How to use a Storage Area to define a Reservoir.

Written by Chris Goodell | August 19, 2010


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

Comments

  1. Tom

    on November 4, 2010

    Can a hydrograph be input into the upstream storage area?

  2. Chris G.

    on November 4, 2010

    Yes! It's entered in the unsteady flow data editor as a lateral inflow.

  3. keinbuck

    on August 17, 2011

    After computing the hydrograph looks plausible. The flow rises to the peak and drops down again. But shortly before the storage area is empty i get an negative flow and the water surface rises up a little again. And there is always a 'warning' after the computing because there is iteration between the dummy cross sections. can you help me?

  4. Chris G.

    on August 18, 2011

    Do you have a lateral inflow into the storage area? If not, adding that might help. If you do have one already, you might consider higher base flow. Also, the minimum elevation specified for your storage area in its elevation-volume curve should be about the same as the invert of the "dummy" cross section. If it is much lower than the cross section, you could cause the dummy cross section to go dry (and that might explain the reverse flow). Also, if it looks like you are getting very low water surface elevations in the dummy cross sections, you might want to try putting pilot channels in there. Good luck.

  5. Anonymous

    on February 17, 2012

    Chris, in this approach, can we model like this, suppose 4 canals come directly to a retention pond and one canal out from the pond.I think you can understand my point. Currently, I'm making a model like this, but model is unstable. I tried a lot to make stable the model.

  6. Chris G.

    on February 17, 2012

    Yes, you can do that. Check to make sure none of the canals are going "dry" during the simulation. Although a storage area can have 0 depth, cross sections cannot.

  7. gsharif

    on November 6, 2012

    Hi there, I am new to HEC-RAS and having some problem with the connection between a reservoir and my stream. This post seems pretty close what I am doing, I think!

    So, I have a small stream and I have modeled the stream with XS and culverts and its working fine. Now there is a small pond area at the side of the stream which I like to include in my model. The pond is not directly on the stream, its just beside the stream but there is a connection to it. So I added a storage area and tried to connect to the stream but seems I have to use a lateral structure. If I input a lateral structure at my stream (close to the stream station where my pond is situated), Now how the water flows from the stream to the pond area? It seems like its not connected. Do I need to make another reach from the storage pond to my main stream (as a second reach)? Then input the lateral structure on that reach? Then I think I need XS of that reach as well? Little confused, need help! Thanks in Advance — Sharif

  8. Chris G.

    on November 7, 2012

    Hi Sharif-

    Take a look at this post: http://hecrasmodel.blogspot.com/2012/11/connecting-river-to-off-channel-storage.html

    Hope it helps.
    Chris

  9. Anonymous

    on November 15, 2012

    I am also new to HEC-RAS, should the reservoir show up on the x-y-z plot? I have a storage area, and it appears to be connected to the river reach, but it never shows up in any of the cross sections

  10. Chris G.

    on November 26, 2012

    Storage Areas do not show up on the XYZ plot, unfortunately.

  11. Anonymous

    on November 28, 2012

    THANK YOU SO MUCH!! I HAVE BEEN TRYING TO FIGURE THIS OUT FOREVER!!!

  12. JEM

    on June 11, 2013

    I am trying to run an unsteady analysis witha storage area upstream of a dam but everytime i start the simulation i get the following message. i have a eleation-volume curve that has increasing valeus of elevation and of volume. my first volume is zero. what am i doing wrong?

    HEC-RAS Error – Incomplete data, the following errors were found:
    Storage Area: StorSverjesjoen
    – Volume Elevation relationship does not have increasing volume.
    – Volume Elevation relationship does not have increasing elevation.

  13. JEM

    on June 11, 2013

    I found an answer!! All the 100 rows must be filled in in the elevation-volume curve of the storage area!!

  14. Chris G.

    on June 11, 2013

    That's odd. You shouldn't have to fill in all 100 rows to define your elevation volume curve. I've done it many times with only a handful of rows. There needs to be the same number of elevation entries as there are volume entries. Perhaps that was the problem.

  15. Scott

    on June 30, 2013

    I got the volume error above and took a look at my stage-storage table. The first five rows had these values for volume: 0.0, 0.0, 0.0, 0.01, 0.01. Below that there were no repeated volumes. I tried just deleting the repeated values. This left empty rows, and I got both the volume and elevation errors above. Then I cut and pasted the table values upward, so there were no empty rows. I no longer got the elevation or volume errors.

  16. Anonymous

    on August 15, 2013

    Hi Chris,

    I am having some problems modeling a dam break currently. The dam itself is located in the middle of a city. Just upstream of the dam is a lake that connects to the dam through a short river(~6000 feet). Currently I am trying to model the lake as a storage area using a storage vs stage curve. This storage area is then connected to my first upstream cross-section in my model(to simulate the lake outlet). In my unsteady flow data I have a stage hydrograph as my boundary condition at my 1st cross-section which uses stages that have been measured from a 1/2 PMP flood.

    So couple questions from this:
    1) Am I modeling this setup correctly? This is only the 2nd dam break I have ever done so I could be wrong.
    2) Do I need an upstream boundary condition at my first cross-section, or does the stage vs storage curve from the reservoir take care of that?

    My model is currently crashing instantly suggesting a problem with my initial conditions but I am not able to pinpoint where so I am assuming something is wrong with my storage area.

    Any help would be greatly appreciated and on a side note this is an amazing help site that I have used constantly since I started my job, thank you so much!

  17. Chris G.

    on August 15, 2013

    It could be that the stage-storage curve and your stage hydrograph boundary condition are in conflict with each other. For your setup, I suggest having a boundary condition at the downstream-most cross section in your model (downstream of the dam-normal depth is a good choice) and a flow hydrograph set as a lateral inflow to your storage area reservoir. That's it. By trying to put a stage hydrograph upstream of the dam but below the storage area, you are forcing a water surface elevation that RAS perhaps doesn't like and then your model blows up. I think it's always better to leave those internal stage boundary conditions out of the model. Instead, put them in as observed stage hydrographs and calibrate your model to them.

    If your model is still crashing, make sure:
    1. First time step inflow, initial conditions flow, and flow through your dam are all consistent.
    2. Model is not going "dry" anywhere.
    3. Time step is sufficiently low (<1 minute to 30 seconds for a dam breach)
    4. Run a steady flow plan and see if that reveals problem areas. Look for lots of red marks on your profile plot, which suggest critical, or close to critical depth. This could mean your n values are too low.
    5. Start simple-just cross sections, then add in structures one at a time. Finally put in the breach. Run the model in between each addition.

    If you're still having problems, send me the model and I'll see if I can diagnose the problem.

    Good luck!
    Chris

  18. Anonymous

    on August 19, 2013

    Am attempting to model through a small upper reservoir (storage area), down a reach through the lower on-stream reservoir to the roadway below.
    Have both storage areas digitized and imported from HEC GEO-RAS. Get the following error upon computing unsteady flow:
    "Lateral Inflow at -RS: was specified in the unsteady flow boundary data but was not used because this location does not exist in the current geometry file"
    Know the model recognizes the upper reservoir, as it prompted to join the reach to the reservoir upon moving the last point into the bounds of the reservoir. How do I made sure the second reservoir is recognized by the model? Do not have a junction, only one stream.
    Any help greatly appreciated.

  19. Chris G.

    on August 22, 2013

    A quick check of the initial conditions tab in the unsteady flow editor (assuming you are doing unsteady flow) will reveal if RAS recognizes your storage area or not. All storage areas require an initial water surface elevation and will be listed in a table at the bottom of the initial conditions tab.
    You could also go to the geometry window and select Edit…Move. Then move the end point of the reach into the middle of the storage area. RAS will give you a message saying indicating it recognizes that you want to connect the storage area to the reach.

  20. kevin butler

    on September 5, 2013

    Could you provide assistance please?
    I am doing a dam break. The reservoir is the most upstream point in the watershed, and there is a stream downstream of it. I'm debating whether this is a lateral or an inline structure. I'm leaning towards Inline because it is in line with the stream downstream of the dam, and it is definitely not lateral. I have 4 x-sections downstream of the dam, and 2 x-sections upstream of the dam (within reservoir). I drew in my storage area (reservoir) so that it overlaps the upstream-most x-section so that it recognizes the connection (as you described), and entered the stage-storage table. I made an Inline structure and entered in the breach data (have it set for overtopping). I entered my unsteady flow boundary conditions: at the upstream-most x-section, I used a Flow Hydrograph obtained from a HEC-HMS model (and set min flow to 100, because my range goes from 0 cfs to 40,000 cfs), and at the downstream-most x-section I used Normal Depth. Finally I set my unsteady flow initial conditions: Initial flow=100cfs @ upstream-most cross-section, and Initial Elevation is 1216 (normal pool of the reservoir). I go to run the unsteady flow and the computation bar is almost entirely red. I have no idea what to do.

  21. Chris G.

    on September 5, 2013

    1. I think it would be better to use a lateral inflow to your reservoir, rather than an inflow to the cross section for your u/s boundary.
    2. What is your computational time interval? should be seconds, not minutes or hours.
    3. Are your cross sections spaced correctly? Use Samuels Equation or Fread's Equation.

    There could be a number of things causing your model to crash right away. Take a look at your initial conditions profile (check box in the upper right hand corner of the WS profile plot) and see if that looks okay. If not, where are the problems? Go check those out. Look in your log output file and check the QDiff and ZDiff tables and see where the discrepancies are between your initial conditions profile and your first time step profile. Keep at it! You'll figure it out.

    Good luck-

    Chris
    @RASModel

  22. Karl

    on March 26, 2014

    Does anyone know if the volume in-put for a storage area is cumulative or incremental? When inputting volume for a storage area for the elevation vs storage curve.

  23. Chris G.

    on March 26, 2014

    It is cumulative.

  24. Mohamed Elgamal

    on April 8, 2014

    I am attempting to carry out a dynamic unsteady state simulation to model the dynamic response of a located mid-way pond in an ephemeral wadi stream that is subjected to a sporadic flooding hydrograph. The question is to identify the part of the flood surge that will succeed to pass by the pond and to enter the downstream wadi reach located d/s of the pond and to identify the part of the hydrograph that will be intercepted by the pond.
    In order to do so, I used the cross section approach to deal with the pond (not the storage approach) because I do need more flow details to be calculated at the pond sections. I started with a dry pond initial condition however I figured out that Hec-ras automatically fill the pond initially and thus no part of the incomming flow is intercepted by the pond despite that the pond has a significant volume to intercept at least 50% of the comming water volume. Can some body guide how to deal with that issue.
    If hec-ras can not model initially dry sections then how does it work with the inundation mapping which basically means wetting drying areas?

  25. Chris G.

    on May 11, 2014

    If there is no outlet flow at the inline structure, then RAS will automatically fill the pond for the initial conditions. To start with a low pond elevation, you must define some outlet flow (gates, pilot flow, etc) so that you have a balance between the inflow (upstream flow hydrograph) and what leaves the dam. Setting an initial conditions stage at the cross section just upstream of the inline structure will help. Read this post for more help: http://hecrasmodel.blogspot.com/2009/09/initial-reservoir-elevation-pilot-flow.html

  26. Chris G.

    on May 11, 2014

    To answer your second question, RAS cannot have a completely dry cross section. You need some water in the main channel at all times. However, the overbanks/floodplains can be dry or wet. Also, storage areas can be completely dry.

  27. Anonymous

    on August 6, 2014

    I am modeling a small stream with a sedimentation basin at the mouth and a downstream weir using quasi-unsteady flow analysis. After inputting all the cross-sections, the inline structure and the storage area, I keep getting this error message: Storage area "sed basin" -does not have initial elevations specified in the steady flow data. But I am not using steady flow… Please help!

  28. Chris G.

    on August 7, 2014

    That's annoying. I believe you found a bug. I tried the same thing with the MBex data set and got the same error message. I could not find a workaround. Even tried adding an initial stage for the storage area in the steady flow editor, but it didn't work. The only thing I can suggest for now is to simulate the storage area as a separate reach with cross sections. I'll forward this on to HEC and hopefully they'll get it fixed for the full release of 5.0. Thanks-
    Chris
    @RASModel

  29. Chris G.

    on August 7, 2014

    Bug message sent on to HEC. I'll reply again once I hear back.

  30. Chris G.

    on August 7, 2014

    Turns out Sediment Transport in HEC-RAS does not handle storage areas. You can have lateral structures though, just not storage areas. HEC is working on a more useful error message. So, for now, you'll have to either omit the storage area all together, or model it as a separate reach with cross sections.

  31. Anonymous

    on November 17, 2014

    Hi,
    I need advice on this problems :
    1.Why in the cross section, there are no storage area cross section. I had joint the reach and the storage area using lateral structure and the XS profile only show the reach end with the lateral structure. In fact, in geometric, I draw the storage area.
    2. How do we connect the reaches when there are storage area between them? I use reach 1 upstream the storage area and reach 2 downstream the storage. it seams like the simulation/profile end before the storage, as my problem in No.1.

  32. Chris Goodell

    on November 18, 2014

    Sorry, but I don't understand your questions. Can you please rephrase them? Thanks.

  33. Anonymous

    on January 7, 2015

    Hi Chris, I have a simple question. I appreciate that if you could respond to me.As you know in Hec ras there are two ways to define the storage 1-Area time depth method. 2-Elevation versus volume curve. If I don't have these kind of data, how can I define the reservoir? what is your approach in such situations?
    Cheers,
    Mike

  34. Chris Goodell

    on January 7, 2015

    That information is required for storage areas. If you don't have it, measure the surface area of the reservoir (this can be easily done in any GIS software application and even in Google Earth), and approximate an average depth. This is not the best method but it will work. Would be better if you had bathymetric data so you could generate an elevation-volume curve. See if you can find a "pre-dam" topo map. That would work as long as there hasn't been a considerable amount of sedimentation in the reservoir since it was constructed.

  35. Lindsay Weatherford

    on February 5, 2015

    Good afternoon Chris! I have been trying for quite some time to rid my breach model of errors. This is my first project modeling a breach and have used the USACE HECRAS Dam Break Study Manual, HECRAS User Manual and also Colorado DNR HECRAS Guidelines to help me model. I am in Ohio but I have not been able to find many resources on this matter over here, even after contacting ODNR.

    I have an unsteady flow model with a simulation time window set for 24 hrs: 29JUL2015 12:00 to 30JUL2015 12:00, computational interval set to 30 sec.

    The Lake is the storage area. I used the elevation vs. volume curve with my normal pool elevation set as the lowest elevation (this is also my initial elevation in the boundary conditions). The boundary condition is lateral inflow hydrograph. I used the inflow data from a HydroCAD analysis output for the 24 hr probable maximum flood event. The maximum flow is 3000cfs so I used a minimum flow of 160cfs to keep the cross sections from drying. I made sure this was the same value at initial time step. I have Internal RS initial Stages checked in the unsteady flow data.

    My last cross section downstream is set to normal depth.

    I have 2 dummy cross sections upstream of my dam (placed 15’ apart) with the stream connected to the storage area. The minimum elevation is my pool/initial elevation for these two sections. I have used cross section spacing according to Samuels equation for the remaining downstream sections. I’ve even tried interpolating to see if it makes a difference. Manning's value 0.05 at banks and 0.03 for channel.

    For the dam I input an inline structure. The weir data includes an emergency spillway at the end of the dam which is 6ft lower than top of dam. Pilot flow set to 160 cfs. I put the lake bottom elevation as the final bottom elevation of breach (20 ft lower than pool elev). I set the Failure mode to overtopping, starting at 29JUL2015 13:00. Other breach data 3:1 side slopes, 100 ft wide bottom.

    The computation blue bar completes the Geometry Processor section but never starts at the Unsteady flow simulation. My error is:
    A change (or known value) in WSEL or EG at a node at river station 10 in reach 1 caused a WSEL below the bottom of the cross section. Check your data for errors.

    RS 10 is my most upstream section connected to the storage area. The profile plot shows my first dummy cross section upstream of the dam having an astronomical spike in EG Max WS El. up in the billions, which makes all the other cross sections appear to be near 0. I tried raising my minimum flow elevation to 500 cfs with no luck. I even tried to space the dummy sections farther apart. I also tried your suggestion to run in steady flow with cross sections only. The upstream condition was set to storage and it wouldn’t let me run with that so I had to delete storage area and ran with a rating curve and it seemed to work fine, even with the inline structure added next.

    I’ve tried moving sections around and changing start elevations and flows and have yet to get the computations to complete. Any advice would be greatly appreciated on what to try next.

    Thanks!

  36. Anonymous

    on February 20, 2015

    Hi Chris. I need to model the sedimentation process of a reservoir. Can I use HEC-RAS to model this or do I need another model? I've heard of HEC-6 but I haven't been able to download it.

    I appreciate your help.

    Thanks.

  37. Chris Goodell

    on March 19, 2015

    Sorry not to respond directly to you in here. I trust your model is still humming along nicely with the work we did to fix it?

  38. Chris Goodell

    on March 19, 2015

    You certainly can. RAS actually works very well simulating reservoir sedimentation.

  39. SamihaT

    on May 22, 2015

    Hi Chris,

    I am new to HEC-RAS. I am trying to model a river between two very large lakes. However, there is no control structures at the upstream or downstream of the river reach.

    1) Should I model the lakes as storage areas? If yes, then "placing the last HEC-RAS cross sections somewhere in the storage area and using a Known Water Surface Elevation as the downstream boundary condition to enter the storage area's water surface elevation" – is this a correct approach? Do it need to assume a control structure at the upstream or downstream for that purpose?

    2) In the same model, there is a small ponding area in the middle of the river, more like a in-between storage (significantly small compared to the lakes). There is a partial sluice gate (does not extend across the whole X section) downstream of the pond area. Does modeling this small storage as ineffective area in the X section a correct approach? Or should I go for off-the channel storage and connect with a lateral structure (there is no such structure there)? Another option I can think of is discontinuing the river and placing a storage area – which I am less inclined to adopt since this is a ponding area within the river. Can you suggestion which one of these would be a better approach?

  40. SamihaT

    on May 22, 2015

    Hi Chris,

    I am new to HEC-RAS. I am trying to model a river between two very large lakes. However, there is no control structures at the upstream or downstream of the river reach.

    1) Should I model the lakes as storage areas? If yes, then "placing the last HEC-RAS cross sections somewhere in the storage area and using a Known Water Surface Elevation as the downstream boundary condition to enter the storage area's water surface elevation" – is this a correct approach? Do it need to assume a control structure at the upstream or downstream for that purpose?

    2) In the same model, there is a small ponding area in the middle of the river, more like a in-between storage (significantly small compared to the lakes). There is a partial sluice gate (does not extend across the whole X section) downstream of the pond area. Does modeling this small storage as ineffective area in the X section a correct approach? Or should I go for off-the channel storage and connect with a lateral structure (there is no such structure there)? Another option I can think of is discontinuing the river and placing a storage area – which I am less inclined to adopt since this is a ponding area within the river. Can you suggest which one of these will be a better approach?

  41. Chris Goodell

    on May 22, 2015

    Personally, if I had the data, I would make the entire thing a single reach with cross sections. No strorage areas. If you do want to do storage areas, you should consider using 2D areas instead. They will better capture any hydraulic gradient and secondary flow patterns. You can connect storage areas or 2D areas directly inline with a 1D reach. No need to place controls at the connection. Just make sure that your storage areas/2D areas don't force the 1D reach to go dry at any time in your simulation. cross sections cannot go dry-your model will crash. With regard to the middle ponding area, I think either of your first two suggestions would work. It just depends on how much detail in your results do you want in that area.

  42. SamihaT

    on May 22, 2015

    Thanks Chris. Just let me reiterate, you mean treating these huge lakes (actually Great Lakes) as part of the reach, thereby taking several X sections of the lake and then putting known water elevation as a boundary condition. Am I right?

  43. Chris Goodell

    on May 22, 2015

    Yes. You could do that. But making them storage areas would probably work just fine since they are so big relative to the river reach. Usually the deciding factor is how fast the water level changes in the lakes, and how much detail you want in your results in the lakes. You should read this post: http://hecrasmodel.blogspot.com/2010/03/dynamic-versus-level-pool-reservoir.html
    Although it compares level pool routing (storage areas) with dynamic routing (cross sections) for dam break simulations, the concepts discussed carry over to conventional modeling exercises as well. The bottom line is dynamic routing will always be more accurate. But under certain conditions, level pool routing will produce similar results to dynamic routing. My guess is the Great Lakes would fit into this category. If you want to send me your model once you have it constructed, I'd be happy to take a look and offer suggestions. Sounds like an interesting model.

  44. SamihaT

    on May 22, 2015

    Thanks a lot, Chris. I appreciate your insights and would like to have your opinion/suggestions once I get the model running.

  45. masauso sakala

    on June 3, 2015

    hi, am modelling a large floodplain. how do i ensure parts of cross sections "depressions" don't fill up before the preceding depressions fill up.(

  46. SamihaT

    on July 22, 2015

    Hi Chris,
    I have followed the procedure described here to connect the reach to an upstream storage area (Moving object and a dot appears at the connecting point).
    1. Do I need to connect the reach and storage area again using storage area connection editor at the top of the geometric data editor (pg 173 User Manual) and then a choose a rating curve/weird?
    2. If not, how can I ensure flow from the storage area to the reach? Is it enough to assign a hydrograph at the unsteady flow editor without following the procedure described in 1?
    Thanks.

  47. Chris Goodell

    on July 31, 2015

    1. No. Moving the stream centerline inside of the storage area is enough for an inline connection.
    2. The stage in the storage area and the reach are intertwined when connected. Whatever flow is entering the storage area will be attenated and then passed to the first cross section in the connected reach. This is all done by HEC-RAS automatically once you make the connection.

  48. Anonymous

    on September 9, 2015

    Greeting Chris – I am currently modeling a 6 sq. mi. watershed with urban/rural mixed characteristics. The routing is normally mostly dry until a storm event. I have noted your comment above where you state that RAS cannot have a completely dry cross section, water is required in the main channel. Is it acceptable to lower part of a cross section 0.25 ft creating something like a 1 ft. X 0.25 ft. triangular main channel with bank stations on either side, inputing a small <10 cfs initial flow condition, and ending the simulation before any reach runs dry?

  49. Chris Goodell

    on September 9, 2015

    Yes. That's one way to do it. An even easier way is to use pilot channels. Geometry window…Tools…Pilot Channels…
    Initial flow (also called baseflow or minimum flow) is also a good idea too. Many times in situations like yours, I'll use a combination of pilot channel and baseflow to get the desired effect. Good luck!

  50. SamihaT

    on October 8, 2015

    Hi Chris,
    I have constructed my model and run a steady analysis. The cross-section downstream of the reservoir is getting a very low flow (though I have assigned a specific flow to that reach in the steady flow editor). In reality, there is no inline structure between the reservoir and the river reach so I am not being able to assign pilot flow to the model. Would you be interested to have a look at it?

  51. Chris Goodell

    on October 8, 2015

    I'm a little busy at the moment to take a look at it. Double check your n values. Make sure they are high enough and you don't have any typos (i.e., too many zeros).

  52. SamihaT

    on October 8, 2015

    Checked already. The n values are obtained from a previous study and is 0.0327-.022. Is there anything else I can check? Can the upstream reservoir be a problem?

  53. Chris Goodell

    on October 27, 2015

    Those n values are very low for low flow conditions. It is likely the previous study used those n values for flood levels. At lower flows, you'll need larger n values.

  54. Chris Goodell

    on October 27, 2015

    You'll have to approximate it somehow. At the very least you should be able to measure the surface area of the reservoir (Google Earth) and then approximate the depth. That will give option 1. Still, that is a crude approximation and it is much better to try to obtain an elevation volume curve.

  55. Anonymous

    on May 12, 2016

    hey!! chris, i wanna know how to take boundary conditions for dam break analysis

  56. Chris Goodell

    on May 12, 2016

    Typically people use a PMF or some other extremely rare design flood event along with a sunny day event (typical conditions at the reservoir).

  57. Unknown

    on May 14, 2016

    What does mean the error "No records were found (the data returned all -902's"?. That's appears when running the post processor

  58. DD

    on May 14, 2016

    What does mean the error "No records were found (the data returned all -902's"). That´s appear when running the post processor. It´s relative to the storage area.

  59. Chris Goodell

    on May 17, 2016

    Usually that happends when the model goes unstable and doesn't finalize an output file as a result. Then when RAS tries to find certain output, it can't and so it returns "-902" values, which are considered null values in RAS coding.

  60. Anonymous

    on July 15, 2016

    The error states Lateral structure has user defined HW connections.The user defined list of RS-weir Sta's has more XSs than are necessary to cover weir profile.When I look at the lateral structures editor there is only one XS that at the end of the weir

  61. Anonymous

    on July 15, 2016

    I'm running an unsteady flow file with a lateral structure adjacent to a levee. The error states as follows: Lateral structure has user defined HW connections. The user defined list of RS-weir Sta's has more XS's than are necessary to cover the weir profile. There must either be A XS that is exactly at the end of the weir profile. OR one and only one XS that is past the end of the weir profile. When I look at the lateral structures editor there is only one XS that is at the end of the weir profile. Not sure what to do here. Using Version 5.0.1.

  62. Chris Goodell

    on July 18, 2016

    You must have more than one XS that is beyond the end of the lateral structure's length defined in the user-defined HW connections. I suggest using the default HW connections if possible.

  63. Bilal Elwan

    on August 12, 2016

    Hi Chris,I have a question.
    How can I model a gate with constant water level in the upstream of the gate (as a reservoir) and the flow is free.

  64. Bilal Elwan

    on August 12, 2016

    Hi Chris,how can I model a gate with constant water level in the upstream of the gate ( as reservoir ).

  65. Chris Goodell

    on August 12, 2016

    Try using the Navigation Dams boundary condition.

  66. Chris Goodell

    on August 12, 2016

    Try using the Navigation Dams boundary condition.

  67. jackie

    on September 9, 2016

    I'm trying to set up a floodplain storage area in the middle of a reach and can't seem to find that particular setup in HEC 5.0. Can you guide me to where I might find a solution for this?

  68. Chris Goodell

    on September 9, 2016

    It's very similar to this post on modeling a reservoir with a storage area, only you don't have an inline structure. Just move the end points of your reaches into the storage area to initiate the connection.

  69. Mohammad Reza Shirzad

    on November 14, 2016

    Hi
    i was trying to analyse a steady flow and when i run analysis i faced some errors such as :
    (A weir line has not been entered for this storage area connection. If there is to be no weir flow, enter a weir line with an
    elevation above expected stages.
    The "start" part of the connection must reference a storage area or cross section.
    The "end" part of the connection must reference a storage area or cross section.)
    but i have no any storage area. so would u please help me about this issue ?

  70. Chris Goodell

    on November 14, 2016

    It sounds like you have a storage area connection, but have not entered the required input data for it. Go to the SA/2D Area Connection editor and either delete the connection, or enter the required input data.

  71. Murthy NLN

    on November 17, 2016

    Hi chris,
    Finally my unstudy model started running after many trails,i have observed that there is no breaching affect on downstream sections after Dam breach. These sections are running only with hydro-graph which was given in the storage area just upstream of inline structure. It is really tankful, if you suggest a solution to my problem.

  72. Chris Goodell

    on November 17, 2016

    Make sure everything is connected properly as discussed in this post and make sure that "Breach this structure" is checked in the breach editor.

  73. Murthy NLN

    on November 17, 2016

    Hi Chris,
    Thanks for quick reply. Yes, I did it, both the Storage area and River reach at start is properly connected and also Breach this structure was be selected.

  74. Chris Goodell

    on November 18, 2016

    Hmmm. Not sure what's happening then. I'd have to see the model to know.

  75. Murthy NLN

    on November 19, 2016

    Hi Chris,
    once again thanks, ok i will share my model with you. how can send it to you.

  76. Chris Goodell

    on December 5, 2016

    Just upload it to Google Drive or DropBox and share the link with me here.

  77. Mohammad Reza Shirzad

    on December 11, 2016

    Hello
    Is it possible to use steady flow analysis instead of using unsteady flow analysis in HEC-RAS?

  78. Chris Goodell

    on December 12, 2016

    Yes.

  79. Clau

    on January 4, 2017

    Hello, I used HEC-GeoRAS to import the geometry to HEC-RAS, and I draw a Storage area on hecgeoras, although I can't connect it to the reach… how can i do it? Thank you

  80. Chris Goodell

    on January 4, 2017

    Once you have the storage area and the reach in the geometry editor, select Edit…Move Objects. Then click and drag the end point of the reach inside of the storage area you want to connect to. That should do it.

  81. Clau

    on January 5, 2017

    Thank you Chris, I was able to do it, although now I'm having trouble with the DSS output from the unsteady flow simulation. When I get the peak flow time for each station, it doesn't seem right. If you have some time to look at it I'd appreciate it. Not sure if it's a computation time or geometry problem. Thank you, best regards.
    https://drive.google.com/drive/folders/0ByqIE1Mzg4xyOXZXTkpvWjM1Y2s?usp=sharing

  82. Chris Goodell

    on January 5, 2017

    You need to run a longer simulation. Also you need to have much tighter cross section spacing, especially where there are large gaps between cross sections.

  83. Steve Browne

    on January 17, 2017

    Hi Chris –

    I am modeling a reservoir in which its inflow is direct from a stream and its outflow is regulated by an 18" circular culvert and a earthen dam/spillway. At low flows, the culvert is plenty to route flow to the downstream reach. How can I best model this, given that inline structures do not contain circular culverts?

    Thanks,
    Steve

  84. Chris Goodell

    on January 17, 2017

    Steve- In RAS Version 5.0.3, you can now put in circular culverts. But for any outlet that is not included in HEC-RAS, you can always use a "user-defined" gate and just put in a rating curve. Hope this helps.
    Chris

  85. Anonymous

    on February 12, 2017

    Hello Chris.

    I would like to know if I can have cross sections beneath the storage area. I don't now much about hec ras and I've always seen that there are only 2 cross sections with the storage area, so can I have a storage area and the cross sections beneath it in its full length?

  86. Chris Goodell

    on February 13, 2017

    I suppose it could be done. Not sure why you would want to though. Make sure you aren't double-counting volume!

  87. Unknown

    on February 15, 2017

    I am modeling a similar situation – a stream connected inline with a storage area. Will the flows from the stream automatically enter the inline storage area or do I need to insert a flow hydrograph to the basin with the flows from the stream? Also, is an inline weir necessary? Thank you

  88. Chris Goodell

    on February 22, 2017

    For inline connections, yes, flows will automatically enter the storage area, provided you have properly made the connection. No additional hydrograph is needed. And you don't need an inline structure.

  89. Anonymous

    on March 29, 2017

    Hello Chris,
    after i draw my reservoir area and connect it to my reach (upstream), the reservoir automatically connects with my last cross section downstream. Is this normal?

  90. Chris Goodell

    on March 29, 2017

    No. Not normal. Is your reach properly drawn in the correct direction (from upstream to downstream)?

  91. Anonymous

    on March 29, 2017

    Yes, it is. I have imported my reach and my cross sections from autocad civil 3D.

  92. Chris Goodell

    on March 30, 2017

    I'm at a loss then. Not sure what could make that happen. If you are able to solve the problem, please share your solution. Thx.

  93. Anonymous

    on April 3, 2017

    Aparently, i couldn't figure out how to import the cross sections through civil 3D so i created manually a reach and copy-pasted them.

  94. Anonymous

    on April 5, 2017

    I am trying to make a dam breach analysis, but i can't quite figure it out and my unsteady flow simulation goes unstable. can i please send you my project to check it out?

  95. Alvin Martinez

    on April 18, 2017

    Hi, Chris

    I've been trying to do sedimentation analysis of a dam reservoir.
    (catchment=3600 km2, annual rainfall=600 to 700 mm)
    I'm using a inline structure (weir) to set a dam with a open spillway.

    It works but the reservoir water level is always more than or equals to full, because of the above setting.

    However, the river is a seasonal river and the water level is not always full even in the rainy season.
    It is plausible that water level is lower than that and the spillout from the weir equals to 0.

    I have 2 questions about this.

    Do you have any ideas about how to simulate reservoir sedimentation in a seasonal river on HEC-RAS?

    Is setting weir a correct approach?

  96. Brittany Garnett

    on May 19, 2017

    Chris,
    I've used a storage area with a lateral structure to model an off-channel raw water reservoir. The model seems to be working well but when I breach the lateral structure my flows in the downstream river are lower than I would expect. I am using a dam breach time of about 1.5hrs and the volume to be drained would end up being 2,290ac-ft (99,752,400cuft)and over the 1.5hr dam breach I would expect approximately 18,472cfs to be flowing at some point (just based on simple math, if I do a broad-crested weir calculations I come up with a similar number) however, the model doesn't show more than approximately 9,700cfs flowing in the river. How do I know that I'm seeing the correct flow or what do you think could be the reason for the low flow?

  97. Chris Goodell

    on May 22, 2017

    I are considering submergence effects? That would effectively reduce your weir coefficient and could account for less flow than you might think.

  98. Anonymous

    on June 20, 2017

    For inline connections, do you have to define two separate river reaches to initiate a connection to the reservoir? Or can this be modeled with one river reach passing through the reservoir on each end?

  99. Chris Goodell

    on June 21, 2017

    They need to be separate. One river/reach on the upstream side, and a different one on the downstream side.

  100. Luke Detwiler

    on August 21, 2017

    Scott, I believe you and I experienced the same problem. I believe there was a rogue row of stage-storage data in your HEC-RAS table. If that is the case, filling all 100 rows incidentally solves the problem, but the underlying problem doesn't require you to fill the entire table to make it work.

    If you were to select all cells in your problematic Elevation Volume Curve using the select all button (top left cell exterior to the value containing cells) and paste the table into a spreadsheet, I believe you would have found a row of data below the perceived end of your storage table.

    When I did this for what I thought was a 3 row storage table, I found the culprit was an entry in row 23, well below what is immediately visible without scrolling in the HEC-RAS application. In general, if you receive 'Volume-Elevation relationship does not have increasing elevation' (or storage) for what seems to be a perfectly increasing table, this could be the problem.

  101. Rengganis Ashari

    on September 9, 2017

    Hi chris, I have a question, I try to make a flow modelling system from reservoir to spillway using a lateral structure in hec ras, but i little bit confuse about how i can Connect the flow from reservoir to lateral stricture and flow from lateral structure to reach?
    I'll appreciate if you can help,
    Thanks

  102. Tommy Duffy

    on September 20, 2017

    Hi Chris,

    I am new to hec-ras and have noticed something that I am not sure is a bug or the intended behavior in ras.

    I have noticed that when I set a pilot flow through the inline structure (dam) as well as an initial flow in the inflow hydrograph to the reservoir that is equal to the pilot flow, that this causes the max water surface to be lower than it should be for the resevoir/dummy xsections/dam. If I increase the pilot/initial flow value then the max water surface profile gets even lower. For design purposes, I need to know whether a specific storm will overtop the dam, and this approach causes my water levels to be artificially low.

    To fix this I thought I could use a pilot flow of 0 and an initial condition of 0, and then add in an initial flow value in the xsection just downstream of the dam. In this way the two dummy cross sections have water as they are connected to the water from the reservoir initial elevation and the downstream elevations have water in them from the initial condition I set for them. The model runs but and at first I thought I had solved the problem. However, when the pilot flow is 0 this causes no water to flow from the dam, even though it is clearly rising above the spillway and even overtopping the dam. The water just keeps on going up until the simulation ends.

    Any insight? I can send a link to my model if it would help.

  103. Chris Goodell

    on September 25, 2017

    Lateral structures must be placed in the river and assigned a river stationing. They are set up to flow from the river to a storage area (or another river, or a 2D area). Flow can go the reverse direction over a lateral structure, if the reservoir is higher in head then the river that the lateral structure is in. It will just show up as "negative" flow.

  104. Chris Goodell

    on September 25, 2017

    Make sure you set your Internal River Station Initial Stage. This is discussed in the last two sentences of the post.

  105. Anonymous

    on June 29, 2018

    Hi, i wanna know how to take boundary conditions for dam break analysis. specially the flow hydro graphs. How do i generate these hydro graphs in order to use as boundary condition. i am using level pool routing.

  106. deepak

    on July 4, 2018

    hi. i am modelling a landslide dammed lake with level pool routing. storage area is at the most upstream of the reach. how do i model the dam as inline structure? and how do i calculate the lateral flow hydrograph for the upstream boundary condition?

  107. faisal farid

    on July 22, 2018

    i am modeling a river with a sedimentation at the upstream lateral structure. But I keep getting this error message: "gate doesnt have any opening data (go to steady flow data editor option". But I am not using steady flow… Can you help me ?

  108. Dennis

    on November 8, 2018

    I have set up an unsteady HEC-RAS model spanning a four months period with widely varying river and dam level conditions. The model runs with relatively small errors at the beginning of the simulation but crashes after about 31 days every time. Changing the simulation start time does not make a difference. Is there a time or memory limit which causes instabilities. My model has storage area just upstream of an inline structure. But I'm sure that's not the problem cause.

  109. Chris Goodell

    on November 10, 2018

    Check your profile plot and see what’s happening just before it crashes. Look for any cross sections that are going dry (or close to it).

  110. HEC-RAS4.1.0

    on November 23, 2018

    I have a question about modeling ponds in steady flow using blocked obstructions. If the pond bank is built lower than the BFE to allow conveyance into the pond, does FEMA allow the blocked obstruction to be set at the bank of the pond to represent the full pond, rather than to the BFE? Thanks

  111. Sam, HEC-RAS 4.0

    on December 4, 2018

    Hi, I'm new to HEC-RAS. I simulated a sediment transport model for 11 years successfully.I also flushed it as well. However, I'm unable to view the change in area in each cross section from the original, after 11 years of sediment deposition and after flushing. The problem seems to be with the geometry files in each case. When I run the model and try to view the results (area) the geometry file remains the same though I change it! What can I do?

  112. Emmanuel Jjunju

    on January 21, 2019

    Hello, we have a 2D model for a very long reach that takes more than 2 days to run. At the end of the simulation, we got the error message "Extrapolated beyond storage vol vs el curve". We know this is because we have a el vs vol curve with a lower elevation (297) than the result from the calculation (ca. 297.5). How is HEC-RAS extrapolating the El vs Vol curve? I can't seem to find an explanation of the method used in the manual. Running the simulation again is an option but may be unnecessary if we can establish whether the interpolation method is acceptable to us.

  113. Chris Goodell

    on January 21, 2019

    I believe it is linear extrapolation off of the last two points of the curve.

  114. Tesfa

    on April 23, 2019

    HI, i'm modeling a dam breach to observe its inundation and to prepare an emergency action plan. To do this i have choose a 1D model and my reservoir is so small that it can best be represented by level pool ( storage area ). So my model has a storage area at its upstream side, 2 cross sections inside the storage an inline structure and multiple cross sections downstream. i have put my inflow as a lateral inflow in the unsteady flow data editor. my downstream bc is a normal depth and i have used a pilot flow with initial RS stage in the unsteady editor. my reservoir is well connected to the river reach. i have choose a time step of 1min and all my cross sections look good. with all this fine adjustment my model is going unstable right away at the begging of the simulation. i can't really figure out how i can improve the model. what do u suggest ??

  115. Chris G.

    on April 24, 2019

    Sounds like you did a good job setting this up. A few things you didn't mention. Is your first time step lateral inflow hydrograph and pilot flow the same? Also, you'll need to put the same amount of flow in the initial conditions flow for the first cross section of the reach.

  116. Unknown

    on August 12, 2019

    I am doing 2D Dam Breach Modelling of Landslide Dam. I have a Lake of about 1500 Km2,I modelled it as the Storage Area.The Input I have is storage Area and Monthly Flow Discharge Data of about 10 Years. I have input Boundary Condition of the Inflow Hydrograph at the start of the Storage Area by seperately defining Boundary condition for the Storage Area and my downstream path have a Boundary Condition as the Normal Depth. The Dam Structure is the weir structure and the failure mode is of piping. The issue which I am facing whenever I simulate my case study it took a lot of time with that I hava a huge iterations of the single time step with the large difference in the WSE and the Cell size.

  117. Awan

    on July 13, 2020

    Hello, I am new to HEC-RAS, I have been using HEC-RAS 5.0.7 (2D) to model dam failure. My current project will include sequential dam break failure of 2 downstream reservoir. FEMA P-946 recommendation is to use dynamic storage routing. I know very little about the procedure for this method. I am having trouble routing dam breach hydrograph from the upstream dam through the storage area of the downstream dam using a dynamic storage routing procedure. Can you please guide me to some publication or guide me through this process.

  118. Chris Goodell

    on July 15, 2020

    Hi Awan. To do dynamic routing through a reservoir in HEC-RAS, you have to model the reservoir with either cross sections (for a 1D simulation) or a 2D area (for a 2D simulation). Modeling the reservoir(s) with storage area does not allow for dynamic routing. You can read more about this in HEC’s TD-39 document. https://www.hec.usace.army.mil/publications/TrainingDocuments/TD-39.pdf

  119. Antonio S

    on October 14, 2020

    Hi Chris, I’m trying to model a dam with a reservoir upstream, I’ve gladly used this page to understand how to model this situation, but now I’ve got this error

    ERROR with Initial Flow for Reach
    The program cannot figure out an Initial Flow condition for ronco-fiumiuniti vallediga because the upstream end of this reach is directly connected to a storage area. Please enter
    an Initial Conditions Flow for this reach in the Unsteady Flow Data editor
    Reading Data for Post Process

    that i cant really how to solve.

    Here a setup for the model

    https://drive.google.com/file/d/1C-AvudL_40uHcv1b_Q75EL3JGic5jPxn/view?usp=sharing.

    Can you help me in this?

  120. Chris Goodell

    on October 14, 2020

    For storage areas, you have to use the lateral inflow boundary condition option. However, for the initial conditions, you have to put in a flow value for the cross section at the upstream end of the reach. this flow is generally the same as the first time step flow in your storage area’s lateral inflow hydrograph.

  121. Sauhard

    on November 4, 2020

    Hey Chris, I am trying to model a natural lake for Dam breach in Hec Ras 2d. Since the ground level itself acts as dam in my case, I don’t know how to model this .Should I modify the terrain by omitting the existing dam terrain and then put weir with similar cross section? Is there any other solution?
    Any way I can make Hec Ras read the existing terrain as dam? I tried copying the terrain profile in weir cross section but the model says weir elevation is lower than 2d flow area elevation.

  122. Chris Goodell

    on November 6, 2020

    Sauhard, use an SA/2D area connection for the dam. Then in the SA/2D area connection editor, copy the terrain profile to your station elevation data for the weir embankment. If you get the error message that the weir elevation is lower than the 2D flow area, you have at least a couple of options: If the difference is small, you can just use the “Clip” button in the SA/2D Area connection editor to fix this problem. If the differences are large, try using larger/longer cells adjacent to your dam. I guess a third option is you could modify the terrain, but I would avoid this. Oh, and you could separate the 2D area to one upstream and one downstream of the dam, then pull the 2D area boundaries down to the “toes” of the dam, that way the neighboring cells will have to be lower than the dam’s crest elevation.

  123. Hassan Rouhani

    on November 10, 2020

    Hi Chris,

    I am a new RAS learner. First, thank you very much for taking the time and writing on this blog. Very helpful.
    After reading this post, and many other posts in other blogs/forums, I still feel that hydraulics modeling in a watershed with a lake is unclear to me. Here is what makes me confused: instead of using a storage or other options, can I let the model just run normally and let the water fill the lake (which is connected to the main stream)? For example, let it run with the average daily value for six months, and then with the design flood values. I think that this way should give reasonable results for natural watersheds with lakes in the mainstream. And this makes life easier. Please correct me if I am wrong.

  124. Chris Goodell

    on November 10, 2020

    Hi Hassan-

    In a way, you are right, it would be a simpler model set up that way. However, depending on the size of your model, waiting 6 months of simulation time could take a long time. Setting your lakes and ponds with initial conditions can help to get your model started up right where you want it, without the long ramp up time.

  125. Hassan Rouhani

    on November 11, 2020

    Hi Chris,
    Thank you for your prompt reply and for your clarification.

  126. meenakshi ramola

    on February 16, 2021

    hi Chris,
    I am performing one-dimensional dam break modeling using HEC-RAS. After adding reservoir I am getting error “Error reading data from path://STORAGE AREA/SA/STAGE//1HOUR/1/ Some missing data was detected (-901)” can you tell what could be the reason, I tried everything but not getting results.

  127. Chris Goodell

    on February 23, 2021

    If your model is crashing, it can’t read from the dss file, which is a common reason to get that error. If your model is crashing, try to fix that and then hopefully the message goes away.

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