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SUNLAND PARK LEVEE REPAIR -

WEST LEVEE

DESIGN DOCUMENTATION REPORT

(100% DESIGN)

Contract No. IBM15D0001 Task Order No. IBM17T0010

August 14, 2019 (Revised August 21, 2019)

SUNLAND PARK LEVEE REPAIR – WEST LEVEE Contract No. IBM15D0001 Design Documentation Report (100% Design) Task Order No. IBM17T0010 August 2019 arcadis.com

SUNLAND PARK

LEVEE REPAIR - WEST

LEVEE

Design Documentation Report

100% Design

Prepared for:

U.S. International Boundary and Water Commission

4171 North Mesa Street

Suite 100C

El Paso, Texas 79902

Prepared by:

Arcadis U.S., Inc.

401 East Main Street

Suite 400

El Paso

Texas 79901

Tel 401 738 3887

Our Ref.:

01991047.0000

Date:

August 14, 2019 (Revised August 21, 2019)

This document is intended only for the use of the individual or entity for which it was prepared and may contain information that is privileged, confidential and exempt from disclosure under applicable law. Any dissemination, distribution or copying of this document is strictly prohibited.

Ardita Dushi, P.E.

Project Manager

Kirk Lowery, P.E.

Design Lead

Joel Mora, P.E.

Deputy Program Manager

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STATEMENT OF LIMITATIONS

This Document is for United States International Boundary and Water Commission (USIBWC) use only.

The scope of services performed within may not be appropriate to satisfy the needs of USIBWC on other projects or the needs of other users. Any use or reuse of this Document or the findings, conclusions, or recommendations presented herein is at the sole risk of the user. The design provided in this Document is based on the previous studies and the reports and references provided by USIBWC.

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CONTENTS

Acronyms and Abbreviations ......................................................................................................................... v

1 Project Information

1.1 General

1.2 Project History

1.3 Scope of Work

1.4 Purpose of Design Documentation Report

1.5 Project Location

2 Existing conditions

2.1 Site Visit

2.2 Survey Data

3 Geotechnical

4 Hydrology and Hydraulics

4.1 Hydraulic Model

4.2 Channel Velocities

5 Project and FEMA Requirements

5.1 General

5.2 Levee and Geotechnical Design

5.3 Freeboard Requirements

5.4 Closures

5.5 Embankment Protection

5.6 Embankment and Foundation Stability

5.6.1 Seepage Analysis

5.6.2 Slope Stability Analysis

5.7 Settlement

5.8 Interior Drainage

5.9 Other Design Criteria for Unique Solutions

6 Civil Design

6.1 Levee Crossings

6.1.1 Borderland Bridge Transition

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6.1.2 Country Club Bridge Transition

6.2 Proposed Levee

6.3 Ramps

6.4 Encroachments

6.5 Subsurface Utility Exploration

6.6 Road Crossings

7 Environmental Considerations

7.1 Environmentally Sensitive Areas

7.2 Culturally Sensitive Areas

7.3 Biological Resources

7.4 Natural Resources

7.5 Restoration Sites

8 Structural Design

8.1 Low Structures

8.2 Levee Closure Structures

8.3 Vehicular Gates

8.4 New Concrete Wall

9 Construction Considerations

9.1 Utility Conflicts

9.2 Construction Outside USIBWC’s ROW

9.3 Long Lead Time Items

9.4 Sole Source Items

9.5 Specialty Contractors

9.6 Estimated Time of Construction

9.7 Contractor’s Technical Requirements

9.8 Traffic Plan

10 Operation and Maintenance

10.1 Operation and Maintenance for Levees

11 References

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TABLES

Table 1. Project Location Summary for CW2

Table 2. Major Crossings along Sunland Park West Levee

Table 3. Existing Structures along Sunland Park West Levee

Table 4. Existing Utilities along Sunland Park West Levee

Table 5. Soil Properties used for Seepage Analysis

Table 6. Soil Properties used for Slope Stability Analysis

Table 7. Slope Stability Results

Table 8. Approximate Wall Elevations near Borderland Bridge

Table 9. Encroachments along Sunland Park West Levee

Table 10. USIBWC Signs for Road Crossings

Table 11. Existing Low Structures on West Levee

Table 12. Vehicular Gates

Table 13. Monthly Rain Days for 0.25-inch Rain Event (Mean Values in El Paso area)

FIGURES

Figure 1. Sunland Park – CW2 Levee Location

Figure 2. Base Flood Elevations (BFE) along Sunland Park West Levee

Figure 3. Simulated Maximum Channel Velocities on West Levee

Figure 4. Steady-State Seepage Results West Levee with Toe Drains (from Kenall 2016)

Figure 5. Exit Gradients at Levee Toe without Toe Drains – Transient Seepage (Sta. 1571+00)

Figure 6. Hydrograph at Sta. 1571+00

Figure 7. Existing Elevations at Borderland Bridge - West Levee

Figure 8. Existing Elevations at Country Club Bridge - West Levee

Figure 9. Typical Levee Section

Figure 10. Valley Creek Restoration Site [Reference: USACE (2009)]

Figure 11. Proposed Concrete Barrier Wall Section

Figure 12. Estimated Construction Schedule

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APPENDICES

Appendix A - Photographic Logs

Appendix A.1 General Observations – Photographic Logs

Appendix A.2 Structures – Photographic Logs

Appendix B - Geotechnical Basis of Design

Appendix B.1 Geotechnical Memorandum

Appendix B.2 Seepage and Slope Stability

Appendix B.3 Settlement

Appendix C - Structural Basis of Design

Appendix C.1 Concrete Slope Paving

Appendix C.2 Concrete Levee Paving

Appendix C.3 Low Structures

Appendix C.4 New Concrete Wall

Appendix D – Subsurface Utility Exploration

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ACRONYMS AND ABBREVIATIONS

Arcadis Arcadis U.S., Inc.

ASTM ASTM International

AT&T American Telephone & Telegraph

BFE Base Flood Elevation

CADD Computer Aided Design and Drafting

CFR Code of Federal Regulations

CoEP City of El Paso

CW2 Canutillo West 2

DDR Design Documentation Report

EPE El Paso Electric

EPW El Paso Water

FEMA Federal Emergency Management Agency fps Foot per second

FXSA Frank X. Spencer & Associates

Kenall Kenall, Inc.

MDJV Munoz and Dannenbaum Joint Venture

NAD 83 North American Datum of 1983

NAVD 88 North American Vertical Datum of 1988

NFIP National Flood Insurance Program

% percent

ROW Right-of-Way

S&BI S&B Infrastructure, Ltd.

SOW Scope of Work

SUE Subsurface Utility Exploration

SWCC Soil-Water Characteristic Curves

TGS Texas Gas Service

TxDOT Texas Department of Transportation

URGFCP Upper Rio Grande Flood Control Project

USACE United States Army Corps of Engineers

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USIBWC United States International Boundary and Water Commission

3D Three dimensional

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1 PROJECT INFORMATION

1.1 General

The United States International Boundary and Water Commission (USIBWC) contracted with Arcadis U.S., Inc. (Arcadis) for the design of the Sunland Park Levee Repair within the Rio Grande Canalization Project under Task Order No. IBM17T0010 of Contract No. IBM15D0001 to provide engineering services for the preparation of plans and specifications. In addition, Arcadis will support USIBWC during the project procurement and contracting process. On September 15, 2018, USIBWC issued Contract Modification 1 seeking to separate the construction documents into two packages: East Levee and West Levee. This report includes the improvements pertaining to Sunland Park Levee Repair - West Levee.

The project team consists of Arcadis and the following subcontractors: Munoz and Dannenbaum Joint Venture (MDJV) and Frank X. Spencer & Associates (FXSA). Altogether, Arcadis and its subcontractors form the Arcadis Team.

1.2 Project History

In September 2010, the USIBWC issued a construction contract to rehabilitate the Sunland Park Levee segment of the Upper Rio Grande Flood Control Project (URGFCP). Construction was completed in November 2012. However, on completion, the levee experienced considerable erosion. The USIBWC contracted with Kenall, Inc. (Kenall) in April 2015 to perform a Forensic Geotechnical Investigation and provide the USIBWC a professional opinion on whether the newly constructed levee segment would perform satisfactorily during the 100-year flood event pursuant to 44 Code of Federal Regulations (CFR) §65.10 (Federal Emergency Management Agency [FEMA]). Kenall identified several construction-related problems, and its investigation found dispersive clay within the existing levee embankment along the entire length of this reach of the levee system. Kenall found that as a result of the erosion of the dispersive clay, the Sunland Park Levee Segment does not meet the National Flood Insurance Program (NFIP) Regulation 44 CFR §65.10(b).

Previous studies for the design of the Sunland Park Levees include:

• “Sunland Park Levee Forensic Geotechnical Investigation” by Kenall, dated July 29, 2016.

• “Design Report for Upper Rio Grande Flood Control Project, Sunland Park Canutillo Levee

Segment” by S&B Infrastructure, Ltd. (S&BI), dated July 23, 2010.

• “Final Technical Memorandum Volume I for Geotechnical Explorations of Levee System within the Rio Grande Canalization Project- Canutillo Levee Segment” by Raba-Kistner Consultants, Inc., dated December 22, 2008.

• “Final Technical Memorandum Volume II for Geotechnical Explorations of Levee System within the Rio Grande Canalization Project- Canutillo Levee Segment” by Raba-Kistner Consultants, Inc., dated December 22, 2008.

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1.3 Scope of Work

The scope of work (SOW) titled “Design Scope of Work, Rio Grande Canalization, Sunland Park Levee Repair in El Paso County, TX and Doña Ana County, NM,” dated March 2, 2017, was provided for this task order. The main project goals are to:

• Address the deficiencies noted in Kenall’s forensic report.

• Provide a design intended to produce levees that fully meet FEMA requirements for 44 CFR

§65.10(b) (1) through (7). The final design is also intended to meet the requirements included in the United States Army Corps of Engineers' (USACE) Engineering Manual 1110-2-1913.

• Remove the existing floodgate gate at the Country Club Bridge (eastside) and design a new gate to withstand the 100-year flood.

• Raise or modify the levee closure structures along the levee alignment that are too low to be operated during flood flows.

The revised SOW, dated August 6, 2018, for the Contract Modification 1 included the following work:

• Separate the construction documents into two packages:

1. Sunland Park Levee Repair – East Levee

2. Sunland Park Levee Repair – West Levee

• Provide catwalk design for access to the low structures that are currently inaccessible during flood flows.

• Provide boundary survey monuments within project limits.

The Sunland Park West Levee is known as the Canutillo West 2 (CW2) Levee and the Sunland Park East Levee is known as the Canutillo East 2 (CE2) Levee. During the design it was discovered that additional survey was needed downstream of the Country Club Bridge. The additional survey could not be completed due to the current river flows. Since the West Levee Solicitation is required in fiscal year 2019 (FY19), on July 10, 2019, USIBWC requested that Arcadis exclude the rehabilitation design for the levee alignment downstream of the Country Club Bridge from this package in order to proceed without delays to Solicitation. Rehabilitation design for the levee alignment downstream of Country Club Bridge will be submitted in an addendum to this report.

1.4 Purpose of Design Documentation Report

This Design Documentation Report (DDR) presents the basis for design for the levee segments and structural components for improvements pertaining to Sunland Park Levee Repair - West Levee.

Proposed levee design downstream of Country Club Bridge will be included in an addendum. East Levee design will be provided in a separate DDR. This DDR includes design assumptions and criteria, calculations, and design approach for all aspects of construction. The design provided in this DDR, which is detailed in the construction drawings and specifications, complies with industry standards and meets the applicable requirements of Subsections 1.2, Project Goal, and 1.5, Project Requirements, and Section 11, Regulatory Requirements, of the SOW.

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1.5 Project Location

The Canutillo West 2 (CW2) levee is located within the United States on land owned or controlled by the USIBWC within its Rio Grande Canalization Project, in El Paso County, Texas, and Doña Ana County, New Mexico. A layout of the project is included on Figure 1.

Figure 1. Sunland Park – CW2 Levee Location

The general location, length, coordinates, and stationing for the Sunland Park Levee Segment of CW2 are summarized in Table 1.

Table 1. Project Location Summary for CW2

General Location Length Starting Station (Sta.)

Ending Station (Sta.)

Starting Coordinates

Ending Coordinates

Borderland Bridge to NeMexas Drain 3.4 miles 1518+56.27 1698+00(1) 31º 53’ 9.2” N

106º 35’ 58.7” W 31º 50’ 17” N

106º 36’ 23” W

Note: (1) Ending Sta. 1698+00 was indicated in the SOW per Task Order IBM10C0018. Due to the change of the centerline alignment, our design dictates that the ending station for CW2 corresponds to Sta. 1697+75.

As explained in Section 1.3, rehabilitation design for the levee alignment downstream of the Country Club Bridge will be submitted separately in an addendum.

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2 EXISTING CONDITIONS

2.1 Site Visit

The Arcadis team visited the site on April 3, 2017 and October 11, 2017 to observe the levee and structure conditions. During the site visits, the Arcadis team observed the pertinent project features, the structures defined by USIBWC as deficient, and the ongoing maintenance activities at the crest of the levee. The existing top of levee consists of an approximately 2-inch-thick gravel layer for vehicle access.

Several access ramps are located throughout the alignment. In some cases, improvements on privately owned properties have encroached on the levee Right-of-Way (ROW) as described in Section 6.4.

Several major and minor public roads intersect the levee segments. The major crossings along the CW2 alignment are included in Table 2. Photographic logs of the general observations are presented in Appendix A.1.

Table 2. Major Crossings along Sunland Park West Levee

The existing structures along the west levee alignment are included in Table 3. Photographic logs and the locations of all the existing structures along the levee reach are included in Appendix A.2. The structure type and size along with survey data are included in the contract drawings.

Table 3. Existing Structures along Sunland Park West Levee

Station Structure Description Structure Size Ownership

1531+75 Montoya Lateral Siphon 3.5’ x 4’ EPCWID1

1535+00 Canutillo Lateral WW#34 4’ x 4.7’ EBID

1562+65 Pence Lateral WW#34A 30” RCP EPCWID1

1593+92 Combined La Union Lateral WW#35 5’ x 4’ EPCWID1

1667+08 Schultz Lateral WW#35C 30” RCP EBID

Approximate Sta. Description Ownership

1518+56 Borderland Bridge City of El Paso

1546+15 Artcraft Bridge Texas Department of Transportation

1666+59 Country Club Bridge City of El Paso

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The known existing utilities are provided in Table 4. The utilities in Table 4 have been field verified using historical documentation and by contacting known utility owners in the area to verify utility locations. We do not anticipate any conflicts with utilities for any of the proposed improvements for this project. The contract documents will require the construction contractor to verify utilities before start of construction.

Table 4. Existing Utilities along Sunland Park West Levee

Utility Station Description Owner Contact Information Notes Known

Conflict?

1518+81 Natural Gas Line

TGS

Saul Magallanes saul.magallanes@onegas.com

(o) (915) 682-7356

(c) (915) 727-6131

4700 Pollard St., El Paso, TX 79930

6” steel line encased in 10” steel, adjacent to downstream of Borderland Bridge.

3’ min cover.

No

1519+56 Water Line EPW Amy Castner acastner@epwater.org

(915) 594-5647

OR

Al Quijano pquijano@epwater.org

1154 Hawkins Blvd., El Paso, TX 79925

36" Concrete H.P.

Top of pipe at El.

3745.

No

1543+39 Overhead Electric

EPE Raul Guel

(915) 543-4015 raul.guel@epelectric.com 100 N. Stanton St. Suite 171

El Paso, TX 79901

Upstream of Artcraft Rd. Runs parallel to OE 1543+56.

No

1543+56 Overhead Electric

EPE

Raul Guel

(915) 543-4015 raul.guel@epelectric.com 100 N. Stanton St. Suite 171

El Paso, TX 79901

Upstream of Artcraft Rd. Runs parallel to OE 1543+39.

No

1545+39 Electrical Conduit

TxDOT

Salvador Perez

(915) 790-4335

Salvador.Perez@txdot.com 13301 Gateway Blvd West, El

Paso, TX 79928

Attached upstream of Artcraft Rd. 5’ min cover.

No

1619+86 Sanitary Sewer

EPW

Amy Castner acastner@epwater.org

(915) 594-5647

OR

Al Quijano pquijano@epwater.org

1154 Hawkins Blvd., El Paso, TX 79925

24" I.D. with 40"steel casing.

Approx. El. 3729 top of pipe.

No

1666+31 Fiber Optic

COEP

Traffic Signals Maintenance Victor Pereda

PeredaVM@elpasotexas.gov

(915) 472-3549

OR

4” line attached upstream of Country Club Rd.

3.5' deep at junction box and

No

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Utility Station Description Owner Contact Information Notes Known

Conflict?

Basilio Ontiveros ontiverosbx@elpasotexas.gov

Office: (915) 212-7075 goes down about 6' as it approaches the levee.

1666+44 Water Line EPW

Amy Castner acastner@epwater.org

(915) 594-5647

OR

Al Quijano pquijano@epwater.org

1154 Hawkins Blvd. El Paso, TX 79925

12" A.C encased in steel pipe. 5’ min cover.

No

1666+83 Fiber Optic

AT&T

Shawn Sather OSP Planning & Engineering ss1038@att.com Cell: (915) 342-3172 Ofc: (915) 595-5118

4" Line. Contact AT&T to verify location.

No

1667+00 Overhead raul.guel@epelectric.com 100 N. Stanton St. Suite 171

El Paso, TX 79901

Runs above downstream of Country Club Rd.

No

1667+16 Natural Gas

TGS

Saul Magallanes saul.magallanes@onegas.com

(o) (915) 682-7356

(c) (915) 727-6131

4700 Pollard St., El Paso, TX 79930

4” aboveground steel line, attached to the bridge itself, downstream of Country Club Bridge. Elevation approaching the bridge is unknown.

El at 3752.

No

1667+30 Electrical Conduit

AT&T

Shawn Sather OSP Planning & Engineering ss1038@att.com Cell: (915) 342-3172 Ofc: (915) 595-5118

Attached downstream of Country Club Rd.

Bridge. About 8 ft deep at the manhole. El at

No

1667+30.

Electrical Conduit

AT&T Shawn Sather OSP Planning & Engineering ss1038@att.com Cell: (915) 342-3172 Ofc: (915) 595-5118

Attached downstream of Country Club Rd.

Bridge. About 8 ft deep at the manhole. El at

No

1696+88 Overhead raul.guel@epelectric.com 100 N. Stanton St. Suite 171

El Paso, TX 79901

Runs parallel to the levee and crosses the levee at Sta.

1696+88.

No

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2.2 Survey Data

FXSA performed surveying services including topographic and boundary surveys of the USIBWC’s ROW.

The topographic survey and the boundary survey for both east and west levees were performed from November 2017 through February 2018 and from November 2017 through April 2018, respectively. The coordinates, bearings, and distances on the topographic and boundary surveys are based on the New Mexico Coordinate System of 1983, North American Datum of 1983 (NAD 83) (2011), Central Zone (3002). These are shown as grid distances and may be converted to surface distances by dividing by the combined scale factor of 0.99973833. The elevations for this project are based on the North American Vertical Datum of 1988 (NAVD 88), Geoid 2012B. The field survey included performing cross-section surveys along the levee alignment at 100-foot intervals for the entire project reach. The survey data were processed to generate a topographic map with elevation contours using Autodesk Civil 3D Software.

3 GEOTECHNICAL

A geotechnical memorandum describing the geotechnical basis of design is included in Appendix B.1. It should be noted that this geotechnical memorandum includes evaluations of both east and west levees per the original SOW.

4 HYDROLOGY AND HYDRAULICS

4.1 Hydraulic Model

USIBWC provided the hydraulic model within the project limits. The SOW specified the use of the 2005 FLO-2D model developed by Tetra Tech. During the project, it was determined that the 2005 model provided was not running correctly; therefore, USIBWC provided us with a 2009 FLO-2D model. We used the 2009 USIBWC FLO-2D model to determine the effects of levee improvements on base flood elevations (BFE) and velocities. The BFE in this model indicates the 100-year flood condition. The BFEs extracted from the 2009 model were used as the basis for determining the required freeboard elevations under the 100-year flood condition.

The model was used to check that the project improvements to the existing levee would not have any impact on the hydraulic conditions. The current model and the required +3 feet freeboard requirements are shown on Figure 2. The required project levee elevations are based on the top of the new embankment fill and below the aggregate roadway as presented in the contract drawings. At the bridge locations, FEMA’s minimum freeboard required is 4 feet within 100 feet of the bridge. However, based on a prior agreement between USIBWC and FEMA, the minimum freeboard required is 3 feet within 100 feet of the bridge.

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Figure 2. Base Flood Elevations (BFE) along Sunland Park West Levee

4.2 Channel Velocities

The estimated channel velocities for the 100-year flood extracted from the 2009 FLO-2D model are shown on Figure 3. Estimated velocities in the Rio Grande channel along the Sunland Park West Levee range from 3.46 feet per second (fps) to 9.64 fps. High channel velocities over 9 fps were encountered south of the Borderland Bridge and at the Country Club Bridge location. Channel velocities slightly higher than 6 fps were encountered downstream of the project reach. It appears that the increase in the velocities at this portion of the levee reflects the narrower channel width.

The difference between the velocities presented on Figure 3 and the velocities presented in Kenall’s 2016 report are likely due to the different hydraulic models used in the previous design and our design. The previous design was based on the USIBWC 2003 Hydraulic Model, and we used the USIBWC 2009 FLO- 2D Model for our design.

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Figure 3. Simulated Maximum Channel Velocities on West Levee

5 PROJECT AND FEMA REQUIREMENTS

5.1 General

The design objectives for this project are to meet FEMA requirements in 44 CFR §65.10(b) (1) through (7), which include: 1) freeboard, 2) closures, 3) embankment protection, 4) embankment and foundation stability, 5) settlement, 6) interior drainage, and 7) other design criteria for unique situations. The new levee should also meet the requirements of the USACE’s Engineering Manual 1110-2-1913 titled "Design and Construction of Levees" (USACE 2000). This section describes the project requirements and basic design criteria for the project.

The SOW for this project required addressing the deficiencies noted in Kenall’s forensic report (Kenall 2016). After a review and evaluation of Kenall’s forensic study, we found other issues that are not in conformance with the FEMA requirements based on the most recent survey and the 2009 FLO-2D model:

1) there is inadequate freeboard up to 10 inches at some locations along the alignment as described in Section 6; 2) there is inadequate freeboard in some locations near structures as described in more detail in Section 6.1; and 3) there are higher channel velocities than those reported in Kenall’s report as described in Section 4.2.

5.2 Levee and Geotechnical Design

The levee design criteria are based on addressing the dispersive clay that exists throughout the levee reach as identified by Kenall. To establish the earthwork design criteria, we evaluated 11 alternatives for treatment of dispersive clay as described more fully in Appendix B.1. Following the design scoping meeting held on December 13, 2017, the USIBWC selected the clay blanket option; thus, dispersive clay

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This alternative, as originally presented by Kenall, involves excavating at least 2 feet of the existing dispersive clay soil and replacing it with imported clay that is not dispersive. The imported clay will be moisture-conditioned and compacted to achieve a well-constructed envelope of non-dispersive soil around the core of the existing levee, which may contain dispersive clay. The dispersive clay at the levee core will be isolated, reducing the threat of internal or external erosion.

The imported non-dispersive clay borrow should classify as CL in accordance with ASTM International (ASTM) D2487, Unified Soil Classification System, with a plasticity index between 15 to 30 and a maximum liquid limit of 45 percent (%). Fat clay should not be used due to the higher susceptibility to desiccation cracking.

The clay borrow must be non-dispersive and meet the testing requirements listed below:

• Crumb Test (ASTM D6572) - Grade 1 (non-dispersive)

• Pinhole Test (ASTM D4647) - ND1 or ND2

• Double Hydrometer (ASTM D4221) – Percent dispersive less than 30

• At least 65% passing a U.S. Standard No. 200 sieve

• One hundred percent (100%) of the dry material passing the 1-inch sieve

• Contain less than 35% sand content by weight.

The embankment fill will be compacted to at least 95% of maximum density at a moisture content above optimum moisture content as determined by ASTM D698, Standard Proctor.

Other levee and geotechnical design criteria include:

• Freeboard will be at least 3 feet above the BFE. The gravel road on the levee will not be included as part of the 3-foot freeboard requirement.

• The levee footprint will not be moved from its currently existing alignment.

• The levee slopes horizontal:vertical (H:V) will be 2.5H:1V or flatter (USIBWC prefers 3H:1V slopes where possible).

• The finished gravel road will be at least 16 feet wide and a minimum of 6 inches thick. The maintenance roadway will slope toward the riverside at 2% along the alignment.

• Ramps along the levee will be designed as shown in the SOW.

• Dispersive clays will not be used in construction.

• Results of seepage analysis will be incorporated into stability analysis.

• Soil properties are based on the previous studies provided by USIBWC.

• Factors of safety will meet the USACE requirements.

Sections 5.3 through 5.9 were considered in the design to satisfy the FEMA and USACE requirements.

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5.3 Freeboard Requirements

We designed the final elevation of the non-dispersive clay cap to be at least 3 feet above the BFE (100-year flood). The BFE is extracted from the 2009 FLO-2D model provided by USIBWC. The landside will be slightly higher due to the 2% cross-slope requirements. The gravel roadway is not included in the freeboard requirements. At the bridge locations, FEMA requires the minimum freeboard to be at least 4 feet within 100 feet of the bridge. However, based on a prior agreement of USIBWC with FEMA, the minimum freeboard required is 3 feet within 100 feet of the bridge. There are two existing bridge crossing locations (Borderland Bridge and Country Club Bridge) along the levee reach where the levee height needs to be increased to 3 feet at/or near the bridge to meet minimum freeboard requirements.

5.4 Closures

Access to the levee closures (sluice gates) that are too low to be operated in floods will be raised to be above the 100-year flood elevations. The levee closures are explained in more detail in Section 8.

5.5 Embankment Protection

The proposed levee is designed to be protected with at least 2 feet of non-dispersive clay cap. The installation of the new non-dispersive clay, topsoil, and vegetative cover is anticipated to protect the levee from erosion due to the floodwaters acting against the levee for short periods of time.

In addition, to evaluate the erosion, the estimated channel velocities for the 100-year flood were compared with published values of permissible velocities. Based on the USACE Engineer Manual (EM) 1110-2-1601 (USACE 1994), the maximum mean channel velocities on clay are 6.0 fps and on grass-covered clay are 8 fps. Channel velocities in the Rio Grande channel along the west levee range from

3.46 fps to 9.57 fps.

Channel velocities over 9 fps are expected at the bridge locations. The Country Club Bridge abutments are covered with concrete slope paving. As a result, no significant hydraulic impact should exist at the bridge location. No riprap (stone) or concrete slope paving is present near the Borderland Bridge abutment. We recommend that concrete slope paving be placed at the Borderland Bridge as shown on the contract drawings to withstand the channel velocities. The existing planter between the two rockwalls will be left in place. The vegetation cover in this planter area will provide erosion protection as this area is surrounded by concrete slope paving.

Channel velocities of slightly higher than 6 fps were encountered downstream of Sta. 1696+00, most likely due to the narrower channel width at that cross section. We anticipate that riprap will be required on the riverside levee slopes downstream of Sta. 1696+00. Levee design downstream of Country Club Bridge will be provided in an addendum.

For the remainder of the alignment, results of the H&H analysis indicate that there is no significant hydraulic impact to the levee slopes as the anticipated velocities on the levee slopes are lower than the mean permissible velocities in the channel.

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5.6 Embankment and Foundation Stability

5.6.1 Seepage Analysis

The previous design (S&BI 2010) included toe drains on the landside to reduce the seepage exit gradients at the landside toe. The seepage analyses in the previous design assumed a steady-state condition, which implies that the water will stand against the levee long enough to enable development of steady-state seepage conditions. Given the relatively short duration of a flood event, Arcadis is in the opinion that a transient seepage condition should be modeled for the seepage analysis in lieu of the steady-state seepage as there is not sufficient time for steady-state seepage to develop.

The forensic study from Kenall (2016) included steady-state seepage analyses for three cross sections with toe drains on the landside. The exit gradients at Sta. 1571+21 from Kenall are shown on Figure 4.

Arcadis analyzed transient seepage without toe drains at Sta. 1571+00 using Kenall’s soil properties without toe drains. The resulting exit seepage gradients were less than 0.5, which is the maximum permissible value per USACE requirements. Based on these findings, Arcadis believes that toe drains are not needed on the landside. The results of the seepage analysis without toe drains are shown on Figure 5.

Figure 4. Steady-State Seepage Results West Levee with Toe Drains (from Kenall 2016)

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Figure 5. Exit Gradients at Levee Toe without Toe Drains – Transient Seepage (Sta. 1571+00)

Additional details for seepage analyses for Sta. 1571+00 and Sta. 1675+00 are presented in Appendix B.2. For these analyses, we have assumed the subsurface profile and soil properties provided by

USIBWC.

Transient Seepage Model: For the long-term condition, we performed transient seepage analysis to determine the pore pressures developed during the 100-year flood. We evaluated the seepage conditions using Geo-Slope software SEEP/W, a finite element program. Seepage evaluations were performed using transient seepage analysis based on the hydrograph extracted from the FLO-2D model provided by USIBWC as shown on Figure 6. No toe drains were assumed in these seepage models.

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Figure 6. Hydrograph at Sta. 1571+00

Unsaturated Characteristics: The saturated permeability values used in the analysis were provided by USIBWC (Table 5). We selected unsaturated soil characteristics for the materials above the initial groundwater. For the transient unsaturated analysis, the Soil-Water Characteristic Curves (SWCC) (i.e., matric suction versus volumetric water content) of the materials were estimated from the sample functions available in GeoStudio. The values of zero-pressure saturated volumetric content used for the soil layers ranged from 0.38 for sand to 0.5 for clay materials. These values were based on the typical volumetric water contents presented in Seep/W manual. Given the SWCC and saturated permeability, the unsaturated permeability versus matric suction functions of the materials were predicted based on the equation of Van Genuchten method included in the SEEP/W software.

Table 5. Soil Properties used for Seepage Analysis

Material Hydraulic

Conductivity (fps)

Vertical to Horizontal Hydraulic

Conductivity Ratio

Clay Blanket 4.9E-08 0.33

Sandy Lean Clay (levee) (1) 4.9E-08 0.33

Sandy Lean Clay (1) 3.0E-08 0.10

Fat Clay (1) 3.0E-08 0.10

Silty Sand (1) 5.0E-05 0.33

Poorly graded Sand (w. silt) (1) 3.0E-04 0.33 Note: (1) Soil properties provided by USIBWC

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Boundary Conditions: We applied two types of boundary conditions for the seepage analysis. For transient seepage analysis, the floodside boundary condition consisted of the 100-year flood event. On the protected side, we applied the seepage face review option for the boundary condition. Seepage face boundary conditions are used when the phreatic surface intersection with the ground surface needs to be determined.

Seepage Analysis Results and Conclusions: In general, a seepage exit gradient of 0.5 or less near the toe of the levee slope (where the exit gradient is defined as the ratio of entry pore pressure divided by the soil weight of an element at the discharge point) is considered acceptable. The allowable exit gradient increases linearly from 0.5 at the landside levee toe.

The transient seepage analyses indicate that significant infiltration of water from flood flows into the river side of the levee embankment is unlikely to result in a steady-state condition. Both cross sections that we analyzed indicated exit gradients of less than 0.5, which is the permissible value.

5.6.2 Slope Stability Analysis

Previous geotechnical studies from Kenall (2016) and S&BI (2008, 2010) indicated that cross sections along the levee were evaluated for seepage and slope stability. Based on our review of these previous geotechnical studies, the slope stability factors of safety were adequate for the proposed work. In this project, minor fills of less than one foot will be added to the levee portions that are being widened to satisfy the 16-foot-wide gravel roadway criteria. Typically, a wider levee means a longer seepage path and an increased stability. Therefore, seepage and slope stability will not be adversely affected by the proposed levee improvements and may be improved where new levees will be wider than the existing levees.

Arcadis acknowledges that we have evaluated the slope stability runs included in Kenall’s forensic report based on the soil properties included in Kenall’s report provided by USIBWC. The slope stability factors of safety appear to satisfy the minimum criteria. In addition, Arcadis selected two cross sections to be analyzed independently from the previous design. The cross sections selected correspond to Sta.

1571+00 and Sta. 1675+00.

Slope stability analyses were evaluated for four loading conditions, or critical cases, per USACE EM 1110-2-1913 “Design and Construction of Levees,” which include:

• End of Construction: This analysis is appropriate for levee raises as proposed in our design. Short-term (Undrained) stability analysis applies to the stability evaluation at the end-of-construction. Total stress analysis with undrained shear strength properties is typically used for low-permeability soils, and effective stress analysis with drained shear strength properties is typically used for free-draining soils. Slope stability was checked for both landside and riverside.

• Rapid Drawdown: This case assumes that a prolonged flood level drops faster than the soil can drain. The floodside slope may become unstable due to development of excess pore water pressures.

• Long-Term Stability (100-year Flood): This condition is critical for the landside of the embankment and applies to stability evaluation for a transient seepage condition. The transient seepage conditions represent a period when the excess pore pressure generated during the design hydrograph has

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• Seismic (Earthquake) Stability Analysis: This analysis was not performed as historical seismic events have not produced ground motions sufficient to require this analysis.

Slope stability analyses coupled with seepage analyses were performed using the Spencer’s Method (a force and equilibrium method) as programmed into SLOPE/W. Stability of the levee slopes depends on several factors including but not limited to: maximum flood elevation and duration, levee geometry and berms, external loads, seepage paths, levee and foundation materials, soil compaction during construction, penetrations in the levee, and drainage layers. These factors are described in more detail as follows:

• Flood: Maximum flood elevation and duration is based on the hydrograph for the 100-year flood extracted from the FLO-2D model as presented on Figure 6. From Figure 6, it can be concluded that, during the 100-year event, the base flood reaches the peak for about 1.5 days and falls back to the levee toe at about 1.1 days. Due to this short duration, the design hydrograph has not been sufficiently long to establish steady-state seepage.

• Geometry: Levee geometry is described in more detail in Section 6.2. We have used levee slopes of 3H:1V for our analysis. Steeper slopes of 2.5H:1V were also analyzed for the cross section at Sta. 1675+00 as presented in Appendix B.2.

• Geotechnical Loads: A vertical surcharge loading of 250 pounds per square foot was assumed to act on the levee crest to reflect potential area loads from operation and maintenance equipment.

• Seepage: We evaluated seepage using transient seepage analysis using the hydrograph presented on Figure 6. Before the flood, the soils are in a partially saturated condition and the degree of saturation increases as the flood seeps through the levee and the levee foundation layers. Due to the short duration of the flood, the seepage path or the phreatic surface will be lower than a steady-state seepage condition as the soil layers will not have sufficient time to become fully saturated. A lower phreatic surface leads to a higher factor of safety for the levee.

• Materials: The subsurface stratigraphy and soil characteristics for the cross sections selected for analysis were obtained from Kenall (2016). The embankment fill material consists of sandy lean clay. The levee foundation consists in general of sandy lean clay and occasionally fat clay. Silty sand and sand underlie the clay soils. The specific stratigraphy included in our analyses is presented in Appendix B.2. For our analyses, we have assumed the soil properties provided from USIBWC (Table 6).

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Table 6. Soil Properties used for Slope Stability Analysis

• Compaction: Proper soil compaction is required during construction for the clay blanket to achieve adequate strength. For our design, a 2-foot-thick clay blanket will encapsulate the existing levee. The new fill will be compacted to at least 95% of maximum density at a moisture content between 0 and +3% of optimum moisture.

• Penetrations: Several penetrations (structures and utilities) exist along the levee alignment. No seepage issues were noticed from our field observations from these levee penetrations.

Penetrations and no seepage issues have been reported by USIBWC personnel. Therefore, we believe that the existing penetrations will not present any potential seepage path.

• Drainage: Toe drains were installed during the previous construction. The toe drains are about 3 feet wide by 4 feet deep gravel-filled trenches at the landside toe. Our analyses of transient seepage conditions indicate that toe drains are not needed along the levee. The existing toe drains will be left in place. Some of the existing toe drains may be damaged during construction.

If damaged, the existing toe drains do not need to be repaired or replaced. However, a new geotextile layer extending 1 foot on each side will be placed above the toe drains and below the new embankment fill in locations where the toe drains are damaged during construction.

Slope Stability Results: The slope stability results are summarized in Table 7 and shown in Appendix B.2.

Material

Moist Unit

Weight (pcf)

Φ, (Effective / Drained) (degree)

C, (Effective / Drained)

(psf)

Φ, (Total /

Undrained) (degree)

C, (Total /

Undrained) (psf)

Clay Blanket 127 29 50 0 1,000

Sandy Lean Clay (levee) (1) 127 29 50 18 100

Sandy Lean Clay (1) 127 28 50 11 175

Fat Clay (1) 118 28 100 13 325

Silty Sand (1) 131 32 0 -- --

Poorly graded Sand (w. silt) (1) 124 34 0 -- -- Notes: (1) Soil properties provided by USIBWC.

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Table 7. Slope Stability Results

5.7 Settlement

Detailed settlement analyses performed in previous studies were evaluated for the proposed work. Due to the age of the levee and the presence of sandy soils, no further consolidation settlement associated with the original levee construction is expected to occur. Settlement analyses presented in Kenall (2016) indicate that a maximum total settlement of 4 inches is anticipated at any location along the levee. As there have been several years since the last construction, we anticipate that most of the settlement has already occurred, and some minor settlement is anticipated for the self-weight of the new fill. A minor increase in height is needed for levee portions that are being widened.

We evaluated potential future settlement for the construction of 2 feet of clay blanket as presented in Appendix B.3. The settlement analysis was based on the USACE EM 1110-1-1904 “Soil Mechanics Design – Settlement Analysis” per FEMA criteria. To accommodate the settlement of the levee during placement of the clay cap, 3 inches of overbuild will be included in the proposed levee design.

Cross Section Case

Minimum Required Factor of Safety (1) Analysis Type Calculated

Factor of Safety

Sta.

1571+00

End of Construction - Landside

1.3 Total Stress

Analysis

3.29

End of Construction - Riverside

1.3 Total Stress

Analysis

3.00

Rapid Drawdown 1.2 Total Stress Analysis

1.79

100-Year Flood 1.4 Effective Stress Analysis

2.72

Sta.

1675+00

End of Construction - Landside

1.3 Total Stress

Analysis

2.98

End of Construction - Riverside

1.3 Total Stress

Analysis

2.98

Rapid Drawdown 1.2 Total Stress Analysis

1.98

100-Year Flood 1.4 Effective Stress Analysis

2.36

Sta.

1675+00 (2.5H:1V Slope on Landside)

End of Construction - Landside

1.3 Total Stress

Analysis

2.62

End of Construction - Riverside

1.3 Total Stress

Analysis

2.99

100-Year Flood 1.4 Effective Stress Analysis

2.03

Note: (1) These factors of safety are recommended by USACE EM 1110-2-1913 for steady-state conditions.

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5.8 Interior Drainage

The interior drainage systems associated with the levee usually include storage areas, gravity outlets, pumping stations, or a combination thereof to control interior drainage. In the event that water ponds against the landside of the levee during heavy rainfall, we evaluated the effect of 1 foot of standing water on the landside on embankment and foundation stability. A conservative steady-state seepage condition was analyzed assuming 1 foot of standing water on the landside for two cross sections as shown in Appendix B.2. The slope stability analyses indicate factors of safety above 2 for these conditions, which are adequate based on the minimum factors of safety in Table 7. Based on our review of surface topographic conditions on the landside of the levee, we do not expect water to pond against the levee for long periods of time, and we do not expect surface runoff on the landside to cause erosion of the levee.

5.9 Other Design Criteria for Unique Solutions

Other design criteria for unique solutions are not applicable in this project.

6 CIVIL DESIGN

6.1 Levee Crossings

Based on the most recent topographic survey completed by FXSA, the existing levee elevation is within 6 inches of the minimum freeboard requirement throughout most of the levee alignment. More variation between the existing levee and the design elevations is found within the 100 feet of the Borderland and Country Club Bridges where the FEMA freeboard requirement is 4 feet. However, due to an agreement of USIBWC with FEMA, the required freeboard within 100 feet of the bridges is 3 feet. For our design, we have used 3 feet of freeboard for the entire levee segment including the bridge crossings.

6.1.1 Borderland Bridge Transition

The northern (upstream) end of the Borderland Bridge was not included in the Arcadis SOW for the project. At the southern (downstream) end of the Borderland Bridge, the existing concrete wall that extends south of the bridge meets the minimum freeboard requirements. However, the existing levee does not meet the minimum freeboard requirement as shown on Figure 7. There is an existing concrete pedestrian path that extends from the back of the sidewalk on Borderland Road down to the riverside bank. The opening on the riverside and the nearby rock wall (east of the walking path) do not meet the freeboard requirement, therefore, the flood control protection is needed in this area. In addition, the existing concrete path slopes from east to west toward the levee road and floodwall on the landside of the levee. USIBWC has indicated that this condition causes runoff to pond on the levee road resulting in a muddy condition and ongoing maintenance problem. For the levee transition in this area, the existing concrete walking path will be left in place and new concrete paving will be added for the full width of the levee road between the floodwall on the west side to the existing concrete walking path on the east side.

The new concrete pavement cross section has been designed to match the existing elevation of the east side of the concrete path and then slope up with a cross slope of 2% to the west side of the levee road

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(along the landside floodwall). This will ensure positive drainage of the levee road from west to east. The longitudinal slope of the eastern (low) side of the new concrete pavement will slope down to the south from approximately Sta. 1518+78 at Borderland Road to Sta. 1520+82+/- at the end of the walking path ramp. The longitudinal slope of the eastern edge of the new concrete pavement will vary from a minimum of 0.5% to a maximum of 30% to match the current existing slope of the concrete path.

The centerline alignment of the new concrete levee road will slope down at 1.18% from Sta. 1519+08 to a low point at Sta. 1519+33 to follow the slope of the eastern edge. The centerline profile of the levee road will then slope up at slopes varying from 0.19% to 1.66% to transition to the design point of vertical intersection (PVI) elevation of the levee road at Sta. 1520+60. Because the designed low point of the western edge of the levee road is below the required flood protection elevation, and the existing floodwall ends upstream of this location at Sta. 1519+53, a new floodwall will be required along the west (landside) of the levee for a distance of 108 feet to Sta. 1520+60. The required length of the new floodwall was determined by calculating the point where the design profile of the western edge of the impervious levee surface crosses the required 100-year plus 3.25 feet freeboard profile in AutoCAD Civil 3D. This point of intersection occurs at Sta. 1520+55; therefore, the proposed end of the new wall was set at Sta.

1520+60. The top of wall elevation was designed to be a minimum of 12 inches above the elevation of the western edge of the new levee aggregate road surface. The top of the new wall was designed at a minimum of 30 inches above the top of the levee road surface, as preferred by USIBWC. The design location and elevations of the new levee and concrete wall are shown on the contract drawings. The design of the new wall is described in Section 8 of the report.

Figure 7. Existing Elevations at Borderland Bridge - West Levee

Like the existing wall, a cast-in-place cantilever reinforced concrete wall is planned south of the existing floodwall near the Borderland Bridge for the levee transition on the landside. The new wall will be an extension of the existing wall.