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Messages - Amy Polaczyk

Using SLAMM / Re: GIS Output
April 26, 2012, 02:02:12 PM
Hello Marissa,

Your GIS output should be output to the same directory as your GIS input files. You can specify the output location (and base name) for the GIS output in the 'file setup" screen  in the "Base Output File Name" line. 


Sorry for the delayed response. The distance to channel factor is something we rarely use in our model applications due to the lack of data for parameterization. The model included with SLAMM is both experimental and conjectural.  It should be used with caution since the model is fairly sensitive to the accretion rate and care must be taken not to add additional uncertainty. That said, there are no assumptions in the model regarding the distance beyond which proximity to the channel has no additional effect. Both this distance (DistEffect) and the minimum effect are specified by the user.  The graph on Page 23 of the technical documentation illustrates that at distances above the DistEffect specified, the effect is not zero but the Dmin value given by the user.  Note, you must have a defined channel (i.e. be running the salinity model) for this effect to be relevant.  Unless you have specific data to parameterize this portion of the model, we do not recommend using it.

Regarding differences in Time Zero and the initial condition, this is common and allows one to double-check the assumptions and data inputs used. At time zero, no accretion or erosion is applied only the model assumptions and any historical land movement that may have occurred in the time between the wetland and elevation data layers used. The causes of time zero discrepancies can include:

- Poorly defined tide ranges or salt elevation parameters
- Areas that are actually diked (or subject to muted tides) are not specified as such
- Incorrect elevation data (non-bare earth LiDAR, units in feet rather than meters)
- Actual changes that have occurred in the wetland since the input wetland layer was collected.
- In addition, SLAMM's conceptual model does not have well-defined ranges for tidal swamp and tidal fresh marsh, these should be changed to reasonable values based on site-specific data

In order to investigate the changes between the initial condition and time zero, we suggest you double check your input data, the location of dikes, and tidal parameters, review aerial photography to determine if the changes you see are reasonable, adjust the minimum elevation in the conceptual model for tidally-influence freshwater habitats and perhaps run the model using the connectivity algorithm.

Hope this information is helpful,
Using SLAMM / Re: gis output
March 02, 2012, 03:52:54 PM

Have you double-checked that the raster is populated with individual numerical values? Please change the raster file extension to .txt and have a look at it in a text editor to determine if the raster generated by SLAMM is providing the correct output (eg, values from 1-26) and let us know. This is not a bug I have encountered before.

Also, please post the version of SLAMM you are using.

Using SLAMM / Re: Input Vs. Output sub sites
September 27, 2011, 01:27:14 PM

The Output subsites have no bearing on the parameters you input. Output subsites simply allow you to capture a map and numerical data for a portion of your study area when the model is run. The raster Output site file that can be associated with a SLAMM project does the same thing but defines the Output sites in a raster file. It has no influence on the input parameters.

In order to add spatially-variable tide, accretion, erosion values, etc. You'll need to use Input subsites that are manually specified in 'Set Map Attributes'.

Hope this clears up your confusion.

Using SLAMM / Re: DEM/3d tool issue
September 23, 2011, 12:53:32 PM
Glad you were able to resolve the issue, Julian.

Thanks for using the forum and for following up on your post.

Using SLAMM / Re: DEM/3d tool issue
September 21, 2011, 06:17:12 PM
Hi Julian,

The misalignment could be due to:

- A systematic horizontal shift between your DEM and wetland layers
- An inaccurate MTL to NAVD88 correction
- The common occurrence of tidal flats and some low-lying marshes falling below MTL based on the SLAMM conceptual model default elevations. You can check this in the Elevation Statistics window

Investigate these possible sources of error and re-post to this thread with any follow-up questions.

Good luck!


You can send the file to me at:

Have a nice weekend!
Hi Jen,

I have an idea as to where the confusion might be. You said:

...where I have a NAVD salt elevation of 0.12 (which is what is entered into the model)...

In the Site Parameters, you should be inputting your salt elevation in meters above MTL, not NAVD. Since the model is expecting a value relative to MTL for that parameter, you may be applying the NAVD88-MTL correction twice...

If you'd like you can send project SLAMM6 file to us and we can have a look at it.

The calculation you need is actually much simpler. Since the vertical datum for both HTU and "meters" is MTL, multiplying the elevation in HTU by the definition of HTU in meters is sufficient to determine the elevation in meters. What you have done below should do the trick:

the 5th percentile elevation for Transitional Salt Marsh is -1.54 HTU. 
HTU in this system is 0.11 meters.
the 5th percentile elevation in meters is thus -1.54*0.11 = -0.17 meters

You do not need to include the NAVD 88 correction in the calculation (unless you specifically require the elevation data relative specifically to NAVD).

It is important to keep in mind that this conversion may change over the study area if the tide range is variable.

The good news is that in SLAMM 6.1 (to be available at the end of the month) the user has the option of viewing the elevation analysis in both HTU and meters.

You also wrote:

This came up because I noticed that in the Conceptual model output it calculated the "Min in HTU" and "Max in HTU" values based on the salt elevation in NAVD 88, rather than on the salt elevation corrected such that MTL = 0.

This shouldn't be the case - could you describe how you determined that?

Best regards,