Risk-based decision making framework for the integrated environmental management of dredging sediments

Abstract

Many environmental management tools have been developed aiming to reduce the impacts of dredging and protect the environment. As this has typically not been done in an integrated way that takes into account the socio-economic, environmental, technical and managerial aspects of dredging, there is a need to develop an integrated decision making tool to manage the impacts of dredging and help decision makers make sustainable decisions concerning dredging. The aim of this study was to develop a risk-based decision making framework for the integrated environmental management of dredging sediments in order to reduce the impacts of dredging and to lower the cost of environmental quality analysis and management. Selection of the best sediment management option using the risk-based approach of integrated environmental management has the potential to help effectively balance and prioritize the various socio-economic, environmental, technical and managerial aspects of dredging. The proposed framework will therefore utilize this concept throughout its six developmental steps. The first step reviews the literature on the impact of dredging and the two main factors that determine its magnitude, namely sediments and dredging technology. In order to manage the impacts of dredging efficiently, the relationship between scientific evidence and dredging activities will be assessed in the second developmental step. This step evaluates historical evidence from three dredging projects undertaken between 2006 and 2008 on the rivers of Sungai Sitiawan and Sungai Dinding, Perak, Malaysia. Monitoring and fish toxicological data from these projects are analyzed to determine their relationship with dredging activities performed in these rivers, with Geographic Information System (GIS) software used to illustrate the relationships found. The third developmental step assesses dredging problems other than the environmental impacts using Driving force-Pressure-State-Impact-Response (DPSIR) analysis, an IEM-based tool. This tool was employed in Malaysia’s dredging industry using interviews and a questionnaire-based survey. Dredging experts, including representatives from port operators, manufacturing companies and dredging contractors, were interviewed in 2008, with the socio-economy and management being found as the main drivers, together with environmental impacts, affecting dredging stakeholders in Malaysia. In 2010, further dredging experts (including marine ecologists, registered chemists, professional and chartered engineers, environmental consultants, university professors and environmental analysts) responded to the questionnaire, with results suggesting that governance of dredging in Malaysia is weak and that it is essential for Malaysia to review its current dredging environmental management tools and practices. The fourth developmental step develops the first stage (screening) of the proposed framework based on understanding provided by the three steps developed previously and demonstrated using Malaysia as a case study. This screening stage utilizes the historical dredging monitoring data and the contamination level in media data into Ecological Risk Assessment (ERA) phases, which have been adjusted for benefits in cost, time and simplicity. Using case studies from Malaysia, the fifth developmental step (Tier 1) shows how Multi-Criteria Decision Analysis (MCDA) can be used to analyze and prioritize dredging areas based on environmental, socio-economic and managerial criteria and is demonstrated for the Tier 1 stage. The results from MCDA will be integrated into Ecological Risk Assessment (ERA) to characterize the degree of contamination found in the areas. Priority areas, their degree of contamination and other concerns are then identified and brought forward to the sixth developmental step (Tier 2 stage). The Tier 2 stage is demonstrated using previous findings and analyzed using MCDA, in order to identify the best sediment management option, accounting for the economic, environmental and technical aspects of dredging.