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Prospect Island
Ecosystem Restoration Project
Solano County, California
Environmental Assessment/
Initial Study
June 2001
US Army Corps
of Engineers
Sacramento District
Department of
Water Resources
State of California
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CONTENTS
1.0
PURPOSE AND NEED FOR ACTION
1
1.1
Proposed Action ....................................................................................................................1
1.2
Purpose and Need for Action ................................................................................................1
1.3
Authority and Background .....................................................................................................1
1.4
Location and Site Description................................................................................................3
1.5
Purpose and Scope of EA/IS ................................................................................................3
1.6
Decisions Needed .................................................................................................................3
2.0
ALTERNATIVES .................................................................................................................................4
2.1
Background ...........................................................................................................................4
2.2
General Description of Alternatives .......................................................................................4
2.3 Open Breach (40-foot-wide) Alternative.................................................................................7
2.4 Proposed Action - Dual Arched Culvert .................................................................................7
2.5 No Action ...............................................................................................................................9
3.0
AFFECTED ENVIRONMENT AND ENVIRONMENTALCONSEQUENCES
12
3.1
Environmental Resources Eliminated from Detailed Analysis ...............................................12
3.1.1 Climate ........................................................................................................................12
3.1.2 Geology/Geography ....................................................................................................12
3.1.3 Water Supply...............................................................................................................13
3.1.4 Water Elevations and Tidal Action ..............................................................................13
3.1.5 Traffic and Circulation..................................................................................................14
3.1.6 Noise ...........................................................................................................................14
3.1.7 Esthetics......................................................................................................................14
3.1.8 Hazardous, Toxic, and Radiological Materials.............................................................15
3.2
Land Use ...............................................................................................................................15
3.2.1 Basis of Significance ...................................................................................................15
3.2.2 Baseline Conditions.....................................................................................................15
3.2.3 Effects..........................................................................................................................17
3.2.4 Mitigation .....................................................................................................................17
3.3
Vegetation and Wildlife..........................................................................................................17
3.3.1 Basis of Significance ...................................................................................................17
3.3.2 Baseline Conditions.....................................................................................................17
3.3.3 Effects..........................................................................................................................21
3.3.4 Mitigation .....................................................................................................................23
3.4
Special Status Species..........................................................................................................23
3.4.1 Basis of Significance ...................................................................................................23
3.4.2 Baseline Conditions.....................................................................................................24
3.4.3 Effects..........................................................................................................................25
3.4.4 Mitigation .....................................................................................................................28
3.5
Fishes....................................................................................................................................29
3.5.1 Basis of Significance ...................................................................................................29
3.5.2 Baseline Conditions.....................................................................................................29
3.5.3 Effects..........................................................................................................................30
3.5.4 Mitigation .....................................................................................................................30
3.6
Soils.......................................................................................................................................31
3.6.1 Basis of Significance ...................................................................................................31
3.6.2 Baseline Conditions.....................................................................................................31
3.6.3 Effects..........................................................................................................................32
3.6.4 Mitigation .....................................................................................................................34
3.7
Air Quality..............................................................................................................................34
3.7.1 Basis of Significance ...................................................................................................34
3.7.2 Baseline Conditions.....................................................................................................35
3.7.3 Effects..........................................................................................................................35
3.7.4 Mitigation .....................................................................................................................36
3.8
Water Quality.........................................................................................................................37
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3.8.1 Basis of Significance ...................................................................................................38
3.8.2 Baseline Conditions.....................................................................................................38
3.8.3 Effects..........................................................................................................................38
3.8.4 Mitigation .....................................................................................................................44
3.9
Public Health .........................................................................................................................44
3.9.1 Basis of Significance ...................................................................................................44
3.9.2 Baseline Conditions.....................................................................................................44
3.9.3 Effects..........................................................................................................................45
3.9.4 Mitigation .....................................................................................................................45
3.10
Recreation .............................................................................................................................45
3.10.1 Basis of Significance..................................................................................................45
3.10.2 Baseline Conditions...................................................................................................45
3.10.3 Effects........................................................................................................................46
3.10.4 Mitigation ...................................................................................................................46
3.11
Cultural Resources................................................................................................................46
3.11.1 Basis of Significance..................................................................................................46
3.11.2 Baseline Conditions...................................................................................................46
3.11.3 Effects........................................................................................................................46
3.11.4 Mitigation ...................................................................................................................47
3.12
Socioeconomics ....................................................................................................................47
3.12.1 Basis of Significance..................................................................................................47
3.12.2 Baseline Conditions...................................................................................................47
3.12.3 Effects........................................................................................................................47
3.12.4 Mitigation ...................................................................................................................49
4.0
CUMULATIVE EFFECTS
50
5.0
COMPLIANCE WITH ENVIRONMENTAL STATUTES
51
5.1 Federal ..........................................................................................................................51
5.2 State...............................................................................................................................52
6.0
COORDINATION AND REVIEW OF THE DRAFT EA/IS
54
7.0
FINDINGS
55
8.0
LIST OF PREPARERS
56
9.0
REFERENCES
57
Tables
Table 1. Vegetation Cover Types on Prospect Island .......................................................................................19
Table 2. Changes in Vegetation Cover Types...................................................................................................22
Table 3. Total, Annual, and Daily Construction Emissions for the Prospect Island Restoration........................36
Table 4. Comparison of Project Construction Emissions with Local and Federal Thresholds...........................36
Table 5. Prospect Island Water Quality Field Data............................................................................................40
Figures
Figure 1. Prospect Island Vicinity Map..............................................................................................................2
Figure 2. Common Features (Berms, Islands, and Channels) of the Alternatives ............................................5
Figure 3. Dual Arched Culvert through Miner Slough Levee ............................................................................8
Figure 4. Existing Vegetation Cover Types.......................................................................................................20
Figure 5. DWR Water Quality Survey Sites.......................................................................................................41
Attachments
Attachment A
Fish and Wildlife Service Coordination Act Report
Attachment B
Endangered Species Correspondence
Attachment C
Department of Water Resources Proposed Monitoring Program
Attachment D
Prime and Unique Farmlands Evaluations and Correspondence
Attachment E
Cultural Resource Correspondence
Attachment F
Prospect Island Economic Analysis
Attachment G
Documents Regarding Seepage Issue and Other Technical Analyses
Attachment H
Comment Letters and Responses to Comments
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1.0 PURPOSE AND NEED FOR ACTION
1.1 Proposed Action The U.S. Army Corps of Engineers (Corps) and the California
Department of Water Resources (DWR) propose to construct the restoration of wetlands and
fish habitat on Prospect Island, located in the northwestern part of the Sacramento-San Joaquin
Delta in Solano County. The island is bounded by the Sacramento River Deep Water Ship
Channel (ship channel) to the west, a remnant of Little Holland Tract to the north, Miner Slough
to the east, and the confluence of the ship channel and Miner Slough to the south (Figure 1).
1.2 Purpose and Need for Action The restoration of wetlands and fish habitat on
Prospect Island was designed to restore environmental resources that have been degraded by
construction and operation of the ship channel and Sacramento River Flood Control Project
(flood control project). The flood control project was implemented to reduce flood damages
throughout the Sacramento River basin and to provide efficient conveyance of floodflows and
sediment carried from upstream areas. Although the flood control project reduces the potential
for flood damage, its construction and operation have contributed to the degradation of
environmental resources along the Sacramento River. The ship channel was constructed to
provide navigation to the Port of Sacramento (Port). Both the construction and operation of the
ship channel have contributed to the environmental degradation of riverine and wetlandhabitats.
Over half of the threatened and endangered plant and animal species in the State of
California depend on wetlands. The proposed restoration work on Prospect Island would
provide tidal wetland habitat that may be beneficial for special status species. Fish species that
may benefit include Delta smelt, chinook salmon, Central Valley steelhead, and Sacramento
splittail. Waterfowl, shorebirds, songbirds, and furbearers would also benefit from restoring an
open shallow water habitat with associated riparian vegetation. This Environmental
Assessment/Initial Study (EA/IS) thoroughly discusses these expected beneficial effects of the
restoration project.
1.3 Authority and Background The Prospect Island Ecosystem Restoration project
was authorized by Section 1135 of the Water Resources Development Act (WRDA) of 1986 (33
U.S.C. 2294) and Section 344(a)(3) of WRDA 1992. The acquisition of 1,228 acres of Prospect
Island by the Bureau of Reclamation (Reclamation) was authorized by House Resolution 2445,
the 1994 Energy and Water Development Appropriations Act. The source of the funds, the
Central Valley Project Restoration fund, was authorized in the Central Valley Project
Improvement Act of 1992, Title 34 of Public Law 102-575. The fund was established to provide
for habitat restoration, improvement and acquisition, and other fish and wildlife restoration
activities in the Central Valley Project area of California. The Energy and Water Development
Appropriations Act of 1995 appropriated funding for the acquisition of additional acreage for
Prospect Island.
On July 16, 1999, the Corps and DWR issued the Finding of No Significant Impact
(FONSI) and Negative Declaration, respectively, based on the July 1999 EA/IS prepared for the
Prospect Island Fish and Wildlife Habitat Restoration Study. The DWR filed the Negative
Declaration and Notice of Determination for the project with the State Clearinghouse on August 4,
1999. Additional information has become available since the FONSI and Negative Declaration
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were issued. Detailed design work determined that the cost associated with the proposed
breach in the ship channel levee would be excessive. As a result, the Corps and DWR have
developed new alternatives that were not addressed in the previous EA/IS and have prepared
the current EA/IS, pursuant to the National Environmental Policy Act, 42 U.S.C. 4321 et seq.
(NEPA), and the California Environmental Quality Act (CEQA), to determine if the new
alternatives result in any significant adverse effects.
1.4 Location and Site Description Prospect Island is located in Solano County in the
northern portion of the Sacramento-San Joaquin Delta. The project area includes a 1,316-acre
parcel purchased in 1994 and shaded riverine aquatic habitat provided by trees growing on the
outer side of the levees. The area is bounded on the east by Miner Slough, the west by the ship
channel, the south by a levee at about ship channel mile 20, and the north by an east-west
levee from Arrowhead Harbor (formerly Five Points Marina) to the ship channel. With the
exception of limited areas near the levees, the topography of the island is generally flat, varying
from +1 foot mean sea level (msl) in the northern third to -5 feet msl in southern portions of the
site.
Prospect Island is located in the extreme downstream portion of the Yolo Bypass and
has levees that are at much lower elevations than levees on other Delta islands. The heights of
these levees are limited to allow for them to be overtopped during flood events. Flooding on
Prospect Island has occurred six times in the last 17 years. Following each of these events, the
State of California and the Federal Government, at considerable expense, repaired the levees
and pumped the island dry to return the land to agricultural use (Attachment F).
1.5 Purpose and Scope of EA/IS The purpose of the EA/IS is to evaluate the effects
on the environment that would result from implementation of wetlands and fish habitat
restoration on Prospect Island. This EA/IS complies with the requirements of NEPA and CEQA.
This EA/IS provides (1) baseline data on existing and without-project environmental
conditions within the designated study area, (2) an evaluation of potential effects on the
environment that would result from implementation of proposed restoration alternatives, and (3)
identification of mitigation measures to avoid, minimize, or offset adverse effects to the
environment that would result from implementation of the alternatives. Additional details and
discussion are provided in the Corps' 1999 Ecosystem Restoration Report (ERR) and EA/IS,
which are incorporated by reference into this EA/IS. In essence, the discussion in this EA/IS
supplements and updates the 1999 environmental document.
1.6 Decisions Needed. In accordance with NEPA and CEQA, the District Engineer
and the Director of DWR must decide, based on the record as a whole, whether the proposed
Prospect Island Ecosystem Restoration Project qualifies for a FONSI and a Negative
Declaration, respectively. If the project does not qualify, then an Environmental Impact
Statement/Environmental Impact Report must be prepared.
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2.0 ALTERNATIVES
2.1 Background. Prospect Island was acquired by the Federal Government (through
the Bureau of Reclamation) with a goal to "restore wetlands and fisheries" as described in the
House Reports accompanying the Energy and Water Development Appropriations Acts of 1994
and 1995. This island offers a unique opportunity for restoration due to minimal subsidence,
which has left elevations in the island interior ranging from +1 to –5 feet msl. Therefore, when
flooded, water depths would be suitable for supporting tidal wetlands including marsh, mudflats,
and shallow water habitats. These habitats are relatively rare in the Delta, and the opportunities
for restoring them are limited. For these reasons, CALFED has identified Prospect Island as a
desired location for restoration and has provided the non-Federal share of project funding
specifically for this site (Corps, 1999). As a result, other sites were not considered during the
development of alternatives. For the same reason, the types of alternatives considered were
limited to tidal wetlands and associated habitats.
During an earlier planning stage for the Prospect Island Restoration Project, six
alternative plans including the no-action plan were formulated, and a preferred plan was
selected and evaluated (Corps, 1999). The selected plan included two levee breaches at the
southern end of the project area, one on Miner Slough and one on the ship channel. During
detailed design of the selected plan, the Corps determined that the cost of constructing a breach
in the ship channel would increase the cost of the project over the limits of the Section 1135
authority. Therefore, the Corps explored other design alternatives.
2.2 General Description of Alternatives. Two alternative designs were developed
that preserve the major habitat benefits of the project while improving circulation within the
island and, thus, water quality. These two alternatives differ from the previous alternatives in
that they include a levee opening at the north end of the project area along Miner Slough. This
option was avoided earlier since providing access to an in-holding property along Miner Slough
was thought to preclude this design. Further consideration led to two alternatives to address the
access problem: (1) purchase the in-holding property and construct a 40-foot-wide breach, and
(2) create a 40-foot-wide opening by placing two 13-foot-high by 20-foot-wide arched culverts,
side by side, and continue to provide access over the culverts.
Similar to the earlier design, both of the alternatives would include the following common
features, including the physical features (i.e., berms, islands, and channels) that are depicted in
Figure 2:
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Berms. The design includes the construction, under dry conditions, of berms along the
interior slopes of existing perimeter levees to add stability to these levees and to provide wildlife
habitat. Some levee sections along the ship channel already have gradual slopes and would
require no additional protection. All other existing levees would be stabilized with embankments
of a 10H:1V slope with a 20- to 60-foot-wide berm at 5.0 feet msl. Project construction would be
phased over 2 years to allow soils to consolidate and to minimize the potential for subsidence
and landside slumps at or near the Prospect Island levees.
Islands. The proposed project includes islands that have been designed to reduce fetch
lengths and associated wind-generated waves and thereby to help protect the levees
surrounding the project. The islands would also provide wildlife habitat. Islands would be.
constructed under dry conditions, have crowns at 7.0 msl, and would be contoured with 5H:1V
slopes to 20- to 40-foot-wide benches at 5.0 feet msl. These benches would transition to
existing grades at 5H:1V slopes..
Plantings. Selected constructed berms and islands would receive plantings to help
prevent wave erosion in the more exposed locations and along the existing Miner Slough levee.
Additional plantings of riparian vegetation on the existing interior slopes of the Miner Slough
levee would provide further protection for this levee. These plantings would be timed to
coincide with breaching. Constructed berms and islands would also receive selected seeding of
native plant materials to establish colonies that could provide seed sources for subsequent
dispersal and colonization.
Channels. A main channel would connect the two openings in the Miner Slough levee.
This channel would be 100 to 450 feet wide and have a bottom elevation of no lower than –5
feet msl. In addition, three dead-end channels would be constructed. Cut and fill would be
balanced on site between islands, levee berms, excavated channels, and a central borrow area
with an excavation depth limited to 2 feet or an elevation of –5.0 feet msl, whichever elevation is
higher.
Monitoring. The construction period would be followed by a 3-year plant establishment
period. During the establishment period, the contractor would monitor the survival of planted
vegetation and replace dead plant material so that the plant survival rate at the end of the
establishment period would be no less than 70 percent. After construction, the non-Federal
sponsor (DWR) would monitor, at their own expense as a separate but related effort, fish,
wildlife, vegetation, water quality, zooplankton, phytoplankton, benthos, bathymetry, and organic
carbon.
Long-Term Operation and Maintenance. After the 3-year establishment period, the
U.S. Fish and Wildlife Service (FWS) would accept responsibility for the long-term operation and
maintenance (O&M) of Prospect Island. FWS would receive funding for long-term O&M from an
endowment fund established with $1.25 million to be granted to DWR from the California Urban
Water Agencies through the Category III program, now administered by CALFED.
Breach at the Southern End of the Project Area. In both alternatives, levees would
be breached to allow tidal action to return to Prospect Island. Each alternative would allow an
average residence time for water within Prospect Island of 1.5 days. Both alternatives would
include a 300-foot-wide breach in the Miner Slough levee at the southern end of the project
area. This breach would be protected by rock and geotextile and have a breach bottom
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elevation set at 0.0 feet msl, with a v-notch bottom elevation set at -5.0 feet msl. Breaches
would be constructed at the end of the second year and final phase of the project after
completion of interior earthwork. The timing of all breach work on the waterside of Miner Slough
levee areas would be limited to a construction window between August 1 and November 30 due
to endangered species constraints. Breach work would be phased to maximize construction in
the dry before actual breaching. After breaching, the remaining excavation work and placement
of rock protection would be scheduled to tidal cycles to minimize in-water work. All work would
be in conformance with the National Pollution Discharge Elimination System criteria and other
environmental protection requirements. Excavated materials would be used to build out the
interior side of the levee at each end of the breach to allow for turn around areas.
As previously described, the two alternatives differ only in the details of the breach at the
north end of the project area along Miner Slough and the manner in which they address the
issue of access to private property south of the opening. The two alternatives and the no-
action alternative are described in the following sections.
2.3 North End - Open Breach (40-foot-wide) Alternative. This alternative would be a
shortened version of the 300-foot-wide breach described above, except that it would not have a
v-notch. At the discretion of the contractor, the construction of this breach would either be
completed in the dry by use of a waterside sheet pile wall or phased and scheduled to tidal
cycles to minimize in-water work, as described above for the 300-foot-wide breach. This
alternative includes the purchase of either the property located along Miner Slough between the
proposed breaches or the right of access to that property.
2.4 North End - Dual Arched Culvert Alternative (Proposed Action). This
alternative would provide a connection between the interior of Prospect Island and Miner Slough
through dual pre-fabricated metal 20-foot-wide by 13-foot-tall arched culverts (Figure 3). Rock
would be placed on the face of the levee slope around the culverts for protection of the slope
and in the bottom of the culverts. This alternative would be completed in the dry by use of a
waterside sheet pile wall. The bottom elevation of the culverts would be set at –5 feet msl. Fill
would be placed over the top of culverts to match the levee road and meet load requirements to
allow road access to the private property.
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2.5 No Action. The July 1999 EA/IS assumed that Prospect Island would continue to
be maintained in a dry state for agricultural production. The document assumed that the
Federal and State Governments would continue to repair levee breaches, pump water out of the
island, and lease the land to farmers for agricultural land use. However, this assumption has
been changed in this EA/IS for the following reasons.
Since federal acquisition of the Island, flood events and Prospect Island levee breaches,
causing flooding of the Island and extended periods without agricultural use, have changed the
existing conditions on the Island to low-value wildlife habitat. The island was last farmed in
1994. The 1995 and 1997 flood events called attention to the high cost of returning the island to
a condition suitable for agriculture. Because Prospect Island is located in the Yolo Bypass and
its levees are required to be maintained at lower elevations than surrounding Delta islands,
Prospect Island will flood more frequently than these other islands. The costs to resume and
maintain agricultural use of Prospect Island would be higher than for other islands in the Delta.
Therefore, the Corps and DWR now assume that a more accurate description of the existing
conditions is that the property is an open space serving as low-value wildlife habitat.
To better understand the economic feasibility of resuming agriculture on the federal
property at Prospect Island, DWR economists prepared an economic analysis of farming on the
Island (Attachment F). The analysis concluded that the risk of future flooding, the suitability of
the site for only low value crops, and current market conditions combine to make it economically
infeasible to return the site from its existing condition to agricultural production in the
foreseeable future. That the agricultural value of Prospect Island is compromised due to
frequent flooding is supported by the following:
• As part of the Yolo Bypass, levee height has been restricted on Prospect Island since
1916.
• The 1995 lawsuit by the agricultural lessee against Reclamation demonstrates
significant agricultural losses on Prospect due to flooding.
• Repairing levee breaches and pumping out the island is estimated to take between 2-6
months (or longer) and delays agricultural activities on the island
• Repairing levee breaches and pumping out the island for agricultural reclamation is
costly; many of the costs have been borne by the government
• As a consequence of the frequent flooding of Prospect, only low–value agricultural crops
have been grown on Prospect.
Levee Height Restriction on Prospect Island. In 1916 the Prospect Island Reclamation
District applied to the State Reclamation Board to construct a tide levee on the lower portion of
Prospect Island. Because Prospect was in the Yolo Bypass, the Reclamation Board granted
approval for the levee but limited its height to 11 feet U.S.E.D. in order not to impede flows of
the Bypass. The construction of tidal levees (to reclaim the land from tidal action) was not
supposed to impede flood flows in the Yolo Bypass flood control system.
In 1963, after the Sacramento Deep Water Ship Channel was built separating Prospect
Island from the rest of the Yolo Bypass, the Sacramento-Yolo Port District which owned
Prospect Island, granted and conveyed to the Sacramento and San Joaquin Drainage District
(State Reclamation Board) a right and easement without recourse to damages for the passage
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of all flood waters of the Yolo Bypass on Prospect Island. This grant revised the height
restrictions on Prospect Island levees to be 15 feet in the north and 13 feet in the south. The
northern portion of Prospect Island was then sold to a private landowner.
Lawsuit by Lessee. When Reclamation acquired Prospect Island in January 1995, it
assumed an existing agricultural lease for the property. Prospect Island flooded in March 1995.
The lessee (Slater Farms Inc.) then sued Reclamation for losses incurred for site preparation
and lost profits for 1996 and 1997 (Reclamation decided to buy-out the lease). Reclamation
repaired the levee and pumped out the island in March-November 1996 and settled the lawsuit
in August 1996. The lessee alleged that Reclamation should have repaired the levee breaches
and reclaimed the land sooner so that a crop could have been planted in 1995. Reclamation
paid nearly $400,000 in settlement for 1995 site preparation (herbicide application, grading) and
1996 and 1997 buy-out of lease (profits they might have made had the lease not been bought
out).
Time to Repair Levees. After flooding, there is usually 2-6 months delay in planting in order
to repair levees, pump out the island, clean ditches, repair pumps, etc. In the case of the 1995
flooding, the delay was even longer because Reclamation had to find funds to pay for these
repairs. According to the agricultural lease for Prospect Island, after flooding, the farmer was
not expected to grow crops that year.
Levee Repair Costs. In general, when Prospect Island was in private ownership (1963-
1995), Reclamation District No. 1667 and DWR paid most of the costs to repair the non-project
levees (Miner Slough and the north and south cross levees) and the Corps paid to repair the
Sacramento Deep Water Ship Channel levee. Since at least the 1980s, the federal government
reimbursed the Prospect Island landowner and Reclamation District No. 1667 for some of the
share of the levee repair and island pump-out costs. These reimbursements were made under
various federal programs, some of which were activated for the Delta by official declarations of
disasters. Most of these federal flood fight and recovery programs were administered by
Federal Emergency Management Agency.
Since 1980, there were levee breaches and flooding in the following years: 1980, 1981,
1983, 1986, 1995, 1997. Expenditures for the Public Law 93-288 program for the 1981 and
1983 flood events show $314,592 in federal funds, $77,599 in State funds, $27,264 paid by
Reclamation District No. 1667 and $71,452 paid by the landowner (Source: DWR economic
analysis, Attachment F). In 1986, Reclamation District No. 1667 (Prospect Island) was denied
FEMA funding for flood-related damages due to the fact that the Ship Channel levee was not
designed to withstand 100-year floods. Reclamation District No. 1667 then applied and was
reimbursed $444,070 from Solano County Office of Emergency Services (AB2536 Cortese Act
1986 State Disaster Assistance Funds) for flood-related damages. The District also attempted
to be reimbursed for another $34,033 of expenses from 1986 flood-related damages, though it
is not clear if this was reimbursed by the government. Note that these data are incomplete
since they do not cover all flood years and may not include all the private landowner levee
expenditures.
Since the federal government acquired the property in January 1995, the US Bureau of
Reclamation has spent $196,000 to repair damages from the 1995 floods. Approximately
$1,700,000 in CALFED funds and $622,000 in Reclamation funds were used to repair extensive
damage from the 1997 floods including levee breaches on Port of Sacramento property. Note
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that it was necessary to repair the Port of Sacramento levee breach in order to pump the entire
Island out and repair breaches on Reclamation property. The government acquired funds to
repair the Port of Sacramento levee breach and pump out its property because the Port did not
have funds to do the work itself.
In addition, the following data are available. The Corps has spent $655,812 from 1980-2000
in maintenance and repairs to the Sacramento Deep Water Ship Channel levee on Prospect
Island. For the period 1981-1999, the DWR Levee Subventions Program has spent $494,661
($181,124 State funds and $313,537 local funds) for maintenance and rehabilitation of non-
project Delta levees.
In conclusion, the large majority of costs to repair levees, pump out Prospect Island, and
maintain the levees was borne by State and federal governments, although the private
landowner also spent considerable money for these tasks. Construction of the project should
improve the condition of the levees. Conversion of the land to wetland should be compatible
with frequent flooding.
Historically low-value crops were grown on Prospect Island. Low-value agricultural crops
such as corn, wheat and safflower have historically been grown on Prospect Island. Higher-
value crops such as vineyard and alfalfa, were presumably not grown because these are multi-
year crops that would be subject to damage during the frequent flooding of Prospect Island. In
1994, the average gross crop revenue per acre for Prospect Island was $430 as compared to
$1,017 for Ryer Island which grows higher-value crops. Ryer Island has not flooded since at
least 1930 and produces in addition to low-return field crops, higher-return crops including truck,
orchard, vineyard, sugar beets, and alfalfa hay. Prospect Island had low-return field crops in
1994 (wheat, grain corn and safflower). These crops were surplus crops-- overproduced crops
that the federal government paid farmers not to grow. According to papers obtained in the 1995
lawsuit of the lessee against Reclamation for losses due to flooding, in 1992, 103 acres of
tomatoes and 288 acres of safflower were grown on Prospect Island for approximately $243,800
in revenues. DWR’s economic analysis states that these agricultural revenues are much less,
on a per acre basis, than the per acre revenues of neighboring agricultural islands and the Delta
as a whole.
Under the no-action alternative, there would be no Federal participation in environmental
restoration in the study area. The 1,228-acre area would continue to be in Federal ownership.
Due to the designed height of the levees around Prospect Island and its history of flooding, it is
assumed that levees will breach again in the near future, probably in the southern part of the
island. The Federal Government is not likely to propose any changes to existing conditions nor
to take any actions to repair breached levees, unless necessary to provide access to the private
property within Prospect Island. These assumptions also apply to the without-project condition.
Certain activities such as operation and maintenance would continue, but may be modified.
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3.0 AFFECTED ENVIRONMENT AND ENVIRONMENTAL CONSEQUENCES
This section describes the baseline and future without-project environmental resources
of the project area, including resources that would not be adversely affected by the project
(Section 3.1) and resources that would be affected by the restoration project (Sections 3.2
through 3.12). The baseline condition for this EA/IS is dry conditions in the interior of Prospect
Island with upland and seasonal wetland habitat. Without the project, however, the island would
eventually flood naturally, causing a change in the types and distributions of cover types. This
section also analyzes the effects on these environmental resources that would result from
implementation of the proposed restoration alternatives. The effects of the No Action alternative
are compared against the baseline dry conditions, while the effects of the Proposed Action
alternative are compared against the without-project condition of a naturally flooded Prospect
Island. Finally, this section identifies mitigation measures to avoid, minimize, or offset adverse
effects to the environment that would result from implementation of the alternatives.
3.1 Environmental Resources Eliminated from Detailed Analysis This section
describes the resources in the project area that would not be adversely affected by the project.
These resources are presented here to add to the overall understanding of the project area.
3.1.1 Climate. The project area is situated in the eastern portion of the Delta where
there is a transitional climate zone between the coastal and inland extremes. The prevailing
winds are from the south primarily because of marine breezes through the Carquinez Strait,
although the sea breezes diminish and winds from the north occur more frequently during the
winter. During the summer, the predominant winds come from a south-southwest direction.
Clear skies predominate throughout much of the year, but storms and tule (ground) fog
frequently occur during the winter months.
Most of the precipitation in the area derives from air masses moving in from the Pacific
Ocean during the winter months. These storms usually move through the area from the west or
northwest. Variations in the climate can occur seasonally and from year to year, affecting
freshwater flow patterns, fish and wildlife habitat, and Delta hydrology (Corps, 1993). Within the
Delta, precipitation can vary greatly, with the wettest areas receiving about 60 inches of rain and
the driest areas receiving 10 inches. The proposed project would have no effects on the
regional or local climate in the area.
3.1.2 Geology/Geography The Delta is located along the western edge of California’s
Central Valley. This valley was formed in the basin of a large sea between 175 and 25 million
years ago. During this period, the area presently occupied by the Sierra Nevada was the
continental margin. A second island mountain island chain lay to the west of this margin. As
these mountains rapidly uplifted, huge volumes of sediment filled the basin. Mountain building
and sedimentation continued to the Miocene (26 to 5 million years ago). Regional subsidence
and deposition in a marine environment ended about 40,000 years ago during the late Eocene.
From the late Eocene to the Pleistocene, continental alluvial deposits accumulated in the basin.
During the Quaternary period, phases of glaciation caused sea levels to fluctuate, as well as
alternating cycles of deposition and erosion.
The Delta began to take on its present form during the end of the last glacial period
about 11,000 years ago as the sea began to rise, filling the alluvial valley of the Sacramento
River. Rivers and streams draining into the area formed a complex network of channels, islands
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and sloughs. Alluvial materials accumulated along the banks of channels, forming natural
levees around islands. Spring rains and high tides caused floods, which easily overtopped
these natural levees forming a network of large, shallow lakes. Highly productive soils formed
behind these levees as detritus from marsh areas accumulated and as nutrient-rich detritus was
deposited by floodwaters. During the period in which hydraulic mining debris was deposited in
channels, increased flooding occurred, and the natural levees were raised. Agricultural
activities in the Delta have resulted in further raising and strengthening of the natural levees and
construction of new levees. The proposed project would have no effects on the geology or
geography in the area.
According to the CALFED document, “Seismic Vulnerability of the Sacramento – San
Joaquin Delta Levees”, dated April 2000, Prospect and Ryer Islands are located in an area of
the Delta where the levees are considered to have low susceptibility to earthquake-induced
failure. Flooding Prospect Island should have no effect on the seismic vulnerability of the
adjacent island levees.
3.1.3 Water Supply. Availability of water supplies in the Delta varies with natural
conditions and upstream development. Natural hydrologic variations cause extreme fluctuations
in monthly and yearly inflows. Winter floods produce Delta flow rates of several hundred
thousand cubic feet per second (cfs), while summer conditions can decrease rates to a few
thousand cfs. The total annual volume of inflow can also vary substantially.
The North Bay Aqueduct delivers water to Solano County and Napa County. Water
contractors who receive this water are concerned about the potential effect on the Barker
Slough pumping plant (which serves the North Bay Aqueduct) from an increase in the Delta
smelt population. Currently, DWR is required to discontinue or reduce pumping whenever
concentrations of smelt larvae exceed a certain threshold. The DWR, Solano County Water
Agency, U.S. Fish and Wildlife Service (FWS), Reclamation, and Corps met to discuss the
water contractors’ concerns. As a result, the FWS's field supervisor for Sacramento sent a
memo to Reclamation to address the water contractors' concerns. The following is an excerpt
from that memo:
It is the Service’s intent that increased larval production associated with
Prospect Island not cause additional pumping restrictions when risk to the overall
population of delta smelt is low. In the 1994 draft Recovery Plan, wide
distribution and high numbers of rearing juveniles have been shown to lower risk
to delta smelt. If these conditions exist, no additional Barker Slough pumping
restrictions will occur due to increased larval production from Prospect Island.
Farmers on Ryer Island expressed a similar concern that additional restrictions may be
placed on their diversions for irrigation. The Corps contacted the Endangered Species Office of
the FWS about the Delta smelt. The FWS informed the Corps that no new additional
restrictions would be placed on Ryer Island as a result of Prospect Island restoration (Thabault,
1998). Therefore, the proposed project would have no effects on the water supplies in the
Delta.
3.1.4 Water Elevations and Tidal Action. Historically, natural Delta islands may have
had less tidal influence as the riparian perimeter thickened, restricting outlet channels. Such
natural islands probably did not support large expanses of open water (deeper than -3 feet
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mean water level) in the interior, and probably had limited tidal action in much of the tule
regions.
Water elevations in the ship channel and Miner Slough are influenced by the daily tide
and periodic flooding events. Tidal information was estimated considering 19 years of record at
the Rio Vista tidal gage in the Delta and using those values (adjusted for location) for the
Prospect Island site. These stage values represent the 1929 National Geodetic Vertical Datum.
The tidal elevation data for the southern tip of Prospect Island are as follows:
Feet (msl)
Mean high-high
4.1
Mean high