1. Predictability of Seabed Change due to Underwater Sand Mining in Coastal Waters of Korea Predictability of Seabed Change due to Underwater Sand Mining in Coastal Waters of Korea Chang S. Kim, Hak Soo Lim and Jinah Kim Korea Ocean R&D Institute Coastal Engineering Division 1270 Sa2Dong Ansan 426-744 South Korea. surfkim@kordi.re.kr 2006ROMS/TOMS Europe Nov 6-8, 2006 Alcala De Henares Spain

2. Abstract Numerical modeling and field experiment have been conducted to predict the seabed change due to underwater sand mining in coastal waters of Korea. The macro-tidal Kyunggi Bay is approximately 20,000 km2, where underwater sand has been extracted approximately more than 20 million m3 annually. Suspended sediment (SS) transport in the water column and sea bed has been a critically important issue to many concerns. In this study, we present the numerical prediction of sediment transport processes such as SS dispersion and consequent change in sediment types in sea bottom. We use full 3-D model ROMS to implement the sediment dynamics by adopting the extensively observed field data associated with modeling inputs and model validation.

3. Seabed Sand Mining Area in Kyunggi Bay, Korea

4. Numerical Model Grid for Kyunggi Bay Curvilinear Orthogonal Grid Terrain-Following Vertical Grid (20 arrays)

5. 3-D Sediment Transport Equations VariableDescription Falling Velocity Concentration of Suspended Sediment Hor/Ver Mixing Coefficients Source/Sink of Sediment Source Conc at the Sea Surface Source Conc. at the Seabed Deposition Rate through sinking, at Erosion RatePorosity Velocity at seabedRMS Tidal Current,

6. Source Concentrations of SS in Kyunggi Bay Source Concentrations of SS in Kyunggi Bay Dredging Volume /hr 1,000 m 3 /hr 300,000m 3 / 12.5 days SS Flux in Over- spilled Water 73.61kg/s Pumping Water Volume : 10 x Loading Volume SS Spilled : 10% od Loading Volume (MMS, 1999) 99%Sand: Composition of Spilled SS 0.5:0.25:0.125:0.0625:0.03125mm 3:3:2:1: 1 7950:7950:5300:2650: 2650 mg/l 98%Sand Composition of Spilled SS 0.5:0.25:0.125:0.0625:0.03125mm 2:2:2:2: 2 5300:5300:5300:5300: 5300 mg/l

7. Volume =3,000,000 m 3 / 12.5day Ø 1 :Ø 2 :Ø 3 :Ø 4 :Ø 5 = 2:2:2:2:2 SS Dispersion (Started during Spring Tide) Bottom Surface

8. Volume =3,000,000 m 3 / 12.5day Ø 1 :Ø 2 :Ø 3 :Ø 4 :Ø 5 = 2:2:2:2:2 SS Dispersion (Started During Neap Tide) Bottom Surface

9. Field Experiment conducted between 14:00 -16:00 on October 12, 2001 in Kyunggi Bay. Model Validation with Field Observed Data (2,000 m 3 3 Barges )

10. Vertical Profiles of SS Concentration Observed and Simulated for 14:00- 16:00 on October12, 2001 in Kyunggi Bay. Comparison of Model Results and Field Observed Data

11. Tidal current of 0.5 m/s Extractuin Volume 300,000 m 3 SS Redistribution at Seabed Based on Particle Size (Model Results)

12. Conclusions Conclusions In this study, a numerical approach using the fully 3-D model ROMS has been conducted to investigate the sediment dynamics arising from the undersea sand mining operation. Fundamental parameters required for model implementation have been obtained through extensive field experiments done in Kyunggi Bay in Korea. In this study, a numerical approach using the fully 3-D model ROMS has been conducted to investigate the sediment dynamics arising from the undersea sand mining operation. Fundamental parameters required for model implementation have been obtained through extensive field experiments done in Kyunggi Bay in Korea. The estimation of sediment source concentration adapted in this study might be very useful for application to other site-specific area. The estimation of sediment source concentration adapted in this study might be very useful for application to other site-specific area. The bottom sediment composition is very important to predict the habit change at the seabed. Three- dimensional evolution of sediment transport shows a variety of dependent parameters on environmental impacts, particularly on the geologic change in benthic habitat. The bottom sediment composition is very important to predict the habit change at the seabed. Three- dimensional evolution of sediment transport shows a variety of dependent parameters on environmental impacts, particularly on the geologic change in benthic habitat.