wetland elevation categories

[katerinapyl]

Hi,

I am a PhD student at UCL, London and I will use the SLAMM model to model the impacts of climate change on coastal and estuarine habitats. My case study is in UK, so I have to change the elevations of wetlands. I saw that I can edit them at the elevation input and analysis table before run the model. But I was wondering if I can change the code to do that. So, I search the code and saw that the wetland elevation ranges (min and max) are only defined as numbers in the initx.inc file and could not find any other equation or parameters defining them. Is that correct? The numbers that are used there as min and max elevation correspond in a particular area or they are standards for USA?

Also, I found the following equations in the code:
MHHW=GTideRange/2  and MLLW=MTL-GTideRange/2. These equations are SLAMM's assumptions or they correspond to the real data, because in my case study does not correspond.

Thank you very much,

[Jonathan S. Clough]

With regards to the first question,

I'm not sure why you would want to edit the conceptual elevation model without going through the interface that was designed for such changes.  The elevation model chosen is loaded and stored each time you load and save a SLAMM6 file, so really the only thing you can edit is the default elevation model that is brought up if you produce a new study.  You can examine the relationship between your site specific elevation data and the chosen conceptual model with the model's GUI.

Yes the code in initx, "SetDefaultCategoryVariables" is the code you would change to modify the defaults.  These were originally coded based on the scientists conceptual model who created the model but have been refined as additional LiDAR data has become available.  Let us know if you have specific questions about individual categories.  Please be careful changing the conceptual model without thought.  I've seen many people make mistakes such as having the dry land lower boundary be 10 meters above MTL because that's where the data showed their land was.  Or having "irregularly flooded marsh" allowed down to MTL or below.  That doesn't make sense because how could this tidal category be "irregularly flooded" at MTL.  We are working on guidance as to which of the elevation ranges it is appropriate to change under which circumstances which I'll try to share shortly.

As to your second question,

This website http://tidesandcurrents.noaa.gov/datum_options.html includes the following definitions that are compatible with the equations given

MHHW,  Mean Higher High Water, The average of the higher high water height of each tidal day observed over the National Tidal Datum Epoch. For stations with shorter series, comparison of simultaneous observations with a control tide station is made in order to derive the equivalent datum of the National Tidal Datum Epoch.

MLLW, Mean Lower Low Water, The average of the lower low water height of each tidal day observed over the National Tidal Datum Epoch. For stations with shorter series, comparison of simultaneous observations with a control tide station is made in order to derive the equivalent datum of the National Tidal Datum Epoch.

GT, Great Diurnal Range The difference in height between mean higher high water and mean lower low water.

MTL, Mean Tide Level, The arithmetic mean of mean high water and mean low water.

Therefore MHHW - MLLW = GT.  If elevations are expressed in terms of MTL, MHHW = GT/2 and MLLW = MTL - GT/2.

Let me know if you continue to have questions about these definitions.

Best regards -- Jonathan

[Jonathan S. Clough]

Please see this link for information about SLAMM elevation defaults.  Please let me know if you have difficulty accessing it:

https://docs.google.com/spreadsheet/ccc?key=0ArsPAkgK5ZypdE5FS0twUXVJRVg0a0N1T0kyX1hDamc&hl=en_US#gid=0