A method for monitoring and control of spill during dredging operations
CEDA Dredging Days 2017 - Sustainable Dredging - Continued Benefits
Lumborg U., Saremi S., Lauridsen P.
Abstract: We show a system that was implemented for quantification of sediment spill for a project in Denmark. The paper shows a reliable method to document spill from a mechanical dredger type. Spill documentation was based on a combination of survey work and numerical modelling to establish the total spill on a day-by-day basis. The dredging project was concerned with establishment of a new access channel to a harbour and the surrounding area included a number of sensitive species. The local vegetation could tolerate a daily spill of not more than 250 m3 as inferred from the initial environmental investigations.
During the initial phase of the dredging works an online current meter was established close to the work area. Along with this, staffed spill monitoring was undertaken during two weeks. The spill was quantified by a series of water discharge and turbidity measurements along the boundary of the work area which provided the sediment flux out of the area. Subsequently, a numerical model was set up and calibrated based on results of the staffed spill measurements. Based on the equation of advection-dispersion (transport), the general currents in the area, turbulent diffusion, the settling velocity of the sediment and the daily dredge rates during the two weeks of staffed spill measurements the model was calibrated to provide the spilled sediment flux out of the area. The model showed good agreement with the measurements.
On a daily basis the contractor would provide the production rates which were fed into the calibrated model which also used the current conditions read from the online station and this provided a very realistic picture of the spill. In this way the Authorities could follow the daily spill in the issued spill reports and through an online web page. The system is easily scalable and can be used for a number of similar dredging projects.
Key words: Sediment spill, monitoring, modelling, impact