하구및 연안생태Coastal management 2015 년 가을학기
Circulation modes Classic view: two layered Net outflow in surface Net inflow in the bottom 6 circulation modes (Elliott, 1976) Classical Reverse 3 layered Reverse 3 layered Discharge Storage
Circulation modes Potomac Complex spatial and temporal variability 43 % classic 22% storage 21% reverse 7% reverse 3 layered 6% discharge 1% 3 layered Complex spatial and temporal variability Lateral variability is more complex
Far field effects Large scale meteorological forcing Kelvin waves Continental shelf waves Coastal trapped waves periods: 2~15 days, length 1000km, wave heights: less than 0.8 m Free-propagation Ecological importance of non local effects Submergence of tidal flat Biased measurement; need to check the non local forcing Turbidity maximum salinity
Estuarine mixing Mixing Salinity as a mixing indicator Adjectives; longer time scale Dispersive: shorter Salinity as a mixing indicator Conservative ocean is only source (35 versus 0.6 ppt) Easy and inexpensive to determine; does not need great precision
Dispersive mixing Scattering of water parcels Tidal sloshing; time averaged flux of particles: dominant Transport = Velocity x concentration Integral seldom vanishes because the phase differences currents and concentration Shear effects; 두 유동물질의 유속차에 의해 생기는 효과 Systematic covariation of velocity and particle concentration Depth Width Cross section Eddy diffusion: not important (>> molecular diffusion) Molecular diffusion; negligible Tidal trapping; temporarily trapped in shoreline indentations released by tidal currents and replaced with new water mass
Forces for mixing Tidal forcing Advective mixing: tidal pumping Dispersive mixing: sloshing shear trapping Wind: important when tidal range is small. Large lagoon. Surface wave, Internal wave
Forces for mixing Fresh water Buoyancy; density difference, gravitational circulation advective mixing Sloping isopycnals pressure gradient classic estuarine circulation Seaward at the surface Landward at the bottom Temporal variations of mixing in a estuary Strong wind; front passage Spring tide; enough currents to break stratifications ; influence nutrient and oxygen supply
Mixing diagram Salinity versus material Can determine if the material is “source” or “sink” Assumptions One-dimensional (longitudinal) mixing Quasi steady state All data are averaged over one or more complete tidal cycles Concentration in fresh water and ocean can change over time; cause problem!!!
Dynamic classification A: highly stratified; lower mississippi Low tidal range Moderate or high discharge B: Partially mixed Chesapeake Bay 2~10 ppt difference vertically Gravitational circulation is typical Moderate or high tide and moderate discharge C: Well mixed; large tidal range, little fresh water C1: vertically homogeneous with laterally reversing net flow C2: vertically, laterally homogeneous
Estuary modification Dredging Widening Make it deeper ABC Widening Damming of river; reduced discharge
Circulation-stratification diagram Hansen and Rattry (1965) Stratification: salinity difference between surface and bottom S/S0 Circulation: “net surface flow”/”fresh water flow” Net surface flow : average of one tidal cycle Fresh water flow: discharge / area
Circulation-stratification diagram Class 1: lagoon, bar built Class 2: partially mixed Class 3: fjord and fijard; advective mixing Class 4: type A; strongly stratified.