Due to SPAM attacks, new members must be approved before posting.  Please email when registering and your account will be approved.

Main Menu

slamm 5 vs 6

Started by Dean, February 23, 2011, 10:38:04 AM

Previous topic - Next topic



Has anyone else noticed some major differences b/t slamm 5.0.2 and 6.0.1 outputs, especially regarding conversion to open water vs estuarine beach?  I seem to be having much more estuarine beach in ver. 6 compared with open water for ver. 5. I'm wondering if this is an error in the code or if something is new in slamm 6 that would be affecting this part of the decision tree. All input parameters were essentially the same. Is there some switch that is set to a different default, like erosion, in ver. 6?  Some of the areas that convert from reg. flooded marsh to estuarine beach start out at 0m of elevation, so I know something's not processing correctly.  

You can see the attached screenshots of the initial condition compared with slamm 5 and 6 ouputs. The only changes b/t the inputs b/t versions relate to using the MTL correction grid, instead of a global site value and some minor modifications (for the better) of the DEM.

Thoughts and suggestions welcome!


Jonathan S. Clough

We haven't seen dramatic differences like that.   

You write "I know something's not processing correctly."  Do you mean that you are using the elevation pre-processor?

Regularly flooded marsh does not convert to estuarine beach, but can convert to tidal flat when it falls below MTL.

So basically, in one simulation these low elevation areas are converting to tidal flat and another case to open water.  The lower elevation boundary for tidal flat hasn't changed and is MLLW (-1.0 "half-tide" units relative to MTL)

The results look a little surprising, though.  Rarely do I see such a strong line between swamp and tidal flat. Usually if swamp converts there are some other fringes in-between.  What does your elevation data look like and what is its basis?

-- Jonathan


Hi Jonathan,

No, I didn't use the pre-processor in either run as both included only lidar-derived DEMs.

Thanks for the correction on estuarine beach. It's correct in the screenshots and rasters, I just misread it.

Good to know that the low elevation for Tidal Flats hasn't changed b/t versions.

There's no swamp class (or little of it) in these screenshots or at this site, just Regularly Flooded Marsh that's abutting the Tidal Flats you see. I've been using a different color scheme than the model's default.

I've been thinking about this some, and it seems that the issue may relate to me having used two sources of data for the different versions. For the version 5 run, I used 1983 landcover data. For v.6, I used 2006 land cover data. For both, I used 2007 lidar elevation data.

The total rise for the v.5 run is a little over 1.1 m, whereas for v.6 it's a little more than 0.9 m. Something you can't see in the screen shots is that the marsh converts to open water only in the last time step for the v.5 run (ie b/t 2075 and 2100). This is essentially the same for the v.6 run, except the change is to Tidal Flat. I'm assuming this means that if the model played out a little longer, so to 1.2 m rise using the custom scenario, that the Tidal Flats would likely turn to open water. I know this should be the same, but given the timesteps and different start date, perhaps I'm capturing the "cusp" of the change.

Any thoughts on this are much welcomed.



Yes I also noted a difference in SLAMM 5.0.2 and 6.0.1. SLAMM 6 showed more beach erosion and much more estuarine beach erosion than SLAMM 5. SLAMM 5 showed tidal flats moving inland further. I used Lidar data, so no pre-processing and the exact same parameters for each run.


Jonathan S. Clough

We're running the model now and noticing similar issues with regularly flooded marsh.

I'm going through the SLAMM5 and SLAMM6 codebase and comparing them.

I found several minor things:

1. In early 2010, we fixed a bug in which historic SLR prior to 1990 might be overcounted.  This only pertains to studies with a NWI Photo date prior to 1990.
2. In SLAMM5 we had set the upperbound (pertains to pre-processor only) of irreg.flood marsh to (MHHW + Salt Elev) / 2.  Now we set this to (1.2 Half Tide Units or MHHW * 1.2)  as a default.  These two figures are often close but not precisely the same.  This value can be set in the elevation analysis window.
3. In SLAMM5 the estuarine beach was assumed to extend to MTL but in SLAMM6, based on NWI classifications it is allowed to extend to MLLW and then converts to water as opposed to tidal flats.  This explains the "tidal flats moving inland further," described above.

Those are the three minor differences so far.  I found no differences in the erosion code, though the Bruun rule can now be turned off for ocean beach.  It is important to note that the lower boundary for all wetland categories can also be set as part of the elevation analysis screen to take advantage of site-specific data.