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

Main Menu

SLAMM Users Guide

Started by Jonathan S. Clough, April 24, 2009, 09:25:52 AM

Previous topic - Next topic

Jonathan S. Clough


In this topic, I hope to post some frequently asked questions about applying the SLAMM Model.  Please feel free to add a new topic if you do not see your question listed here:

GIS Projections:  It is recommended that an equal-area projection is utilized to avoid the potential for error in calculating surface area statistics.  

Site Data:

1.) I am having trouble understand the "water depth" input.  Could you clarify how one would develop this input?  In the documentation, you say "meters below MTL".  How would you estimate this?

This is not an important input to the model unless you are modeling a system in which sea level is falling.  We have not modeled such a site in many years.  (Projected Sea Level Rise almost always is greater than equal to projected rates of isostatic rebound)  To answer your question, though, this would be the depth of water two meters from shore (the depths in-between are interpolated.)  However, we haven't tested this accretion code in many years now.  Also, this should be replaced by code to read bathymetry data in the mid-term future.  You should find the model to be completely insensitive to this (vestigal) parameter.

2) We are having some trouble finding information on Mean High Water Spring.  Any thoughts as to the best source for this information.  The COOPS data does not appear provide MHWS.

This is an interesting issue.  In recent years and model applications I have replaced the concept of MHWS with the concept of frequency of inundation.  I usually define MHWS as the elevation above MTL that is expected to flood less than one time per month.  This usually lines up fairly closely with the dry-land/wetland boundary.  

"Spring Range" is available as part of NOAA tide table data.  However, this "MHWS" is actually the mean high water (not MHHW) on the dates of new moon or full moon and it is often quite close to the MHHW-MLLW range.  What we are really looking for is an elevation that floods infrequently enough so that we predict dry land above that elevation and wet lands below.  Based on consultation with wetland scientists a frequency of once per month was deemed as appropriate.  

You can use either NOAA tide predictions to try to derive this value or NOAA historic tide data.  Or, you can use a regional relationship, often something like 1.33 to 1.5 times the Great Diurnal Tide Range.

When the model is re-worked some of these parameters will need to be renamed for clarity sake.  (and some removed altogether!)

Frequency of Large Storms:  This parameter reflects the frequency of overwash for

Tide Range Inland vs. Tide Range Oceanic: These parameters were split up when the model was run with a single site record.  The inland tide-range reflects the tide range in a location where dry land is prevalent.  However, we generally keep these two parameters the same and parameterize gradients in tide ranges using the model's sub-site capabilities.

Do not forget that these "site" parameters can become "subsite" parameters by defining subsites in the set-map attirbutes mode.  Each of these parameters can be assigned to an individual polygon instead of a whole site.

Salinity Module:  

  • The salinity sub-model was written as part of the STAR grant as the original model was not working well when there was significant freshwater influence.   (Required as marsh-type is more highly correlated to salinity than elevation when fresh-water flow is significant, Higinbotham et. al, 2004)
  • We never originally had funding or scope to write the salinity portion of the model under STAR but managed to squeeze it in under the original scope.  The resulting model is therefore simple.  There are several nuances to applying this model (e.g. manner of defining estuaries and flow-vectors) that have never been adequately documented and are not likely to be so.  The salinity model is essentially unsupported by us at the current time (for use by other users than ourselves).
  • The salinity model does currently have funding to be significantly updated and refined under a TNC conrract.  That work is expected to be completed within the next six months.  Therefore, this "original" version of the salinity model is not expected to be fully documented or supported at any time as we are instead putting our efforts towards the refinement and documentation and support of that model.

Jonathan S. Clough

Most of you are probably aware that there is a more formal SLAMM Users guide here: