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,