Subsided Island Restoration Plan in the Sacramento-San Joaquin Delta Subsided Islands

Subsided Island Restoration Plan in
the Sacramento-San Joaquin Delta
The Natural Heritage Institute
Subsided Islands
Subsided Islands
•Microbial
oxidation
•Consolidation
and shrinkage
•Wind erosion
•Burning
•Withdrawal of
natural gas and
groundwater
Seismic Vulnerability
Probability of Exceedance vs. Number of Levee Failures For 50 Year Return Period
Source: CALFED, 2000. Seismic Vulnerability of the Sacramento-San Joaquin Delta Levees. Levees
and Channels Technical Team, Seismic Vulnerability Sub-Team
Flooded Islands
Mildred Island
Leveed in 1921
Flooded in 1983
Salinity Intrusion
Vulnerable Levees
Moderate Earthquake (25%
chance over 50 years)
>10 Levee Breaches
Subsided Islands
Flooded Island(s)
Saltwater intrusion
Salt H20
Erosion on unprotected
interior faces of levees
Delta water exports shut
down until levees can be
repaired and salinity levels
reduced.
Salinity Impacts
Mean Tidal Daily Salinity at Rock Slough
Source: DWR, 1990. DWRDSM1.
Twitchell Island Study
Demonstration of
Techniques for
Reversing the
Effects of
Subsidence in the
Sacramento San
Joaquin Delta
We know we can
reverse subsidence,
the question is how
long will it take?
USGS-DWR Subsidence Mitigation Wetland Ponds, Twitchell Island
14
Mean Accretion (cm)
12
Core Bulk densities: 0.07 to 0.19 g/cm3
Underlying peat: 0.36 to 0.51 g/cm3
10
8
6
4
2
36.0
36.4
36.4
35.2
35.2
37.9
37.3
35.1
0
W1998 E1998 W1999 E1999 W2000 E2000 W2001 E2001
Mean accretion rates (+ Standard Error) from cryogenic soil cores.
West Pond (W) flooded to 25 cm, East Pond (E) flooded to 55 cm.
Black areas and numbers are organic matter %.
Data are Preliminary and Subject to Change
Conculsions/Next Steps
• Flooded conditions arrest
further subsidence
• Need additional water
quality analysis
• Need to expand test plots to
larger scale
Strategic Island Selection
Bethel
Island
Subsided
Volume (mcy)
Bradford
Island
Holland
Island
Hotchkiss
Tract
Jersey
Island
Sherman
Island
Twitchell
Island
Webb
Tract
30
27
46
4
34
142
57
97
Risk of Seismic
Failure
Med
Med
Med
Med
Med
High
Med
Med
Percent Salinity
Increase
-
-
12%
-
40%
41%
19%
24%
Percent
CALFED
Agency Owned
-
-
-
-
-
84%
83%
-
Other Public
Ownership
<10
%
11%
<10%
<10%
95%
2%
-
5%
Adjacent to
Tidal Wetlands
No
No
No
No
No
Yes
No
Yes
Landscape Gradient Conceptual Model: Migration corridors composed of emergent aquatic
vegetation and shallow tidal sloughs provide transient habitat value to migrating aquatic and nearaquatic species not currently provided by riprap and steep-sided levee banks. Regional linkages
reduce isolation effects of piecemeal project implementation. Regional biogeochemical cycling is
linked to sediment movement and establishment and maintenance of first-order tidal channel
networks.
Sherman Island
Aerial photo
Existing Levees
Elevation
Elevation and aerial
Percent Organic Content of Soils
Soils map
5-Year Restoration Design
16,000 AF
Draft
56,000 AF
Draft
Rice fill
demo site
6-12 MCY
200 acres of
restored tidal
wetlands
Cutoff levee
110,000 CY
Cross levee
840,000 CY
Tule ponds
(1,022 acres)
440,000 CY
10-Year Restoration Design
220 acres of
restored tidal
wetlands
Cutoff levee
140,000 CY
32,000 AF
Draft
24,000 AF
Draft
1,200 acres of
restored tidal
wetlands
Cross levee
1.7 MCY
Expanded tule
ponds
(1,830 acres)
30-Year Restoration Design
Expanded
tule ponds
(3,135 acres)
Cross levee
1.3 MCY
Cross levee
580,000 CY
Rice fill
16-32 MCY
2,000 acres of
restored tidal
wetlands