ENST 471 ppt3

ENST 471 ppt3 - Physical processes: All transport, mixing,...

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Physical processes: All transport, mixing, and fate of pollutants is dictated by physical processes within the estuary pend the next two weeks discussing Spend the next two weeks discussing physical processes emember pollutants have immediate Remember pollutants have immediate, cascading, and long-term effects
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Empirical classification • Salinity stratification along the estuary axis • Consider freshwater volume (R) over ingle tidal cycle single tidal cycle • Use denominator of tidal volume (V) • Units typically for each are m 3 • Therefore R/V is unitless
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Current flow in estuaries • Total flow= mean flow + tidal flow +turbulent fluctuations • Turbulence is random and occurs as long as there is primary flow idal flow is regular ebb and flow caused by • Tidal flow is regular ebb and flow caused by tidal oscillations • Mean flow is what remains and can change g based upon riverine discharge, seasons, and wind • Riverine discharge extremely important in case of eastern NC estuaries
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R/V 1.0 or greater Intense turbulence Highly stratified, entrainment, shear R/V 0.1-1.0 alinity does not vary with depth R/V < 0.005 Salinity does not vary with depth Slightly stratified, Turbulent mixing g R/V 0.005- 0.1
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stuarine Transport Estuarine Transport Processes Advection : Directional mixing of a specific property Advection is the transport of a conserved scalar quantity that is transported in a vector field (x,y,z). good example to have in mind would be the – A good example to have in mind would be the transport of pollution in a river: the motion of the water carries the polluted water downstream. arried with the mean flow. Carried with the mean flow. – Salinity is an excellent tracer
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stuarine Transport Estuarine Transport Processes • Advective mixing occurs on longer time scales than turbulence - dyes, radionuclides, nd salinity (most common tracers) and salinity (most common tracers) 1) conservative constituent - concentration not altered by biogeochemical processes, hanges primarily via mixing (i e Na Cl) changes primarily via mixing (i.e., Na, Cl) 2) in most estuaries salt derived from ocean source (35 ppt) 3) easy and inexpensive to use salinity as marker of mixing processes
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Dispersive Mixing • Scattering of particulates and dissolved parcels of water in the estuary from: 1) tidal sloshing – avg. flux of particles by oscillating tidal currents - dominant longitudinal mixing process ) hear effects sults from different velocities of 2) shear effects - results from different velocities of parallel currents. 3) eddy (turbulent) diffusion - random scattering of water and particles by random molecular or eddy motions. material transported down concentration gradient 4) molecular diffusion - always several orders of magnitude less than turbulent (eddy) diffusion 5) tidal trapping -water temporarily trapped within shoreline indentation 6) stability - stratification can resist mixing between layers
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Estuarine mixing and transport processes • Mixing of an estuary dictates the fate and transport of nthropogenic inputs
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This note was uploaded on 01/03/2009 for the course ENST 471 taught by Professor Noble,rachael during the Spring '08 term at UNC.

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ENST 471 ppt3 - Physical processes: All transport, mixing,...

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