Benedet, L.; Finkl, C.W., and Dobrochinski, J.P.H., 2013. Optimization of nearshore dredge pit design to reduce impacts on adjacent beaches.
The magnitude of the effects of nearshore dredge pits on adjacent beaches depends on a range of parameters, including seabed geomorphology, local wave climate, sediment supply, and pit design characteristics (e.g. distance offshore, depth of cut, cross-shore and alongshore extents, shape of pit). Delft3D, a morphological model developed by Deltares, was used to investigate relationships between dredge pit design parameters and impacts on adjacent beaches. The purpose of this study was to identify design parameters that affected the magnitude of dredge pit effects on adjacent beaches. An ancillary purpose was to develop a scientific basis for dredge pit design recommendations for beach restoration and other sediment needs of coastal infrastructure projects. Dredge pit design sensitivity tests were conducted using Delft3D. A schematic model was constructed using shore-parallel contours and tests for a single-wave condition and for an annual wave climate. The depth of the cut and the cross-shore length of the dredge pits greatly influenced the magnitude of the dredge pit impacts on the adjacent beaches. The distance of the borrow pits from the shore influenced the magnitude and location of the impacts (because of the oblique wave incidence). An inverse relationship was verified between the water depth where the borrow was located and the magnitude of its impacts on adjacent beaches. Dredge pit impacts on adjacent beaches can be reduced significantly by designing narrow, elongated parabathic pits with have a shallow cut depth. Depth of cut increments had pronounced effects in shallow water (2–6 m), but in water depths greater than 8 m, gradual depths of cut increments of 2 m did not significantly affect its impact on adjacent beaches. Results of this study indicate that the effects of dredge pits on adjacent beaches can be reduced by half by adopting optimal pit designs while maintaining the same dredging volume.