하구및 연안생태Coastal management 2015 년 가을학기

Water balance (Pritchard, 1952) positive estuaries : evaporation < freshwater Negative estuaries : evaporation > freshwater Neutral : evaporation = freshwater

Water balance (Pritchard, 1952) No loger in common use Most estuaries are positive!!

Geologic classifications(topography) Coastal plain; Drowned river valley; most common. since the last Ice Age, which is within the last 10–15,000 years V shaped cross sections Salt marsh estuaries; lack of a major river; estuary-salt marsh connections;

Geologic classifications(topography) Lagoons; Bar-built: Also drowned river valleys, but recent sedimentation has kept pace with their drowning so that they have a characteristic bar across their mouths Shallow 1~2 m Physical process; wind dominated 80,000 years ago, 6m above present level raised ridge system eroded during glacial period  transformed to bar at present day Common on all continents

Geologic classifications(topography) Fjord: Drowned glacial troughs. Fjord-type estuaries occur where valleys have been deeply eroded by glaciation: West of Scotland, Fjords in Norway, Sweden, Alaska, British Columbia, New Zealand, such as the coasts of Norway, Western Scotland, Alaska, and New Zealand. Rock bar: 1. can not scour that part because ice began to float 2. scoured material accumulated; Depth 800m; sill 10~90 m U-shaped Fjards: firths; No u-shaped deep basin; shallow; isostatic rebound of the continent due to cessation of ice loading; rebound rates:15 m per 1000 years

Geologic classifications(topography) Tectonic Fauting, graben formation, land slide, volcanic eruptions San Francisco Bay Much variability

Circulation Residence time of a water parcel is function of circulation pattern “Residence time / biogeochemical turnover” determines degree of hydrodynamic dominance Flux of all martials (nutrients, pollutants, salt, sediments, detrital matter, plankton) need information regarding circulations Estuarine bathymetry  circulation Defined as the residual water movements; short term effects are averaged out

Circulation Residual movements depends on the time scale for averaging; usually 1, 2 tidal cycles Need systematic measurements over an extended time period. Time averaged currents make up the circulation: net currents, tidal currents, tidal residuals nontidal flaows

Types of Circulation Passive factors : curvature and friction effects Circulation energy: solar heating: also contribute to wind, rainfall, SST Gravitational attraction between moon (sun) and ocean water Freshwater input : rainfall; major cause Tide; 3rd important Wind stress; second major cause wave; not very important Passive factors : curvature and friction effects Geometry Bathymetry : curvature and friction effects Ice cover, human activities (dredging, channelization, damming, diversion)

Three main driving force Gravitational circulation :due to fresh water runoff Tidal circulation Wind-driven circulation

Gravitational Circulation Induced by density and elevation difference Mixing with wind + tide Freshwater: tilt seaward : seaward movement Seawater: tilt up-estuary: river ward Equipontential surface: no net movement Important for residence time calculation: 1 R inflow and 24R exchange Temperature effects: in arctic region: cold fresh water will mix with ocean water that makes gravitational circulation in lagoon: no fresh water input: large evaporation; 90 ppt !: inverse estuarine circulation; usually wind is high and this “inverse circulation” might not be important Coriolis effects : surface: stronger right side down stream, bottom left side  questionable

Tidal circulations “tidal pumping” Oscillatory: but interact with bathymetry in nonlinear and complex way; spatial velocity gradient High tidal circulation; Shallow depth + large tidal range Gravitational and tidal circulation can be equally important Ebb directed on one side and flood directed other side: because of boundary interaction not because of “Coriolis effects” No net loss or gain of water but movement of material happens.

Wind driven circulations Important in lagoons; open water, shallow, small tidal range, low fresh input. Highly variable However, some circulation can be related with wind 4 x 10-5 radians(0.4 m per 10 km); 10 m/s “Wind tides” in Texas: period of few hours Modify gravitational circulation.