SAND BORROW AREA DESIGN REFINEMENT TO REDUCE MORPHOLOGICAL IMPACTS: A CASE STUDY OF PANAMA CITY BEACH, FLORIDA, USA.

Luana Taiani, Lindino Benedet, Lucas Silveira, Stephen Keehn, Nicole Sharp, Rafael Bonanata

Abstract


The coastline of Panama City Beach, Florida (FL) has been stricken by several hurricanes during the last decades, especially after 1995. In 1998, beach nourishment projects started being implemented to address the impacts of the hurricanes on the coast. Sources of sand for that purpose are commonly from borrow areas located just offshore of the nourishment site. Impacts of these nearshore dredge pits on adjacent coasts will depend on incident wave conditions, nourishment sediment characteristics and some features of the borrow pit (distance from the shore, depth of cut, cross-shore extent, alongshore extent and orientation - Bender & Dean, 2003; Benedet & List, 2008). The practical goal of the current study was to mitigate for the negative potential effects by discovering the less impactful design of dredge pit geometries on the Borrow Area S1 in Bay County-FL. Five different cut widths and excavation depths within the permitted limits were herein evaluated. Evaluation of morphological impacts on adjacent beaches was carried with the processed-based morphodynamic model Delft3D, calibrated and simulated for a period of 13 years. Results were evaluated in terms of beach volume changes compared against a baseline simulation (no action).Switching from Alternative 1 (6,260,000 m³) to Alternative 2 (5,380,000 m³) does not result in a substantial reduction of the borrow area’s projected impact. The cut depth is still deep, and the surface area is unchanged. Alternative 3 (3,555,000 m³) is able to provide more substantial reductions in the borrow area’s impact. By reducing the acreage of the borrow area and switching to a uniform cut depth, the projected impact of the borrow area decreases 39% for 1.56 km along the downdrift beach. Under Alternatives 4 (3,060,000 m³) and 5 (2,755,000 m³), the impacts of the borrow area are projected to be less than 3.75 m³/m/yr. While both alternatives are viable, Alternative 5 minimizes potential impacts, and has a uniform cut depth and a volume that still satisfies the project’s requirements. Given these considerations, Alternative 5 is the preferred alternative. Additionally, all the alternatives increase the net-accretion along 6.5 km of Shell Island between 0.25 to 1 m³/lm/yr., a valuable side effect in a region with high net erosion. By conducting various simulations an optimal borrow area design has been identified that reduces its effects on the adjacent beaches.

Keywords


dredge pit; erosion hot-spot; Delft3D

References


Bender, C.J; Dean,R. 2003. Wave field modification by bathymetricanomalies and resulting shoreline changes: a review with recent results. Coastal Engineering.v.49 (08). 125-153.http://dx.doi.org/10.1016/S0378-3839(03)00061-9

Benedet, L. & List, J.H., 2008a. Evaluation of the physical process controlling beach changes adjacent to nearshore dredge pits. Coastal Engineering. Volume 55 (12). 1224-1236.http://dx.doi.org/10.1016/j.coastaleng.2008.06.008

Benedet, L. & List, J.H., 2008b. Evaluating the effects of dredge pit design parameters on erosion and accretion of adjacent beaches. Proceedings of the 31st International Conference on. Coastal Engineering. 629-637.

Coastal Planning & Engineering, Inc. 2007. Panama City Beaches, Florida Nearshore Borrow Area Impact Evaluation Phase I: Numerical Modeling Calibration Report. Boca Raton, Florida 35 p.

Coastal Planning & Engineering, Inc. 2010. City of Destin, Florida, East Pass Inlet Study & Management Considerations. Boca Raton, FL, 87 p. with appendices.

Delft University of Technology, 2008. SWAN Scientific and Technical Documentation. Delft, the Netherlands, 101 p.

Deltares, 2011. Delft3D-FLOW, Simulation of Multi-Dimensional Hydrodynamic Flows and Transport Phenomena, Including Sediments, User Manual, Part of Hydro-Morphodynamics. Delft, the Netherlands, 674 p.

Divins, D.L., and D. Metzger, 2007. NGDC Coastal Relief Model, retrieved September 2007, http://www.ngdc.noaa.gov/mgg/coastal/coastal.html

Hanson, H., Kraus, N.C., 1989. GENESIS: Generalized Model for Simulating Shoreline Change, Report 1, Technical Reference. US Army Corps of Engineers, Washington, DC, 185 p. with appendices.

Hartog, W.M., Benedet, L.B, Walstra, D.J. R., van Koningsveld, M., Stive, M. J.F., and Finkl, C.W. 2008. Mechanisms that Influence the Performance of Beach Nourishment: A Case Study in Delray Beach, Florida, U.S.A. Journal of Coastal Research, 24(5) 1304–1319.http://dx.doi.org/10.2112/06-0749.1

Lesser, G. R.; Roelvink, J. A.; van Kester, J. A. T. M.; Stelling, G. S. 2004. Development and validation of a three-dimensional morphological model. Coastal Engineering. Vol. 51. P. 883-915.http://dx.doi.org/10.1016/j.coastaleng.2004.07.014

Lesser, G. R. 2009. An approach to medium-term coastal morphological modeling. TU Delft, PhD Thesis.

Tolman, H. L., 1997: User manual and system documentation of WAVEWATCH-III version 1.15. NOAA / NWS / NCEP / OMB Technical Note 151, 97 pp.

Tolman, H. L., 1999: User manual and system documentation of WAVEWATCH-III version 1.18. NOAA / NWS / NCEP / OMB Technical Note 166, 110 pp.

Walstra D.J.R., Chesher T., Davies A.G., Ribberink J., Sergent P., Silva P., Vittori G., Walther R., van Rijn L.C., 2005. Intercomparison of the state of the morphological models In SANDPIT Sand transport and morphology of offshore mining pits. L.C. van Rijn, R.L. Soulsby, P. Hoekstra, A.G. Davies. Edts. Aqua publications, The Netherlands, ISBN 90-800356-7-X.

Walstra, D.J.R., L. C. Van Rijn, M. Boers and J.A. Roelvink, 2003. Offshore sand pits: verification and application of a hydrodynamic and morphodynamic model. Proceedings of Coastal Sediments.


Full Text: PDF

Creative Commons License
This work is licensed under a Creative Commons Attribution 3.0 License.