Determination of Possible Wetland Mitigation Sites Using NC-Crews and an Integer Linear Programming Formulation

Abstract

The objective of this project was to develop an optimization model for wetland mitigation site selection using a geographic information system for rating wetlands and traditional operations research methodologies. This project was conducted using a GIS based wetland assessment procedure entitled North Carolina Coastal Region Evaluation of Wetland Significance (NC-CREWS) developed by the North Carolina Department of Environmental Resources' Division of Coastal Management (DCM). NC-CREWS rates possible mitigation sites by the wetland functions they could perform if fully restored. Using this component of NC-CREWS, a conceptual model to optimize the selection of restoration sites based on their functions was developed and tested on a small, fabricated example to test workability. This model was adapted to include possible restoration site ratings from an actual watershed in Craven County, NC, provided by DCM. The 0-1 integer programming model that was developed was tested using trials to address issues of problem size, functional unit level required, and order of sites used in the model. Of the 180 tests, all but 37 reached an optimal solution by 200 million iterations of a branch-and-bound algorithm. The problem size and number of functional units required had little impact on the solution time. The ordering of sites as supplied to the model resulted in nonfeasible solutions if sites were chosen based on a physical characteristic such as size or perimeter length. Given the assumptions made in the model it is possible to derive a list of possible mitigation sites to use for improving field recognizance.