Importance Weighting of Impacts in Environmental Impact Studies

Abstract

Environmental impact studies typically compare and evaluate many impacts covering a wide range of considerations including socioeconomic, human interest, geoenvironmental, and political factors. Therefore, evaluation of the importance of impacts in the decision-making process is not an easy task. Information on the environmental impacts of the investigated action and its alternatives can often best be presented in a comparative form. Such a comparison not only defines the issues, but also provides a clear basis for decision making. This study presents systematic methods used for comparing and evaluating impacts using the cesspool system in the city of Jeddah, Saudi Arabia, as a case study. A structured importance weighting approach relying on a ranked paired-comparison technique and an unranked paired-comparison technique has been used in this study. These decision-analysis techniques basically involve a series of comparisons between impacts and a systematic tabulation of the numerical results of these comparisons. An Environmental Evaluation Systems (EES) and an Unranked Decision Matrix (UDM) have been developed for comparison and evaluation of 17 impacts of the cesspool system. The results of the study provide the necessary guidelines for Jeddah Municipality and Jeddah Water and Wastewater Department to deal with the current problems and future planning of the sewage system in the city.