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Tidal Flat accretion rate control

Started by Ibe, July 14, 2015, 07:36:21 AM

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Ibe

July 14, 2015, 07:36:21 AM Last Edit: July 14, 2015, 07:40:36 AM by Ibe
I am using SLAMM to simulate change in marsh areas in Somerset county (Maryland) and facing an issue.
Technical documentation tells that "Tidal Flats" (TF) accretion is added according to "Beach Sedimentation Rate" (BSR) parameter or an optional accretion feedback model. By varying BSR, I get TF and high marsh accretion rate. Following parameters are used:

Parameter                                     Global
Description                               Deal Island
NWI Photo Date (YYYY)               1987
DEM Date (YYYY)                       2012
Direction Offshore [n,s,e,w]       West
Historic Trend (mm/yr)               4.97
MTL-NAVD88 (m)                       -0.027
GT Great Diurnal Tide Range (m)       0.552
Salt Elev. (m above MTL)               0.367
Marsh Erosion (horz. m /yr)       1.8
Swamp Erosion (horz. m /yr)       1
T.Flat Erosion (horz. m /yr)               6
Reg.-Flood Marsh Accr (mm/yr)       2
Irreg.-Flood Marsh Accr (mm/yr)       5.1
Tidal-Fresh Marsh Accr (mm/yr)       3.5
Inland-Fresh Marsh Accr (mm/yr)    0
Mangrove Accr (mm/yr)               0
Tidal Swamp Accr (mm/yr)             0
Swamp Accretion (mm/yr)               0
Beach Sed. Rate (mm/yr)               2.5
Freq. Overwash (years)               0
Use Elev Pre-processor [True,False]   FALSE


I am wondering "How do we bring down TF values and at the same time not inflate marsh accretion rate?'

Appreciate your help to understand more on this issue. Thanks.

marco.propato

I am not sure I understand the question.

BSR controls  sedimentation rate of TF and beaches, while marshes are controlled by separate accretion rates values. So there is no built-in connection between the rate marsh and TF/beaches accrete. 

Maybe you meant asking if you could assign different sedimentation rates for TF and beaches. This unfortunately can only be done through modifying the function TSLAMM_Simulation.TidalFlat_Sed in the source code. Hopefully in the future, a NEW SLAMM version will have this option.

Ibe

I am getting more TF which, as per documentation, is controlled through beach sedimentation. So I went on to change beach sedimentation rate to indirectly change TF accretion rate. But it seems that those two are not interlinked that way.
So if I have to reduce TF then what do you suggest I should change in parameter sheet I provided. Please suggest. Thanks.

marco.propato

I am still confused on what is the problem you are having. Are you predicting too much TF in the future? Or at time zero?

If it is at time zero, then the conversion to TF is not controlled by accretion but by the fact that your marsh elevations are initially too low with respect to the modeled tides and thus the areas are converted to TF.

If it is in the future, it all depends on the rate of SLR and time horizon. If SLR is not so high then TF will not convert to water fast enough. TF looses elevation at a rate of (BSR-SLR) mm/yr and normally converted to open water when it falls below -1 HTU (but you can change it if you think it is not corresponding to your study area).


Ibe

Yes, predicting too much TF in the future.

Ibe

I have downloaded source code and couldn't find function "TSLAMM_Simulation.TidalFlat_Sed". Here is hierarchy of folders:

....SLAMM6.2_Open_Source\trunk

Can you please guide me where to look for that function and how to compile and run it? Thanks.

marco.propato

Functions are defined inside the source files. The one you are interested in is defined in the file transfer.inc

As written also in the Technical Documentation document, you need Delphi to compile the source code.

Ibe

One of the comment was: "....TF looses elevation at a rate of (BSR-SLR) mm/yr and normally converted to open water when it falls below -1 HTU (but you can change it if you think it is not corresponding to your study area). "
Is it also defined in transfer.inc? (I looked but couldn't find it there)

Also, I don't have delphi and it seems to cost a bit. Is there any other compiler not being costly or free -- any suggestions? Please let me know. Thanks!

marco.propato

You can change the elevation ranges of all land cover classes through the Elevation Analysis window. See User Guide document.

There are other compilers, Free Pascal for example. We have not tested the compatibility with recent codes but last time it was tried, some of the syntax needed to be modified. Therefore some work may be required to successfully build a working executable.

Ibe

So when we set -1 HTU as min elev then basically we mean to say -0.276 meters as minimum elevation (as 1 HTU = 0.276 meters), right? or is it + 0.276 meters?

marco.propato

Since SLAMM uses MTL as elevation datum (e.g. h=0 at MTL), then, if your Great Diurnal Tide Range in the study area is set to GT=0.552 m, an elevation h=-1 HTU=- 0.276 m.

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