Tahirih Lackey, Joseph Gailani, Sung-Chan Kim, David King, Deborah Shafer


Model studies have been conducted to investigate the potential coral reef exposure from proposed dredging associated with development of a new deepwater wharf in outer Apra Harbor, Guam. The Particle Tracking Model (PTM) was applied to quantify the exposure of coral reefs to material suspended by the dredging operations at proposed sites. Key PTM features include the flexible capability of continuous multiple releases of sediment parcels, control of parcel/substrate interaction, and the ability to track vast numbers of parcels efficiently. This flexibility has allowed for model simulation of the combined effects of sediment release from clamshell dredging, of chiseling to fracture limestone blocks, of silt curtains, and of flocculation. Because the rate of material released into the water column by some of the processes is not well understood or a priori known, the modeling protocol was to bracket parameters within reasonable ranges to produce a suite of potential results from multiple model runs. Data analysis results include mapping the time histories and the maximum values of suspended sediment concentration and deposition rate. Following exposure modeling, the next phase of the analysis has been an ecological assessment to translate the PTM exposure level predictions into predicted amounts of coral reef damage. The level of potential coral reef impact will be an important component of the final selection process for the new deepwater berthing site.


dredging; lagrangian; sediment transport; numerical modeling

Full Text:



Asaeda, T, and Wolanski, E. 2002. Settling of muddy marine snow. Wetlands Ecology and Management 10, pp 283-287.

Bridges,T., Ells, S., Hayes, D., Mount, D., Nadeau, S., Palermo, M., Patmont, C., and Schroeder, P. 2008. The Four Rs of Environmental Dredging: Resuspension, Release, Residual, and Risk. ERDC/EL TR-08-4. U.S. Army Corps of Engineers, Engineer Research and Development Center, Vicksburg, MS.

Dollar, S., Hochberg, E., Hancock, H., LaPonte C., and Doctor, M. 2009. Assessment of Benthic Community Structure in the Vicinity of the Proposed Turning Basin and Berthing Area for Carrier Vessels Nuclear (CVN) Apra Harbor, Guam. Prepared for TEC Inc., Honolulu, Hawaii. Volume 9: Appendix J of Draft Environmental Impact Statement / Overseas Environmental Impact Statement, Guam and CNMI Military Relocation, Relocating Marine from Okinawa, Visiting Aircraft Carrier Berthing, and Army Air and Missile Defense Task Force.

Hayes, D. F., Borrowman, T. D., and Schroeder, P R. 2007. "Process-Based Estimation of Sediment Resuspension Losses During Bucket Dredging" Proceedings, XVIII World Dredging Congress 2007, WEDA, Lake Buena Vista, Florida, USA.

Hayes, D., and P.-Y. Wu. 2001. Simple approach to TSS source strength estimates. In Proceedings of the WEDA XXI Conference, Houston, TX, June 25-27, 2001.

Johnson, B. H. 1990. User's Guide for Models of Dredge Material Disposed in Open Water, Technical Report D-90-5, U.S. Army Engineer Waterways Experiment Station, Vicksburg, MS.

Johnson, B.H., Kim, K.W., Heath, R.E., Hsieh, B.B., and Butler, H.L. 1993. "Validation of A three- Dimensional Hydrodynamic Model of Chesapeake Bay," Journal of Hydraulic Engineering, Am. Soc. Civil Eng. 119(1), 2-20.

King, D.B. and Galvin, C.J. 2002. Coastal Sediment Properties. Coastal Engineering Manual, Part III, Coastal Sediment Processes, Chapter III-1, Engineer Manual 1110-2-1100. Washington, DC: U.S. Army Corps of Engineers.

MacDonald, N.J., Davies, M.H., Zundel, A.K., Howlett, J.D., Demirbilek, Z., Gailani, J.Z., Lackey, T.C., and Smith, S.J. 2006. "PTM: Particle Tracking Model Report 1: Model Theory, Implementation, and Example Applications" Technical Report TR-06-02, U.S. Army Corps of Engineers, Engineer Research and Development Center, Vicksburg, Mississippi, USA.

Sea Engineering. 2009. Current Measurement and Numerical Model Study for CVN Berthing – Draft Report – Apra Harbor, Guam. Report prepared for: TEC, Inc. Charlottesville, VA. 216pp.

Sea Engineering. 2010. Physical Oceanographic Monitoring of Dredging and Construction Activities at Kilo Wharf: September 2008 – December 2009; Apra Harbor, Guam. Report prepared for: TEC, Inc. Charlottesville, VA. 146pp, plus Appendices.

Smith, S.H. 2007. Ecological Assessment of Stony Corals and Associated Organisms in the Eastern Portions of Apra Harbor, Guam. Report prepared for Naval Facilities Engineering Command Pacific, Pearl Harbor, Hawaii.

U.S. Army Corps of Engineers. 2005. Silt Curtains as a Dredging Project Management Practice. ERDC TN-DOER-E21. U.S. Army Corps of Engineers, Engineer Research and Development Center, Vicksburg, MS.

Weston Solutions and Belt Collins Hawaii. 2006. Sediment Characterization for Construction Dredging at Charlie, Sierra, and SRF Wharves, Apra Harbor, Guam. August.

Weston Solutions and Element Environmental. 2010. Additional Dredged Material Chemical Characterization at Polaris Point, the Former SRF Wharf, and the Turning Basin for Proposed CVN Wharf Alternatives, Apra Harbor, Guam, Final report. March.

Zundel, A. K. (2005). "Surface-water Modeling System reference manual, Version 9.0" Brigham Young University Environmental Modeling Research Laboratory, Provo, UT.