Morphodynamic-numerical simulations of dredged matter open disposal.
Type:
Presented during:
CEDA Dredging Days 2005 - Dredging: The Extremes, Rotterdam
Authors:
Wurpts A., Mewis P. and Zanke U.C.E.
Abstract: Open disposal of dredged matter in coastal areas is common practice all over the world. Especially if cohesive sediment is considered it’s a known fact that the location where the long-term deposition takes place may essentially differ from the disposal-site. Knowledge of the transport and fate of disposed sediment improves the economic and environmental aspects of off-site disposal.
Dredged matter which is placed at a disposal site usually differs from the local bottom-sediment with respect to grain sizes and grain size distribution. Moreover the bottom-topography at the disposal site changes due to the added sediment. The two aspects mentioned above usually lead to a "violation" of the local morphodynamic equilibrium state which is followed by a "reaction" of the topography (eg. increased erosion, changing sorting of the local sediment-mixture). Another important aspect related to unconfined disposals is the interaction between the disposed matter and the surrounding flow-field (e.g. density currents) which can become a dominant transport mechanism in the nearfield of the placement site.
This contribution deals with the development of a morphodynamic-numerical simulation model. SMOR3D consists of several modules which are fully coupled in a time-explicit mode. The model-approach consists of a 3D flow solver which is coupled with several transport modules for suspended sediments, bed-load sediment and salt. The movable bottom topography is balanced by a bed-model. All sediments (natural background and disposed matter) are represented by several fractions of different properties. The model allows the discrimination of disposed matter from the natural background sediment at every location and time.
Results of numerical simulations of disposals by means of bottom doors and split barges are shown. The results are in good agreement with SPMC-measurements carried out in the nearfield of different disposal locations.
Keywords: disposal, numerical model, morphodynamic, fate, suspended sediment, silt