Introduction
Estuaries around the globe exhibit more mixing during one phase of the tidal cycle
relative to the other. Typically, there is more mixing during flood than during ebb (Fig. 1,
taken from Macready and Geyer, 2010, inspired by Jay, 1991, and Jay & Musiak, 1994)
but the opposite can also happen in some systems, such as salt-wedge estuaries (ref).
This enhancement of mixing during one
phase of the tidal cycle is herein referred to
as “asymmetric tidal mixing.” It has been
recognized that asymmetric tidal mixing can
enhance or compete against the residual
circulation in estuaries produced by density
gradients, traditionally recognized as
gravitational circulation. The studies that
have pointed to the importance of residual
circulation produced by asymmetric tidal
mixing have been essentially theoretical and most of them have assumed lateral
uniformity in estuaries.
The proposition that the circulation induced by asymmetric tidal mixing can be as large
as gravitational circulation still needs exploration with observations that quantify
turbulence levels in flood and ebb. The point of this concept is that estuarine circulation
is not the same as gravitational circulation. Gravitational circulation is essentially
produced by density gradients established by the interaction between river discharge
and ocean waters in semienclosed basins. But in addition to density gradients, the
spatial gradients in tidal currents can also produce residual circulation, sometimes
referred to as circulation induced by lateral advection. Really related to tidal stresses
(Zimmerman). Now, it is suggested that tidal variations in mixing, asymmetric tidal
mixing, can also contribute. When lateral variations in bathymetry are considered,
limited numerical results show that the circulation induced by tidal stresses may be
approximately cancelled by the circulation produced by asymmetric tidal mixing (Fig. ).
These findings are revealing and provocative. They motivate further questions, for
instance: are theoretical results observable in the field? Under what circumstances is
the circulation induced by tidal mixing dominant? What are the effects of lateral
variations in bathymetry on the circulation driven by asymmetric tidal mixing? How do
lateral currents and spatial variations in tidal currents modify this circulation? These are
questions that need to be addressed in order to advance fundamental understanding of
estuarine hydrodynamics.
Objectives
1
The overall objective of this 4-year project is to advance understanding of the role of
asymmetric tidal mixing on the residual circulation in estuaries, and to place this role in
the context of fundamental estuarine hydrodynamics.
Specific objectives are to:
1) obtain observational evidence on the relative relevance of asymmetric tidal mixing in
the residual circulation of estuaries; and
2) investigate the influence of lateral variability of bathymetry and flows on the relevance
of asymmetric tidal mixing in the residual estuarine circulation.
The hypotheses related to these objectives are that i) circulation induced by asymmetric
tidal mixing is observable in systems with strongly seasonal but weak river discharge
and strong tidal currents, as suggested by theory, and ii) lateral variations in tidal flows
produced by transverse bathymetric changes will cause residual circulations that will
compete against the circulation produced by asymmetric tidal mixing. These
hypotheses are anchored on the background information related to the general topic of
flows induced by asymmetric tidal mixing.
Background
Residual circulation along estuaries (u) has traditionally been regarded as densitydriven, associated with an along-estuary (x direction) balance between pressure
gradient and friction (e.g. Pritchard, 1956; Hansen & Rattray, 1965):
0  g


x

z
H
g 
 2u
dz  Az 2
 0 x
z
(1)
where overbars denote tidally averaged quantities. Pressure gradient forces per unit
mass are given by the first two terms on the right hand
side of eq. 1. These accelerations are associated with
the water level slope /x caused by the river flowing
toward the ocean, and with the longitudinal density
gradient /x. Frictional effects, given by the last term in
eq. 1, are represented by a time- and space-uniform
vertical eddy viscosity Az. Also in eq. 1, g is acceleration
caused by gravity, z is the vertical direction and o is a
reference water density. Across the estuary, the
momentum balance is assumed between lateral pressure
gradient and Coriolis (geostrophic balance). Equation 1 combined with geostrophy and
a mass balance in which the vertically integrated flow yields the river discharge,
features a two-layer vertically sheared circulation (Fig. 2). The two-layer flow consists
2
of tidally averaged outflow at the surface and inflow underneath, associated with linear
dynamics (Fig. 2). This flow is generally referred to as gravitational circulation.
For the same dynamical framework, lateral variations in bathymetry can change the
spatial structure of the
gravitational circulation. Tidal
residual flows change from
vertically sheared to laterally
sheared (Fig. 3). Vertically
sheared exchange flows
develop over nearly flat bottoms
(lower right panel of Fig. 3),
while laterally sheared
exchange flow appears over
cross-sections with transverse
variations (all other panels in
Fig. 3).
Invoking the influence of Earth’s rotation along the estuary and of friction across the
estuary, still within the context of linear dynamics, the momentum balance becomes
symmetric for along- and across-estuary directions (e.g. Kasai et al., 2000):
 2u
 g
 fv  A
 g

z z 2
x  0

dz;
x
H
0

 2v
 g
fu  A
 g

z z 2
y  0
0

 y dz
(2)
H
where f is the Coriolis parameter and y is the across-estuary direction. According to this
set of equations, density-driven flows respond to the pressure gradient (right hand side
of eqs. 2) and are modified by friction and/or by rotation (both on the left hand side of
eqs. 2). Whether density-driven flows are modified by friction or rotation, or by both,
can be determined by the ratio of friction to rotation as represented by the nondimensional Ekman number, Ek, given by Az/(fH2), where H is a reference depth (can be
the maximum depth). This number could be regarded as a dynamic depth of the basin.
Low Ek (<~0.01) indicates Coriolis accelerations dominating over friction, which
translates into a dynamically deep basin. Analogously, high Ek (>~0.1) represents
dynamically shallow basins where friction is more important than Coriolis accelerations.
At low Ek (deep basin with Coriolis dominance) the exchange flow will be vertically
sheared and affected by rotation (middle-column, upper most panel of Fig. 4). For high
Ek, exchange flows are laterally sheared and the outflows appear in two branches that
are essentially symmetric to the deepest channel (middle column, lowest panel of Fig.
4). In essence then, exchange flows will be sensitive to the dynamic depth of the basin.
But are they sensitive to the width of the basin?
3
The answer to this question can be determined by looking at the same linear dynamics,
but now also in terms of the non-dimensional width of the basin as given by the Kelvin
number, Ke. This number compares the actual width of the basin (in m) to the internal
radius of deformation
(also in m). Solutions
demonstrate that depth
and width are crucial to
establish whether
exchange flows will be
laterally sheared or
vertically sheared (Fig.
4). At low Ek
(dynamically deep
basins, upper row in Fig.
4), exchange is laterally
sheared for large Ke
(dynamically wide basin,
like a gulf) and vertically
sheared for small Ke (dynamically narrow basin, like a fjord). For intermediate Ek
(middle row in Fig. 4), exchange flows are mostly vertically sheared but with marked
lateral variability in wide basins (high Ke). Over dynamically shallow basins associated
with large Ek (lower row in Fig. 4), exchange flows are laterally sheared regardless of
the basin’s width. These results underscore the importance of dynamic depth and width
to determine the shape of exchange flows.
During the last decade, it
has been suggested that
the influence of tides can
alter exchange flows
through non-linear
advective accelerations
(Lerczak and Geyer, 2004;
Scully et al., 2009; Huijts
et al., 2009). This is
analogous to the effect of
tidal stress on residual
circulation proposed
several decades ago (e.g.
Nihoul and Ronday, 1975).
These ideas suggest that
the essential dynamics in
4
estuaries is non-linear because of advective accelerations (Lerczak & Geyer, 2004).
So, in addition to Coriolis and frictional effects balancing the driving pressure gradient,
the advective accelerations can also contribute to the balance. This variety of forcings
was addressed by Cheng and Valle-Levinson (2009) in terms of the competition
between friction and Coriolis, through Ek, and between advection and Coriolis, through
the Rossby number Ro . This number equals U/fL, where U is a dominant flow and L is
a lateral scale of the flow, such as the width of the basin. Small values of Ro (<0.1)
represent dynamically wide basins, while large Ro values (O(1)) indicate narrow basins.
The exchange flows structure can then be placed in the parameter space of dynamic
depth Ek and dynamic width Ro (Fig. 5). Such exchange flows structure is consistent
with linear dynamics for small and intermediate Ro in the sense that laterally sheared
exchange flows develop over shallow basins (top row of Fig.5, left two panels) and over
deep but wide basins (lower left panel). The only discrepancy with linear theory is in the
upper right panel (Fig. 5). Over narrow (large Ro) and shallow (large Ek) basins the
effect of advective accelerations is to cause vertically sheared exchange flows, instead
of laterally sheared. Therefore, advective accelerations are expected to be influential in
basins where Ro and Ek are near 1, where the along-estuary dynamics can be
synthesized as:
u'
u'
u'
u'
 2u
 g
 v'
 w'
 fv  A
 g

2
z
x
y
z
x  0
z
0

 x dz
(3)
H
where the primes denote tidal variations and w is the vertical component of velocity.
Huijts et al. (2009, 2011) have been able to describe the flow structure associated
separately with density-gradients and river discharge (gravitational circulation), tidal
stress, Coriolis, channel curvature and wind.
The results above and those by Jay (1991) and Stacey et al. (2001; 2008) have pointed
out that asymmetries in tidal mixing can also drive a net circulation that reinforces or
competes against the gravitational circulation. Asymmetries in tidal mixing arise from
the frictional term upon considering tidal mean (ū) and tidal fluctuating flows (u’):
 2u
  u   
u' 
A

A

A '
z z 2 z  z z  z  z z 


(4)
where the first term on the right hand side represents mixing related to the mean eddy
viscosity and the mean vertical shear. The second term represents asymmetries in tidal
mixing arising from the covariance between tidal fluctuations in eddy viscosity and tidal
oscillations in vertical shear. Recent numerical experiments (Cheng et al. 2013) over
idealized, flat and laterally uniform estuaries describe the qualitative and quantitative
structure of the residual circulation produced by asymmetries in tidal mixing ua (Fig. 6).
5
Values of width-averaged ua can be calculated with the non-dimensional relationships
derived by Cheng et al. (2010) for z coordinates:
z
4   a 2
u ' 
2
ua 
z

D

A
'
d ;
z

 
3 Az  x
D

 a
3

x
2D 3

u '
0 z
  A '  d dz
(5a)
(5b)
z
DD
where  is a dummy variable and D is the non-dimensional water column depth.
Solution (5) shows that ua is determined by the lowest order tidal current (u’) and the
tidal variation of vertical mixing (Az’). Explain each term.
In estuaries where  > 0.1H, it is more appropriate to use σ coordinates than z
coordinates (e.g. Giddings et al., 2011). For normalized () coordinates equations (5)
become (see Cheng et al., 2013):
̅̅̅̅
𝑔 𝜕𝜂
𝑎
𝑢𝑎 = 𝑍̅
𝜕𝑥
′
𝜎 𝜎′
𝜎 1 ̅̅̅̅̅̅̅
′ 𝜕𝑢 𝑑𝜎 ′
𝑑𝜎′
−
𝐴
∫−1 ̅̅̅̅
∫
𝑧
−1 ̅̅̅̅
𝐴
𝐴
𝜕𝜎′
𝑧
𝑧
′
′
̅̅̅̅̅̅̅̅̅̅̅̅̅̅̅̅̅̅
̅
1 𝜎 1 0 ̅̅̅̅̅̅̅̅̅̅̅̅̅̅̅̅̅
′ 𝜕 (𝐴
′ 𝜕 (𝐴′ 𝜕𝑢
′ 𝜕 (𝐴′ 𝜕𝑢 )] 𝑑𝜎′′} 𝑑𝜎′,
̅̅̅𝑧 𝜕𝑢 ) + ̅̅̅̅̅̅̅̅̅̅̅̅̅̅̅̅̅̅
+ 𝑍̅ ∫−1 {̅̅̅̅
[𝑍
𝑍
)
+
𝑍
∫
𝑧
𝑧
𝜎′
𝐴
𝜕𝜎′′
𝜕𝜎′′
𝜕𝜎′′
𝜕𝜎′′
𝜕𝜎′′
𝜕𝜎′′
𝑧
(6a)
where = (z-)/D, 𝐷 = 𝜂 + 𝐻, η is surface water elevation, H is the undisturbed water depth, and
1/𝐷 2 = 𝑍̅ + 𝑍′. Also,
̅̅̅̅
𝜕𝜂
𝑎
𝜕𝑥
+
=
0 𝜎 1 ̅̅̅̅̅̅̅̅̅
𝜕𝑢′
𝑍̅ ∫−1 ∫−1̅̅̅̅𝐴′ 𝑧 ′ 𝑑𝜎′ 𝑑𝜎
0
𝐴𝑧
𝜕𝜎
𝜎 𝜎′
𝐴𝑧
𝑔 ∫−1 ∫−1̅̅̅̅𝑑𝜎′𝑑𝜎
̅̅̅̅̅̅̅̅̅̅̅̅̅̅̅̅̅̅̅̅̅̅
′
̅̅̅̅̅̅̅̅̅̅̅̅̅̅̅̅̅̅̅̅̅̅
̅
0 𝜎 1 0 ̅̅̅̅̅̅̅̅̅̅̅̅̅̅̅̅̅̅̅̅̅
𝜕
𝜕𝑢′
′ 𝜕
′ 𝜕𝑢
′ 𝜕
′ 𝜕𝑢
̅̅̅̅
∫−1 ∫−1{̅̅̅̅
∫ [𝑍 ′ 𝜕𝜎′′(𝐴
𝑧 𝜕𝜎′′)+𝑍 𝜕𝜎′′(𝐴 𝑧 𝜕𝜎′′)+𝑍 𝜕𝜎′′(𝐴 𝑧 𝜕𝜎′′)]𝑑𝜎′′}𝑑𝜎′𝑑𝜎
𝐴 𝜎′
𝑧
0
𝜎 𝜎′
𝐴𝑧
𝑔 ∫−1 ∫−1̅̅̅̅𝑑𝜎′𝑑𝜎
.
(6b)
Under normalized vertical coordinate, ua depends also on tidal variations in currents and
Az, but also on tidally averaged Az. Explain each term.
Numerical results (Cheng et al., 2013) show that in periodically stratified estuaries (left
column of Fig. 6), where tidal currents UT are ≥1 m/s and river flows uf are a few cm/s,
ua is robust and reinforces the gravitational circulation ug. It even can dominate the
6
residual circulation signal (Fig. 6 & 7). In moderately stratified estuaries (UT <1 m/s and
uf < 5 cm/s, middle column of Fig. 6), ua competes against ug in parts of the water
column but reinforces ug in other portions. In contrast, in highly stratified estuaries (uf >
6-7 cm/s, right column of Fig. 6) ua competes against ug but it can be relatively weak
(Fig. 6 & 7).
7
So, according to theory, ua can contribute to estuarine circulation in systems with strong
tidal currents (>1.1 m/s), but most markedly in periodically stratified estuaries, where
river inflow remains weak (Fig. 7). It
follows then that highly seasonal
systems like the Guana-TolomatoMatanzas in Florida (GTM) are
appropriate candidates to try to
observe the influence of ua in the
estuarine circulation. In fact, a system
in Brazil, with strong tidal currents >1.2
m/s and marked seasonal freshwater
input, represents an excellent natural
laboratory to address objective 1
(obtain observational evidence on the
relative relevance of ua in the residual
circulation of estuaries). This will allow
testing of hypothesis i) circulation induced by asymmetric tidal mixing is observable in
systems with strongly seasonal but weak river discharge and strong tidal currents, as
suggested by theory.
8
Very little research has been done on the lateral structure of ua over transverse
variations in bathymetry and its competition with other drivers of estuarine circulation.
Over laterally varying bathymetry, the form for ua is the same as equation 6a but the
expression for the along-estuary slope contained in that equation is slightly different, to
include a cross-channel y integration (Cheng et al., ):
̅̅̅̅
𝜕𝜂
𝑎
𝜕𝑥
+
=
𝐵
0 𝜎 1 ̅̅̅̅̅̅̅̅̅
𝜕𝑢′
𝐴′ 𝑧 ′ 𝑑𝜎′ 𝑑𝜎𝑑𝑦
∫0 𝐻 ∫−1 ∫−1̅̅̅̅
𝐴
𝑧
𝜕𝜎
𝐵𝐻 0 𝜎 𝜎′
𝑔 ∫0 ̅ ∫−1 ∫−1̅̅̅𝑑𝜎′ 𝑑𝜎𝑑𝑦
𝑍
𝐴𝑧
̅̅̅̅̅̅̅̅̅̅̅̅̅̅̅̅̅̅̅̅̅̅
̅̅̅̅̅̅̅̅̅̅̅̅̅̅̅̅̅̅̅̅̅̅
𝐵𝐻 0
𝜎
1 0 ̅̅̅̅̅̅̅̅̅̅̅̅̅̅̅̅̅̅̅̅̅
𝜕 ̅̅̅ 𝜕𝑢′
𝜕
𝜕𝑢̅
𝜕
𝜕𝑢′
(𝐴𝑧
) + 𝑍′
(𝐴′ 𝑧
) + 𝑍′
(𝐴′ 𝑧
)] 𝑑𝜎′′} 𝑑𝜎′ 𝑑𝜎 𝑑𝑦
∫0 ̅ ∫−1 ∫−1 {̅̅̅ ∫𝜎′ [𝑍 ′
𝑍
𝜕𝜎′′
𝜕𝜎′′
𝜕𝜎′′
𝜕𝜎′′
𝜕𝜎′′
𝜕𝜎′′
𝐴𝑧
𝐵𝐻 0
𝜎 𝜎′
𝑔 ∫0 ̅ ∫−1 ∫−1 ̅ 𝑑𝜎′ 𝑑𝜎 𝑑𝑦
𝑍
𝐴𝑧
A couple of papers by Burchard say what. Results obtained by Peng Cheng (Fig. 8)
suggest that, much like gravitational circulation, ua changes from vertically sheared over
flat bottom to laterally sheared over a triangular bathymetry. Interestingly, the structure
of ua seems to compete against the tidally averaged circulation produced by tidal stress
(or nonlinear advection). In the channel ua produces outflow, while tidal stress produces
inflow. Over shoals, the opposite flow directions develop. If these results can be
generalized to other bathymetries and under diverse forcings, which is what is proposed
as objective 2 (investigate the influence of lateral variability of bathymetry and flows on
the relevance of asymmetric tidal mixing in the residual estuarine circulation), then the
basic dynamics will be controlled by equation 2, instead of the combination of 3 and 4.
Also, hypothesis ii) lateral variations in tidal flows produced by transverse bathymetric
changes will cause residual circulations that will compete against the circulation
produced by asymmetric tidal mixing will be challenged. It is evident that the theory for
development of ua over channels with no bathymetric variations is well established but
has not been tested with observations. It is also clear that theoretical results need to be
generalized for ua under lateral variations in bathymetry and on the role that lateral
circulation might have on ua. Observations on the transverse structure of ua are also
needed to test the theory. These are the issues addressed in this proposal.
Approach to address objectives
A combination of observations and numerical model experiments will be used to tackle
the objectives of this four-year-long investigation. Observations in two estuaries with
tidal currents that exceed 1 m/s will be used to address objective 1 and part of objective
2 in years 1, 2 & 3. Numerical simulations, based on the Regional Ocean Modeling
System (ROMS), will be used to address objective 2 in years 1 to 4.
9
Study Site
Observations to address objective 1 and part of objective 2 will be obtained in a tropical
Amazonian estuary in Brazil. This estuary is chosen because it exhibits tidal currents
≥1.1 m/s and weak freshwater input most of the year. In coastal Amazonia, there is a
marked seasonality in pluvial precipitation and freshwater input. Therefore, estuaries in
these locations with tidal currents >1 m/s (according to lower right corner of Fig. 7?) are
likely to exhibit residual flows induced by asymmetric tidal mixing most of the year.
Periods influenced by freshwater input will provide further comparisons to theory relative
to residual flows induced by river and density gradients (Cheng et al., 2011, Cheng et
al., 2013). This estuary is also optimal to test the two working hypothesis as there are
portions of the basin where lateral effects are expected to be relevant and other parts
where lateral variability should be weak.
The Amazonian system to study, the Taperaçu estuary, is one of 23 estuaries in a
region characterized by remarkable coastline irregularities (Souza FIlho et al., 2009).
This estuary is located near the city of Bragança, very close to the Equator at 0º53’S
(Fig. X). It is a funnel-shaped estuary with a width of ~3 km at the entrance and
decreasing to 250 m at Castelo, 13 km upstream, which is the junction with Taici creek.
Along its length, the estuary exhibits 3 meanders and a rather complicated bathymetry
of channels and shoals that shift from one side of the estuary to the other. The
entrance features two channels with depths of 10 and 6 m, with respect to mean low
10
water. Near the head of the estuary, the bathymetry becomes much simpler as it
displays a U-shape.
Tides in the Taperaçu estuary are semidiurnal and markedly distorted from the entrance
to the head (Asp et al., 2012). Mean tidal amplitudes attenuate from 2.5 m at the
entrance to 1.5 m toward the head. Tidal currents exceed 1.2 m/s in both ebb and flood
and are close to 90º ahead of tidal elevation (Asp et al., 2012), which is typical of “short
estuaries” (Friedrichs, 2010). The pluvial and wind regimes of the coastal Amazon area
are determined by the position of the Inter-tropical Convergence Zone (ITCZ). In
August-September the ITCZ remains close to 10ºN, while in March-April it migrates to a
couple of degrees south of the Equator, directly affecting coastal Amazonia with
precipitation (Souza Filho et al., 2009). Most of the rainfall (73%) occurs in this season
of ITCZ influence (Moraes et al., 2005). This is also the season of weakest winds but
largest swell influence (Pianca et al., 2010). Wind waves tend to be dissipated at ebb
shoals outside the estuary and are thought to play a lesser role in the circulation of the
estuary (Asp et al., 2012). Thus, the Taperaçu estuary represents an ideal place to
address the objectives of this investigation with its strong tidal forcing, weak freshwater
input. Besides, it shows transverse cross-sections near the entrance where lateral
11
variations are expected to be influential (for objective 2) and sections where lateral
processes may be minimal (for objective 1).
Methods to address objective 1
Objective 1 (obtain observational evidence on the relative relevance of asymmetric tidal
mixing in the residual circulation of estuaries) will be studied exclusively with
observations. It is evident from equation Y that the observations needed to assess the
influence of ua on the residual flow are current velocity u and vertical eddy viscosity Az
profiles. For gravitational circulation, measurements of river discharge, density field and
bathymetry, as well as of Az, are needed.
Moored instruments will be deployed at two locations: one near the head of the estuary,
at Castelo, and one at the mouth. These two sites are within one tidal excursion from
each other but will provide contrasting conditions because of their dissimilar bathymetry
and width. The near-head mooring at Castelo will allow addressing objective 1. Time
series of current velocity profiles will be obtained over one month, in two consecutive
months, at the deepest part of the cross-section during dry (year 2 of 4) and wet (year 3
of 4) seasons. The strategy will be to measure 0.25 m bins, every second, during 10
minute-bursts with an RD Instruments 1200 kHz acoustic Doppler current profiler
(ADCP, in our possession) operating on mode 12 (ping rate up to 20 Hz). Three bursts
will be recorded per hour, with 10 minutes of no-data between bursts. These are
settings that maximize the battery life and time coverage of up to one month. After the
first month of data collection, the deployment will be repeated to sample the following
month.
Such sampling strategy will allow estimates of Reynolds stresses <u’’w’’> and <v’’w’’>
(where double primes denote fluctuations relative to a 10-min average, itself
represented by the <>) with the variance method (e.g. Lohrman et al., 1990, Stacey and
Monismith, 1999). Data collection will also allow estimates of turbulence dissipation 
via the structure function (Wiles et al. 2006). This approach has proven successful in a
one-month deployment at the James River, Virginia (Figure from Kim). Values of  will
be supplemented with tidal-cycle profiles obtained with a self-contained microstructure
profiler (SCAMP, manufactured by Precision Instruments Inc.) through estimates of
Thorpe length scales (Lt). These measurments will be obtained during trips to deploy
and retrieve the ADCP. Measured values of <u’’w’’> with the ADCP and  with the
SCAMP and with the ADCP will then be used to derive values of Az. Values of  derived
with the SCAMP will cover a much shorter period than the period sampled by the
ADCP. However, these records will provide additional estimates of  to assess the
consistency of Az values. This procedure will be described in the Analysis section.
Analysis
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Timeline
Project Management
Broader Impacts
This proposal seeks to study a phenomenon that can affect the entire US eastern
seaboard. Findings generated from the study will help understand the causes for the
appearance of high frequency (periods smaller than the inertial period) perturbations,
semidiurnal residuals, that modify storm surges. Such perturbations can reach
amplitudes of up to ~0.3 m above and below subtidal surge, which for hurricane Sandy
represented ~50% for the total surge signal in the South Atlantic Bight. For Irene, the
semidiurnal surge was closer to 60% of the total surge in the same region. Tide-storm
interactions that cause semidiurnal residuals will also affect the timing of maximum
surge, relative to high tide. Probability density functions related to arrival of storm
surges will thus be affected by semidiurnal residuals. Better understanding of these
residuals will also help to refine storm surge predictions and risk analysis for the entire
eastern US seaboard.
This proposal will use data already available from NOAA. Objectives require no
supplementary efforts for data to be collected by this project. In this way, ongoing
efforts and investments are being leveraged. In addition to disseminating findings in
peer-reviewed journals, we will disseminate our results to coastal managers in northern
Florida and Georgia (water management districts and estuarine research reserves),
where the semidiurnal residuals amplify. We will disseminate findings also through
newsletters of the Southeast US Atlantic Coastal Ocean Observing System
(SEACOOS) and the Mid-Atlantic Regional Association Coastal Ocean Observing
(MARACOOS).
Project will support one graduate student, Kirsten Nielsen, at the University of Florida
who will be co-supervised by M. Olabarrieta and A. Valle-Levinson. Kirsten will be in
charge of compiling and analyzing data, together with Valle-Levinson, and of
implementing and analyzing numerical simulations in conjunction with Olabarrieta.
Kirsten will also participate in the dissemination of results to K-12 students in
Gainesville, Florida. This activity will make her formulate results of the project in an
understandable way to lay audiences and will also allow her to practice her presentation
skills.
The project will also support one undergraduate student at University of Florida to help
with identification of storms, data retrieval, compilation and analysis. The
undergraduate student will be selected from applicants to the University Scholars
program, which provides a small stipend to participants. In order to encourage the
recruitment of highly qualified students we will supplement the stipend offered by the
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University. We will actively attempt to recruit a member from an underrepresented
group, through the Minority Mentorship Program, also organized by the University.
Depending on the student’s standing, we will recruit the same or different student each
of the three years. The undergraduate student will participate in the project during fall
and spring semesters, but not in the summer.
During the summer, a high school student from an underrepresented group will also be
recruited to help with the same activities. The high school student will be recruited
through announcements to teachers in the 5 high schools of Gainesville: Buchholz,
Eastside, Gainesville, Loften and Santa Fe. Valle-Levinson delivers lectures on Ocean
Sciences to those schools occasionally so he knows the teachers. Selection will be
made on the basis of teacher recommendations and a brief essay on how the student
thinks this experience would benefit her/his scientific knowledge.
The purpose of recruiting undergraduate and high school students is to spark their
interest in the topic. Students will be taken for visits to the NOAA gauging stations at
Mayport and Fernandina Beach, which are the closest to Gainesville, for them to see
how data are collected. Pre-internship and post-internship questionnaires will be
carried out to assess the effectiveness of the research experience for these students.
Qualitative assessment will be effected through interviews with students before their
participation in the project and after their participation. Interviews will ask open-ended
questions such as: How do you expect this program to benefit your professional career?
Why are you participating in this program? How important do you think is to understand
perturbations to storm surge? How will your research allow better adaptations and
mitigation strategies for global sea level rise? The same questions will be asked after
the conclusion of the activity in order to determine whether there is a change in attitude
of the participants. Additional questions at the conclusion of the program will ask how to
improve the experience and whether the participants would recommend the program to
other students.
Material and relevant results derived from this project will also be incorporated in
classes taught by the PIs at the University of Florida: Physical Oceanography, Data
Analysis, Linear Waves, Littoral Processes, and Fluid Mechanics. The involvement of
both PIs, Valle-Levinson and Olabarrieta, enhances the participation of
underrepresented groups in science.
Results from Prior NSF Support
“Collaborative Research: Asymmetric circulation in wind-driven bays. OCE-0551923 &
OCE-0726697. 8/1/04-7/31/07 & 10/1/07-9/30/09.” Intellectual Merit. The grant
supported observations, analysis, analytical and numerical experiments on wind-driven
and tidally driven circulations in semi-enclosed basins affected by rotation. A total of 19
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publications have resulted from this grant and 2 more have been submitted. Broader
Impacts. This project trained 2 PhD students and one Post-Doctoral investigator.
“Panamerican Advanced Studies Institute on Contemporary Issues in Estuarine
Physics. IOISE-0614418. 09/06/06-01/03/08.” Intellectual Merit. The grant sponsored a
course on estuarine physics with the participation of 30 advanced PhD students and
postdoctoral researchers from the Americas and 12 lecturers. Broader Impacts.
Lectures were compiled in a textbook published by Cambridge University Press.
“Collaborative Research: Impact of secondary circulation and mixing of estuarine
exchange flows. OCE- 0825876. 08/2008-08/2012.” Intellectual Merit. The grant
supported observations and analysis on lateral variations in mixing in estuaries. A total
of 6 publications have resulted from this grant and 5 more are in preparation. Broader
Impacts. The grant sponsored 4 PhD students and one undergraduate student.
“Reversing circulation structure in arid, tropical estuaries. OISE-1157675. 05/15/1204/30/13.” Intellectual Merit. The grant is supporting preliminary data collections in wet
and dry seasons at a tropical estuary in northern Brazil, where hypersaline conditions
prevail during part of the year. The data will provide preliminary information to prepare a
full-scale proposal to NSF. Broader Impacts. Three graduate students from the US have
participated in the field work in Brazil. Moreover, a total of 20 Panamerican students will
participate in May in a short course on the potential effects of sea level rise on estuarine
hydrodynamics.
15
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