January 18, 2020, 02:30:33 AM


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General Discussion / model validation
Last post by gverutes - January 16, 2020, 06:31:59 AM

I recently applied SLAMM in Mexico along the Yucatan coast.  Can someone point me to validation examples from previous applications...perhaps in the US Gulf of Mexico?

Much appreciated,
Using SLAMM / whether the SLAMM model can be...
Last post by zhiliehui1 - January 09, 2020, 03:03:38 AM
Dear sir?
      In a study by my research group, it is necessary to predict the change of coastal wetland vegetation and the distribution of ground salinity in the future SLR scenario. We have successfully performed small area studies with SLAMM, and we do not know whether SLAMM is applicable to global scales.I remember the technical documentation mentioning that the coastal zone can be divided into subsites. Whether the global scale can divide multiple sub-areas according to the direction to the sea and set rough model parameters for research. If we want to carry on this research, do you have any good suggestions?
      Look forword to your reply.
Using SLAMM / Re: why the results with and ...
Last post by zhiliehui1 - December 03, 2019, 06:59:14 PM
Thank you for your detailed explanation. My problem has been solved. Thank you again.
Using SLAMM / Re: why the results with and ...
Last post by Jonathan S. Clough - November 15, 2019, 01:36:25 PM
With regards to Question 1:

Thank you for your question, I'm not sure this is adequately addressed in the technical documentation.

The way that the "include dikes" and "dike location raster" works is that the model uses the connectivity algorithm to see if there is a connection between the land behind the dike and a "salt water source."  Specifically, the categories "riverine tidal," "estuarine water," "tidal creek," and "open ocean." must not appear behind the dike.  Otherwise the dike location raster will not work and the results will be no different.

You may check the connectivity of your site using the connectivity map option when setting up your model.

With regards to Question 2:

The time-zero run is a very important step.  To the extent possible, it should not be any different than the model's initial conditions.  It tests that the conceptual model, the wetland coverage, the elevation data, and the tide range data are all consistent.  In the results the initial condition is shown as "0" and the "time zero" result is shown as the first date of the simulation.

From the tech doc:
SLAMM can also simulate a "time zero" step, in which the conceptual model can be validated against the data inputs for your site. The time-zero model predicts the changes in the landscape given specified model tide ranges, elevation data, and land-cover data. Any discrepancy in time-zero results can provide a partial sense of the uncertainty of the model. There will almost always be some minor changes predicted at time zero due to horizontal off-sets between the land-cover and elevation data-sets, general data uncertainty, or other local conditions that make a portion of your site not conform perfectly to the conceptual model. However, large discrepancies could reflect an error in model parameterization with regards to tide ranges or dike locations, for example, and should be closely investigated.
Using SLAMM / why the results with and with...
Last post by zhiliehui1 - November 14, 2019, 01:40:26 AM
I am a student from China. I had several problems using slamm:
1\ I want to simulate the influence of the presence and absence of dikes on the coastal wetlands in the current and future situations. The data type of the dikes I used is the type of position and height. In the execution window, I made the Settings including and excluding dikes respectively, as shown in the screenshot below.However, the result is consistent with the fact that there is no dike, but obviously this is not consistent with the actual situation, please help me how to solve this problem.

2\In the process of model simulation, I noticed there are run model for NWI photo date (0) in execution window , refer to the technical manuals, but I still don't quite understand, why no matter whether the check this option, the result is 0 year which is not  consistent with the   starting year wetland distribution  in simulation , please help me to solve, whether in the simulation of actual need to check this option.
thanks a lot for your help sincerely
There always will be outliers in terms of the elevation to wetland to tide range relationship.  (Influences of ground water can have fresh marsh occurring lower, or wind tides can have salt marsh occurring higher.  Also, elevation data can be uncertain especially in areas of high vertical relief.  Or wetland maps have horizontal error. So we very often have outliers outside of the modeled range for wetland categories.)

In general, you don't need to include these elevation outliers in your accretion to elevation relationship.  Those wetlands that fall below the modeled lower range (we often set this to approximately the fifth percentile of the wetland elevations) will be lost at "time zero."  You can then check to see if this is reasonable or not based on satellite imagery and make changes if required. 

Those wetlands that fall above the modeled higher range will be set to the accretion rate modeled at the highest range.  We usually do not model those wetlands as "drying" because they are too high, assuming some other local factor has those wetlands perched at that elevation.  So they will generally remain persistent unless the SLR becomes extreme. 

Overall, the accretion model should try to match the majority of the data (5th to 95th percent confidence interval?) and not worry about the outliers.

Hope this is helpful, thanks!
Model Formulation & Parameters / Re: Specifying accretion as a ...
Last post by slammdunk - October 29, 2019, 06:55:29 PM
Hello Jonathan,

Thank you for in-depth and easy to follow instructions. Your response helped clear a lot of my confusion.

A follow-up question I have is, on the SLAMM accretion spreadsheet it states under the min and max "not parameters but reflective of elevation range of wetland type". Would it be better to have min and max across the whole estuary being modeled or would it be better to have the average min and max of vegetation types around SET tables?

Happy to hear that you like the username!

First calculate the longest term average elevation-change rate for your SET tables that you have available.

Then calculate the elevation of the SET table relative to MTL in "half-tide units."  As a reminder, half-tide units are "elevation-in-meters / (0.5 * GTU-in-meters )"

Then, plot these data on a graph so you can understand the relationship between SET elevation and measured elevation changes.   

A line using the accretion spreadsheet data can then be fit through the data to the best of your capability.

e.g. Fig 4 from https://www.sciencedirect.com/science/article/pii/S1364815216302705#fig4

Often SET tables are not set at elevations throughout the tidal range and are focused up around MHW so you would need to estimate the other portions of the range or use a model such as MEM3 to help fill out the relationship between marsh platform elevation and predicted accretion rates.

This is a quick birds-eye view of the procedure, please ask specific questions about the spreadsheet and we will answer them ASAP.

Love the user name BTW.

Regards!  - -Jonathan
Model Formulation & Parameters / Specifying accretion as a func...
Last post by slammdunk - October 01, 2019, 04:19:42 AM
Hello Jonathon and Marco,

I am new to SLAMM and have had some difficulties understanding how to vary accretion rates as a function of cell elevation for different NWI wetland codes. I am hoping you can provide some more guidance on how to go about this.

I would like to use surface elevation change data from SETs that were placed in marsh and mangrove regions. Rather than breaking up the dataset for subsites around each SET, I would like to have accretion rates vary with elevation and tidal range for marsh and mangroves. I'm not certain about how to input this data into SLAMM though. Could you provide a step by step overview?

I have read through the user manual and technical guides, and have tried playing with the Excel SLAMM6_Accretion file included with the download. However, I'm still confused about how to go forward.  ???  Could you also provide an overview of the SLAMM6_Accretion file- bit of an introduction on how to utilize the spreadsheet?

Thank you ahead of time for all your help!   :)
Using SLAMM / Re: Floating point error
Last post by andybell - September 19, 2019, 08:13:20 AM
Hi Johnathan,
thanks for the helpful reply.

Yes, the same 10m resolution data set works in 6.0 but not in 6.7
I tried the 2m resolution set in 6.0 and it went to write to disc then crashed...unsurprisingly; they are pretty big files.

I have ordered more memory for the laptop and will try the binary option for both datasets in 6.7 as you advise.

If this doesn't work I will zip up the 10m data for you to diagnose stepwise in 6.7, but that will be my last option knowing how busy you are.
All the best
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