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Distance to channel factor and different result between 0 time and current cond

Started by katerinapyl, March 02, 2012, 05:32:45 AM

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katerinapyl

I am trying to include the Distance to channel factor in my model and the manual does not have many details on that. I have the excell file where I can test the values Dmin and DistEffect but I cant understand what values are appropriate for my site. Is there a specific assumption underneath or it is empirical?
For example, is there an assumption that there is no effect after 500m? Also, after the distance beyond which proximity to the channel has no additional effect, the min effect after the 500m is 0 (no effect at all) or sth else??

Also, I have different results between the 0 time and the current time. I am using LIDAR data so I dont use the Preprocessor. Is it sth wrong or SLAMM depicts the input data on the 0 time and at the current time updates the elevation taking into account sth, for example the accretion or the subsidence??

Thank you

Amy Polaczyk

Hello,

Sorry for the delayed response. The distance to channel factor is something we rarely use in our model applications due to the lack of data for parameterization. The model included with SLAMM is both experimental and conjectural.  It should be used with caution since the model is fairly sensitive to the accretion rate and care must be taken not to add additional uncertainty. That said, there are no assumptions in the model regarding the distance beyond which proximity to the channel has no additional effect. Both this distance (DistEffect) and the minimum effect are specified by the user.  The graph on Page 23 of the technical documentation illustrates that at distances above the DistEffect specified, the effect is not zero but the Dmin value given by the user.  Note, you must have a defined channel (i.e. be running the salinity model) for this effect to be relevant.  Unless you have specific data to parameterize this portion of the model, we do not recommend using it.


Regarding differences in Time Zero and the initial condition, this is common and allows one to double-check the assumptions and data inputs used. At time zero, no accretion or erosion is applied only the model assumptions and any historical land movement that may have occurred in the time between the wetland and elevation data layers used. The causes of time zero discrepancies can include:

- Poorly defined tide ranges or salt elevation parameters
- Areas that are actually diked (or subject to muted tides) are not specified as such
- Incorrect elevation data (non-bare earth LiDAR, units in feet rather than meters)
- Actual changes that have occurred in the wetland since the input wetland layer was collected.
- In addition, SLAMM's conceptual model does not have well-defined ranges for tidal swamp and tidal fresh marsh, these should be changed to reasonable values based on site-specific data

In order to investigate the changes between the initial condition and time zero, we suggest you double check your input data, the location of dikes, and tidal parameters, review aerial photography to determine if the changes you see are reasonable, adjust the minimum elevation in the conceptual model for tidally-influence freshwater habitats and perhaps run the model using the connectivity algorithm.

Hope this information is helpful,
Amy

katerinapyl

My aim is to include the D factor into the accretion model but not to take into account the salinity.

In the  manual it is mentioned that if the turbidity factor  is not defined into the freshwater flow parameters or defined equal to 1 the accretion rates are not modified. So in that case the salinity is not taken into account but the channel has been defined (of course I need to specify the the boundaries and the origin of the channel in the screen map) and thus the Distance to channel can be calculated and therefore the D factor can be taken into account?

But what about the rest parameters - slope and swamp elevation (I run a simulation where they are not specified and an  error occurs asking for the rest flow paramerers..)

On the other hand, if the turbidity factor is not equal to 1 the calculated accretion rates are multiplied by the specified turbidity factor, meaning that the salinity model is included into the simulation. In that case do I also need to specify the salinity factor (S) into the accretion model? Or if I specify the S factor into the accretion model do i need to also include the salinity model??

Thank you in advance
Katerina

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