So I've been trying to setup some basic input files for SLAMM so I can play around with the software some.
I'm pretty sure I have correctly set up the DEM and Slope inputs, but I'm having trouble understanding the NWI input.
What steps should I take to ready NWI files for SLAMM?
I've looked at the US Fish and Wildlife NWI files in ArcGIS, and read the SLAMM guides on converting to SLAMM categories.
How would you go about doing this?
Any help would be greatly appreciated.
Thanks for this question. It's a good one. I'll answer now quickly and let Marco fill in any details I've missed:
General steps are:
- 1. take your wetland polygon shapefile and add a SLAMMCLASS column to the associated database (dbf)
- 2. assign SLAMM classes using the NWI-to-SLAMM crosswalk -- The latest version delivered with SLAMM 6.7 is SLAMM Cowardin NWI code lookup_10.xlsx
- 3. QA/QC your resulting polygons in GIS and ensure that the crosswalk works for your site. This is an important step. There are sometimes ambiguities between estuarine beach and tidal flat in the NWI code that you will want to correct. Due to these ambiguities the crosswalk may also assign mangrove or cypress swamp in areas where they do not exist. Use Table 4 of the Technical Documentation to assist you.
- 4. Convert the resulting shapefile to a raster with the precise dimensions as the elevation/slope raseter. Be sure that the projection of these rasters has the units of "meters" rather than feet
Marco -- any advice that I missed?
Let me add some practical details. You cannot edit and save a dbf in excel and then save it. So, we usually:
(1) make a copy of the dbf (saved the old one as *_old.dbf just in case of mistakes).
(2) open the new dbf in excel and copy the land cover attributes
(3) paste them into the lookup excel file
(4) as Jonathan wrote, check if all the codes have been crosswalked and if not try to determine the correct crosswalk.
(5) Copy the crosswalked column (from row one to the last, not the entire column)
(6) Open the dbf using Open Office Calc.
(7) Paste the data as a new attribute column (e.g. SLAMMCLASS) and save. (Sometime saving is not possible because the precision of some attribute columns. You can change them accordingly in the first row, e.g. Length,N,10,5 is the attribute Length with 10 digits total and 5 digits after the comma).
Good luck, Marco
Thanks for the advice. I followed your steps and managed to create a SLAMM NWI atrributes raster, which I clipped and converted to the DEM/SLOPE cell sizes.
I managed to run the basic SLAMM file inputs, but when it finishes running, I get a blank screen instead of a map.