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Elevation output

Started by planetsandman, April 27, 2011, 09:09:31 AM

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At each time step, SLAMM calculates elevation (elev-SLR+ Accretion), is there any way to get this elevation as a raster output for each time step?

Jonathan S. Clough

Now that you mention it, yes.  

There's a new beta version available here:

This may be considered an "alpha test" of the new model capabilities.

Please email me with any questions or bug reports.


Differences since the previous version:

  • Integrated Monte Carlo (Latin Hypercube) uncertainty analysis funded by Ducks Unlimited.
  • Integrated Sensitivity analysis created to fulfill requirements of a Gulf of Mexico Foundation contract
  • Elevation maps may be output for each time-step along with other GIS maps.  Elevations are output in "meters above MTL" units. (funded by USGS contract)
  • SLAMM color designations may now be loaded from and saved to disk as separate files so they can be copied from one project to another.  (funded by USGS contract)
  • An area in the map can be designated as "freshwater influenced" and it is then subject to an alternative flow-chart. (created to fulfill requirements of a Gulf of Mexico Foundation contract).
  • Can display an NAVD88 correction map to QA that production
  • Elevation Analysis is performed and displayed in Meters as well as "half-tide units."  (Much better for microtidal systems.)
  • Erosion maps showing in which cells erosion was predicted to occur may be produced.
  • Vegetated Tidal Flat variable accretion model replaced with "tidal fresh marsh" variable accretion model.
  • Minor interface improvements & bullet-proofing.


Documentation of these capabilities is nonexistent or incomplete but I'll add some information here.

Uncertainty Analysis:

An integrated Monte-Carlo uncertainty analysis is not included.  The user may specify the types of distributions and key statistics for almost all input variables.  Changes in most parameters are "multipliers" by existing parameter values.  This enables a single distribution to represent uncertainty over many "sub-sites" simultaneously.  Depending on the specific variable and the amount of available information, any one of several distributions may be most appropriate.  The interface supports normal, lognormal, triangular, and uniform distributions.

The model is then set to run for numerous iterations, sampling from each of these distributions.  Efficient sampling from the distributions is obtained with the Latin hypercube method (McKay et al., 1979; Palisade Corporation, 1991).

For elevation uncertainty and NAVD88 uncertainty, a stochastic analysis is possible in which multiple equally-likely digital elevation maps are produced using "spatial autocorrelation" in the manner of Heuvelink[1],[2].  [1] The recommended method is Heuvelink's iterative approach to create a set of equally likely elevation maps with spatial correlation.  Recommendations from Hunter & Goodchild 1997, Darnell et al. 2008, and Hunter & Goodchild, 1995. [2] Error Propagation in Environmental Modelling with GIS, G.B.M. Heuvelink, 1998.

Results are saved to CSV files and a log-file is produced.

Access this capability through the "Uncertainty / Sensitivity Setup" button on the "Execute" screen.

Sensitivity Analysis:

This is a "one at a time" sensitivity analysis.  Each parameter is incremented or decremented by a given percentage over all sub-sites and the results are saved.  Results are saved to Excel files and a log-file is produced.

Access this capability through the "Uncertainty / Sensitivity Setup" button on the "Execute" screen.

Elevation Maps:

Access this capability through the "GIS File Options" button on the "Execute" screen.

SLAMM color designations:

Access this capability through the "save" and "load" buttons on the "Legend" screen.

Freshwater Influence:

If you define an area as having a fresh-water flow "Extent Only", we have changed the flow chart from "Swamp" to "Tidal Swamp," from "Tidal Swamp" to "Tidal Fresh," then to "Brackish," then to "Salt Marsh".  When there is no freshwater influence defined, swamp gets converted to brackish immediately.

So this would just be defining a polygon as having fresh water flow influence as opposed to any information about the extent of the flow or the salt wedge.  

1. To use the fresh water extent capability, under Set Map Attributes, click "Show... Fresh Flows" at the upper left.  
2. Add a "fresh flow"
3. Define the boundary with the "define boundary" button.
4. Important! click on "F.W. Extent Only" under that button.
5. Areas within the polygon you have defined will be subject to the flow chart as shown above.
6. No other parameters are required.


The link to the new beta version appears to be broken...

Jonathan S. Clough


Is the elevation output the minimum elevation or true elevation referenced to MTL?

Jonathan S. Clough

This is an excellent question.  It is the mean elevation of each cell as referenced to MTL in meters.  (We do not convert back into NAVD88.)