A. Valle-levinson et al., Observations of intratidal variability of flows over a sill/contraction combination in a Chilean fjord, J GEO RES-O, 106(C4), 2001, pp. 7051-7064
Underway velocity measurements were carried out for the first time in a Chi
lean fjord using an acoustic Doppler velocimeter with the purpose of elucid
ating the intratidal variability of flows through a pass, Paso Galvarino. T
he pass included a sill, where the bottom sloped by roughly 30%, and a coas
tline contraction of -90%. The relatively small dimensions of the pass allo
wed for rapid sampling of the flow evolution throughout the tidal cycle. Th
e backscattered sound signal from the velocimeter and from an echo sounder
were used to describe the vertical excursions of the pycnocline throughout
the domain and to identify regions of enhanced vertical mixing within the p
ass. The spatial variability of the flow in the pass was consistent with un
iform two-layer flow. At the narrowest section of the contraction the pycno
cline dropped sharply around both maximum flood and maximum ebb, while the
flow accelerated downstream relative to the tidal flow. The slope of the py
cnocline changed sign from flood to ebb, which was atypical of other fjord
observations but could be explained by the transitions from subcritical to
supercritical flow. These transitions switched location at either side of t
he narrowest section of the contraction. Leeward of this section, increased
sound backscatter suggested intensified turbulence that extended over a gr
eater area during ebb than during flood because the distance between the po
int of pycnocline drop and the end of the pass was longer during ebb. Enhan
ced vertical mixing within the pass was reflected in the tidally averaged f
ields by a three-layer flow that consisted of near-surface and near-bottom
flow converging toward the pass and flow around the pycnocline diverging aw
ay from the pass.