An Evaluation of GIS Prioritizations for Selecting Wetland Mitigation Sites: Cook Inlet Case Study

Abstract

Recent scientific research has demonstrated the multitude of ecosystem services and functions provided by wetlands. Despite the astronomical cost that would be required to replace these vital services with manmade mechanisms, humans have a long history of filling and destroying wetlands for development. Recent decades have seen wetland protection improve under the aegis of Section 404 of the Clean Water Act (CWA). The CWA requires compensatory mitigation for wetlands destroyed during development, but specific mitigation requirements remain vague and many projects continue to fail. Developing better wetland mitigation site selection would provide improvements to mitigation without requiring a CWA amendment. Sites have traditionally been chosen based on geographic or monetary convenience. This study explores an increasingly popular method of selection: GIS prioritizations. GIS prioritizations can increase the efficiency, repeatability, and transparency of site selection. This project analyzes a case study in Cook Inlet, Alaska utilizing a GIS prioritization to locate high quality mitigation lands to compensate for a bridge proposed by the Knik Arm Bridge and Toll Authority. Mitigation is required because the construction will destroy 390 acres of wetlands. To determine the most appropriate mitigation locations, 3047 nearby parcels were evaluated using 8 selection criteria. The results ranked all parcels and identified the most suitable sites to compensate for the proposed effects of the bridge. This study also compares the effectiveness of GIS prioritizations to other selection methods. GIS prioritizations were determined to be the most efficient technique for analyzing and ranking thousands of parcels. Initiating mitigation planning with a GIS prioritization can effectively direct fieldwork to just a subset of potentially high value wetlands. Hopefully better site selection with GIS prioritizations can improve overall wetland mitigation. Such improvements would not only fulfill the mitigation requirements under the CWA, but also effectively preserve remaining wetlands for future generations.