2016_DWSC_Closure_Study.pdf

TASK 7: DRAFT REPORT

Deep Water Ship Channel Closure Structure

Alternatives Study

Prepared for:

Prepared by:

17885 Von Karman Ave., Suite 500 Irvine, CA 92614

November 3, 2016

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Deep Water Ship Channel Alternatives Study iii

TABLE OF CONTENTS

1. Study Purpose and Scope

1.1 Study Purpose

1.2 Study Tasks

2. Study Area and Background

2.1 Flood Risk Management Study

2.2 Port Operations and Ship Requirements

3. Study Goal and Objective

3.1 Considerations

4. Target Audience

5. Problems

5.1 Flooding

5.2 Levee Conditions

6. Opportunities

7. Formulation of Alternatives

7.1 Permanent Structures

7.2 Temporary Structures

8. Alternatives Considered Further

9. Ranking Considerations

10. Comparison of Alternatives and Initial Ranking

10.1 Matrix Construction

10.2 Rationale for the Assigned Values

11. Matrix Methodology

12. Results

13. Discussion

14. Refined Alternative Array

14.1 Earthen Levee and Rock Berm

14.2 Sector Gate

14.3 Steel Barge Gate

14.4 Summary

15. References iv

LIST OF TABLES

Table 1. Floodplain Area during a 0.5% (1/200) Annual Chance Exceedance Levee Failure or Overtopping

Table 2. Number of Structures by Category in 0.2% Exceedance Probability Flood

Table 3. Levee Problems and Failure Probabilities in the Study Area

Table 4. Summary of Final Alternatives

LIST OF FIGURES

Figure 1. Vicinity Map

Figure 2. Study Area

Figure 3. West Sacramento Area 2‐year through 500‐year floodplains, Index Point #7, from USACE 2015a

Figure 4. Land Use Map

Figure 5. Critical Facilities Map

Figure 6. Levee Index Points

Figure 7. Earthen Levee

Figure 8. Rock Berm

Figure 9. Sector Gate

Figure 10. Steel Barge Gate

ATTACHMENTS

Attachment 1 – Initial Summary of Alternatives

Attachment 2 – Cost Estimate Summaries

1. Study Purpose and Scope

1.1 Study Purpose

The purpose of this Closure Structure Alternatives Study (the Study) is to provide analysis of alternatives to reduce the flood risk posed by the breach created in the Yolo Bypass Levee when the Deep Water Ship Channel (DWSC) was constructed. Flood risk is increased due to the resulting reliance on more than 17 miles of navigation levee to manage water surface elevations in the DWSC by excluding Yolo Bypass flows. Alternatives considered include both temporary and permanent closure structures, with the permanent closure structures including both operable and non‐operable structures/features.

1.2 Study Tasks

The following is a brief outline of the main study tasks:

Identification of the study goals and objectives Identification of Problems, Opportunities, and Methodology for Analysis Identification of Alternatives Comparison of Alternatives ‐ Initial Ranking Analysis of Alternatives Comparison of Alternatives – Secondary Ranking Completion of a Draft Report Stakeholder Outreach Completion of a Final Report and Executive Summary

As a “reconnaissance level” analysis, alternatives have been considered at a conceptual level of detail. Planning tools such as decision matrices and parametric cost estimates are used to assess how alternatives rank among categories such as financial impacts/tradeoffs, environmental costs, navigation impacts, risk management, and operation and maintenance costs, for example.

2. Study Area and Background

The City of West Sacramento (City) depends on levees for the safety of its residents.

Approximately 50‐miles of levees along the Sacramento River, Yolo Bypass, and Sacramento Bypass comprise the flood system protecting the City. Construction of the DWSC by the U.S. Army Corps of Engineers (USACE) created a breach in the Yolo Bypass levee along the western boundary of the City. The flood threat associated with this breach was addressed by the construction of “navigation” levees along the west bank of the DWSC and the north and south banks of the turning basin and harbor. These three levees comprise nearly 30 miles of the flood system protecting the City although they are not recognized as part of the Federally‐authorized flood control system. Figure 1 is a vicinity map, and Figure 2 is a map of the system and local study area.

Figure 1. Vicinity Map

Figure 2. Study Area

The breach of the Yolo Bypass Levee by the DWSC in combination with the deficiencies identified in the Port North, Port South, and DWSC West levees pose significant risks to the City during a large flood event. The difference in stage between the Yolo Bypass and the DWSC during a 200‐ year event is approximately 10 feet. A breach in the DWSC West levee could result in severe flooding both north and south of the Port.

2.1 Flood Risk Management Study

USACE completed a Final General Reevaluation Report (GRR) and Final EIS/EIR that considered the feasibility of reducing flood risk (USACE, 2015a and 2015b). The GRR was completed to reevaluate the previously authorized project which was found to be inadequate to address the residual flood risk for the West Sacramento area (USACE 2015a). The cost of the recommended plan in the GRR is approximately $1.19 billion, with a projected cost of $1.63 billion over its 17‐year implementation period.1

The GRR recommends a comprehensive plan of levee improvements to achieve WSAFCA’s minimum goal of 200‐year flood protection. Near the Port of West Sacramento (Port), this plan includes a total of approximately 26 miles of improvements to the Port North, Port South, and DWSC West levees (USACE, 2015a). Notably, the GRR recommended levee improvement plan does not actually protect the Port itself because it is on the water side of the levee improvements.

A permanent operable closure structure was evaluated as part of the alternatives evaluation in the GRR. The proposed structure was a sector gated structure with a 200 foot wide opening, a base elevation of ‐37.0 feet, and top of structure elevation of 34.0 feet. The proposed location was approximately 500 feet north of the South Basin Main Drain Pumping Plant. Cost of the structure (October 2014 price level) was approximately $519,429,000 (USACE, 2015a). The alternative containing the operable closure structure was eliminated due to cost inefficiencies.

2.2 Port Operations and Ship Requirements

The Port of West Sacramento was opened in 1963 following construction of the DWSC by USACE that was Congressionally‐authorized by the Rivers and Harbors Act of 1946 and initiated in 1949.

The Port includes a harbor, a turning basin, and a 1.5‐mile‐long shallow‐draft barge canal with an 86‐foot‐wide and 600‐foot‐long navigation lock between the harbor and the Sacramento River.

(USACE 2015a) It was constructed as a bulk cargo port to serve the agricultural and natural resource industries of Northern California. The Port’s primary cargos were historically rice, wheat, woodchips, logs and fertilizer, and in 2007 cement was introduced. Annual cargo throughput prior to 1999 was approximately 1 million tons, but has dropped steadily to a baseline of approximately 320,000 tons since 2009, primarily rice exports. As of mid‐2015, cement imports have increased consistent with the economic recovery and cement tonnage is expected to be approximately 240,000 tons in 2016.

1 Following finalization of the GRR in December, 2015, the Chief of Engineers’ Report was finalized in April, 2016.

Depending on the cargo and relative weight, the required depth due to a ship’s draft can range from approximately 25 feet, for bulk rice shipments of 12‐13,000 tons, to 30 feet for cement shipments of 30,000 tons. The current alternatives study therefore considers 30 feet as the minimum required channel depth, which is consistent with the current Federally‐authorized depth for the navigation channel. The allowable height that would have to be accommodated if any closure structure extended vertically—such as with a lift gate—is the height of the lowest existing bridge, the Benicia Bridge, at 135 feet.2

Over the past six years, the annual vessel counts have ranged from 20‐28 ships with an annual average of 24. The monthly average for any one month in the six year period ranged from 0.5 vessels in August to 2.7 vessels in May, November, and December, with an overall monthly average over the 72 month period of 2 vessels. The greatest number of vessels in the period was seven, during December 2013.3 These counts exclude vessel traffic at the privately operated Yara terminal. Cemex also operates a private terminal on the ship channel and will likely add to these vessel counts in the future.

As described in the March 2013 Port of West Sacramento Business plan, the previous operating model of the Port had been financially unsustainable due to on‐going operating deficits. Since the introduction of a landlord operating model in July 2013, the Port has eliminated its operating deficits and is growing positive cash flows through expansion and diversification of real estate lease revenues.

3. Study Goal and Objective

As mentioned above, the underlying goal of the study is to reduce the risk of flood damages to West Sacramento. The specific objective to meet this goal is to “identify a range of alternatives for closing the gap between the Yolo Bypass Levee and Deep Water Ship Channel East Levee in order to reduce flood risks.” The closures evaluated could either be temporary or permanent.

3.1 Considerations

While the objectives are simple statements of the intended purposes, they are informed by numerous considerations. The following considerations have been identified as important items in the development and analysis of alternatives.

The primary goal of WSAFCA is to achieve at least a 200‐year level of protection for the City as soon as possible, but no later than 2025 as required by Senate bill 5.

Both 100 year and 200 year flood events will be evaluated in the analysis using the water surface elevation (WSE) of the Yolo Bypass as the design condition.

2 Pers. Comm., Greg Fabun, Flood Protection Manager, City of West Sacramento, Dec 17, 2015; and meeting notes with City management, Oct 28, 2015

3 Pers. Comm., Greg Fabun, Flood Protection Manager, City of West Sacramento, Dec 17, 2015

Alternative plans should evaluate and consider the costs of ongoing levee operation and maintenance.

Project implementation must consider the operation of the Port and impacts to channel maintenance. Timing of the implementation, both during construction and during operation, should be considered in alternative development and analysis.

Economic viability will be evaluated through comparison of project costs and benefits, and include both construction and O&M costs.

Alternatives will include the consideration of environmental impacts and required permitting for implementation. These will be described in general terms but more detailed analysis would be required prior to project implementation.

The objectives and considerations will be used to inform and guide the planning process which includes the identification of problems, opportunities and methods of analysis as well as the identification of alternatives.

4. Target Audience

There are several relevant target audiences of this study:

WSAFCA (specifically, the City of West Sacramento, Reclamation District 900, and Reclamation District 537) and the Port of West Sacramento. Specific individuals representing these stakeholders—such as civil works/flood control managers, Port operations and business managers, environmental specialists, planners, etc.—will be identified through internal meetings. Information developed in this initial study will enable these decision makers to compare alternatives developed as part of this study and with operable closure structure alternatives presented in the USACE GRR.

Stakeholders that will be involved in the implementation of any of the recommendations coming from this study include the following agencies that either have a regulatory role or would need to be involved in coordination prior to and/or during project implementation.

o U.S. Army Corps of Engineers o U.S. Fish & Wildlife Service o National Marine Fisheries Service o U.S. Coast Guard o Central Valley Flood Protection Board o California Department of Water Resources o California Department of Fish & Wildlife o California State Water Resources Control Board o California Department of Boating and Waterways o Yocha Dehe Wintun Nation o California Delta Stewardship Council

The general public, landowners, NGOs, and other interested parties.

5. Problems

The following flooding problems that are relevant to the current study are associated with existing conditions, and are discussed in the sections below:

Flooding o Life Safety o Flood Damage o Environmental and Agricultural Resources

Levee Construction Design, Methods, Materials, and Foundation o Erosion, Overtopping and Vegetation o Site Specific Levee Problems

5.1 Flooding

The City of West Sacramento is located at the confluence of the American and Sacramento Rivers, and adjacent to the Yolo Bypass (see Figure 2). It is within the floodplain of the Sacramento River.

During large flood events, the City is an urban island that depends on the successful performance of nearly 52 miles of levees that help protect against the inflow of flood waters.

The region has a long history of flooding that prompted the 1917 authorization of the current flood control system which began with the Sacramento River Flood Control Project (SRFCP) levees and includes the Central Valley Project (CVP) and the 1956 completion of Folsom Dam. During the flood of record in 1986, an estimated 650,000 cfs flowed past the Sacramento metropolitan area in either the Sacramento River or Yolo Bypass. (USACE, 2015a)

The State standard for urban flood protection in California requires levees to have a top elevation equal to the mean 0.5% (1/200) Annual Chance of Exceedance (ACE) water surface profile, plus three feet of freeboard, plus an allowance for wave run‐up, plus one foot to account for climate change. Portions of the levees do not meet this standard, as mentioned in the 2015 GRR, in which damages resulting from overtopping or failure of surrounding levees during a 0.5% ACE event as potentially flooding most of West Sacramento. Table 1 displays the floodplain area that was modeled. Figure 3 shows flood depths ranging from 0.1 to 30 feet associated with various ACE events (USACE, 2015a).

Figure 3. West Sacramento Area 2‐year through 500‐year floodplains, Index Point #7, from USACE 2015a

In addition, the GRR mentions the anticipated issuance in the near future of updated FEMA floodplain maps for West Sacramento that will show portions of the City within the 100‐year floodplain. Due to this new mapping within the floodplain, development in the City will be constrained until a project is put in place that provides protection from the 100‐year event.

Table 1. Floodplain Area during a 0.5% (1/200) Annual Chance Exceedance Levee Failure or Overtopping

(source: USACE 2015a)

Economic Impact Area

Total Acres

Total Square Miles

North Basin 5,468 8.5

South Basin 6,822 10.7

TOTAL 12,290 19.2

Life Safety

The consequences of flooding due to a levee failure would be catastrophic, with nearly the entire population of approximately 50,000 at risk. Daylight loss of life is estimated at 124 individuals, and nighttime at 90 individuals. As described in the 2015 USACE GRR, even a levee breach during a 4% (1/25) ACE event would put the population at risk with flood depths potentially up to 10 feet. Moreover, the Sacramento Area Council of Governments in 2007 predicted that the population of West Sacramento would increase by 64% from 2007 to 2030, with a population of 73,500 in 2030.

Flood Damage

West Sacramento is urbanized with commercial, industrial, residential, and public buildings, and rural farm lands. The current flood risk poses a threat of extensive damage to this infrastructure as well as to the potential loss of life, injuries, illnesses, and other health and safety problems.

Extensive damage to utilities, roadways, major interstate transportation corridors, and other infrastructure systems would also likely occur. The GRR states the following:

“Significant damages to structures would be expected, as well as loss of life, injuries, illnesses, and other health and safety concerns. Flooding in the West Sacramento area could trigger an uncontrolled release of hazardous and toxic contaminants into the waterways surrounding West Sacramento. Transportation through the area would be severely hampered by a major flood. Critical infrastructure could be rendered nonfunctional for an extended period of time after a flood. Impacts to critical infrastructure would have a significant impact on the ability of the community to react to and recover from a significant flood event. Emergency costs associated with evacuation, flood fighting, fire and police, and government disruptions would occur. Debris cleanup would be a substantial undertaking. Wildlife populations occupying these areas would be adversely affected by flooding. In summary, a flood in West Sacramento would cause massive damages.” [Note: While the predicted average increase of approximately

2‐3% per year has not actually occurred since 2007, suffice to say an overall and significant increase in population has been projected.]

Figure 4 shows the land use in the City of West Sacramento north of the DWSC. The population of 50,000 within the City that was mentioned above is housed within 19,903 units. Additionally, there are 734 commercial and industrial structures, 46 public structures, and 27 park facilities which would all be affected by a flood event. Table 2 summarizes the number of damageable structures within the 0.2% (1/500) ACE floodplain. Total value of property in that floodplain is estimated at $4.53 billion. Single‐event damages for the 1% (1/100) ACE flood are anticipated to exceed $3.6 billion. (USACE 2015a).

Table 2. Number of Structures by Category in 0.2% Exceedance Probability Flood

(source: USACE 2015a)

Structure Count By Damage Category

Category Count

Commercial 365

Industrial 424

Public 98

Residential 12,951

TOTAL 13,838

Critical infrastructure is always a concern during flood and other emergency conditions. Figure 5 depicts many of the facilities listed below which are all within the area of potential flooding described above (USACE 2015a), and are shown for the northern portion of the City.

Essential Services

Regional USPS mail processing center USACE Bryte Yard Facility The regional Department of Water Resources Flood Fight facility The California Highway Patrol Academy (a key facility in state emergencies) West Sacramento City Hall Police Stations Fire Stations Bryte Bend Water Treatment Plant

At Risk Population Facilities

St Claires Home for the Elderly River Bend Nursing Facility

Transportation

Union Pacific Main Railroad Line

AMTRACK

Interstate 80 U.S. Highway 50 The Port of West Sacramento

Figure 4. Land Use Map

Figure 5. Critical Facilities Map

Impacts to Environmental and Agricultural Resources

Environmental and agricultural resources could also sustain major damage during a flood event.

Of the land area within the City, 22.6% is either farmland or open space. If a catastrophic flood event occurred resulting in inundation of 10‐15 feet, land damages alone are estimated to be $238 million. These values are based on the 1% (1/100) ACE event. (USACE 2015b)

A flood event could also cause severe public health hazards. Flooding in the city could release and spread stored hazardous materials creating hazardous conditions for the public and the environment, and potentially contaminating the Sacramento River and Delta surface waters as well as soil and groundwater. Flood damage to homes and other structures could render them dangerous due to structural damage as well as contamination. Additionally, the floodwaters and ponds left behind could provide a wide breeding ground for mosquitoes and other disease vectors. Effects to the water supply system could be particularly severe in a flood event, and could leave residents and businesses without a reliable water supply for a significant amount of time, as a single break in a water delivery pipe or main could contaminate the entire city’s water supply.

5.2 Levee Conditions

Levee deficiencies pose a great threat even if peak flood flows do not occur. These deficiencies potentially stem from design limitations, construction methods, and materials. Both WSAFCA and USACE have identified severe deficiencies with the Port North, Port South, and DSWC levees that include perviousness, under seepage, foundational inconsistency, stability, and erosion. Deficient levee height is also a problem.

Material Deficiencies

In general, many of the levees in the study area were originally constructed with material dredged from the river and placed into a trench between two starter dikes.4 Therefore the embankment is made up of pervious sands and gravels that transmit water during floods. In addition, the foundations upon which the levees were constructed is made up of the former river‐ bed including meanders and oxbows, which adds differential material in the foundation to the problems of perviousness and underseepage. Inadequate compaction along with assorted objects (such as dead trees and branches) have been found buried in the embankments. Slope failures have been observed during high river stages and where water seepage occurs. (USACE, 2015a).

Erosion and Vegetation

The Sacramento River channel is sediment‐starved due to higher than “natural” velocities caused by confining levees and adjacent development that have created a narrow channel. Therefore there is a risk of erosion and undercutting by river flows.

4 It is currently unknown whether this is true for the DWSC levees.

The GRR describes that at many areas of the study area there are both vegetation and encroachments on or near levees. The vegetation includes native vegetation, landscaping, gardens, and encroachments that include houses, utilities, outbuildings, swimming pools, etc.

These are problematic due to their complicating effect on maintenance and flood fighting as well as their contributing effect on the instability of the levees themselves.

Site Specific Levee Problems

Site specific levee problems where a significant probability of failure exists is identified and described in detail in the GRR. The magnitude of subsequent flood damage would of course depend upon the location of the levee breach, severity of the storm, and river flows at the time of a potential levee failure. Problem areas are briefly described below and are associated with “index points,” shown in Figure 6 and consistent with the GRR (USACE 2015a).

The most relevant location to the current alternative analysis is Index Point 7 at the Deep Water Ship Channel West (DWSCw). This is the location where a closure alternative is being studied. Yet it is noteworthy that several locations within the SRFCP affecting West Sacramento could cause flooding within the City especially if a breach of the DWSC West Levee occurs concurrent with breaches in the Port North, Port South, and Yolo Bypass Levee during a large flood event.

The levees in the North Basin include the Sacramento River North (SRN), Yolo Bypass (YB), Port North (PN), and the Sacramento Bypass (SB) levees. The levees in the South Basin include the Sacramento River South (SRS), South Cross (SC), Deep Water Ship Channel East (DWSCe), DWSCw, and the Port South (PS) levees.

Of the nine levees listed, the following number of levees are considered to have the following deficiencies and probabilities of failure. The relevant index points are indicated.

Table 3. Levee Problems and Failure Probabilities in the Study Area (source: USACE 2015a)

Levee 1 Problem Probability of

Failure 2 (%) Seepage Stability Erosion Overtopping Vegetation

SRN #1 X X X X X 95.6

SRN #2 99.4

YB #3 X X 99.9

PN X X n/a

SB #4 X X X 80.9

SRS #5 X X X X 69.6

SRS #6 42.6

SC X X X n/a

DWSCe X X X n/a

DWSCw #7 X X X 99.2

PS #8 X X X 23.1

1 Numbers indicate applicable Index Points per Figure 6 2 Probabilities based on condition of water being at the top of the levee; this occurs at different flood frequencies depending on the location of the specific levees with respect to localized flood flows.

Figure 6. Levee Index Points

Deep Water Ship Channel West Levee

The difference in stage between the Yolo Bypass and the DWSC during a 200‐year event is approximately 10‐feet, and a breach in the DWSC West levee would result in severe flooding both north and south of the Port. This flooding scenario was illustrated in the GRR and is shown in Figure 3 based on a single levee breach in the DWSC Levee near its point of intersection with the Yolo Bypass Levee (Index Point #7). The figure depicts a suite of flood frequencies ranging from the 50% (1/2) ACE to the 0.2% (1/500) ACE. As shown in the 10‐yr inundation map, the flood water from Yolo Bypass enters the DWSC and backs up to the Port of West Sacramento, then overtops the Port South Levee and DWSC East Levee. Port North levee is overtopped during a 25‐ year event. These floodplains indicate extensive flooding over a majority of the City starting with the 2% (1/50) ACE flood event.

6. Opportunities

An obvious opportunity to reduce the flood risk in the City of West Sacramento is to improve the structural integrity and/or height of levees within the study area. That is the primary recommendation of the USACE GRR. However, the current alternatives analysis is intended to identify a standalone alternative to the DWSC gate closure structure that was studied within the GRR but that was eliminated from consideration due to cost considerations. As such, the closure structure is independent of the need to improve the DWSC west levee downstream of the structure, and/or improve the Port North levee, Port South levee, and the DWSC East levee north of where a closure structure would be located.

Since the DWSC was constructed by breaching the Yolo Bypass Levee, the flood risk is from floodwaters entering the study area through the levee gap created by the DWSC. The opportunity therefore exists to develop a closure structure for the levee gap that provides a more cost‐ effective solution compared to the structure studied in the GRR, and potentially more cost‐ effective than the components of the GRR Recommended Plan for fixing 22 miles of levees.

The benefits of the closure structure go beyond reducing threats to life and structural flood inundation damages. They also include the avoided costs of business impacts, loss of employment, clean up, health effects, and traffic and rail disruption. Further, many of these avoided costs would not only affect the Port and the businesses and residents of the City, but would also provide regional and Statewide benefits.

7. Formulation of Alternatives

In the course of this analysis it became apparent that two major sets of alternatives should be considered:

(1) Temporary structures that would provide interim risk reduction but that would need to be removed after the flood threat subsides. A temporary structure may be considered advantageous while the overall GRR recommended plan is designed and funded; and

(2) Permanent structures that would either provide maritime vessel passage or not provide passage. These would include operable gate structures that are alternatives to the sector gate recommended in the USACE GRR, and non‐operable, reconstruction of the levee.

a. Permanent structures were considered for their compatibility with a vehicle bridge to provide access across the DWSC and/or public access as, for example, an extension of Enterprise Blvd.

b. Permanent structures were considered for two operating conditions: always closed unless navigation is required, or always open unless a flood threat is imminent.

The assessment of the two major sets of alternatives differs. For example, the expectation for the implementation time to open and close a closure structure is relatively short for the permanent solutions—on the order of hours or minutes—while a much longer time—days or even weeks depending on the availability of construction equipment and material—is to be expected for an interim solution.

Specific alternatives considered as part of each set of solutions are given below.

7.1 Permanent Structures

This set of solutions includes permanent operable (PO) gates and permanent closures (PC). Cost efficiencies could be attained through the use of modified construction methods, resized navigation openings, or alternative gate structures. The permanent closures considered in this study include:

1. USACE Sector Gate (PO)

2. Sector Gate with Diversion (PO)

3. Resized Sector Gate (PO)

4. Steel Barge Gate (PO)

5. Lift Gate (PO)

6. Operating Bulkhead Gate (PO)

7. Navigation Barrier Gate (PO)

8. Rolling Gate (PO)

9. Pneumatically‐Actuated Steel Plate Gate (PO)

10. Rock Berm or Earthen Levee (PC)

11. Sunken Barges (PC)

Each of the operable solutions has the potential variation of leaving the structure in either the normally open or normally closed position. A normally open position supports navigation more easily in that no action is needed to allow maritime traffic to pass. A normally closed position more effectively supports flood risk management in that no action is needed to provide flood protection. A normally closed gate may also provide vehicular transportation benefits to those alternatives that could support a roadway.

The following sections describe each of the permanent solutions considered.

Attachment 1 displays details including photographs and renderings that further explain how these alternatives function.

USACE Sector Gate

A sector gate consists of two hinged gates in the shape of part of a circle (or sector) that swing inward towards the channel and act as a barrier to flow. This alternative is the same sector gate alternative presented by the USACE in the GRR. The sector gate recommended in the GRR has a 200 foot wide opening, a base elevation of ‐37.0 feet, and top of structure elevation of 34.0 feet for a total gate height of 71 feet. The structure would consist of conventionally reinforced concrete and post tensioned concrete supported on a pipe pile foundation. The concrete structure would use float‐in construction. The concrete shell would be built similar to barge type construction in a graving site adjacent to the project site. The float‐in design eliminates the need for cofferdams, structure site dewatering systems, and a structure site bypass.

The sector gate recommended in the GRR did not include a roadway. Due to the non‐linear alignment of the radial gates, a roadway on top of the gates is limited with the arrangement shown in the GRR. A maintenance road can be accommodated. A two‐lane road can also be accommodated albeit with limited vehicular speed, some larger vehicle limitations, and some modifications to the monolith and its alignment with the tie in T‐wall. The modification to the shape of the monolith together with the modified alignment of the tie in T‐wall maintains the flood barrier but also allows the roadway across the sector gate to transition more smoothly to the roadway across the T‐walls.

Sector Gate with Diversion

This alternative is a modification of the USACE sector gate alternative only in that the method of construction is changed. Rather than using a float‐in construction this alternative is intended to include diversion of the water in the DWSC with on‐site construction. All other elements are the same as the USACE sector gate. This alternative was considered only to determine if a more cost effective sector gate is feasible. An initial assessment showed that the cost difference was not significant for this level of feasibility and this option was not evaluated further. However, if the sector gate option is selected, this variation should be considered.

Resized Sector Gate

This alternative is similar to the USACE sector gate but the height and width are minimized by constraining the channel. In order to realize savings from the smaller gate size, the width would need to be reduced to a point where not all current traffic that travels the DWSC to the Port would be accommodated. This effectively eliminates current maritime use. Other alternatives that also eliminate maritime use have a significantly lower cost. Based on this initial assessment, no further evaluation of this alternative was made.

Steel Barge Gate

The steel barge gate consists of a floatable barge that is operated by swinging the gate open and closed, and resting it atop landing supports in the open/closed position. The barge gate would seat onto a slab/cutoff wall that can resist uplift. However, the steel barge gate cannot be opened when the difference in the water level on both sides of the gate is significant.

A roadway can be added across the barge for vehicular traffic. The width of the barge gate would need to be increased to accommodate construction of a road. This alternative is able to integrate the road with the gate and realize significant savings from the dual construction.

Lift Gate

A lift gate consists of a large plate that is lowered into position to form a barrier that acts as a barrier to flow. A lift gate requires an overhead structure for lifting the plate as well as a concrete foundation. The lift gate needs to be able to be lifted above the elevation needed for clearance of the maritime traffic. The total height of the gate is 71 feet (see section 7.1.1) and maritime traffic requires a 130 feet clearance above a normal water elevation of 5 feet giving a top of structure elevation of 211 feet. The foundation at the invert of the DWSC is at an elevation of ‐ 37 feet giving a full structure height of approximately 250 feet.

Lift gate fabrication is more straightforward and typically less expensive than a sector gate given that there are no curved members. However, a lift gate is going to be a more expensive option than the sector gate for this specific set of circumstances:

Lift gates become more inefficient to design as they become wider (200 feet wide at DWSC) compared to a sector gate because the lift gates span from one side of the channel to the other, acting like a beam.

The lateral load due to the hydrostatic (water) forces on the proposed gates is very large.

One advantage that lift gates typically have over sector gates is that they have smaller foundations. Considering the estimated number of piles required to resist the lateral load, the foundation for the lift gate would be just as large as the sector gate foundation.

The proposed clear height for the lift gate is very high. The seismic force resistance system for the lift gate towers will be similar to high rise building and will be expensive to implement. Seismic loads on the lift gate towers will be high considering the likely foundation conditions in the river and the importance of the structure.

The lift gate may have settlement issues. The closure structure will be located in an area likely to have soft ground conditions. Both gate foundations will be subject to settlement.

However, because the gate is attached to two towers located 200 feet apart, the gate may bind in its tracks if there is differential settlement. The sector gate with a traditional concrete monolith is tied together so differential settlement is less likely.

The proposed lift gate is large, and providing an integrated roadway for either regular vehicular traffic or for maintenance vehicles can readily be accommodated with a bridge on top of the structure, considering that the gate leaf itself is straight.

Operating Bulkhead Gate

The operating bulkhead gate is similar to the lift gate except than when open, it is stored in the horizontal, lifted arrangement to reduce the effects of wind and seismic loads (compared to a traditional lift gate). Because of the horizontal storage, the total height can be reduced to approximately 180 feet to allow for maritime traffic clearance. The foundation requirement is still very large leading to a high capital cost that overshadows relatively smaller savings resulting from the horizontal storage.

The operational method of this gate would require a separate roadway bridge, parallel to the operating bulkhead gate that would also have to be lifted to clear the shipping traffic. This alternative does not provide any advantage as compared to the lift gate; therefore, no further evaluation of this alternative was made.

Navigable Barrier Gate

The gates operate by rotating a plate from a horizontal position along the channel bottom into a vertical position to create the barrier. The plate is hollow and fills with water when it is submerged and stored along the channel bottom. When operated, it empties as it emerges from the river.

Due to the method of operation, a navigable barrier gate cannot support an integrated roadway.

It also does not support construction of a maintenance road.

Rolling Gate

When in the open position, this gate is stored in a recessed “slot” in the lock wall built into the bank of the channel. The gate operates by being mechanically rolled into position to create a barrier to flow. Similar to the lift gate, a large foundation is required resulting in a total capital cost higher than a sector gate. If the gate is kept in the normally open position, the dry storage results in longer life span. This longer life span is not realized if the gate is left in the normally closed position. The rolling gate cannot be opened when the water level is not the same on both sides of the gate.

A rolling gate can support an integrated roadway for either regular vehicular traffic or maintenance. The straight alignment of the gate is compatible with a roadway.

Pneumatically‐Actuated Steep Plate Gate

For this type of gate, the steel plates in the structure are hinged at the bottom and raised by inflating a bladder. The structure is permanently mounted at the channel bottom and fixed to a reinforced concrete foundation using clamp plates and anchor bolts. The plates lie flat until the bladder is inflated by pumping air inside the rubber body until the design height or pressure is reached. Due to the method of operation, a steel plate gate cannot support an integrated roadway. A separate structure would be required to support a roadway for either regular vehicular traffic or maintenance.

While gates of this type have been used throughout the world, the manufacturer has never built one at the required 70‐foot height. 5 To avoid potential risk, no further evaluation of this alternative was made.

Rock Berm or Earthen Levee

This alternative includes a rock berm that is placed across the channel to effect a water barrier.

Sheetpile cut off walls would be included in the berm for the permanent design to prevent through seepage and under seepage. Small tainter gates or sluice gates could be incorporated into allow for flushing of water upstream and downstream of the berm.

This alternative is not operable and precludes maritime traffic. A roadway for vehicular traffic and maintenance can be incorporated into the rock berm and significant savings from the dual construction would be realized.

A variation of this alternative is to construct using earth rather than rocks. The footprint of this alternative is larger than the rock berm because the placed soil material must be of sufficient width to prevent through‐seepage and under seepage. If the earthen levee is chosen for implementation, the design should meet the same level of protection currently provided by the adjacent levees upstream and downstream. To increase the level of protection of only the closure levee would be unnecessarily cost inefficient since the adjacent, tie‐in levees would drive the overall level of protection. Any additional level of protection should therefore be accomplished consistently across the DWSCe levee, the Yolo Bypass levee, and proposed closure levee.

The evaluation of either the rock berm or earthen levee is the same so they are considered as a single alternative in this initial assessment.

Sunken Barges

For the permanent structure category, this alternative would use multiple barges that are floated into position, then scuttled, in order to close off the channel. Several barges would be required to create the barrier. Positioning the barges to create an effective barrier would be difficult.

Moreover, limiting leakage to create an effective permanent barrier would also be difficult.

Because of this, no further evaluation of this alternative was made.

7.2 Temporary Structures

Two of the permanent structures, above, could also be used on a temporary basis primarily in the event of emergencies when flooding becomes imminent. These structures would preclude navigation for a period of time until the ship channel could be reopened. These temporary, non‐ operable closures (TC) generally involve significant effort and construction equipment to remove.

5 The largest existing installation to‐date is on the Nanming River in China, at 200 feet by 25 feet (pers. comm., Henry Obermeyer, February 2016).

Note that further evaluation could occur to address the potential of the following options related to variable closure of the ship channel as a function of flood risk. Once identified, it could become formalized in an Emergency Action Plan.

Viability of having a cost effective rock berm closure that is removed following every flood season. This would effectively create a seasonal port. While the navigation patterns currently indicate no clear cut seasonal distribution of maritime traffic, the possibility for the concept could be evaluated.

The frequency of closure considering not only the available warning time but also the levee performance that may not depend on an overtopping water surface condition.

Identification of the triggers to institute an emergency closure as related to the evacuation plan. For example, one trigger could be when the WSE reaches the 25‐year frequency level, and the next trigger could be if the bypass begins to fail.

Risk related to an assumption of variable West Levee failure could be identified. That is, what frequencies of flooding could be sustained with little damage to allow a temporary closure to remain open.

Rock Berm

Similar to the alternative described in Section 7.1.10, a rock berm would be placed across the channel to create a barrier. Once the flood event has passed, the rocks are removed.

Because of this structure’s intent being temporary:

No sheet pile is incorporated to prevent seepage (as exists in the permanent version of the Rock Berm).

No roadway would be incorporated for vehicular traffic.

The temporary rock berm would take at least a week to construct. Because of the lack of timely emergency response, no further evaluation of this alternative was made.

Sunken Barges

Multiple barges would be stationed at the port and floated into position, then scuttled, in order to close off the channel. Several barges would be required to create the barrier. It’s unlikely that the Port can easily store these barges on a permanent basis without impacting its operations. In addition, positioning the barges to create an effective barrier and limit leakage would be difficult.

Because of the operational difficulties, no further evaluation of this alternative was made.

8. Alternatives Considered Further

A description of each alternative was provided in Section 7. The following alternatives which passed the initial screening evaluation, are being considered:

For the operable gates, two versions of each alternative is considered where possible: the gate normally left open and normally left closed.

Attachment 1 includes further details on these alternatives.

9. Ranking Considerations

The tasks that represent this Closure Structure Alternatives Study including the identification, comparison, and analysis of alternatives, are intended to offer a “reconnaissance‐level” phase analysis utilizing a “proof of concept” approach. As such, the initial rankings will consider the following criteria and considerations in a nominal ranking that avoids detailed quantification. In order to best convey the relative rankings for each criterion, a visual matrix has been used that helps immediately identify advantages and disadvantages of each alternative within each criterion. Colors (green, yellow, and red) are used to quickly convey best and worst choice alternatives. In addition to the colors used, the matrix will also convey the relative weighting of importance of each criterion by varying their respective row heights.6 Narrative explanations will accompany the alternatives, below, that provide reasoning and justification for the rankings.

The following criteria were considered in the alternative evaluation:

Enhanced Flood Risk Management – all of the alternatives provide flood risk management.

However, some of the alternatives provide an enhanced level of protection. Enhancements considered were (1) if passive positive closure is provided so that a “normally closed” position achieves flood control without any action, (2) a maintenance road can be integrated into the alternative, and (3) a flood evacuation road can be provided.

Capital and Design Cost – this evaluation is based on engineering judgement. Conceptual level cost estimates will be prepared for select alternatives.

Time to Open/Close – the time required for closure is how much warning time must be provided to close the structure so that it can withstand floodwaters. Closure time can be impacted by the head differential on each side of the structure (such as occurs with the Rolling Gate). With short warning times and quickly rising water surface elevations, closures that take too long to close would be ineffective. In later phases of the study, the actual warning time for design storms should be investigated along with correlation to “critical” water surface elevation levels. Opening time has a direct impact on how quickly maritime traffic can be accommodated along the DWSC. Similar to closing times, opening times can be impacted by the head differential on each side of the structure.

6 The “importance” weight assigned to each criterion is based on judgment and subsequent verification among the study group.

1. USACE Sector Gate (PO)

2. Steel Barge Gate (PO)

3. Lift Gate (PO)

4. Rolling Gate (PO)

5. Rock Berm or Earthen Levee (PC)

Supports Navigation – this factor addresses how easily the current level of maritime traffic can be supported.

Supports Bridge Construction – this factor addressed whether a road can be integrated into the gate structure.

O&M Effort – the overall benefit of any closure needs to consider the level of effort related to both initial and ongoing operational and maintenance efforts of the closure structure itself. Any associated impacts on O&M of the surrounding levee system are not considered herein.

Relative Project Impacts – this factor considers the differential impacts among alternatives which would primarily accrue to short‐term water quality impacts during construction, long‐ term post‐construction water quality impacts, and long‐term aesthetic impacts. Water quality is a potential issue due to a reduction in water circulation that would take place with longer‐term closures unless smaller gates are installed allowing flow to the Port.

Aesthetics—mostly visual—could be considered a negative impact if the closure structures were large enough to be seen for several miles such as may occur with the lift gate or that may occur with large stockpiles of adjacent rock as would need to occur for the temporary rock berm.

10. Comparison of Alternatives and Initial Ranking

The “Alternatives Matrix” on page 32 consists of criteria considerations on the left‐hand column and the alternatives along the top.

10.1 Matrix Construction

The criteria are arranged in their order of priority, with “enhanced flood risk management” and “capital and design cost” at the top and “relative project impacts” and “O&M effort” at the bottom. In order to capture these priorities, each criterion is assigned a “factor value” which is used in the evaluation described in Section 10.3, “Matrix Methodology,” below.

The following table indicates the various factor values that are assigned.

The “rating” for each alternative for each criterion is shown in a qualitative manner, with “high,” “medium,” and “low” reflected by the green, yellow, and red cells, respectively.

Criterion "Factor Value" displayed as Row Height

Enhanced Flood Risk Management 90

Capital and Design Cost 80

Time to Open / Close 55

Supports Navigation 50

Supports Bridge Construction 50

O&M Effort 45

Relative Project Impacts 40

10.2 Rationale for the Assigned Values

Enhanced Flood Risk Management – The first consideration in this factor is whether the alternative provides a passive closure to floodwaters, or if implementation is required for flood control. Operable gates that are normally left in the closed position and opened only to allow for immediate passage of maritime traffic are considered passive protection and provide an enhanced level of flood risk management. An alternative that provides a maintenance road for use during a flood event contributes to enhanced flood risk management. An improved road that also allows for evacuation provides additional enhancements. A road on a gate was only considered to provide an evacuation route if the gate is operated normally in the closed position. A normally open gate would likely not be well utilized by evacuees as the location is normally not seen as providing an evacuation route. A “high” value to this factor was assigned if all 3 conditions were met (passive flood control, maintenance road, evacuation road.) A “low” value was assigned if there was no passive control of floodwaters (i.e. implementation is required to achieve flood protection).

All other alternatives were assigned a “medium” value.

Capital and Design Cost – Engineering judgement was used to identify high to low capital costs based on past experience with these types of closures and/or published magnitudes of costs. Clearly, the sector gate alternatives are relatively more expensive as is the rolling gate. The pneumatically‐actuated steel plate gate and rebuilding the levee/berm are the least expensive.