Hydrography of the Russian River Estuary - Sonoma County Water ...

easily over denser estuarine waters in the absence of tidal and wind mixing. Later in the
afternoon, during the weak flood tide, an inflow of 5-20cm/s was observed extending
several feet down from the surface. While supported by the tide, this surface-amplified
inflow is primarily due to an afternoon/evening sea-breeze that is felt on the estuary
between Paddyʼs Rock and the mouth.
Figure 3.10. Water levels (top panel) and profiles of along-channel speed (bottom
panels) at Paddy's Rock on 11-12 July 2009, during a tidal cycle with a range of ~3 ft
and Guerneville river flow of 110 cfs. Negative velocities indicate flow toward the mouth.
Along-channel currents on 11-12 July 2009 (Figure 3.10) are stronger and observed
throughout the 22ft-deep water column, with an intriguing vertical structure. At low tide
on the morning of 11 July, a 5ft layer of low-salinity water is observed to be flowing
seaward. This reverses to an inflow over the uppermost 10ft during the subsequent
flood tide. However, by the time of the afternoon ebb tide, the afternoon sea-breeze has
started and the 17h00 profile shows the uppermost 2ft moving landward due to surface
wind stress while the waters between 2ft and about 12ft depth are seen to move
seaward due to barotropic tidal pressure gradients. Below this, the near-bottom waters
are moving landward (establishing a 3-layer flow structure, with mid-depth waters
flowing seaward between surface and bottom waters). This sub-pycnocline inflow is also
evident in the 15h00 profile and most dramatically seen in the profile at spring high tide
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