Mc bride, aundrea tribal habitat conference 2010 final
-
Upload
northwest-indian-fisheries-commission -
Category
Travel
-
view
685 -
download
1
Transcript of Mc bride, aundrea tribal habitat conference 2010 final
POCKET ESTUARY RESTORATION FEASIBILITY ASSESSMENT
AND TOOLS DEVELOPED
AT TWO SITES IN WHIDBEY BASIN
Tribal Habitat Conference 2010
Aundrea McBride and Eric BeamerSkagit River System Cooperative
Camano Island State Park
Possession Park
We examined two sites in Whidbey Basin to determine the feasibility of restoring pocket estuary habitat. (The 2 were selected from an initial cut of 100 sites)
Restoration Feasibility Questions
If we restore habitat, will salmon and other fish use it?
Will restored habitat be sustainable ? Will a restored site become tidally
inundated? Will the channel be open in ~100 years?
What are the landscape-scale considerations for restoration ?
Fish Prediction Based on Compilation Assemblage from Skagit Bay Pocket Estuaries Juvenile chum and wild
Chinook salmon dominate the assemblage early in the year
followed by staghorn sculpins in late spring,
shiner perch and sticklebacks in summer, and
surf smelt in early fall. (Beamer et al. 2007).
Figure 2. Seasonal fish assemblages for shallow intertidal habitat in lagoon-type pocket estuaries with a salinity greater than 20 ppt. (from Beamer et. al. 2007)
A - Overall Fish Assemblage
0
50
100
150
200
250
Feb Mar Apr May Jun July Aug Sep Oct Nov Dec
Av
era
ge
Fis
h P
er
Se
t
B - Salmon Assemblage
0
20
40
60
80
100
120
Feb Mar Apr May Jun July Aug Sep Oct Nov Dec
Av
era
ge
Fis
h P
er
Se
t
C - Sculpin Assemblage
0
10
20
30
40
50
60
Feb Mar Apr May Jun July Aug Sep Oct Nov Dec
Av
era
ge
Fis
h P
er
Se
tD - Flatfish Assemblage
0.00.10.20.30.40.50.60.70.80.9
Feb Mar Apr May Jun July Aug Sep Oct Nov Dec
Av
era
ge
Fis
h P
er
Se
t
A - S kagit B ay, Lagoon P E S hallow
I n t er t idal, >2 0 ppt
0
5 0
10 0
15 0
2 0 0
2 5 0
S. Prickleback
Gunnels
Pipefish
Peamouth Chub
Stickleback
Shiner Perch
Surf Smelt
Sandlance
Herring
Salmon
B - S kagit B ay, Lagoon P E S hallow
I n t er t idal, >2 0 ppt
0 . 0
2 0 . 0
4 0 . 0
6 0 . 0
8 0 . 0
10 0 . 0
12 0 . 0Bull trout
Cutthroat
Chum0+
Pink0+
Coho (H)
Coho (W)
Chin (H)
Chin (W)
C - S kagit B ay, Lagoon P E S hallow
I n t er t idal, >2 0 ppt
0 . 0
10 . 0
2 0 . 0
3 0 . 0
4 0 . 0
5 0 . 0
6 0 . 0
Prickly Sculpin
Pacific Staghorn
Other MarineSculpins
D - S kagit B ay, Lagoon P E S hallow I n t er t idal,
>2 0 ppt
0 . 0
0 . 2
0 . 4
0 . 6
0 . 8
1. 0English Sole
Starry Flounder
Predicting Channel Sustainability
Tools we used:
A hydrodynamic model (a refinement of the Whidbey Basin model incorporating finer scale LiDAR data, a theoretical bathymetry for pocket estuary channels and marshes developed from channel cross section data at other sites, and field maps of the sites)
Sediment grain size distribution data, and
Hydraulic geometry relationships.
We applied the tools to two restoration scenarios at Possession Park, and
Figure 5. Site map. Sediment moves from the bluff to the spit. The spit is an accretion shoreform (net sediment gain). The pink area behind the spit is low (below MHHW) as is the wetland (green area). The possible relict channel is mapped on darker vegetation that stands out against the pervasive vegetation in the low areas. The shape of the vegetation is typical of tidal channels (sinuous). The stream continues up the slope beyond what is shown. The parking area, restroom building, road and some trails are on fill. The north parking lot is uneven in elevation and has low spots.
one scenario at Camano Island
State Park
Answers From The Model
high tide
low tide flood tide
ebb tide
Figure 9. Tidal inundation model for scenario 1. Once connected to tidal inundation at the proposed location, the entire existing marsh surface would be flooded at high tide. Arrow length represents tidal velocity. Arrow direction indicates tidal flow direction across the marsh surface. Colors indicate bed shear stress—maximum occurs at the inlet channel during ebb tide. The diagrams represent water on the marsh surface and do not represent bridges or other built structures.
The existing marsh will get wet if connected to Possession Sound
Even more so if scenario 2 is implemented
high tide ebb tide
low tide flood tide
Figure 10. Tidal inundation model for scenario 2. Once connected to tidal inundation at the proposed location, the entire marsh surface of the existing marsh would be flooded at high tide. Arrow length represents tidal velocity. Arrow direction indicates tidal flow direction. Colors indicate bed shear stress—maximum bed occurs at the inlet channel during ebb tide. The diagrams represent water on the marsh surface and do not represent bridges or other built structures.
Low TideFlood
High Tide Ebb
Tool #2: Sediment Data
To predict the critical shear stress for clearing sediments from the inlet channel deposited by longshore drift
Comparing Measured Grain Size to Modeled Shear Stress
crit = Rg(s – f)Dj
where crit = the critical shear stress value for the Dj measured in Pascals, j =the grain diameter cumulative frequency by weight (dimensionless), s = the sediment density (2.65 kg m-3), f = the density of marine water (1.025 kg m-3), g = the acceleration due to gravity (m/sec2), and R = 0.003 is Shield’s parameter for gravel dominated sediments.
Table 1. Comparing crit to the bed shear stress calculated by the hydrodynamic model.
Scenario crit D50 (PA) crit D75 (PA) bed from model (PA) peak velocity from
model (m/s) 1 4.18 11.47 10 1.77 2 4.18 11.47 10 1.59
Table 1. Comparing crit to the bed shear stress calculated by the hydrodynamic model.
Grain size fraction by weight
Grain diameter (mm)
crit (Pascals)
bed (Pascals)
peak velocity from model (m/s)
D50 5 2.39 10 1.97
D65 9.6 4.59 10 1.97
D80 13.5 6.45 10 1.97
D85 20 9.56 10 1.97
D90 25 11.95 10 1.97
Tool #3: Hydraulic Geometry
To predict if the proposed inlet channel size will be at equilibrium relative to the pocket estuary size based on a regression of width to size ratios for similar, stable pocket estuaries in Whidbey Basin.
Relationship Between Inlet Channel Width and Pocket Estuary Area
y = 9.8837x0.4154
R2 = 0.473p = 0.013
y = 3.8879x0.5152
R2 = 0.9063
1
10
100
1000
10000
0.1 1 10 100 1000 10000 100000
total intertidal area (ha)
inle
t ch
ann
el w
idth
(m
)
Whidbey Basin pocket estuaries
Williams et al. 2002 San Francisco Bay data
scen
ario
2
scen
ario
1
Relationship Between Inlet Channel Width and Pocket Estuary Area
y = 9.8837x0.4154
R2 = 0.473p = 0.013
y = 3.8879x0.5152
R2 = 0.9063
1
10
100
1000
10000
0.1 1 10 100 1000 10000 100000
total intertidal area (ha)
inle
t ch
ann
el w
idth
(m
)
Whidbey Basin pocket estuaries
Williams et al. 2002 San Francisco Bay data
Possession Predictions
Scenario 1 is probably too small to be sustainable based on comparison, but scenario 2 could be sustainable based on size (just barely)
Scenario 2 would require inlet channel clearing or some type of engineering solution to clear the coarsest 25% of sediment
Camano Predictions
This site is on the small end, but it is probably sustainable if restored. Channel clearing could be improved by 2 factors: The inlet could be located down drift from
the boat ramp to divert the coarsest 15% of sediments.
The hydraulic head due to freshwater has not been considered and will improve inlet bed shear stress for clearing sediment, especially in the winter when the coarse sediment will be coming through.
Landscape-Scale Context