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Analytical Benthic Flux Model Forced by Surface-Gravity Waves

Analytical Benthic Flux Model Forced by Surface-Gravity Waves. Application to the South Atlantic Bight. j.n. king U.S. Geological Survey Florida Integrated Science Center Fort Lauderdale, FL, USA. Definition ◊ Model ◊ SAB ◊ Conclusions.

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Analytical Benthic Flux Model Forced by Surface-Gravity Waves

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  1. Analytical Benthic Flux Model Forced by Surface-Gravity Waves Application to the South Atlantic Bight j.n. king U.S. Geological Survey Florida Integrated Science Center Fort Lauderdale, FL, USA Definition ◊ Model ◊ SAB ◊ Conclusions

  2. Benthic flux is the rate of flow of some quantity across the bed of a water body, per unit area of bed. • Benthic flux is a vector quantity, where the vector is oriented normal to the bed. • Benthic flux units are a function of the quantity under consideration: • volume quantity: L3 T-1 L-2 (=LT-1) • mass quantity: M T-1 L-2 • Benthic flux is a transient process. Definition :: Benthic Flux Definition◊ Model ◊ SAB ◊ Conclusions

  3. Benthic flux is the rate of flow of some quantity across the bed of a water body, per unit area of bed. • Benthic flux is a vector quantity, where the vector is oriented normal to the bed. • Benthic flux units are a function of the quantity under consideration: • volume quantity: L3 T-1 L-2 (=LT-1) • mass quantity: M T-1 L-2 • Benthic flux is a transient process. Definition :: Benthic Flux Definition◊ Model ◊ SAB ◊ Conclusions

  4. newer … older • Also known as: • Seepage • Irrigation • Flushing • Ventilation • Percolation • Sub-tidal pump • Submarine ground water discharge (SGD) • Submarine ground water recharge (SGR) • Submarine pore water exchange (SPE) • Related processes: • Deposition & Resuspension • Bio-turbation • Bio-irrigation • Salt fingering • Fluidization of sediment in the surf zone Burnett et. al. (2003) • Benthic flux is independent of direction: • benthic discharge (flux): gw => sw • benthic recharge (flux): sw => gw • Benthic flux is independent of water body: wetland, river, lake, estuary, lagoon, ocean • Benthic flux is independent of location in the water body: surf zone, shelf, deep ocean Definition◊ Model ◊ SAB ◊ Conclusions

  5. Processes that Drive Benthic Flux Definition◊ Model ◊ SAB ◊ Conclusions

  6. Surface-Gravity Wave over Rigid, Porous Media +z 4Unknowns – 4Equations Assume z=0 +x (DFSBC) (KFSBC) (DBBC) z=-h (KBBC) (Bernoulli) (velocity potential) Reid & Kajiura (1957) (Darcy) Definition◊ Model ◊ SAB ◊ Conclusions

  7. Definition◊ Model ◊ SAB ◊ Conclusions

  8. Generalized Analytical Modelfor Benthic Water Flux King, Mehta & Dean (2008?) Definition◊ Model ◊ SAB ◊ Conclusions

  9. Moore (1996) Moore (1999) Definition◊ Model ◊ SAB ◊ Conclusions

  10. Estuaries Ocean 0.08 dpm/L 0.01 dpm/L Moore (1996) A 226Ra= 0.19 dpm/L SAB A 226Ra.Excess= 0.19-0.01-0.08 = 0.10 dpm/L Moore (1999) VSAB.InS = 20km × 320km × 10m = 6.4×1013L Tresidence.226Ra = 30d Å 226Ra.Excess= 0.10×(6.4×1013)÷30 =2.1×1011dpm/d Definition◊ Model ◊ SAB ◊ Conclusions

  11. 7 dpm/L Pore Water Moore (1996) A 226Ra= 0.19 dpm/L SAB Ocean Estuaries 0.08 dpm/L 0.01 dpm/L Å 226Ra.Excess=2.1×1011dpm/d QMoore=2.1×1011÷7 =3×1010L/d =350m3/s qMoore=0.5cm/d Definition◊ Model ◊ SAB ◊ Conclusions

  12. Three (nearshore) processes: Tidal pumping on sloped beach 130m3/s or 37%QMoore Wave set up 190m3/s or 54%QMoore Terrestrial hydraulic gradient (from Younger,1996) 14m3/s or 4%QMoore Linear sum = 14+130+190 = 334m3/s or 95%QMoore Li and others (1999) Definition◊ Model ◊ SAB ◊ Conclusions

  13. bathymetry from Riedl et al. (1972) Riedl et al. (1972) canonical canonical Riedl et al. (1972) Riedl et al. (1972) Application of Case I to SAB shoaled and damped Definition◊ Model ◊ SAB ◊ Conclusions

  14. 1.3dpm/L 0.2dpm/L Martin et. al. (2006) Wave mixed zone Moore & Wilson (2005) 7dpm/L? Moore & Wilson (2005) Definition◊ Model ◊ SAB ◊ Conclusions

  15. Updated Moore (1996) 0.5 dpm/L 7 dpm/L 0.19 dpm/L Pore Water A 226Ra= 0.19 dpm/L SAB Ocean Estuaries 0.08 dpm/L 0.01 dpm/L Pore Water QMoore= 2.1×1011÷0.3 = 7×1011L/d = 8100m3/s qMoore= 11cm/d Definition◊ Model ◊ SAB ◊ Conclusions

  16. Waves matter!Surface gravity waves advect pore water constituents into surface waters. Shelf-wide processes are probably larger contributors than near-shore processes. = 8,100m3/s too large? What about bedform effects? Conclusions Definition◊ Model ◊ SAB ◊ Conclusions

  17. Future Work (?) • Wave mixed-zone: other forcing mechanisms transport pore water constituents onto the wave-mixed zone • Density gradients • Pressure gradients • Concentration gradients • Episodic gradients • Numerical model! Definition◊ Model ◊ SAB ◊ Conclusions

  18. Questions?

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