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Initial condition (time zero)

Started by caroline, August 21, 2013, 11:30:57 PM

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I am working in northern Maine. I am fiddling with my salt elevation and finally got the initial condition/1983 (my NWI year) to practically match in my region. Yay! I initially started with 8.6 m (the highest spring tide on historical NOAA tide sheets) for the salt elevation, but realized that was incorrect after reading the forum, so based on 4.11 m I ran it again. I used the GT from NOAA (5.87)/2 x 1.4 (the average to multiply by per the forum), as per the forum technique, to get 4.11. This is close to what was used by the FWS in this region on two SLAMM studies (3.99 and 4.08).

Although this helped my problem- two low spots in my lidar were converting from undeveloped dry land to transitional marsh and ocean beach- it still was way over a 5% difference (which I have read in this forum is the cutoff for more accurate results). So I played around with the elevation pre-processor and it looked as if a value of '2' m would work. So I used it, and now my initial condition (time zero) and 1983 match! However this number is not really 'science' but an educated guess; is that acceptable when running the model? If they match up does that mean I 'guessed' correctly? I am assuming (from other posts too) that my salt elevation is not in line with my elevation data. This region has very high tides, could that have something to do with it? Thanks for any advice or ideas!



August 23, 2013, 07:37:28 PM #1 Last Edit: August 23, 2013, 07:46:19 PM by marco.propato
Hi Caroline,
I am not sure I have understood what you have done. I can see that you have lowered your initial salt elevation but that was not enough. However, it is not clear what you have done with the preprocessor. It seems that your data are LiDAR, therefore the pre-processor should be turned off. Also, I am not sure what the value 2 m refers to.

Another analysis you can make to estimate your salt elevation is to use historical daily inundation data. Based on our experience, "salt elevation" may usually be defined as the elevation that is expected to flood at least once per month. This frequency of flooding information is usually available from local NOAA tide gauges.

In any case, when you make a choice for your parameters, I would say that it is acceptable as long as it is defensible (e.g. literature, somebody expert, people knowing the area telling you that these low lines are actually flooded frequently, etc.).

Hope it helps,



Thanks Marco,

I had the elevation pre-processor set to false. What I mean is I clicked on the 'Set map attributes' button then selected 'analysis tools' 3D view and boxed in my region of concern. I then slid the toggle from MLLW, to MTL, to MHHW to Salt Boundary to see how they looked. The areas flooded (visually) with the higher Salt Elevation, but didn't when I set it to 2. Hope this makes more sense. Thanks.


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