Abstract

 Almost nine years ago the Flemish Government initiated the development of a monitoring tool for sediment quality. This finally resulted in the year 2000 into a routine monitoring network based on a Triad approach, in which 150 locations are sampled each year with a recurrence every four years.
  In the beginning, there was a lack of good sediment quality guidelines, but it was decided to use the geometric mean of the concentrations of the different contaminants found at five locations. These five locations were located in relative undisturbed areas and during a first classification no ecotoxicological effects were observed and the biological quality was good. Since then these quality guidelines have been slightly changed by increasing the number of the "reference" locations to twelve. Currently, these sediment quality guidelines will be further founded by an intensive evaluation of the results of the 640 sampling locations that were already sampled.
  Now the question rises whether these sediment quality guidelines have to be formalised into standards. This would give the government an extra tool to urge water managers to do an effort for the ecological restoration of the sediments. However based on hydraulic and nautic requirements in the Flemish streams there is at the moment a need for the removal of approximately 28 million m3. Due to the high contamination of these sediments, which are regarded as waste, the destination options are limited and the removal becomes very expensive. The introduction of in-situ standards will increase the amount of sediment that has to be removed tremendously and thus also the costs. Therefore, it seems better to introduce well-founded sediment quality guidelines, which are not used as standards. In this way the government can invest more money in the prevention of the high input of sediments and contaminants.