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

3.2.2 – Current velocities at Heron Rookery
Heron Rookery is 7.4km from the mouth, well beyond a tidal excursion of the mouth and
typically beyond the reach of salinity intrusions during stronger river flow. However,
during the low-flow summer and fall seasons in 2009, saline waters were observed at
depth at Heron Rookery – sometimes trapped there and no longer connected to the
main body of saline waters in the outer estuary. Tides and winds are also important
here. Representative data are plotted below for days on which the tidal range was ~3ft,
~1ft, 0ft and ~4ft respectively (Figures 3.12, 3.13, 3.14, 3.15) – with range varying as a
result of ocean tides and mouth constrictions. Current speeds over 30cm/s are observed
during spring tides and near-surface during all conditions.
Currents in the evening of 28 August 2009 (Figure 3.12) are moderate, with an inflow of
10cm/s extending down to about 12ft during the late flood tide. On the subsequent 3ft
ebb tide, seaward flows are over 20cm/s above the pycnocline at about 7ft; a strong
shear is observed with currents zero a foot lower, immediately below the pycnocline.
Figure 3.12. Water levels (top panel) and profiles of along-channel speed (bottom
panels) at Heron Rookery on 28-29 August 2009, during a tidal cycle with a range of
~3ft and Guerneville river flow of 63 cfs. Negative velocities indicate flow toward the
mouth.
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