Transcript pptx

Spatial and Temporal Trends in Tidal Flat
Shape in San Francisco Bay
Josh Bearman, Carl Friedrichs, Bruce Jaffe, Amy Foxgrover
Main Points
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.
Aerial Photo of flats near Dumbarton Bridge, South San Francisco Bay
Courtesy http://asapdata.arc.nasa.gov
Spatial and Temporal Trends in Tidal Flat
Shape in San Francisco Bay
Josh Bearman, Carl Friedrichs, Bruce Jaffe, Amy Foxgrover
Visit Josh at TheHotSeats.net
Main Points
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.
Aerial Photo of flats near Dumbarton Bridge, South San Francisco Bay
Courtesy http://asapdata.arc.nasa.gov
South Bay Salt Pond Project
• 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.
What moves sediment across flats?
Ans: Tides plus concentration gradients; (i) Due to energy gradients:
Tidal advection
High energy waves
and/or tides
Low energy waves
and/or tides
Higher sediment concentration
Tidal advection
High energy waves
and/or tides
Low energy waves
and/or tides
Lower sediment concentration
1
What moves sediment across flats?
Ans: Tides plus concentration gradients; (ii) Due to sediment supply:
Tidal advection
Sediment source from
river or local runoff
Low energy waves
and/or tides
Higher sediment concentration
“High concentration
boundary condition”
Net settling of
sediment
Tidal advection
Lower sediment concentration
“High concentration
boundary condition”
Net settling of
sediment
2
Maximum tide and wave orbital velocity distribution across a linearly sloping flat:
z = R/2
h(t) = (R/2) sin wt
h(x,t)
z=0
z = - R/2
x=0
x
x = xf(t)
Spatial variation in tidal current magnitude
Spatial variation in wave orbital velocity
3.0
1.2
UW90/UW90(L/2)
UT90/UT90(L/2)
1.4
1.0
0.8
Landward TideInduced Sediment
Transport
0.6
0.4
0.2
x=L
Z(x)
0
0.2
0.4
0.6
x/L
0.8
1
2.5
2.0
Seaward Wave-Induced
Sediment Transport
1.5
1.0
0.5
0
0.2
0.4
0.6
0.8
1
x/L
3
Spatial and Temporal Trends in Tidal Flat
Shape in San Francisco Bay
Josh Bearman, Carl Friedrichs, Bruce Jaffe, Amy Foxgrover
Main Points
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.
Aerial Photo of flats near Dumbarton Bridge, South San Francisco Bay
Courtesy http://asapdata.arc.nasa.gov
Spatial and Temporal Trends in Tidal Flat
Shape in San Francisco Bay
Josh Bearman, Carl Friedrichs, Bruce Jaffe, Amy Foxgrover
Main Points
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.
Aerial Photo of flats near Dumbarton Bridge, South San Francisco Bay
Courtesy http://asapdata.arc.nasa.gov
South San Francisco Bay Tidal Flats:
South San
Francisco Bay
700 tidal flat profiles in 12 regions,
separated by headlands and creek mouths.
MHW to MLLW
MLLW to - 0.5 m
San Mateo Bridge
0
4 km
Dumbarton Bridge
12
1
11
2
3
10
4
9
8
5
Semi-diurnal tidal
range up to 2.5 m
7
6
6
Dominant mode of profile shape variability
determined through eigenfunction analysis:
Amplitude (meters)
Across-shore structure of first eigenfunction
South San
Francisco Bay
MHW to MLLW
First eigenfunction
(deviation from mean profile)
90% of variability explained
MLLW to - 0.5 m
San Mateo Bridge
Mean + positive eigenfunction score = convex-up
Mean + negative eigenfunction score = concave-up
Dumbarton Bridge
Normalized seaward distance across flat
Height above MLLW (m)
Mean profile shapes
12 Profile regions
1
11
2 3
10
4
9
5
4 km
6
8
7
Normalized seaward distance across flat
7
Significant spatial variation is seen in convex (+) vs. concave (-) eigenfunction scores:
8
4
10-point running average
of profile first
eigenfunction score
Convex
Eigenfunction score
12 Profile regions
0
1
Concave
2 3
-4
4
2
5
0
-2
8
9
4 km
10
6
8
7
6
11
3
9
5
Convex
2
1
10
4
7
Regionally-averaged
score of first
eigenfunction
11
4
Concave
12
Tidal flat profiles
8
11
10
2 3
4
9
5
2.3
0
2.2
-2
Concave
3
5
7
9
Profile region
11
.6
r = + .92
.4
.2
0
0
-2
-.2
Concave
1
3
5
7
9
Profile region
11
-.4
2
r = - .82
0
1
-2
2.1
.8
Deposition
2
Fetch
Length
Concave
1
3
1
Convex
4
Eigenfunction score
r = + .87
3
2
5
7
9
Profile region
11
Convex
4
7
6
Convex
4
Eigenfunction score
2
2.4
Net 22-year deposition (m)
Eigenfunction score
Tide
Range
1
Eigenfunction score
2.5
Mean tidal range (m)
Convex
0
40
30
2
Grain
Size
0
20
r = - .61
-2
10
Concave
1
3
5
7
9
Profile region
11
8
Average fetch length (km)
1
4 km
4
Profile
regions
12
Mean grain size (mm)
-- Tide range & deposition are positively correlated
to eigenvalue score (favoring convexity).
-- Fetch & grain size are negatively correlated to
eigenvalue score (favoring concavity).
0
9
Tide + Deposition – Fetch
Explains 89% of Variance in Convexity/Concavity
South San
Francisco
Bay
4
Observed Score
Modeled Score
MLLW to - 0.5 m
San Mateo Bridge
r = + .94
r2 = .89
2
0
Dumbarton Bridge
Modeled Score
= C1 + C2 x (Deposition)
+ C3 x (Tide Range) – C4 x (Fetch)
Concave
-2
1
3
5
7
Profile region
Profile
regions
12
1
9
11
10
2 3
4
9
5
6
11
Flat elevation
Eigenfunction
score
Convex
MHW to MLLW
8
7
Seaward distance across flat
10
Spatial and Temporal Trends in Tidal Flat
Shape in San Francisco Bay
Josh Bearman, Carl Friedrichs, Bruce Jaffe, Amy Foxgrover
Main Points
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.
Aerial Photo of flats near Dumbarton Bridge, South San Francisco Bay
Courtesy http://asapdata.arc.nasa.gov
(Jaffe et al. 2006)
11
Eigenfunction
score
10-point running average
of profile first
eigenfunction score
Regions
12
11
10
1
2 3
4
9
5
6
Eigenfunction
score
4 km
8
7
Regionally-averaged
score of first
eigenfunction
12
Eigenfunction
score
10-point running average
of profile first
eigenfunction score
Regions
12
11
10
1
2 3
4
9
5
6
Eigenfunction
score
4 km
8
7
Regionally-averaged
score of first
eigenfunction
Inner regions (5-11) tend
to be more convex
12
Variation of External Forcings in Time:
Sed load at delta
(Ganju et al. 2008)
South San
Francisco Bay
MHW to MLLW
MLLW to - 0.5 m
San Mateo Bridge
Dumbarton Bridge
San Jose
13
- Trend of Scores in Time (+ = more convex, - = more concave)
1
11
10
2 3
4
Region 2
Region 1
Region 3
Score
-1
-1
9
5
6
8
7
0
-2
-1
Region 4
Region 6
Region 5
0
Score
1
0
0
-2
-1
Region 7
-2
Region 8
4
Score
4 km
0
-2
2
0
4
2
2
1
0
0
Region 9
Region 12
Region 11
Region 10
Score
Regions
12
0
2
1
-1
1
1900
1950
Year
2000
1900
1950
Year
2000
-1
1900
1950
Year
2000
14
- 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)
1
11
10
2 3
4
Region 2
Region 1
Score
-1
-1
9
5
8
7
Region 3
6
Region 6
Outer
regions
0
-2
-1
Region 4
Region 5
0
Score
1
0
0
-2
Inner regions
-1
Region 7
-2
Region 8
4
Score
4 km
0
-2
2
0
4
2
2
1
0
0
Region 9
0
2
Outer
regions
Region 12
Region 11
Region 10
Score
Regions
12
1
-1
1
1900
1950
Year
2000
1900
1950
Year
2000
-1
1900
1950
Year
2000
14
- Trend of Scores in Time (+ = more convex, - = more concave)
CENTRAL VALLEY SEDIMENT DISCHARGE
- Outer regions become more concave as
sediment discharge decreases
Region 2
4
4
2
-2
-1
Score
*
-2
2
0
2
-1
Region 8
4
4
Score
6
6
2
4
0
2
6
4
2
-2
Region 9
2
*
6
2
4
0
2
1
2
6
4
1
2
0
Region 12
0
6
*
1
2
1900
1950
Year
2000
6
4
4
-1
2
2000
6
4
Region 11
Region 10
1950
Year
0
4
Region 7
Score
Region 6
*
6
4
1900
2
Region 5
1
6
4
-2
2
Region 4
0
*
6
-1
2
1900
1950
Year
2000
4 km
9
5
8
7
Sediment
Disch. (MT)
*
0
2 3
6
Sediment
Disch. (MT)
6
Region 3
0
11
10
4
Sediment
Disch. (MT)
*
-1
-1
1
Sediment
Disch. (MT)
Score
Region 1
Regions
12
Outer
regions
Inner regions
*SIGNIFICANT
Outer
regions
15
- Trend of Scores in Time (+ = more convex, - = more concave)
PACIFIC DECADAL OSCILLATION
- No significant relationship to changes in shape
1
11
10
2 3
4
Region 2
-1
1
0
0
0
-1
0
Score
1
1
1
0
-2
0
0
-1
-1
1
4
1
2
1
2
0
2
0
1
0
0
-1
0
-1
0
-1
-1
-1 -2
Region 8
4
0
0
Region 7
Region 12
1
1
1
0
2
1
0
0
0
-1
1
1900
1950
Year
2000
-1
1900
1950
Year
2000
-1 -1
Outer
regions
Inner regions
Region 9
Region 11
Region 10
7
PDO Index
1
PDO Index
Region 6
Region 5
0
8
-1
-1
Region 4
Score
1
-2
-1
9
5
6
0
4 km
PDO Index
1
-1
-2
Score
Region 3
-1
1900
1950
Year
2000
PDO Index
Score
Region 1
Regions
12
Outer
regions
16
- 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
Region 2
-.2
-.4 -2
Region 4
0
.2
Score
.3
0
0
Score
.6
*
.3
0
0
2
*
Score
2
.5
1
0
0
.6
.3
0
Region 12
Region 11
.6
*
*
0
.3
0
1
1950
Year
1
Region 9
0
Region 10
1900
0
-.3 -2
Region 8
4
*
0
2000
.4
0
-.2 -1
2
2
Region 6
1
Region 7
4
-.4
Region 5
*
-2
0
0
-.3 -1
-2
0
.2
0
1
0
-1
1900
1950
Year
2000
-.2 -1
-.3
1900
1950
Year
2000
8
7
Bed
change (m)
0
0
4 km
9
5
6
Bed
change (m)
-1
4
Region 3
-1
11
10
2 3
Bed
change (m)
.3
1
Bed
change (m)
Score
Region 1
Regions
12
Outer
regions
Inner regions
*SIGNIFICANT
Outer
regions
17
- Trend of Scores in Time (+ = more convex, - = more concave)
SAN JOSE RAINFALL
- Inner regions more convex when
San Jose rainfall increases
Region 2
0
15
20
Score
0
15
-2
Region 6
* 15
0
Region 7
Region 8
*
2
0
20
4
15
2
10
0
20
20
1
10 -1
4
10
10
Region 5
*
0
15
10
10 -2
Region 9
20
2
20
15
1
15
10
0
10
Region 12
Region 11
Region 10
20
20
20
0
2
1
15
15
15
-1
1
1900
1950
Year
10
2000
1900
1950
Year
San Jose
Rainfall (in)
10 -1
Region 4
Score
15
-2
-2
Score
20
0
10 -1
2000
10
1900
1950
Year
2000
4 km
9
5
6
San Jose
Rainfall (in)
15
4
San Jose
Rainfall (in)
20
11
10
2 3
Region 3
20 -1
-1
1
San Jose
Rainfall (in)
Score
Region 1
Regions
12
8
7
San
Jose
Outer
regions
Inner regions
*SIGNIFICANT
Outer
regions
18
- Trend of Scores in Time (+ = more convex, - = more concave)
CHANGES IN TIDAL RANGE THROUGH TIME
- No significant relationships to temporal changes in tidal range
1
11
10
2 3
4
Region 2
-2
1.7 -1
1.7
Region 4
Score
0
1.8
0
0
-2
1.7 -1
Region 7
Region 8
1.8
4
Score
Region 6
1.8
1
2
1.7
0
1.7 -2
4
1.8 2
2
1
0
1.7 0
1.7
1.8
1.8
1.7
Region 12
1.8
0
2
1.8
1
-1
1
1900
1950
Year
1.7
2000
1900
1950
Year
1.7 -1
2000
Outer
regions
Inner regions
Region 9
Region 11
Region 10
7
1.7
Region 5
1.8
8
Tidal
Range (m)
0
-2
Score
1.8
9
5
6
Tidal
Range (m)
-1
1.8 0
4 km
Tidal
Range (m)
Score
1.8 -1
Region 3
1.7
1900
1950
Year
2000
Tidal
Range (m)
Region 1
Regions
12
Outer
regions
19
Temporal Analysis: Multiple Regression
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
–––
–––
Less 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)
12
1
2
11
San Jose
3
10
4
9
5
6
8
7
20
Spatial and Temporal Trends in Tidal Flat
Shape in San Francisco Bay
Josh Bearman, Carl Friedrichs, Bruce Jaffe, Amy Foxgrover
Main Points
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.
Aerial Photo of flats near Dumbarton Bridge, South San Francisco Bay
Courtesy http://asapdata.arc.nasa.gov