Overview: This option should be used if you have done any customization to your previous FFMP shapefiles that you would like to preserve. The approach is to first select the customized areas in your previous FFMP shapefiles, then select the areas surrounding these in the downloaded FFMP shapefiles, and mosaic them together. It is important to remember that there should be no gaps or missing basins after the two versions are mosaicked. In addition, there should be no overlapping basins.
It is highly recommended that the basin selection be done in a way that is hydrologically-organized to try to avoid gaps or overlaps. This can be accomplished in a number of ways depending on what you are comfortable with. A couple of suggestions are:
Whatever selection method you choose, it is imperative to check the boundaries between the previous and new basins. Of particular concern are the areas where the previous basins flow into the new basins, or vice versa. Your selections should result in a seamless mosaic of basins without any gaps or overlaps.
The following procedure will describe how to make basin selections based on the Huc field. It also may be helpful to download this HUC shapefile to use as an overlay.
a) Make xxxx_aggr_basins the active theme. From the Theme menu, select Query to open the Query Builder window.
Construct a query that looks like:
( [Huc] = XXXXXXXX ) or ( [Huc] = XXXXXXXX ) ... or ( [Huc] = XXXXXXXX )
where XXXXXXXX are the HUC numbers in the list you made above. Click New Set and close the Query Builder window. The basins in the specified HUCs should now be selected in xxxx_aggr_basins.
b) Make basins_all the active theme. Repeat the above query procedure to select the basins in the specified HUCs in basins_all.
After selecting these basins, open the basins_all attribute table. From the Edit menu, select Switch Selection. Now the basins outside of the specified HUCs should be selected. Close the attribute table.
c) It is important to be aware that some HUCs may be only partially represented in the xxxx_aggr_basins shapefile but fully (or mostly) represented in the basins_all shapefile. This will often occur along the outer boundaries of xxxx_aggr_basins because the expanded domain for FFMP Advanced will extend beyond the xxxx_aggr_basins domain.
To make it easier to identify this and other gap or overlap issues, make both xxxx_aggr_basins and basins_all the active themes. From the Theme menu select Convert to Shapefile. This will create new shapefiles containing only the selected basins. We will call these new shapefiles previous.shp and new_download.shp.
Use these shapefiles to zoom in and check for gaps or overlaps in the basins. If there are gaps or overlaps, you may need to return to the xxxx_aggr_basins and basins_all shapefiles and add to or take away from the current selections.
This will be an iterative process until the selections are how you want them with no gaps or overlaps along the boundaries between the selected previous and newly downloaded basins.
After finalizing the selections, you are ready to mosaic the two versions of the basins. Make the two shapefiles with your final basin selections the active themes. From the Bsn-Tools menu, select Merge Active Themes to mosaic the basins. Name the new shapefile basin_mosaic.shp.
You are now ready to update the hydrologic-connectivity links.