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Using SLAMM / Floating point error
Last post by andybell - September 17, 2019, 04:01:03 PM
I have just installed SLAMM 6.7 on my laptop (8GB Ramm on windows 10)
I am trying to run a model that I have downscaled from 2m to 10m resolution, but get an error when it reaches 6% in reading the site characteristics. The error reads "Invalid Floating Point Operation". The error comes up when the 6% progress is met

Any clues what might cause this?
Many thanks in advance


Using SLAMM / MTL parameter for station in H...
Last post by - August 14, 2019, 09:04:18 AM

I have been struggling to understand how to use the parameter MTL - NAVD88 and would like to check whether my assumptions are correct :)

I believe that since my topgraphic data (DEM) is not projected into any vertical datum, it would be enough to use a factor that would correct the DEM in terms of MTL, right?

If this is right, I would need to factor of correction which accounts for the Tide Mean Level minus the Local Datum level, right?

The station I am considering as input is the Tsim Bei Tsui (ID=1366), which provides the following diagram: ; (diagram attached to the message too).
You cannot see attachments on this board.

Is it correct that I should apply the paremeter as" MSL (2001-12) minus Local datum"? In this case, based on the diagram, I would have to use it equals 1.46m.

Can anyone please help me?

Using SLAMM / Re: NWI
Last post by Jonathan S. Clough - August 12, 2019, 01:55:53 PM
NWI is a product of considerable technical expertise from US FWS that includes satellite data, infrared photography data, photographic interpretation, and considerable GIS expertise.

You do not need an NWI data set to use SLAMM however.  You do need some sort of high-quality vegetation land-cover polygons that can be cross-referenced to the SLAMM categories.

Last post by Jonathan S. Clough - August 12, 2019, 01:52:11 PM
Hello:  Thanks for your interest in the model.

1. "ASTER DEM standard data products are produced with 30m postings, and have Z accuracies generally between 10 m and 25 m root mean square error (RMSE)."  I'm afraid that that Z accuracy is not going to be compatible with modeling the effects of 1-2 meters of SLR on marsh systems.  You will need LiDAR or ifSar.  I would say you wouldn't want a vertical RMSE of above 25 cm.

2.  In US applications we get MHHW and MLLW data from NOAA gauges.  You can use whichever type of tide gauge or water level monitoring data that you have available -- long term data are best.

3.  The SLAMM model usually assumes that tidal flats have a lowest elevation at MLLW.  That means that you would need aerial imagery that is tidally coordinated (taken at low tide) 

Best regards -- Jonathan
Last post by ommg - July 25, 2019, 10:47:09 PM
Sir I am completely new to work on slamm I have the following questions

1.Is Aster DEM is relevant instead of Lidar data.
2.Where to get the MHHW,MLLW DATA?
3.I am working on tidal how to define the polygon class for the tidal flat?

looking forward for first reply as I am eager to work on this model.
Thank you. :)
Using SLAMM / Re: NWI
Last post by rezaul - July 12, 2019, 04:37:17 AM
i got 2 queries,
1. how to produce NWI data ( i was looking for a more clear answer as i am not that expert in GIS)?
2. If I use ASTER GDEM data other than LiDAR, will I face any problem with my result?
Thanks for the reply. I have soil saturation turned off, the dike layer is correctly rendering in the "Set map attributes", and I'm defining the entire area protected by dikes.

I've sent you an email with some screen shots showing my execution options, the dike layer rendering, and the output showing land cover change even in the diked areas.

A potential work around to this problem is changing the diked areas to "Developed Dry Land" and running the simulation with the "Protect Developed Dry Land" option. This takes some additional pre-processing and post-processing of the rasters but it does work.

The cells are updated every time step, correct.

SLAMM actually tracks partial conversions of cells over time -- it was originally created many years ago when computers were much less powerful and cell sizes were therefore much larger (150-500meter).  For this reason it has always tracked multiple land types in each cell.  For this reason the tables of output are not always precisely what you would get when adding up the area of the raster maps.  After erosion to tidal flat, the elevation of the cell would be set to the elevation of the flat or MTL if there is no adjacent flat. 

In some of our older runs we found that the flat itself, became protective against further erosion at the marsh-to-open-water interface.  For this reason marshes erode directly to open water. ; line 627

-- Jonathan

You are correct.  However, soil saturation is not affected by dikes which could be causing the differences you are seeing.   Try turning soil saturation off.

Are you rendering the dike layer in "Set map attributes" to ensure that the software is interpreting your data layer correctly?  

And I think you get this, but you define the entire area protected by dikes using "classic" mode rather than the location of the dike itself.  

If none of these answer your question, feel free to post or email me some screen caps showing what you are seeing.

Thanks!  -- Jonathan
I'm running some simulations of SLAMM with and without the classic dike layer (specifying land protected by dikes). Aren't these dikes supposed to keep land cover from changing? Per the technical guide: "In the traditional model, if a cell is defined as protected by a dike or levee it is not permitted to change."

When I run the simulations, land cover is changing even in cells protected by dikes. If I compare this diked-scenario with the same simulation but with dikes turned off, the only differences between the two results are in areas "protected" by dikes. So clearly the dikes are having some effect on land cover change, but not the effect I expected. I thought they would completely prevent any land cover change in the diked area.

Am I incorrect in my interpretation of how the dike layer works? I'm using the most recent version of SLAMM (6.7 beta).
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