Abstract
Results from 3 yr of hydrographic time series are shown for Willapa Bay, Washington, a macrotidal, partially mixed estuary whose river and ocean end members are both highly variable. Fluctuating ocean conditions - alternations between wind-driven upwelling and downwelling, and intrusions of the buoyant Columbia River plume - are shown to force order-of-magnitude changes in salinity gradients on the event (2-10 day) scale. An effecticve horizontal diffusivity parameterizing all up-estuary salt flux is calculated as a function of riverflow: results show that Willapa's volume-integrated salt balance is almost always far from equilibrium. At very high riverflows (the top 15% of observations) the estuary loses salt, on average, while at all other riverflow levels it gains salt. Under summer, low-riverflow conditions, in fact, the effective diffusivity K is large enough to drive a net increase in salinity that is 3-6 times the seaward, river-driven salt flux. This diffusion process is amplified, not damped, by increased tidal forcing, contrary to the expectation for baroclinic exchange. Furthermore, K varies along the length of the estuary as ∼5% of the rms tidal velocity times channel width, a scaling consistent with density-independent stirring by tidal residuals. To summarize Willapa's event- and seasonal-scale variability, a simple diagnostic parameter space for unsteady estuarine salt balances is presented, a generalization from the Hansen and Rattray steady-state scheme.
Original language | English |
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Pages (from-to) | 2413-2427 |
Number of pages | 15 |
Journal | Journal of Physical Oceanography |
Volume | 34 |
Issue number | 11 |
DOIs | |
Publication status | Published - 1 Nov 2004 |
Keywords
- density (specific gravity)
- diffusion
- hydrographic surveys
- oceanography
- rivers
- salts
- tides
- time series analysis
- wind effects
- fluctuating ocean conditions
- tidal forcing
- Willapa Bay, Washington
- wind-driven upwelling
- estuaries
- estuarine dynamics
- mixing
- river discharge
- salinity
- North America
- United States
- Washington [United States]
- Western Hemisphere
- world