Spatial Accuracy Assessment of Wetland Permit Data
Kelly, Nina M., Cartography and Geographic Information Science
An important aspect of coastal management in the United States continues to be wetland management. Despite federal, state, and local legislation designed to limit the alteration of wetland habitat, wetland loss continues because of substantial urban development along the coast (USGS 1996). Measures of the change in wetlands vary, as they are often confounded by different methods of measurement and the resulting different estimates of wetland extent (Rolband 1995; Shapiro 1995). One method of measuring change to wetlands is to analyze the permits that are filed when a wetland is altered. The record of permit activity in an area provides an underutilized source of information on wetland change, which might be used in environmental analysis to determine spatial patterning of wetland alteration--an important predecessor to understanding cumulative impacts of individual wetland alteration (Kelly 1996). This research examines in detail the spatial accuracy and precision of sample Permit Records in coastal North Carolina. The paper presents overall accuracy measures and attempts to account for error by reviewing it with respect to three factors: the direction of the error, the scale of the map accompanying each permit, and the date of permit filing. I also suggest a method to assess the utility of the dataset for spatial environmental analysis and recommend methods for improving the quality of locational data inclusion.
The Permit Record as a Tool for Wetland Management
Since the late 1970s, proposals to alter the natural environment in the United States have required a federal permit, issued following an evaluation of that permit request by relevant governmental agencies. The primary law governing wetland management is Section 404 of the Clean Water Act, which was passed in 1972 and was recently re-authorized. Section 404 regulates the deposition of fill material in wetlands (Dennison and Berry 1993) and requires a permit to be filed with the U.S. Army Corps of Engineers (Corps) prior to any wetland alteration (with some exemptions). In the southeast United States, these permits have since 1978 been collected in the offices of the relevant reviewing agencies and now serve as a record of wetland alterations in the country over nearly two decades. These files--hereafter called the Permit Record--serve as a useful management tool in several ways. First, while the acreage figures in the Permit Record are only estimates, they have been used to create inventories of wetland change that are a crucial part of the picture of a changing environment (Mager and Thayer 1986; Field et al. 1988; Mager and Rackley 1991; Kentula et al. 1992; Montana Audubon Society 1993). These studies make note of the fact that estimates of change from these files can be influenced by inadequate measures of wetland loss included in some permit cases, and by difficulties early in the Clean Water Act process of defining a wetland (Tiner 1994). Because of these difficulties, wetland inventories are only estimates of change. Second, the information contained in the Permit Record--which includes such information as location, amount of change, and notes from habitat specialists regarding the condition of the habitat--could serve many important environmental and coastal management applications. For example, the spatial information contained in the dataset could be used to aid in mitigating siting and restoration planning by highlighting areas where excessive amounts of wetlands have been altered. Wetland mapping projects could be focused in areas that have experienced large wetland changes. Third, the analysis of cumulative impacts of piecemeal alterations requires accurate location of historic wetland site alterations (Kelly 1996). While the intent of the information contained in the permit file was not originally provided to assist in cumulative impact assessment, it is often suggested as useful in this regard. The accuracy of these datasets is unknown, and a complete analysis of the quality of the data is needed. …