hydrographs that had data entered in the table (as opposed to DSS), and that had a flow multiplier factor, would caused the program to crash when the Plot button was pressed.
40.
Summary Output Tables. Summary Output tables crashed when tabulating multiple plans when the first one had not been computed.
41.
Channel Modifications. The method for computing main channel bank stations for channel modification editor was improved.
42.
Errors, Warnings, and Notes window. The Copy to clipboard button cause the program to crash. This has been fixed and now the data can be copied to the clipboard.
43.
Stage and Flow Hydrograph Plot. The stage and flow hydrograph plot window had a problem when viewing lateral structures that had a river station 8 characters in length. The appropriate DSS paths were not found and the data that is in the DSS file was not plotted.
44.
User Specified Reach Order. When the geometry had a user specified reach order for computations, and one of the reaches in the system had a storage area for a boundary condition, the program would produce an error trying to write the boundary condition file.
45.
Renaming River Reaches. Renaming a river reach did not change the name in the steady flow DSS Connection information.
46.
USACE Survey Data Format. The USACE Survey format sometimes has more than one decimal place in the RS field, this caused problems in RAS, when this occurs, only the first period is retained.
47.
Culvert Editor. The culvert editor had a problem that it left one of the text fields with a grey background (thus un editable) when switching between culvert shapes.
48.
Open Air Overflow Gates. Open Air Overflow gates had a graphics problem on the XS plot when there was more than one gate group with open air gates.
49.
Background Maps. The background raster images for the geometry schematic are limited in path lengths of 127 characters. When a longer path was used, the program generated an error that was not helpful. Now it displays a dialog that informs the users that the path length is too long.
50.
Node Names. When the node names start with a number, some of the quick links, like jump to a cross section from the bridge editor, go to the wrong cross section. This bug has been fixed.
51.
Water Temperature Modeling. There was an error when the computed water surface went below the first point on the hydraulic property tables from the preprocessor.
52.
RAS API Interface. The RAS Controller service had an error in the Output_GetNodes function. This has been fixed.
53.
Sediment GUI. The caption on the sediment data window now reflects the new file name when it is Saved AS Sediment and Quasi-Unsteady files now alert users if the attempt is made to close RAS without saving.
54.
Metric Units Problems in Sediment Editors. Rating curve stage in Quasi Unsteady flow editor was labeled as m2 for SI units - changed to m. The Temperature Editor labels SI Temp as F - Changed to C. Max erosion depth was limited to less than the user specified depths, due to this variable not being converted to English units for the computations. When using SI units RAS used sediment densities of 1.19, 0.835 and 0.385, these were inappropriate and have been changed to 1489, 1041 and 480 kg/m3 for Sand, Silt and Clay respectively. Flow-load rating curve was not converted to English units before being sent to the computational engine, which expected it in English units.
55.
Sediment Computations Through Bridges. There were a few Computational bugs for bed change determination at bridges, which were fixed.
56.
Downstream Boundary Conditions for Sediment Computations. If a user specified a downstream boundary condition that either went supercritical or even below the cross section, the software tried to use it. Current version of the sediment module is limited to subcritical flow calculations, so downstream boundaries are now limited to critical depth and higher.
57.
Sediment Plots. Gradation and flow-load plots were being plotted in an arithmetic scale, these were changed to log scale plots. Several additional sediment plot types have also been added, including the ability to plot cross section bed change.
58.
Copeland Stable Channel Method. A bug was introduced into the computation of average depth for this method in the 4.0 beta release. This bug has been fixed for the final 4.0 release.
59.
Water Quality Rate Constants. Water quality rate constants Beta1 and Beta2 were not being stored correctly when a project was saved. This problem has been fixed.
60.
Water Quality Data Entry (cloudiness). Cloudiness may be entered directly or computed from observed solar radiation. The cloudiness computation routine did not work well for large datasets and sometimes crashed the program. The problem has been fixed.

The following is a list of bugs that were found in version 3.1.3 and fixed for version 4.0:
1. Velocity Output at Bridges. During unsteady flow calculations, if reverse flows occurred through a bridge, the software would report values of zero for velocities at the cross section just upstream of the bridge. This was only an output mistake, and did not effect the computation of the water surface and flow.
2.
Family of Rating Curves for Unsteady Flow. For bridges, culverts, storage area connections, and lateral structures, in which a family of curves are generated from the Unsteady flow pre-processor, several changes have been made to the code that generates these curves. The previous version of HEC-RAS was on occasion getting some bad points in the curves, which would cause all of the curves in that zone to have a problem. We have fixed several known problems, as well as improved the way we interpolate between the curves.
3.
Submerged Culvert Flow. When the outlet of a culvert is submerged, the culvert can act as a siphon if the inlet is also submerged. In some cases, RAS was treating the culvert as a siphon even though the water surface at the inlet was slightly below the top of the culvert (that is, the inlet was not fully submerged).
4.
Storage Area Connections. Having more than 10 storage area connections in the model could, in rare cases, cause a "GUI didn't allocate arrays large enough," error.
5.
Perched Bridges. A perched bridge (the low chord on the bridge is higher than minimum elevation in the overbanks) that was being modeled as a cross section with a lid, was not always computing flow in the overbanks properly.
6.
Dam Break Piping Failure. During a dam break, the transition from a piping failure to an open breach was not always being computed correctly.
7.
Bridge Momentum Computations. For a bridge that was being solved with the momentum method, version 3.1.3 would allow a slight drop in the energy grade line as the calculations proceeded from the downstream internal bridge section to the upstream internal bridge section. Version 4.0 will disregard the momentum solution if this happens (and usually defaults to the energy solution).
8.
Bridge Pressure and Weir Flow Computations. For bridges with pressure and weir flow, the reported flow distribution (the amount of flow in the channel versus the left and right overbanks) was not always correct. This was only an output reporting problem, not a problem with the calculations of the water surfaces.
9.
Pump Station Inflow to a Storage Area. For a storage area that was receiving flow from a pump station, the inflow to the storage area was being incorrectly reported in some cases. This was not a problem with the computations (i.e. the correct flow was being used
10. GIS Data Import of Levees. The data importer would not import levees unless the cross section bank stations were also imported.
11.
Importing HEC-HMS Version 3.0 and Greater Flow Data from HEC-DSS. With the release of HEC-HMS version 3.0, there was a change to they way flow data was sent to HEC-DSS files. Before all data was sent as single precision numbers. Now HEC-HMS sends all its results as double precision numbers. Previous versions of HEC-RAS (Version 3.1.3 and earlier) were only set up to read the data as single precision numbers. So, versions 3.1.3 and earlier of HEC-RAS would not correctly read flow data from HEC-DSS if it was created by HEC-HMS version 3.0 and later. If you are still using HEC-RAS 3.1.3 or earlier, users can download HEC-DSSVue and a special plug-in that will allow you to convert a double precision HEC-DSS file to a single precision HEC-DSS file. HEC-DSSVue and the plug-in are available from our web page.
12. Cross Section Interpolation. A few data sets were sent to us where the cross section interpolation routines were not correctly interpolating geometry and/or other cross section properties. Many of these data sets had cross sections with “Lids”, while some were problems with interpolating Manning’s n values.
13.
Lateral Structure Stationing. If a lateral structure did not start at a stationing of zero, it was not always located exactly correct along the cross sections.
14.
Metric Units Output for Hydraulic Radius. The program was incorrectly reporting the Hydraulic radius to the 2/3 power in the output. This was a conversion from English to metric units error.
15.
Abutment Scour Problem. On occasion the program would compute a projected abutment/road embankment length that was incorrect. This only came up under rare circumstances, and depended on how the stationing of the cross section just upstream of the bridge, and the approach cross section, were entered.
16.
K2 Factor for Abutment Scour. This factor was being interpolated from a graph that was presented in an earlier version of the HEC-18 manual. For abutment attack angles that were very mild, the interpolated values were not very good. The latest HEC-18 manual now has an equation. We have changed the code to use this equation.
17.
Pipe Arch Culverts. For very small pipe arch culverts, the user would enter a Rise and the program was incorrectly calculating the span. This was only for Pipe Arch Culverts with smaller than 18 inch corner radius.
18.
Corrugated Metal Box Culverts. Many corrugated metal box culverts actually have sloping inward side walls and rounded corners
19
at the top. The slope of these walls and the curvature of the corner radius can vary with manufacturers. HEC-RAS does not account for the sloping wall or the rounded corner radius. User’s must come up with an equivalent span and rise in order to match the area correctly. It is suggested to use the correct rise, and adjust the span to get the correct area of the culvert. That way the program will get the transition from low flow to pressure flow at the correct elevation.
19.
Storage Area of a Cross Section for Unsteady Flow. HEC-RAS was incorrectly calculating the available storage area above a permanent ineffective flow area, when the permanent ineffective area intersects the ground between the first two or last two points of the cross section.
20.
Limit of 500 Hydrograph Output Locations for Unsteady Flow. The previous version of HEC-RAS had a limit of 500 locations for output hydrographs when performing unsteady flow calculations. The problem was also enhanced by the fact that HEC-RAS automatically computed output hydrographs at specific locations by default. This limit has been done away with. The number of hydrograph locations is now allocatable, and only limited by the memory in your computer.
21.
Restart File for Unsteady Flow Calculations. There were some problems in reading a Re-Start file for use as initial conditions of an unsteady flow run. These problems have been corrected.

Support Policy
Technical support for program users within the Corps of Engineers is provided through an annual subscription service. Subscribing offices can expect full support from HEC staff in the routine application of the program. Users are strongly urged to consult with HEC staff on the technical feasibility of using the program before beginning a project with unique requirements. Extended support for large or complex projects can be arranged under a separate reimbursable project agreement.
Support can not be provided to users outside the Corps of Engineers. Domestic and foreign vendors are available that provide fee-for-service support similar to the support provided to subscribing Corps offices. Such service agreements are between the user and the vendor and do not include HEC staff. Vendors do contact HEC on behalf of their users when unusual problems or errors are encountered. A list of vendors can be found at http://www.hec.usace.army.mil/ .
Reporting of suspected program errors is unrestricted and we will reply to all correspondence concerning such errors. We are continuously working to improve the program and possible bugs should always be reported. Reports should include a written description of the steps that lead to the problem and the effects that result from it. If we cannot reproduce the reported problem, we may ask you to send a copy of your project.
Report program errors through the following channels:
• Go to our web site at www.hec.usace.army.mil then go to the HEC-RAS support page.
• Send email to hec.ras@usace.army.mil on the internet.
• Write to:
U.S. Army Corps of Engineers
Hydrologic Engineering Center
609 Second Street
Davis, CA 95616 USA.