Development of a strategy for maintenance dredging and relocation under the restrictions of a national park
Type:
Presented during:
WODCON XVII: "Dredging in a Sensitive Environment" - 2004, Hamburg, Germany
Authors:
H. Manzenrieder, F. Spingat and C. Manzenrieder
Abstract: Based on time-limited permissions for relocation the appropriate authority increasingly requires evidence for the fate and environmental impacts of dredged material.
This paper describes the development of a monitoring strategy suitable for the increased requirements of sensitive habitats. The strategy covers the complete dredging cycle from the excavation through to the transport and eventual disposal of the material.
While chemical and physical analysis of dredged material as well as consideration of the volume of dredged material are typically considered in standard investigations in the context of the OSPAR- and HELCOMConventions, the monitoring concept developed here has allowed evaluation to be made of specific relocation impacts in an environment within which variation in sediment transportation processes is high; This strategy extends beyond the relocation site to the control and supervision of the dredging process onboard the dredger unit itself to meet the approval-specific requirements.
To build up time series of all relevant parameters pertinent to the relocation activities is not cost effective.
Selective indicator values have thus been used. Of particular relevance as indicators of environmental response are the turbidity and the dynamics of bottom sediments (deposition/erosion), both values being highly stochastic in nature. An understanding of these parameters and their natural variation provides however the background for characterising the anthropogenic effects in the protected areas. In relation to the zero state relocation accompanying measurements this approach provides a direct and objective evaluation basis for monitoring of the impacts of the dredging operations.
The encompassing nature of this strategy which combines measurement of environmental response together with on-board monitoring of the dredging process has been fundamental in gaining acceptance of the necessary maintenance dredging campaigns.
A realized implementation for measuring and documentation of solid matter, routes, position and time of disposal has thus been in use for more than 6 years on the hopper dredger Seekrabbe of the authority operating in the National Park "Niedersächsisches Wattenmeer", the paper thus describes problems that have required solution and the key results achieved.
Keywords: turbidity, seabed dynamic, natural variation, on-board monitoring, National Park