Delineation and Classification of Prairie Pothole Wetlands Using GIS and Aerial Photos

Abstract

The prairie pothole region of North America, encompassing parts of North and South Dakota, Minnesota, Montana, Iowa, and the Canadian prairie provinces, is characterized by numerous shallow wetland depressions. For decades, many of these glacially-created prairie pothole wetlands were drained for farming or other purposes. Now in some watersheds, restoration of drained depressions is being considered as a potential option for reducing total annual and/or peak flood flows from the watershed. As part of a hydrologic study to evaluate the effect of restoring depressions on reducing streamflows, a GIS-based process was developed to delineate and classify prairie pothole depressions on a regional scale. Using ArcView GIS and the HEC-GeoHMS extension, the original digital elevation model (DEM) of a drainage basin was subtracted from a filled, depressionless DEM grid, creating a new grid with only the depths in all of the depressions. This depth grid, which was converted to an ArcView polygon theme, was used to calculate the surface area, volume, and average depth (volume/area) for each depression. Classification of the depressions utilized aerial photos (digital orthoquads), USGS digital quad maps, National Wetlands Inventory data, and flow direction data generated by HEC-GeoHMS.