Investigation strategies for water bottom sanitation in the Netherlands are generally based on borehole and sampling information alone. This may be a valid for small channels but in natural rivers, where the lateral variation of the contaminated layer is considerable, this strategy will lead to extensive investigations to asses the layer thickness and sanitation dredging DEM adequately. A combination of very high resolution seismics, echo sounding, sampling boreholes and chemical analysis of borehole samples has successfully been introduced. This combination is preferred due to the lateral variability in thickness, top- and base level of the sediment. A typical investigation starts with bathymetric and seismic data acquisition in cross sections every 50 m (direction of highest variability). In part of the cross section a borehole is planned and sampled. The bore hole plan is based on an initial seismic interpretation. Every visible layer in the core is chemically analyzed. The top of the first clean layer is the base of the contamination. This level is integrated in the seismic data, resulting in detailed information on the variability of the contaminated layer. A digital elevation model (dem) of the contaminated layer can be made by interpolation top and base level of the contaminated sediments between cross-sections. The model based on a multiple source data sets provides a better basis for quantification of dredging volumes and establishing a sanitation dredging model. [read article]
Stema-Systems provides tools and complete systems that allow high resolution seismic survey's to be operated from even very small vessels. The Silas interpretation software has advanced signal processing techniques and bottom layer classification tools for extensive use of the seismic or ground penetrating radar data sets.