Spatial and Temporal Trends in Tidal Flat Shape in San Francisco Bay
Josh Bearman, Carl Friedrichs, Bruce Jaffe, Amy Foxgrover
Aerial Photo of flats near Dumbarton Bridge, South San Francisco BayCourtesy http://asapdata.arc.nasa.gov
1) On tidal flats, sediment (especially mud) moves away from high concentration
areas and towards areas of weaker energy.
2) Tides and/or abundant sediment supply favor a convex upward profile;
waves and/or sediment loss favor a concave upward profile.
3) South San Francisco Bay provides a case study supporting these trends,
both in space and in time.
Main Points
Spatial and Temporal Trends in Tidal Flat Shape in San Francisco Bay
Josh Bearman, Carl Friedrichs, Bruce Jaffe, Amy Foxgrover
Aerial Photo of flats near Dumbarton Bridge, South San Francisco BayCourtesy http://asapdata.arc.nasa.gov
1) On tidal flats, sediment (especially mud) moves away from high concentration
areas and towards areas of weaker energy.
2) Tides and/or abundant sediment supply favor a convex upward profile;
waves and/or sediment loss favor a concave upward profile.
3) South San Francisco Bay provides a case study supporting these trends,
both in space and in time.
Main Points
Visit Josh at TheHotSeats.net
• First ponds leveed in 1854
• Currently 26,000 acres of salt ponds in South Bay
• October, 2000• 61% of ponds sold to large
conglomerate of GOs, NGOs, private foundations.
South Bay Salt Pond Project
High energy wavesand/or tides
Higher sediment concentration
Lower sediment concentration
Tidal advection
Tidal advectionHigh energy waves
and/or tidesLow energy waves
and/or tides
Low energy wavesand/or tides
What moves sediment across flats? Ans: Tides plus concentration gradients; (i) Due to energy gradients:
1
Higher sediment concentration
Lower sediment concentration
Tidal advection
Tidal advectionSediment source from
river or local runoffLow energy waves
and/or tides
What moves sediment across flats? Ans: Tides plus concentration gradients; (ii) Due to sediment supply:
“High concentrationboundary condition”
Net settling of sediment
“High concentrationboundary condition”
Net settling of sediment
2
Maximum tide and wave orbital velocity distribution across a linearly sloping flat:
x x = xf(t)
Z(x)
z = R/2
z = - R/2x = 0
h(x,t)
h(t) = (R/2) sin wtx = L
z = 0
0 0.2 0.4 0.6 0.8 1
1.4
1.2
1.0
0.8
0.6
0.4
0.20 0.2 0.4 0.6 0.8 1
3.0
2.5
2.0
1.5
1.0
0.5
x/L x/L
UT9
0/U
T90(L
/2)
UW
90/U
W90
(L/2
)
Spatial variation in tidal current magnitude
Landward Tide-Induced Sediment
Transport
Seaward Wave-InducedSediment Transport
Spatial variation in wave orbital velocity
3
Spatial and Temporal Trends in Tidal Flat Shape in San Francisco Bay
Josh Bearman, Carl Friedrichs, Bruce Jaffe, Amy Foxgrover
Aerial Photo of flats near Dumbarton Bridge, South San Francisco BayCourtesy http://asapdata.arc.nasa.gov
1) On tidal flats, sediment (especially mud) moves away from high concentration
areas and towards areas of weaker energy.
2) Tides and/or abundant sediment supply favor a convex upward profile;
waves and/or sediment loss favor a concave upward profile.
3) South San Francisco Bay provides a case study supporting these trends,
both in space and in time.
Main Points
Spatial and Temporal Trends in Tidal Flat Shape in San Francisco Bay
Josh Bearman, Carl Friedrichs, Bruce Jaffe, Amy Foxgrover
Aerial Photo of flats near Dumbarton Bridge, South San Francisco BayCourtesy http://asapdata.arc.nasa.gov
1) On tidal flats, sediment (especially mud) moves away from high concentration
areas and towards areas of weaker energy.
2) Tides and/or abundant sediment supply favor a convex upward profile;
waves and/or sediment loss favor a concave upward profile.
3) South San Francisco Bay provides a case study supporting these trends,
both in space and in time.
Main Points
South San Francisco Bay Tidal Flats:
1
23
4
5
6
7
89
10
11
12
0 4 km
700 tidal flat profiles in 12 regions, separated by headlands and creek mouths.
Semi-diurnal tidal range up to 2.5 m
San Mateo Bridge
Dumbarton Bridge
South San Francisco Bay
MHW to MLLW
MLLW to - 0.5 m
6
San Mateo Bridge
Dumbarton Bridge
South San Francisco Bay MHW to MLLW
MLLW to - 0.5 m
Dominant mode of profile shape variability determined through eigenfunction analysis:
Ampl
itude
(met
ers)
Across-shore structure of first eigenfunction
Normalized seaward distance across flat
First eigenfunction (deviation from mean profile)90% of variability explained
Mean + positive eigenfunction score = convex-upMean + negative eigenfunction score = concave-up
Mean concave-up profile (scores < 0)Hei
ght a
bove
MLL
W (m
)
Mean profile shapes
Normalized seaward distance across flat
Mean tidal flat profile
Mean convex-up profile (scores > 0)
12 3
45
6 7
8
10
11
12 Profile regions
4 km
9
7
12 3
45
6 7
8
10
11
12 Profile regions
4 km
10-point running average of profile first
eigenfunction score
Convex
Concave
Convex
Concave
8
4
0
-4
Eige
nfun
ction
sco
re
Tidal flat profiles
4
2
0
-2
Regionally-averaged score of first
eigenfunction
9
Significant spatial variation is seen in convex (+) vs. concave (-) eigenfunction scores:
12
3 4
5 6
7
8
9 10
1112
8
-- Tide range & deposition are positively correlated to eigenvalue score (favoring convexity).-- Fetch & grain size are negatively correlated to eigenvalue score (favoring concavity).
12 3
45
6 7
8910
11
12 Profile regions
4 km
Profile region1 3 5 7 9 11
4
2
0
-2
3
2
1
0
Aver
age
fetc
h le
ngth
(km
) Convex
Concave
Eige
nfun
ction
sco
re
r = - .82
Fetch Length
1 3 5 7 9 11
4
2
0
-2
40
30
20
10
0
Profile region
Mea
n gr
ain
size
(mm
) Convex
Concave
Eige
nfun
ction
sco
re
r = - .61
Grain Size
1
.8
.6
.4
.2
0
-.2
-.41 3 5 7 9 11
4
2
0
-2
Profile region
Net
22-
year
dep
ositi
on (m
) Convex
Concave
Eige
nfun
ction
sco
re
Depositionr = + .92
Profile region1 3 5 7 9 11
4
2
0
-2
2.5
2.4
2.3
2.2
2.1
Mea
n tid
al ra
nge
(m)
Convex
Concave
Eige
nfun
ction
sco
re
Tide Ranger = + .87
9
12 3
45
6 7
8910
11
12 Profile regions
1 3 5 7 9 11
4
2
0
-2
r = + .94r2 = .89
Profile region
Observed ScoreModeled Score
Eige
nfun
ction
scor
e
Modeled Score = C1 + C2 x (Deposition)+ C3 x (Tide Range) – C4 x (Fetch)
Convex
Concave
Increased tide
range
Increased
deposition
Increased
fetch
Increased
grain size
Convex-upwards
Concave-upwards
Seaward distance across flat
Flat
ele
vatio
n
San Mateo Bridge
Dumbarton Bridge
South San Francisco Bay
MHW to MLLW
MLLW to - 0.5 m
Tide + Deposition – Fetch Explains 89% of Variance in Convexity/Concavity
10
Spatial and Temporal Trends in Tidal Flat Shape in San Francisco Bay
Josh Bearman, Carl Friedrichs, Bruce Jaffe, Amy Foxgrover
Aerial Photo of flats near Dumbarton Bridge, South San Francisco BayCourtesy http://asapdata.arc.nasa.gov
1) On tidal flats, sediment (especially mud) moves away from high concentration
areas and towards areas of weaker energy.
2) Tides and/or abundant sediment supply favor a convex upward profile;
waves and/or sediment loss favor a concave upward profile.
3) South San Francisco Bay provides a case study supporting these trends,
both in space and in time.
Main Points
12 3
45
6 7
8910
11
12 Regions
4 km
Eige
nfun
ction
scor
eEi
genf
uncti
onsc
ore
10-point running average of profile first
eigenfunction score
Regionally-averaged score of first
eigenfunction
12
12 3
45
6 7
8910
11
12 Regions
4 km
Eige
nfun
ction
scor
eEi
genf
uncti
onsc
ore
10-point running average of profile first
eigenfunction score
Regionally-averaged score of first
eigenfunction
Inner regions (5-11) tend to be more convex
12
San Mateo Bridge
Dumbarton Bridge
South San Francisco Bay
MHW to MLLW
MLLW to - 0.5 m
Sed load at delta
San Jose
Variation of External Forcings in Time:
(Ganju et al. 2008)
13
12 3
45
6 7
8910
11
12 Regions
4 km
Sco
reS
core
Sco
reS
core
-1
-2
0
-2
4
2
0
2
1
-1
0
-1
1
0
-1
4
2
0
0
-1
0
-2
0
-2
2
1
0
1
-1
Region 1
Region 4
Region 7 Region 8
Region 5
Region 2 Region 3
Region 6
Region 9
Region 12Region 11Region 10
1900 1950 2000 1900 1950 2000 1900 1950 2000Year Year Year
- Trend of Scores in Time (+ = more convex, - = more concave)
14
12 3
45
6 7
8910
11
12 Regions
4 km
Sco
reS
core
Sco
reS
core
-1
-2
0
-2
4
2
0
2
1
-1
0
-1
1
0
-1
4
2
0
0
-1
0
-2
0
-2
2
1
0
1
-1
Region 1
Region 4
Region 7 Region 8
Region 5
Region 2 Region 3
Region 6
Region 9
Region 12Region 11Region 10
1900 1950 2000 1900 1950 2000 1900 1950 2000Year Year Year
- Trend of Scores in Time (+ = more convex, - = more concave)- Outer regions are getting more concave in time (i.e., eroding)- Inner regions are not (i.e., more stable)
Inner regions
Outerregions
Outerregions
14
12 3
45
6 7
8910
11
12 Regions
4 km
Sco
reS
core
Sco
reS
core
-1
-2
0
-2
4
2
0
2
1
-1
0
-1
1
0
-1
4
2
0
0
-1
0
-2
0
-2
2
1
0
1
-1
6
4
2
6
4
2
6
4
2
6
4
2
6
4
2
6
4
2
6
4
2
6
4
2
6
4
2
6
4
2
6
4
2
6
4
2
Region 1
Region 4
Region 7 Region 8
Region 5
Region 2 Region 3
Region 6
Region 9
Region 12Region 11Region 10
1900 1950 2000 1900 1950 2000 1900 1950 2000S
edim
ent
Dis
ch. (
MT
)S
edim
ent
Dis
ch. (
MT
)S
edim
ent
Dis
ch. (
MT
)S
edim
ent
Dis
ch. (
MT
)Year Year Year
Inner regions
Outerregions
Outerregions
* * *
* *
*
*
*SIGNIFICANT
- Trend of Scores in Time (+ = more convex, - = more concave)CENTRAL VALLEY SEDIMENT DISCHARGE- Outer regions become more concave as sediment discharge decreases
15
12 3
45
6 7
8910
11
12 Regions
4 km
Sco
reS
core
Sco
reS
core
-1
-2
0
-2
4
2
0
2
1
-1
0
-1
1
0
-1
4
2
0
0
-1
0
-2
0
-2
2
1
0
1
-1
Region 1
Region 4
Region 7 Region 8
Region 5
Region 2 Region 3
Region 6
Region 9
Region 12Region 11Region 10
1900 1950 2000 1900 1950 2000 1900 1950 2000Year Year Year
1
0
-1
1
0
-1
1
0
-1
1
0
-1
1
0
-1
1
0
-1
1
0
-1
1
0
-1
1
0
-1
1
0
-1
1
0
-1
1
0
-1
PD
O In
dex
PD
O In
dex
PD
O In
dex
PD
O In
dex
Inner regions
Outerregions
Outerregions
- Trend of Scores in Time (+ = more convex, - = more concave)PACIFIC DECADAL OSCILLATION- No significant relationship to changes in shape
16
12 3
45
6 7
8910
11
12 Regions
4 km
Sco
reS
core
Sco
reS
core
-1
-2
0
-2
4
2
0
2
1
-1
0
-1
1
0
-1
4
2
0
0
-1
0
-2
0
-2
2
1
0
1
-1
Region 1
Region 4
Region 7 Region 8
Region 5
Region 2 Region 3
Region 6
Region 9
Region 12Region 11Region 10
1900 1950 2000 1900 1950 2000 1900 1950 2000Year Year Year
.3
0
-.3
.2
0
-.2
.6
.3
0
0
-.4
.3
0
-.3
0
-.2
-.4
.4
0
.6
.3
0
1
.5
0
.6
.3
0
.2
0
-.2
0
-.3
B
edch
ang
e (m
)
Bed
chan
ge
(m)
B
edch
ang
e (m
)
Bed
chan
ge
(m)
Inner regions
Outerregions
Outerregions
*SIGNIFICANT
- Trend of Scores in Time (+ = more convex, - = more concave)Relationship to preceding deposition or erosion- Inner and outer regions more concave after erosion, more convex after deposition
* *
* *
**
17
12 3
45
6 7
8910
11
12 Regions
4 km
Sco
reS
core
Sco
reS
core
-1
-2
0
-2
4
2
0
2
1
-1
0
-1
1
0
-1
4
2
0
0
-1
0
-2
0
-2
2
1
0
1
-1
Region 1
Region 4
Region 7 Region 8
Region 5
Region 2 Region 3
Region 6
Region 9
Region 12Region 11Region 10
1900 1950 2000 1900 1950 2000 1900 1950 2000Year Year Year
20
15
10
20
15
10
20
15
10
20
15
10
20
15
10
20
15
10
20
15
10
20
15
10
20
15
10
20
15
10
20
15
10
20
15
10
San
Jo
seR
ain
fall
(in
) S
an J
ose
Rai
nfa
ll (i
n)
San
Jo
seR
ain
fall
(in
) S
an J
ose
Rai
nfa
ll (i
n)
Inner regions
Outerregions
Outerregions
*SIGNIFICANT
- Trend of Scores in Time (+ = more convex, - = more concave)SAN JOSE RAINFALL- Inner regions more convex when San Jose rainfall increases
*
* *
18
SanJose
12 3
45
6 7
8910
11
12 Regions
4 km
Sco
reS
core
Sco
reS
core
-1
-2
0
-2
4
2
0
2
1
-1
0
-1
1
0
-1
4
2
0
0
-1
0
-2
0
-2
2
1
0
1
-1
Region 1
Region 4
Region 7 Region 8
Region 5
Region 2 Region 3
Region 6
Region 9
Region 12Region 11Region 10
1900 1950 2000 1900 1950 2000 1900 1950 2000Year Year Year
1.8
1.7
1.8
1.7
1.8
1.7
1.8
1.7
1.8
1.7
1.8
1.7
1.8
1.7
1.8
1.7
1.8
1.7
1.8
1.7
1.8
1.7
1.8
1.7
T
idal
Ran
ge
(m)
T
idal
Ran
ge
(m)
T
idal
Ran
ge
(m)
T
idal
Ran
ge
(m)
Inner regions
Outerregions
Outerregions
- Trend of Scores in Time (+ = more convex, - = more concave)CHANGES IN TIDAL RANGE THROUGH TIME- No significant relationships to temporal changes in tidal range
19
12
3
4
5
67
89
10
11
12
Significance (slope/std err)
Region Mult Reg Rsq CV Seds SJ Rainfall Dep/Eros
r1 0.82 4.21 ––– –––
r2 0.73 3.19 ––– –––
r3 0.71 3.07 ––– –––
r4 0.55 2.10 ––– –––
r5 0.95 8.18 ––– 3.43
r6 0.53 ––– ––– 1.51
r7 0.35 ––– 1.39 –––
r8 0.47 ––– 1.29 1.12
r9 0.66 2.03 ––– 2.4
r10 0.94 3.41 ––– 7.77
r11 0.46 1.05 ––– 1.37
r12 0.51 1.39 ––– –––
Temporal Analysis: Multiple RegressionLess Central Valley sediment discharge: Outer regions more concave.
More San Jose Rains: Inner regions more convex.
Recent deposition (or erosion): Middle regions more convex (or concave)
San Jose
20
Spatial and Temporal Trends in Tidal Flat Shape in San Francisco Bay
Josh Bearman, Carl Friedrichs, Bruce Jaffe, Amy Foxgrover
Aerial Photo of flats near Dumbarton Bridge, South San Francisco BayCourtesy http://asapdata.arc.nasa.gov
1) On tidal flats, sediment (especially mud) moves away from high concentration
areas and towards areas of weaker energy.
2) Tides and/or abundant sediment supply favor a convex upward profile;
waves and/or sediment loss favor a concave upward profile.
3) South San Francisco Bay provides a case study supporting these trends,
both in space and in time.
Main Points