NWI Project FAQs

Frequently Asked Questions

Q. Who uses these maps?

Wetland inventory maps are used by private citizens, developers, consultants, landowners, water resources managers, fish and wildlife managers, and local units of government. These maps are used to identify the need for wetland permits, assessing completeness of permit applications, identifying the amount and type of wetlands that might be impacted by proposed development projects, screening for development constraints, assessing potential wetland mitigation costs, scoping the level of effort required for more detailed field delineation, evaluating flood storage potential, identifying strategic locations for wetland restoration, and assessing the quantity and quality of habitat for wetland dependent species.

Q. What is the smallest wetland mapped by the NWI update?

A. The Minnesota NWI update intends to meet or exceed the federal wetland mapping standard which requires a target mapping unit (TMU) of at least ½ of an acre. The TMU is the smallest unit that is consistently mapped and tested; however, it does not preclude mapping of wetlands that are even smaller. The minimum size threshold for a wetland to be included is 1/20th of an acre.

Q. When will the updated NWI be available for my region of the state?

A. The NWI update is planned to occur in phases. The first mapping phase began in December 2010 for 13-counties in east-central Minnesota. The update for this area was completed in May 2013. Updates are presently underway for southern and northeastern Minnesota. Updated NWI data for entire state is scheduled to be complete by late 2019. More information on the project schedule can be found in the project plan.

Q. How reliable and accurate will the updated NWI be?

A. Map accuracy includes identification accuracy, classification accuracy, and positional accuracy. For the first mapping phase, we achieved a 93.4% accuracy for wetland identification and a 77.8% accuracy for wetland classification (types).

Horizontal positional accuracy is difficult to ascertain for wetland maps. Horizontal accuracy measures rely on comparing positions of well-defined points in the mapped data and the same points derived from a high-accuracy dataset such as survey grade GPS. Wetlands rarely have well-defined boundaries. Apparent wetland boundaries can change seasonally or annually depending upon climate conditions and other factors. The primary control of horizontal accuracy will be the positional accuracy control of the base imagery. Initial estimates indication a root mean square error of less than 2.0 meters for the imagery.

Q. What is the process for reviewing data and ensuring map accuracy? Will the data be field checked?

A. The review process will include two-stage quality assurance testing against control data sets, field-checking of some sites, and an opportunity for stakeholders to review the draft data. Due to the expense, field checking can only be performed on a limited subset of the data. However, checking will be conducted in a manner that allows for a statistical extrapolation. Additional details can be found in the quality assurance project plan.

Q. Will there be an opportunity to appeal a wetland determination if they believe that a wetland has been erroneously included or omitted in the inventory?

A. We welcome input from stakeholders; however, it is important to remember that the NWI was never intended to serve as jurisdictional wetland delineation and should not be used as such. Wetland inventories determined from aerial photography and other remote sensing information cannot be expected to be able to precisely determine jurisdictional wetland boundaries for the purposes of wetland permitting. Qualified wetland professionals should perform wetland delineations for this purpose in the field. The NWI is a planning and assessment tool that indicates a high probability of the presence of wetlands in a location.

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