Beaver River Watershed Wetlands
How were the wetlands mapped?

Method

How was this data gathered?

According to the agreement between the Natural Resources Research Institute, and project funder, DNR Coastal Program, 1:24,000 color infrared photos, taken in September 1997 and acquired from Minnesota DNR, were digitally scanned at high resolution (800 DPI), geo-referenced (rectified) to the USGS Digital Ortho Quads (DOQ's) using an Arcview image warping routine. Each photo needed between 20 and 40 points to achieve the required degree of accuracy. These digitally rectified aerial photos served as the base for identifying both upland forest and wetlands. Wetland classification followed U.S. Fish and Wildlife Service conventions for the National Wetlands Inventory. The completed GIS wetlands layer is available in ESRI's shapefile, ESRI's Geodatabase, and ESRI's ArcInfo "export file" formats

Aren't current wetlands maps good enough?

National Wetlands Inventory (NWI) maps are outdated, and contain numerous errors. The photos used to do the NWI air photo interpretation were 1:80,000 black and white photos taken in November 1978. Forested and shrub wetlands were often mis-interpreted because of northern Minnesota's red clay soils, and in several cases, forested ravines were mis-identified as wetlands. Wetland boundary placement is imprecise because of the high-altitude photography used. Extensive areas of emergent wetlands were not mapped because of the November photo date.

Here is an example of the difference between the National Wetlands Inventory (NWI) wetlands and NRRI's GIS layer created for this project:

(click on the image for a closer look)