Wetland Mitigation Map

I was asked by Tryon Creek Watershed Council (TCWC), to create a project that would clearly show the areas in the watershed where wetland mitigation projects could be done. This way, if anyone applying for a permit impacts a wetland within the Tryon Creek Watershed, they will have an idea of where they can do in-kind mitigation in the same watershed. Seeing as Tryon Creek is not already a part of any existing wetland mitigation bank, this is an important step in allowing this type of restoration work to take place.

Let's assume someone wants to build on land within the Tryon Creek Watershed and it is going to have unavoidable impacts on a creek, stream, or wetland. Let's also assume that they have decided to do in-kind mitigation for the project, but do not know where to begin finding appropriate land within the watershed on which do do this mitigation. Since, as we have learned, the watershed does not fall within an existing mitigation bank, they might turn to TCWC to find a place to carry out their mitigation. The Watershed Council did not have an easy way to help them find an answer... until now.

We will first look at the types of data needed to perform the analyses necessary to reach the results the Council was looking for.

Above are the files that were found in order to complete the mapping processes. A much larger amount of files was eventually whittled down to this list. This list does not include any layers that were created in the process of making the final maps. Much searching ensued since very few sources overlap, and I even got help from a previous PCC GIS project with use of the watershed boundary created for the interactive map on the TCWC website (thanks Hunter Bradshaw!). The two wetland layers were obtained (with help from Alexis Barton) by emailing the cities of Portland and Lake Oswego to obtain exactly what we were looking for.

• DEM -  Oregon Spatial Data Library 
• Streams -  Metro Regional Land Information System (RLIS) 
• Tax Parcels -  Multnomah County ,  Clackamas County 
• Watershed - Hunter Bradshaw
• Wetlands -  Oregon Spatial Data Library , City of Lake Oswego, City of Portland
• Zoning -  Metro RLIS 

All of this data was then imported into ArcGIS Pro and - with many stops, starts, trials, errors, tutoring sessions, and a little confusion about why something didn't work seventeen times, but then worked the eighteenth - some results started to emerge that looked ended up looking even better than expected.

As stated above, approximately 2,287 acres of land meets the conditions: tax lots within 500 feet of existing streams or wetlands that are not zoned POS or PF. The resulting table of addresses, owners, acreage and zoning of each parcel will be submitted to the Tryon Creek Watershed Council for further review.

Some data was not as robust as I would have liked. The Clackamas County tax lot dataset did not include ownership info. This means that an extra step would be required to find out who owns what if the need arises to contact those landowners. Time constraints prevented this from happening.

Another dataset that did not produce any meaningful results was the soils data. We were hoping to find hydric soils that might predict where future wetland creature could occur, but there was not enough to go off of from what was found, so that idea was scrapped.

A Topographical Wetness Index (TWI) was produced using a Digital Elevation Model (DEM) raster, which was intended to show where water accumulates throughout the watershed based on slope and flow, but, again, it did not add enough helpful information to be useful. The DEM was, however, used to produce a hillshade base layer.

There were some hiccups along the way as well. Some analysis tools did not work as intended at first and had to be retooled to fit the outcome expected. For example, as mentioned above, the spatial join between the zoning and tax lots initially did not return the correct zoning information for several parcels, so a parameter had to be changed in order to get the more accurate data to show. Much of this can be prevented with more experience. The learning process is still fun and productive!

From here, any prospective restoration project will have to come to TCWC to find an appropriate in-kind mitigation site. TCWC will then contact any landowners necessary to request permission to perform the mitigation on their property.

A tool has been included with the project files that will allow for all of this analysis to be redone with updated data, which is especially important since ownership of land changes all the time.