A METHOD FOR IDENTIFYING A NEW OFFSHORE DREDGING DISPOSAL SITE BASED ON ENVIRONMENTAL SENSITIVITY

摘要

HR Wallingford has developed an effective yet simple method to assist in the selection of new offshore disposal sites for dredged material. To reduce the carbon footprint of its dredging and disposal activities, our client Harwich Haven Authority is seeking to identify a new disposal site closer to Harwich Haven than the existing disposal site, which is approximately 30 km offshore. A detailed literature review was undertaken to ascertain what data and information sources were available to inform the site selection exercise. Ten sensitive environmental features and marine activities were identified that are potentially susceptible to the effects of dredged material disposal. These ten features were compiled into a series of Geographical Information System (GIS) data layers, and areas were allocated a sensitivity score to reflect the vulnerability of the feature to disposal activities. To determine the overall sensitivity across the study area, all ten GIS layers were combined to create a colour-coded map which highlighted areas of high and low sensitivity. The sensitivity map identified a suitable area of low sensitivity closer to Harwich Haven. Sediment plume dispersion modelling was carried out using the HR SEDPLUME RW model, and an output from the model was overlaid onto the sensitivity map to show the spatial extent of deposition from the sediment plume. The greatest level of deposition was confined to the area of low sensitivity; however the plume was shown to extend into some areas of high sensitivity, highlighting areas for further investigation during the detailed site characterisation stage, which HR Wallingford is currently carrying out to support a licence application. This paper describes the information that was used to inform the site selection exercise, the development of the GIS, and discusses the advantages and disadvantages of the site selection approach.