FAQ
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General
Problem after updating to 1.8.0
Problem:
I updated RAMMS::Avalanche (or Debrisflow) to version 1.8.0, but now I cannot run any simulations. RAMMS is stuck with "Create .xy-file", see Figure 1 below.
Solution 1:
- Open the "Additional Preferences" (Help -> Advanced... -> Additional Preferences... -> Edit) and check, if you have the "X64" option set to 1 (see Figure 2 below). If you do not find this option, then just add a new line (before the END tag) and enter
X64 1
Then click "Save" and "OK" and try again to run a simulation. If this does not work, then most probably some C++ libraries are missing on your system. Please see solution 2 below.
Solution 2:
- Open RAMMS
- Then use the function "Install C++ libraries" (Help -> Advanced... -> Install C++ libraries) to install the libraries (you will need Admin privileges to do that).


_JUSTCOMPUTEDRANGE is undefined...
Question: I tried the new update, but when I try to open an old file, the following error message appears:
% Tag name _JUSTCOMPUTEDRANGE is undefined for structure IDLITVISDATASPACE.
% Execution halted at: IDLITVISDATASPACE::GETXYZRANGE 1758
% _IDLITVISUALIZATION::GETXYZRANGE 1170
% IDLITVISNORMALIZER::COMPUTE2DPADDING 797
% IDLITVISNORMALIZER::ONDATACOMPLETE 1052
% IDLITVISNORMALIZER::SETPROPERTY 409
% RAMMS_GET_ID_OBJ 408
% RAMMS_OPENSIMULATIONNOW 1065
% RAMMS::CREATEROCKVIS 229
% RAMMS_OPENROCKOUTPUTFILE 12117
% RAMMS_OPENOUTPUTFILEMANYEVENT 10620
% IDLRTMAIN 183
% $MAIN$
Can you help me?
Solution:
- close RAMMS
- remove this directory: "C:\Users\<your username>\.idl" (if you specified Preferences in RAMMS, then you have to re-set them)
- now you should be able to start and use the new version. I strongly suggest only to use the new version (Rockfall) from now on. The speed of the handling is much improved, much easier to use RAMMS!
- if you again use the old version (Rockfall), then this problem could happen again.......
How do I create a license request file?
Did you already install RAMMS?
If No, you have to download and install RAMMS first, before proceeding to the next steps!
If Yes, then do the following:
Unable to allocate memory: to make array.
February 2nd 2021
Problem:
I try to run a simulation, but instead of the results, I get the following error message:
Error-Messages:
% Unable to allocate memory: to make array.
Not enough space
% Execution halted at:
What is going wrong here?
Answer:
The following issues can have an influence on the memory management of RAMMS:
- Do you use a large ortho-image that you overlay? This could be the problem here. Reduce the resolution of your ortho-image and try again.
- Calculation domain: Do you use a narrow calculation domain? If not, please have a look in the manual on how to define an ideal calculation domain (for avalanche and debris flow simulations).
- Dump Step: By increasing the dump step, you decrease the amount of memory needed to open a simulation file.
- Simulation resolution: A very good (=small) simulation resolution increases the amount of memory needed to open a simulation file.
No map found, continue search?
October 25th 2021
Problem:
I have two tif-files, a topographic map and an orthophoto, but I don’t understand why they don’t appear in the program and why it says that it doesn’t find any map or orthophoto. What can I do?
Answer:
- Both topo map and orthophoto must be in the same coordinate system as the DEM you used to create the project in RAMMS.
- For topo map and orthophoto, you need the corresponding world-file (tfw-file) to the tif-file. Otherwise, RAMMS will not find the files.
Illegal subscript range: ZAHL.
September 21st 2021
Problem:
I entered the license key, but with one character too little. Now when I want to start RAMMS, this warning appears. I can not start RAMMS at all. What should I do?
Answer:
Delete the file "license.dat" in the folder "license" in the RAMMS installation directory, then it should work again.
Missing text in colorbar and plots
February 3rd 2021
Problem:
I updated RAMMS today and the text is now missing from the scale bar and from the line profile plot. Any fix for this?
Answer:
You can fix this bug by running RAMMS in ”Windows 7 Compatibility Mode”.
Please do the following:
- Exit RAMMS
- Open Windows Explorer and navigate to your RAMMS installation folder.
- Right-click on RAMMS.exe
- Choose the tab Compatibility
- select the checkbox ”Run this program in compatibility mode for:”
- choose Windows 7 from the dropdown menu
- and then click Apply and OK.
- Restart RAMMS.
All your plots and colorbars should be ok now.
IDL System Error
February, 2nd 2021
Problem:
When trying to start RAMMS, the following error message appears:
A system error was detected during tool creation: RESTORE: End of file encountered. Unit: 101, File: ....\ramms_prefs.sav
What do I do now?
Answer:
Delete the file indicated in the error message (....\ramms_prefs.sav).
By deleting this file, your preferences (working directory, map-directory, ortho-image-directory, etc.) will be deleted. When restarting RAMMS, you have to redefine your preferences.
How to convert .dwg file (AutoCAD) to ASCII DEM
In the following we will describe how to convert a .dwg file (e.g. from AutoCAD) to an ASCII DTM file with ArcGIS. For the steps listed below you need ArcGIS with the Spatial Analyst extension enabled.

Can you make the gif animations repeat or do they only run once?
Answer
Yes, you can make gif animations repeat. Please do the following:
- Open ‘Additional Preferences’ (button in left vertical toolbar or menu ‘Help -> Advanced… -> Additional Preferences… -> Edit’)
- and then change the parameter GIFANIM_REPEAT_COUNT to the number of repetitions you want to have.
- Do not forget to click Save and OK.
- Create a new gif animation and import it into Powerpoint.
Can I import DXF-files into RAMMS?
Answer:
Yes, you can, but this is work in progress. Please get in contact with us and we gladly help!
Unable to invoke method on NULL object reference: .....
What is going on here?
This warning (see first image below) is mostly connected to a corrupt "preference file". The "IDL System Error" is mostly the reason for this warning, see second image below.
Solution:
Delete the file "ramms_prefs.sav" mentioned in the "IDL System Error". Then RAMMS will start again. If you specified RAMMS preferences (working-, map- or ortho-directories), then you have to re-specify them.
Avalanche
When and why does the Voellmy model work well for Avalanches?
Answer:
Avalanches
The Voellmy model – coupled with the calibrated parameters – can be used to
- (1) predict the runout distance and
- (2) predict the maximum flow velocity of extreme, large snow avalanches.
This is one of the important research results from the Vallée de la Sionne test site. The Voellmy parameters that we recommend describe the front of a dry-snow avalanche. Because the front defines the runout distance and maximum velocity the Voellmy model will work.
However, the Voellmy model will not describe the avalanche flow behind the front, at the tail of the avalanche. Here, measurements show an increase in the friction (a rapid decrease in speed). This effect causes avalanches to elongate and eventually deposit mass. Therefore, the Voellmy model will not predict the deposition behaviour.
The Voellmy model has difficulties to predict the runout of small avalanches, which sometimes begin immediately to deposit or “to starve”. Of course, small avalanches can be modelled using higher μ and ξ values, but this is a very ad-hoc approach.
What numerical solution technique does RAMMS use?
Answer:
In all RAMMS versions (Avalanche and Debrisflow) up to Version 1.5.01, an ENO (Essentially Non-Oscillatory) scheme was used to numerically solve the governing differential equations (Christen et al., 2010). However, the numerical solution was implemented on strictly orthogonal grids. This improves computational speed, but introduces numerical instabilities especially in steep terrain.
The new Version 1.6.20 uses the same second order ENO scheme, but now on general quadrilateral grid. This new scheme improves numerical stability, but slows the computational speed somewhat. The introduction of this stable ENO scheme allows us to use lower H_cutoff values minimizing mass loss during calculations. The standard value of H_cutoff is 0.000001 m.
What friction models are used in RAMMS?
Answer:
RAMMS (Avalanche and Debrisflow modules) employs a Voellmy-fluid friction model. This model divides the frictional resistance into two parts:
- a dry-Coulomb type friction (coefficient μ ) that scales with the normal stress
- and a velocity squared drag (coefficient ξ).
This model has found wide application in the simulation of mass movements, especially snow avalanches. The Voellmy model has been in use in Switzerland for a long time and a set of calibrated parameters is available.
How is cohesion used in RAMMS::Avalanche?
Answer:
Since Version 1.6.20 the basic Voellmy equation has been modified to include cohesion, see equation below, where C is the cohesion of the flowing material. Unlike a standard Mohr-Coulomb type relation this formula ensures that S→0 when both N→0 and U→0. It increases the shear stress and therefore causes the avalanche or debris flow to stop earlier, depending on the value of C.
This formula has been established using chute experiments with flowing snow (Platzer et al., 2007a and Platzer et al., 2007b). Snow has different cohesive properties depending on snow temperature. Wet snow avalanches have higher cohesion values; dry snow avalanches have lower cohesion values. Cohesion can help reduce spurious numerical diffusion in runout zones, providing a clearer delineation of the deposition zone. Cohesion values (unit Pascal) may be entered in the Mu/Xi tab of the Run Simulation window.
Recommended values may be found in the following:
- Dry snow: 0 – 100 Pa
- Wet snow: 100 – 300 Pa
Please use cohesion values with care!
Does RAMMS take terrain curvature into account?
Answer:
Since Version 1.6.20, the normal force N now includes centrifugal forces arising from the terrain curvature. We use the method proposed by Fischer et al. (2012) which was specifically developed for RAMMS.
The centrifugal acceleration ƒ is both a function of the avalanche velocity and terrain curvature. Typically this increases the friction, causing the avalanche to slow down in tortuous and twisted flow paths. It can change the location of the deposition once the flow leaves the gully.
Curvature may be activated/deactivated via the menu ‘Help → Advanced… → Curvature’.
How long does it take to perform a simulation?
Answer
The time required to simulate an avalanche or a debris flow is a function of the finite volume grid resolution and the size of the calculation domain. Typically we use 5m resolutions and the simulations require around 10 minutes. We usually perform the initial simulations at 10 m resolution and therefore we have results in 1 or 2 minutes. When we have a solution that we like we might take a look at the problem at 2m resolution.
Debrisflow
How do I speed up my debris flow simulation?
Problem: My debris flow simulation takes ages to calculate. I use a 0.5m resolution. Do you have any suggestions on how to speed up my simulation? And sometimes I get this error message:
Error-Messages:
% Unable to allocate memory: to make array.
Not enough space
% Execution halted at: RAMMS_OPENBINARYOUTPUT 2237
% RAMMS_OPENOUTPUTFILE 10730
% RAMMS_OPENOUTPUTFILEEVENT 10590
% IDLRTMAIN 183
% $MAIN$
Answer:
There are several important issues that affect your simulation speed and also your (RAMMS) memory management:
- Dump Step: By increasing the dump step (when starting a simulation, e.g. 10s instead of 5s), you decrease the amount of memory needed to open a simulation file.
- Calculation domain: Do you use a narrow calculation domain? If not, please have a look in the manual (section 3.5.4) on how to define an ideal calculation domain.
- Simulation resolution: A very good (=small) simulation resolution increases the amount of memory needed to open a simulation file.
- Do you use a large ortho-image that you overlay? This could also be a memory problem. Reduce the resolution of your ortho-image (do not forget to change the .tfw file too) and try again.
How does erosion work in RAMMS?
Answer: Erosion is explained in this article.
How is yield stress (cohesion) used in RAMMS::Debrisflow?
Answer:
Since Version 1.6.20 the basic Voellmy equation has been modified to include yield stress (cohesion), see equation below, where C is the cohesion of the flowing material. Unlike a standard Mohr-Coulomb type relation this formula ensures that S→0 when both N→0 and U→0. It increases the shear stress and therefore causes the avalanche or debris flow to stop earlier, depending on the value of C.
This formula has been established using real scale experiments with debris flows in Illgraben (VS). Yield stress can help reduce spurious numerical diffusion in runout zones, providing a clearer delineation of the deposition zone. Yield stress (cohesion) values (unit Pascal) may be entered in the Mu/Xi tab of the Run Simulation window.
- Recommended values: Debris Flow: 0 – 2000 Pa
Please use cohesion values with care!
When and why does the Voellmy model work well for Debrisflows?
Answer:
Debris flow
The “best” constitutive model for debris flows is still a very open question in the scientific community. We recommend using the Voellmy model until a better model is found. Voellmy basically has only two parameters and after some calibration a useful solution can usually be found. With Voellmy one can control the flow velocity (parameter xi) and runout distance (mu).
One reason Voellmy is useful is that it only requires two parameters to calibrate. The turbulent term dominates the frictional behavior when the flow is moving rapidly and the Coulomb term is dominant when the flow is moving slowly, allowing the model to be approximately calibrated to observations of flow velocity and the stopping location of the flow front.
Finding the “right” debris flow model is more difficult than finding the “right” snow avalanche model because debris flows are two component systems (fluid, solid). Much of the behaviour of a debris flow — including the stopping process — involves the interaction between the fluid-solid components. Thus, without a two component model, it will be unlikely that we are able to model all aspects of debris flows. The Voellmy model mixes the two components and therefore models the debris flow when the components volumes are constant and well mixed. This assumes, of course, that the relative portions of solid and fluid remain the same, from head to tail of the event. This is hardly true
Why use a hydrograph for debris flow modelling?
Answer:
There a several good reasons.
Firstly, hazard mitigation experts are often interested in the flow behaviour only near the fan. Calculating the movement of the debris flow in the torrent is a time consuming and often useless task. Therefore using a hydrograph can often cut calculation times dramatically.
Another reason is that it is impossible to describe the initial conditions of debris flows as a "block release". There are cases where block release is a good approximation of reality (e.g. dam breaks), but, in general, it does not accurately reflect the starting conditions of flows from intense precipitation.
Read this publication for more information on this issue:
Deubelbeiss, Y.; Graf, C., 2013: Two different starting conditions in numerical debris-flow models – case study at Dorfbach, Randa (Valais, Switzerland)
Rockfall
Overhanging face
October 14th 2021
Question:
I want to model rockfalls from a rockface above a road. But the rockface has an area which is overhanging. Does your software allow for overhanging rockfaces to be modelled.
Answer:
- Unfortunately, overhanging rock faces cannot be modelled in RAMMS.
To model overhanging rock faces, you would have to do some work-arounds:
- Cut the DEM, such that the overhanging part is not part of the DEM anymore, and then model this part of the DEM. If rocks will fall out of the overhanging ceiling, then you could project the part of the ceiling to the DEM below, and use fix or variable Z-Offsets to model these falling rocks.
- Then model the part above the overhanging face. You will have to create a DEM, where the part below the overhanging face does not exist anymore. This is ok, as rocks from above the overhanging part will not affect the area below the overhanging face.
Forest Cover Height
October 14th 2021
Question:
We have a query about the Zh-height value assumed in the calculations. The manual notes that Zh varies between 5m and 30m, with a default value of 30m, see Figure 1 below. We were therefore expecting to be able to specify a Zh in the calculation but can not see where we can do this. We therefore wondered if the open forest, medium forest and dense forest options assume different Zh values or if they assume the default value of 30m that we can not change.
The maximum tree height we are expecting is also less than 30m and is around 20 to 25 metres. Another reason we were looking to see if we can change the height.
Answer:
- The default Zh-value for all forest types is 30m.
You can change the Zh-value by doing the following:
- Open RAMMS
- click the "Additional Preferences" button (left vertical toolbar, at the bottom)
- and then add the following line (before the END keyword):
SHOW_FOREST_PARAMS 1 - then click 'Save' and 'OK', and open one of your input files. You should now be able to change the forest height values, see Figure 2 below.
Beware: you could also change the forest-drag-values. We suggest you use the default values from RAMMS. If you have good reasons to decrease or increase the drag values, this is the way to change the drag-values.