Early Wetland Detection

Don’t MIRE your project in a Wetland!

National Wetland Inventory Mapping – “Know the (data) Gaps”

The National Wetland Inventory (NWI) is a widely used database employed by Wetland Scientists and produced by the United States Fish and Wildlife Service (USFWS) that affords the user an aerial view of locations that may have hydrological conditions conducive to support wetlands. It’s an excellent tool employed early in project planning. However, as the illustrations indicate (Figures 1 and 2), not all NWI mapped wetland data are accurate..

Figure 1. Wetlands shown on NWI Map.

Figure 2. Actual view on the ground, a soybean field.









NWI data are created with the help of detailed analysis of high altitude infrared imaging by individuals and computer models who are tasked with identifying areas that are wet or hold water. These show up as dark areas on the mapping. Depending on the time of year the aerial data were obtained, this could result in showing wetlands where none exist or in areas that tend to be seasonally wet. A very wet spring could have resulted in the misidentification of the above mapped area.

Another important NWI data gap, consists of forested wetlands. These tend to be under-represented (appear smaller) or are not captured at all in the NWI data. As the images illustrate (Figures 3 and 4), the canopy is so thick the infrared camera cannot penetrate the vegetation.

Figure 3. Forested canopy hides a wetland from NWI cameras.

Figure 4. Actual view on the ground of wetland under canopy.










Our staff of experienced wetland professionals will work with you and your project team. The NWI is a critical tool when employed early and used in combination with additional available data to augment accuracy of interpretation. The skills of our staff permits ASC Group to bring more accurate decision-making tools to your projects. Our understanding of the NWI data gathering process and how those data are interpreted keeps projects on time by eliminating unnecessary surprises.

By Stuart Jennings, M.A., PWS
ASC Group Senior Ecologist
614.268.2514 ext.3447