00_31_19-1_4_A_2_201205 Upper Brownsville Levee Design Report TT REDACTED.pdf

International Boundary and Water Commission United States Section

Upper Brownsville Levee Rehabilitation

Cameron Counties, Texas

Contract No. IBM09D0006 Order No. IBM11T0002

Design Report Final Design Submittal

May 2012

TETRA TECH, INC.

17885 Von Karman Ave, Suite 500 Irvine, California 92614

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Upper Brownsville Levee Rehabilitation

Cameron Counties, Texas

Design Report Final Design Submittal

Prepared for:

International Boundary and Water Commission

United States Section 4171 North Mesa, Suite C100

El Paso, Texas 79902

Prepared by:

Tetra Tech, Inc.

17885 Von Karman Avenue, Suite 500 Irvine, California 92614

Upper Brownsville Levee Rehabilitation Contract No. IBM09D0006 Cameron County, Texas Order No. IBM11T0002 iii Final Design Report

TABLE OF CONTENTS

1. Purpose of Project

2. Review of Previous Reports and Studies

2.1 Environmental Assessment

2.2 Surveying and Mapping

2.3 Survey Control Lines

2.4 Right-of-Way

3. Field Investigation

4. Hydrology and Hydraulics

4.1 Hydrology

4.2 Hydraulic Model

4.3 Gateway International Bridge

5. Compliance with Code of Federal Regulations, Title 44, Section 65.10

5.1 Freeboard

5.2 Closures

5.3 Embankment Protection

5.4 Embankment and Foundation Stability

5.5 Settlement

5.6 Interior Drainage

5.7 Other Design Criteria – Sediment Transport

5.8 Operation Plans

5.9 Maintenance Plans

5.10 Ongoing FEMA Study Efforts

6. Geotechnical Recommendations

6.1 Settlement

6.2 Seepage

6.3 Slope Stability

6.4 Evaluation of Recent Fill Placement

6.5 Levee Embankment and Toe Drain Material Specification

6.7 Traffic Surface

7. Civil Design

7.1 Existing Facilities

7.2 Gatewell Structures

7.3 Top of Levee Raising and Widening

7.4 Effects of Reduced Cross Section on Water Surface Elevations

7.5 Top of Levee Access Road

7.6 Roadway Intersections

7.7 Maintenance Access Ramp

7.8 Union Pacific Railroad

7.9 Maintenance Recommendations

7.10 Bridge Closure Device

7.11 Vegetation Removal Zone

8. Engineer’s Opinion of Probable Cost

9. Conclusion

10. References iv Final Design Report

APPENDICES

Appendix A – Existing Structures within USIBWC ROW Appendix B – Field Investigation Forms and Photos Appendix C – HEC-RAS Model Outputs Appendix D – Gateway International Bridge Memorandum Appendix E – Survey Control Data Appendix F – Engineer’s Estimate of Probable Cost Backup Appendix G– Geotechnical Evaluation Report For Placed Fill Appendix H– Geotechnical Report Addendum Upper Brownsville Levee v Final Design Report

LIST OF TABLES

Table 2.1 – Survey Control Line Summary Table 2.2 – Rehabilitation outside Existing Levee Right-of-Way Table 2.3 – Existing Structures within USIBWC Right-of-Way Table 2.4 – Existing Landside Toe Locations with Less Than 15 Feet Table 3.1 – Summary of Existing Gatewells from Field Investigation of Sub-Reach 4 Table 4.1 – Hydraulic Summary along Donna Pump to Brownsville Sub-Reach 4 (100-

Year Flood Discharge) Table 4.2 – Top of Levee Increase along Donna Pump to Brownsville Sub-Reach 4 Table 5.1 – Minimum Factors of Safety Table 6.1 – Soil Density and Strength Parameters Table 6.2 – Computed Factors of Safety Table 7.1 – Maintenance and Replacement Summary for Existing Structures Table 8.1 – Engineer’s Estimate of Probably Cost for Levee Rehabilitation – Donna Pump to Brownsville Sub-Reach 4

LIST OF FIGURES

Figure 1.1 – Location Map (Donna Pump to Brownsville Levee System) Figure 1.2 – Location Map (Sub-Reach 4) Figure 3.1 – Existing Gatewells Identified during Field Investigation of Sub-Reach 4, Gatewells 131 to 171 Figure 3.2 – Existing Gatewells Identified during Field Investigation of Sub-Reach 4, Gatewells 172 to 205 Figure 4.1 – Locations of HEC-RAS Cross Sections Figure 4.2 – U.S. Levee Embankment, Access Roads, and U.S. Department of Homeland

Security Border Security Fence Figure 5.1 – Maximum Average Daily Flow by Water Year Recorded at USIBWC Gage

No. 04-4692.00 below Anzalduas Dam Figure 7.1 – Typical Section Showing Levee Improvements – Top of Levee Remove and

Replace Detail Figure 7.2 – Typical Section Showing Levee Improvements – Levee Raising and Widening

(Landside) Figure 7.3 – Typical Section Showing Levee Improvements – Levee Raising and Widening

(Riverside) Figure 7.4 – Typical Maintenance Access Ramp vi Final Design Report

1 Final Design Report

1. Purpose of Project

The United States Section of the International Boundary and Water Commission (USIBWC) operates and maintains the approximately 65-mile Donna Pump to Brownsville levee, which is part of the Lower Rio Grande Flood Control Project (LRGFCP) levee system, located in Hidalgo and Cameron Counties, Texas. The existing levee system was designed to protect the existing farmlands and commercial/residential buildings against the 100-year flood event. The 2006 Federal Emergency Management Agency’s (FEMA) decertification of the levee system has resulted in public and local government pressure to upgrade the levees to meet the certification requirements of National Flood Insurance Program (NFIP) regulations (44 CFR 65.10). The USIBWC contracted with Tetra Tech to provide engineering services to prepare levee rehabilitation improvement design and construction documents for the Donna Pump to Brownsville levee project.

As part of the effort to design rehabilitation improvements for the levee to meet the FEMA levee certification requirements for the Donna Pump to Brownsville levee system, Tetra Tech completed the following:

Review of a detailed field inspection (performed by USIBWC operation and maintenance [O&M] crews)

Review of all previous reports and studies Visual inspection of the existing gatewell structures (approximately 284) Geotechnical investigations and analyses Field surveys of the levee centerline and right-of-way (ROW) mapping

The minimum freeboard elevations were provided by USIBWC, and minor hydraulic analysis was performed. According to the minimum top of levee spreadsheet, the water surface elevation is 3 feet below the minimum freeboard elevations. The levee rehabilitation will raise the existing levee to a minimum elevation determined by USIBWC. The side slopes of the levee will be cleared of all vegetation with a stem or trunk greater than ½-inch diameter. All levee side slopes that are disturbed during vegetation removal or affected by grading will be reseeded to establish ground cover. On the riverside, the maximum levee side slope will be 3H:1V (horizontal to vertical); on the landside, it will vary between 3H:1V and 2.5H:1V. The top of the levee will be reconstructed to provide a minimum width of 16 feet in most locations, with 6 inches of flexible material (caliche based) on the roadway surface. USIBWC requested that Tetra Tech identify areas where the landside horizontal width is less than 15 feet wide. In these identified areas, USIBWC has determined that the side slopes may be graded at 2.5:1 to maximize the horizontal width.

The design work was utilized in the preparation of plans, specifications, and an engineer’s estimate of probable cost to rehabilitate the levee to withstand the 1-percent-annual-chance level flood (100-year flood) and address design related criteria of the FEMA levee certification requirements (44 CFR 65.10).

2 Final Design Report

This project covers the approximately 65-mile Donna Pump to Brownsville reach of the LRGFCP levee system, extending 16 miles and 49 miles within Hidalgo County and Cameron County, respectively (Figure 1.1). For planning purposes, the reach has been divided into five sub-reaches. The proposed levee rehabilitation investigation and design described in this report relate to the Upper Brownsville Levee Rehabilitation (Sub-Reach 4), which extends approximately 12 miles within Cameron County (Figure 1.2).

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Figure 1.1 – Location Map (Donna Pump to Brownsville Levee System)

4 Final Design Report

Figure 1.2 – Location Map Upper Brownsville Levee Rehabilitation (Sub-Reach 4)

5 Final Design Report

2. Review of Previous Reports and Studies

2.1 Environmental Assessment

USIBWC completed an environmental assessment (EA) in September 2007 (USIBWC 2007).

The proposed project evaluated in the EA would increase the flood containment capacity of the Donna Pump to Brownsville levee system by raising the elevation of a number of levee segments to meet a 3-foot freeboard design criterion for flood protection. Height increases of up to 2 feet were proposed to satisfy the design freeboard requirement. The increase in levee height would result in an expansion of the levee footprint due to lateral extension of the structure. Structural improvements may be required for some levee segments where seepage is a potential problem.

A memorandum submitted to USIBWC documents Tetra Tech’s understanding of and assumptions about the 2007 EA (Tetra Tech 2011c). The following assumptions have been incorporated into the design of the Donna Pump to Brownsville levee system:

The levee is centered in the 160-foot-wide survey corridor.

The levee footprint can be expanded on one side by 24 feet with an additional 15 feet allowed for clearing and grading of the service area. This expansion can occur on either the landside or riverside of the levee.

Any proposed expansion of the levee footprint would be located on the landside, except where expansion on the landside is constrained by permanent fencing, canals, and/or ROW, in which case expansion on the riverside would be required.

The proposed subsurface seepage improvement to include toe drains on the landside of the levee is currently being refined and incorporated in the design plans.

Per FEMA and U.S. Army Corp of Engineers (USACE) requirements for levee certification, the design of the levee system will include a minimum vegetation-free zone of 15 feet from the levee toe or to ROW on the landside and riverside.

The proposed vegetation removal within the levee expansion corridor has been evaluated and accepted by USIBWC.

Ongoing Section 106 consultation with the Texas Historical Commission will be performed by USIBWC.

All levee improvements are anticipated to be within the 160-foot-wide survey corridor as indicated in the EA. The Texas Historical Commission has requested that preliminary plans be submitted for its review as part of the Section 106 consultation.

6 Final Design Report

2.2 Surveying and Mapping

Melden & Hunt, Inc., conducted field surveys along the project levee in January 2011. Existing drainage features, ROW markers, and centerline survey markers were surveyed. The existing ROW markers were verified and, if needed, missing markers will be reestablished based on the recorded ROW. New ROW markers will be installed per USIBWC guidelines.

A survey control plan will be prepared to be included in the design plans to include levee alignment, levee stationing, ROW information, and survey control points.

The horizontal control for the surveying and mapping was established based on the Texas State Plane Central North American Datum of 1983 (NAD83) in feet, and the vertical control was established based on the North American Vertical Datum of 1988 (NAVD88) in feet.

2.3 Survey Control Lines

For the levee remediation design, the existing levee centerline and stationing were obtained from USIBWC survey field books and field survey verification. Design features and existing facilities that are part of this project will be located in the field during construction, based on their positioning relative to the levee centerline.

The existing centerline alignment indicated in the USIBWC survey field books differs from the alignment indicated by the field centerline markers. As a result of research and investigation, an alignment was compiled using the survey field book data and the field survey to correct the field book centerline alignment. The corrected centerline alignment is within the top of the levee. The revised centerline alignment and the stationing are different from those shown in the original survey field books. There is no direct correlation between the USIBWC field book centerline stationing and the as-built plans. There are currently two separate stationings listed in the USIBWC survey field books. From information obtained in response to request for information (RFI) No. 2, it was determined that because of the discrepancies in the USIBWC survey field books, a new survey control line stationing will be used. The first survey control stationing is from Donna Pump to the Hidalgo and Cameron County line, and the second is from the county line to the end of the levee. The following is a summary of the survey control line stationing from Donna Pump to Brownsville.

Table 2.1 – Survey Control Line Summary

Design Sub-Reach Location Begin Station End Station 1 Hidalgo County 1+00.00 0+43.03 2 Cameron County 0+43.03 635+50.41 3 Cameron County 635+50.41 1270+72.00 4 Cameron County 1270+72.00 1904+85.12 5 Cameron County 1904+85.12 2566+63.04

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2.4 Right-of-Way

The ROW documents, which were provided by USIBWC, were used to prepare a map for use in the design. The surveyor used this information to re-establish ROW markers in the field if they are missing. The existing levee was verified to be within the existing ROW. Rehabilitation of the levee will be conducted within the existing levee ROW except for locations indicated in Table 2.2.

Table 2.2 – Rehabilitation outside Existing Levee Right-of-Way

Begin Station End Station Private Property Owner 1763+00 1765+00 Geo ID: 71-1330-1330-0000-00

BROWNSVILLE PUBLIC UTILITIES BOARD

PO Box 3270 Brownsville, TX 78523-3270

1795+00 1802+00 Geo ID: 07-9800-2080-0015-00

EL SABINO INC.

5805 N Laguna Circle South Padre Island, TX 8597-7608

Geo ID: 76-0020-0100-0100-01

LEGGETT VICKI MICHELLE WATERS IND EXCRX ESTATE

OF WALT O. WATERS

RR 1 Box 688A Harlingen, TX 78552-9689

1862+00 1866+00 Geo ID: 76-0020-0100-0100-01

LEGGETT VICKI MICHELLE WATERS IND EXCRX ESTATE

OF WALT O. WATERS

RR 1 Box 688A Harlingen, TX 78552-9689

By overlaying the ROW on an aerial photograph, it was determined that several property owners have existing structures within the ROW. These existing structures have been identified and submitted to USIBWC, Real Estate Department. The existing structures within the ROW are summarized in Table 2.3; exhibits depicting existing structures within USIBWC ROW are provided in Appendix A.

On May 16, 2012, USIBWC has noted to Tetra Tech that temporary easement to construct riprap along river sideslope (Design Station 1885+10.00 to 1898+00.00) has been obtained (R.O.W.661C and R.O.W. 662C).

8 Final Design Report

Table 2.3 – Existing Structures within USIBWC Right-of-Way

Approximate Levee Design Station

Owner Contact Information

1327+00 Geo ID: 79-0110-0800-0901-00 Prop ID: 160358

DIAZ MARIA HILARIA CAVAZOS

24 Holly Lane Brownsville, TX 78520-8320

1319+00 Geo ID: 79-0110-0800-0020-00 Prop ID: 160330

DIAZ MARIA HILARIA CAVAZOS

24 Holly Lane Brownsville, TX 78520-8320

1749+00 Geo ID: 71-1330-1330-0000-00 Prop ID: 116215

BROWNSVILLE PUBLIC UTILITIES BOARD

PO Box 3270 Brownsville, TX 78523-3270

1831+00 to 1864+00 Geo ID: 01-0000-0080-0081-00 Prop ID: 27431

NOPHAL EDGAR JR.

175 Duval Street Brownsville, TX 78526-4087

Geo ID: 01-0000-0090-0111-00 Prop ID: 27445

STUART JERRY R.

2519 Maple Springs Dallas, TX 75235

Geo ID: 01-0000-0090-0081-00 Prop ID: 27440

LAURIN ROSARIO T.

5566 Windridge Drive Cincinnati, OH 45248-1743

Geo ID: 01-0000-0090-0110-00 Prop ID: 27444

YBARRA MIGUEL

c/o Jerry or Maria L. Stuart 2519 Maples Springs Dallas, TX 75235-8225

Geo ID: 01-0000-0090-0080-00 Prop ID: 27439

HERNANDEZ JESUS

208 D Street Brownsville, TX 78520-4128

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Table 2.3 – Existing Structures within USIBWC Right-of-Way (Continued)

Station

Owner Contact Information

1831+00 to 1864+00 (Continued)

Geo ID: 01-0000-0080-0820-00

NO OWNER INFORMATION

Geo ID: 01-0000-0060-0080-00 Prop ID: 27417

MARTINEZ ELVIA GLORIA

514 D Street Brownsville, TX 78520

Geo ID: 01-0000-0090-0070-00 Prop ID: 27438

LAURIN ROSARIO T.

5566 Windridge Drive Cincinnati, OH 45248-1743

Geo ID: 01-0000-0060-0090-00 Prop ID: 27418

GARZA ANTONIO

414 D Street Brownsville, TX 78520-4130

Geo ID: 01-0000-0090-0120-00 Prop ID: 27446

RAMIREZ JOSE DE JESUS & TERESA M.

254 D Street Brownsville, TX 78520-4128

Geo ID: 01-0000-0080-0070-00 Prop ID: 27430

YBARRA FRANCISCO N. ET UX

2106 W. Arbor Street Harlingen, TX 78552-7401

Geo ID: 01-0000-0090-0091-00 Prop ID: 27442

GOMEZ LUIS LAURO & ROSALVA H.

15 Soto Drive Brownsville, TX, 78520-9420

Geo ID: 01-0000-0060-0120-00 Prop ID: 27421

RAMIREZ JOSE PABLO ET UX

254 D Street Brownsville, TX 78520-4128

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Station

Owner Contact Information

1831+00 to 1864+00 (Continued)

Geo ID: 01-0000-0070-0090-00 Prop ID: 27424

GARZA RAQUEL R.

414 D Street Brownsville, TX 78520-4130

Geo ID: 01-0000-0060-0100-00 Prop ID: 27419

HERNANDEZ MANUEL S.

536 D Street Brownsville, TX 78520-4131

Geo ID: 01-0000-0080-0110-00 Prop ID: 27435

GARCIA RAFAELA

344 D Street Brownsville, TX 78520-4129

Geo ID: 01-0000-0060-0110-00 Prop ID: 27420

CHARLES ERNESTINA

665 Habana Street Brownsville, TX 78526-1845

Geo ID: 01-0000-0090-0100-00 Prop ID: 27443

MEJORADO JORGE MARTIN

224 D Street Brownsville, TX 78520-4128

Geo ID: 01-0000-0080-0120-00 Prop ID: 27436

BUSTOS FRANCISCO & FRANCISCA

354 D Street Brownsville, TX 78520-4129

Geo ID: 01-0000-0070-0100-00 Prop ID: 27426

YANEZ JOSE MARIO & ISABEL

434 D Street Brownsville, TX 78520-4130

Geo ID: 01-0000-0080-0090-00 Prop ID: 27433

HERRERA DONATO

324 D Street Brownsville, TX 78520

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Station

Owner Contact Information

1831+00 to 1864+00 (Continued)

Geo ID: 01-0000-0090-0090-00 Prop ID: 27441

GOMEZ LUIS LAURO & ROSALVA H.

15 Soto Drive Brownsville, TX 78520-9420

Geo ID: 01-0000-0060-0070-00 Prop ID: 27415

ABREGO CARLOS

1755 N Vermillion Avenue Brownsville, TX 78521-6716

Geo ID: 01-0000-0080-0100-00 Prop ID: 27434

LOPEZ MARIA

334 D Street Brownsville, TX 78520

Geo ID: 01-0000-0070-0120-00 Prop ID: 27428

DELGADO ALFONSO M & MARY JAY

444 D Street Brownsville, TX 78520

Geo ID: 01-0000-0070-0111-00 Prop ID: 27427

RODRIGUEZ CARLOS & GUADALUPE F.

446 East D Street Brownsville, TX 78520-4130

Geo ID: 01-0000-0070-0070-00 Prop ID: 27423

GARZA ANTONIO JR. ET UX

414 D Street Brownsville, TX 78520-4130

Geo ID: 01-0000-0070-0070-00 Prop ID: 27423

GARZA ANTONIO JR. ET UX

414 D Street Brownsville, TX 78520-4130

12 Final Design Report

Tetra Tech has identified locations along the Upper Brownsville Levee where the distance from the landside toe to the ROW, existing property fence, or DHS border wall is less than 15 feet (Table 2.4). In such areas, the landside side slope will be excavated to a 2.5H: 1V side slope to provide the maximum horizontal width possible.

Table 2.4 – Existing Landside Toe Locations with Less Than 15 Feet

Begin Station End Station Comments 1398+00 1399+00

Existing levee side slopes have been graded to 2.5:1 to provide the maximum horizontal width possible to existing ROW, property fence line or DHS Border Wall.

1404+00 1405+00 1414+00 1415+00 1422+00 1423+00 1502+00 1509+00 1593+00 - 1696+00 1698+00 1764+00 - 1771+00 1776+00 1797+00 - 1807+00 1821+00 1832+00 - 1834+00 1837+00 1842+00 1849+00 1883+00 1884+00 1874+00 1875+00

ROW = right-of-way

13 Final Design Report

3. Field Investigation

The Tetra Tech team conducted a field investigation from January 3 to 7, 2011. The investigation was conducted by driving and walking the entire length of the Upper Brownsville Levee system while visually assessing the existing flood protection elements. Notable findings and the existing conditions of the levee during the walk were documented with photographs, and georeferenced locations were recorded with a GPS unit. During the field investigation, the team used a summary maintenance field log prepared by USIBWC. The field log indicates gatewells that need repair as part of the operation and maintenance and sluice gates that need to be replaced.

Heavy vegetated areas on either the landside or riverside of the levee prevented the team from verifying several inlet and outlet structures.

A construction note within the design plans instructs the contractor to clean out or clear the area to allow USIBWC to inspect the gatewells and determine the necessary action. The trees and bushes within the levee’s vegetation-free zone need to be completely removed for completion of the investigation and to satisfy USACE/FEMA requirements. The existing gatewells are shown on Figure 3.1 and Figure 3.2. Photographs of the existing levee features are included in Appendix B.

Several gatewells need to be cleaned out because the pipe is silted up and the existing ground is higher than the invert of the pipe. Several gates were observed to have missing parts that prevent them from sealing, making them inoperable. USIBWC has requested a complete replacement of gates, rather than adding or replacing a stem or gate blocks. The findings from the field investigation are summarized in Table 3.1.

The field investigation did not include an inspection of the operation of the sluice gate within the gatewell. It was determined that the USIBWC Mercedes O&M crew is currently performing this activity and that the maintenance summary sheet in the field log provided by USIBWC was sufficient for Tetra Tech’s structural verifications (Duran 2011). USIBWC will modify the Tetra Tech scope of work to reflect this revision. The USIBWC Mercedes O&M crew’s field investigation from January to February 2011, findings are included in Table 3.1.

14 Final Design Report

Figure 3.1 – Existing Gatewells Identified during Field Investigation of Upper Brownsville Levee, Gatewells 131 to 171

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Figure 3.2 – Existing Gatewells Identified during Field Investigation of Upper Brownsville Levee, Gatewells 172 to 205

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Table 3.1 – Summary of Existing Gatewells from Field Investigation of Upper Brownsville Levee

Structure USIBWC Inspection Notes

J.J: 3/8/11 Cleaned and lubed guides and stem. Ran gate open and close.

Knocked off a lot of surface rust off the bottom of the ring. Set screw rusted, needs minor concrete repair.

J.J: 3/8/11 Cleaned and lubed guides and stem. Ran gate open and close.

Knocked off a lot of surface rust off the bottom of the ring. Needs minor concrete repair.

J.J: 3/8/11 Cleaned and lubed stem and guides. Ran gate open and close. The ring is pitted and will not seal. The brackets, nuts and bolts that were installed to fix the left guide are corroded.

133L

J.J: 3/8/11 Ran gate open and close. Had to dig out the caliche out of the gate latch slots in order to close the gate. Cannot check the bottom seal of the gate due to too much water. Therefore can't certify. Lateral drain needs clearing of trees.

J.J: 3/7/11 Cleaned and lubed guides and stem. Ran gate open and close. The stem needs a stop nut on the bottom part to prevent gate from coming off the guides. The collar needs adjustment and smaller diameter bolts to allow the collar to shift sideways. So the stem is not binding and causing the gate to come off the guides when open.

J.J: Plugged str. Needs a foot of dirt to completely fill up the str. Need to clear trees growing out of the str. Needs painting.

J.J: 3/7/11 Str. Needs 2 1/2 feet of dirt to completely fill up the str. Need to clear trees growing out of the str.

J.J: 3/7/11 Cleaned and lubed guides and stem. Ran gate open and close good seal. Bottom of ring rusty and stem is missing the stop nut. - Headwalls need concrete work.

J.J: 3/7/11 Lubed and oiled stem and guides. Ran gate open and close. Bottom ring pitted won't seal. Landside headwall needs replacement or repair.

J.J: 3/7/11 Lubed and oiled stem and guides. Ran gate open and close. Seals good, bottom part of the ring is rusty. Headwalls need concrete work.

J.J: 3/1/11 Cleaned and lubed guides and stem. Ran gate open and close.

Bottom of ring is rusty. - Stop screw to the stop nut us corroded

J.J: 3/1/11 Str. Has no hardware. Str. Was plugged with a metal plate, and concrete on the bottom seal.

147AL

Right guide is missing all three blocks and bottom bolt and nut. Guide is loose. Left guide is missing the two bottom blocks, bolts, and nuts. Gate will not seal properly.

Bottom nuts and bolts to both guides are corroded.

J.J: 2/25/11 Cleaned and lubed the guides and stem. Ran gate open and close.

There's rust by the bottom of the ring. Good seal.

J.J: 2/25/11 Did not inspect due to bees inside the marker pipe by the structure.

J.J: 2/25/11 Cleaned and lubed the guides and stem. Ran gate open and shut.

Good seal. 2 nuts and bolts to gear assembly are corroded, but gear assembly works good. Needs some concrete work.

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152 J.J: 2/25/11 Did not inspect due to low oxygen level. 18.8 153 J.J: 2/25/11 Did not inspect due to low oxygen level

J.J: 2/25/11 Lubed and cleaned the guides and stem. Ran gate open and close.

L/S headwall needs a grill, headwall has a drop, it's a safety hazard.

155 Not Inspected by USIBWC 158 Not Found 159 Not Found

J.J: 2/24/11 Lubed and cleaned guides and stem. Gate won't open all the way.

Need to modify stem. The gate lacks about 1/4" to seal flush with ring. - Need to remove the frozen stop nut, install a new stop nut and adjust it right. - Bolts to both guides are corroded. Still holding but corroded. - Grill needs modification to accommodate wheel. - Gate ring 9 bottom half rusted needs mortar on top of ring.

J.J: 2/24/11 Plugged, Str. Needs 7 1/2 ft. of dirt to fill up str. - Real safety hazard. Need to cut two bolts sticking up from pedestal housing. It's a trip hazard.

J.J: 2/24/11 Plugged - Entrance handle to str. Is broken with sharp edges.

Needs to be cut off with cutting torch. Str. Needs 4 1/2" of dirt.

J.J: 2/24/11 Plugged - About 2" of the floodside drain pipe is exposed and broken on the end. Str. Needs 4' of dirt to fill to the top.

169 J.J: 2/24/11 Plugged - Str. Needs 4 1/2' of dirt to fill up the top.

170 J.J: 2/24/11 Plugged - Str. Needs 2 1/1' of dirt to fill the str.

J.J: 2/23/11 Lubed and cleaned guides and stem. Ran gate open and close.

Good seal. Stem needs a stop nut to prevent gate from going past the seal.

J.J: 2/23/11 Lubed and cleaned guides and stem. Ran gate open and close.

Good seal. Need to replace the stop nut and re-adjust. - Bottom nut and bolt to the U/S side guide is broken off.

173 J.J: 2/23/11 Plugged Str. Needs 4ft. Of dirt to completely fill the str.

J.J: 2/23/11 Cleaned and oiled guides and stem. Ran gate open and close. - Good seal. - Gate has two broken chips on top of gate but still seals. Stem needs a stop nut on top of stem to prevent gate from passing the seal. And needs a stop nut on bottom stem to prevent gate from coming off the guides. - Nuts and bolts to the U/S guide corroded.

176 J.J: 2/23/11 Str. Needs 2ft of dirt to completely fill the str.

177 Not Found

177L

J.J: 2/23/11 - Cannot inspect due to too much water in the well. - Need to vactor out water. - Might need to berm the floodside headwall. With H.E. and set a pump.

J.J: 2/17/11 Cleaned and oiled guides and stem. Ran gate open and close.

Cannot check the bottom seal because there's a foot of slushy muddy water.

Landside headwall needs concrete work. 3 nuts to pedestal gear box corroded.

J.J: 2/17/11 Cleaned and oiled guides and stem. Ran gate open and close.

Right guide is loose and needs adjustment. When gate is raised all the way it comes off the guides because of the loose right guide. Needs work. Landside headwall needs concrete work.

180 J.J: 2/17/11 Plugged Str. Needs a foot of dirt to fill to the top

J.J: 2/17/11 Plugged - Needs 2 1/2ft of dirt to completely fill up to the top of str.

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181A

J.J: 2/17/11 Lubed guides and stem. Ran gate open and close. Has a good seal. 15 inches from the face of the ring towards the landside pipe there is a 1/2" crack all the way around the drain pipe that needs to be mortared and sealed. Both headwalls need concrete work.

181AL

J.J: 2/17/11 The gate was closed and we lubed the stem and opened the gate.

Did not go into well because of too much water. Cannot inspect until the water is vactored out. F/S headwall needs concrete work. And clearing of grasses.

J.J: 2/17/11 Plugged, concrete broken up. Needs 1ft of dirt to fill up to the top of str.

183 J.J: 2/16/11 Str. Needs 2 ft of dirt to fill to the top of the str.

184 J.J: 2/16/11 str. Needs 1 foot of dirt to completely fill up to the top.

J.J: 2/16/11 Cleaned, lubed guides and stem. Ran gate open and close. Gate seals good. Stem is missing the stop nut.

187 Not Found 188 J.J.: Str. Needs 5ft of dirt to fill up to the top of the str.

J.J: 2/16/11 Lubed guides and stem. Ran gate down but won't close all the way because there is a foot of slushy mud in the well. Needs to be vactored out.

190 Not Found 191 Not Found 191AL Abandoned Gatewell 191L Not Inspected by USIBWC

J.J: 2/16/11 Inline str. With no hardware or gate. Headwall on the landside plugged. Pipes from the in-line str. To the floodside headwall are open

193 J.J: 2/16/11 Plugged needs 2 ft of dirt to fill up to the top of str.

194 J.J: 2/16/11 Plugged needs 2 ft of dirt to fill up to the top of str.

195 Lou: 2/15/11 Str. Well has 2 ft drop to the dirt.

196 Lou: 2/15/11 PLUGGED - Str. Well uncovered has a 2' drop to the dirt.

Lou: 2/15/11 Completely underwater - needs either vactor or 2" pump to pump out the water.

201 Lou: 3/23/11 2/15/11 PLUGGED - needs about 2 ft of dirt in well.

198 Lou: 2/15/11 PLUGGED - Lacking about 4 ft of dirt.

Lou: 2/15/11 Need vactor to remove about 2 ft of water in order to inspect.

Also needs lighter grill installed preferably expanded metal. (floodside has pipe going from str. To 24" round well where it turns about 45 degrees to the headwall. This is uncovered and a major safety hazard.). Not Inspected by

USIBWC

204 Lou: 2/15/11 PLUGGED - Has metal plate cover, bolted down.

204L Not Inspected by USIBWC

205 Not Inspected by USIBWC

19 Final Design Report

4. Hydrology and Hydraulics

4.1 Hydrology

No hydrologic analysis was performed by Tetra Tech for this project. Based on a study completed by USIBWC in 2003, the design flood for the LRGFCP is based on a peak flow of 250,000 cubic feet per second (cfs) at Rio Grande City, which attenuates to 235,000 cfs at Peñitas. During the design flood, Anzalduas Diversion Dam and Retamal Diversion Dam would each divert 105,000 cfs into the United States and Mexico. Flow diversion during the design flood would limit flood flows through the Brownsville-Matamoros area to 20,000 cfs (USIBWC 2007).

4.2 Hydraulic Model

The hydraulic analysis of the project reach along the Rio Grande was provided by USIBWC (2003). The hydraulic model was created using the Hydrologic Engineering Center-River Analysis System (HEC-RAS) program, version 3.0 (USACE 2001). The 2003 model was based on the geometrical cross-sectional data used in a 1992 HEC-2 model for the channel of the Rio Grande and the floodways in the United States. The Rio Grande data were modified for the established Restricted Use Zone (floodplains on both sides of the Rio Grande) and additional bridges and to include data for 24 additional new cross sections that were surveyed.

The 2003 HEC-RAS model contains 153 cross sections between Anzalduas Diversion Dam and the downstream extent of the U.S. levee embankment near Brownsville, and it extends beyond the limits of this study at the upstream end. A total of 113 HEC-RAS cross sections are located within the project limits for the Donna Pump to Brownsville levee rehabilitation; 33 HEC-RAS cross sections are located within Upper Brownsville Levee. The locations of HEC-RAS cross sections within Upper Brownsville Levee are shown on Figure 4.1.

The computed water surface elevations for the design discharge of 20,000 cfs were used in the hydraulic analysis for the levee rehabilitation (Table 4.1). The elevations in the model are referenced to the NAVD88. The outputs from the HEC-RAS model are included in Appendix C.

20 Final Design Report

Figure 4.1 – Locations of HEC-RAS Cross Sections

21 Final Design Report

Table 4.1 – Hydraulic Summary along Donna Pump to Brownsville Upper Brownsville Levee (100- Year Flood Discharge)

HEC-RAS

River Station

Invert Elevation

(feet)

Water Surface

Elevation (feet)

Flow Velocity (feet/second)

Top Width (feet)

Froude Number

73.8 14.64 49.97 3.5 1,933.27 0.13

72.9 14.14 49.31 1.83 5,789.94 0.08

72.2 10.74 48.72 3.34 3,727.23 0.12

70.7 15.64 47.76 2.74 1,962.03 0.1

70.5 12.34 47.61 3.22 2,319.55 0.12

70.2 15.44 47.45 2.84 4,389.66 0.1

67.4 15.84 44.96 3.11 6,658.7 0.13

67.25 13.14 44.71 3.95 6,939.18 0.14

64.7 11.64 43.15 3.11 5,891.24 0.11

63.8 7.84 42.81 2.4 4,195.46 0.09

62.5 10.24 42.23 3.57 3,009.07 0.13

61.3 3.04 41.65 2.39 4,190.06 0.1

59.9 9.14 40.55 3.58 2,741.37 0.13 59 4.14 40.15 3.38 3,862.51 0.12

58.8 6.64 40.11 2.65 3,542.62 0.1

58.3 5.64 39.83 3.3 405.77 0.13

57.7 2.74 39.59 3.1 1,516.32 0.11

56.9 7.54 39.26 2.84 1,542.04 0.12

56.7 5.84 38.95 3.15 430.51 0.14

56.1 9.64 38.22 3.53 440.92 0.17

55.5 0.94 37.2 4.52 243.6 0.19

55.25 2.94 36.91 4.09 445.75 0.15

55.23 -0.16 36.93 3.49 428.27 0.13

55.215 Railroad bridge

55.21 -0.16 36.88 3.5 425.29 0.13

55.2 -0.16 36.88 3.5 425.2 0.13

54.5 -1.46 36.61 3.21 720.25 0.11

54.49 4.94 36.51 3.85 486.11 0.14

54.475 Southbound Gateway International Bridge

54.47 4.94 36.47 3.86 485.33 0.14

54.46 4.94 36.47 3.86 485.32 0.14

54.45 0.64 36.46 3.86 366.27 0.14

54.435 Northbound Gateway International Bridge

Note: All elevations are based on NAVD88.

The minimum amount that the top of the levee must be raised was determined by USIBWC and provided as part of the design. The necessary increases in top of levee elevation are indicated in Table 4.2. It is noted that river station (RS) 73.8 of the existing levee needs to be raised to satisfy FEMA’s freeboard requirement of 3 feet. The total length of the existing levee within Upper Brownsville Levee is approximately 12 miles, per USIBWC limits.

22 Final Design Report

Table 4.2 – Top of Levee Increase along Donna Pump to Brownsville Upper Brownsville Levee

HEC-RAS

River Station

Existing Top of Levee

Elevation1 (feet)

Water Surface

Elevation2 (feet)

Existing Freeboard

(feet)

Minimum Top of Levee

Elevation (feet)

Increased top of Levee3

(feet)

73.8 51.70 49.97 1.73 52.97 1.27

72.9 52.69 49.31 3.37 52.31 0.00

72.2 51.97 48.72 3.25 51.72 0.00

70.7 51.38 47.76 3.62 50.76 0.00

70.5 51.06 47.61 3.45 50.61 0.00

70.2 51.30 47.45 3.85 50.45 0.00

67.4 49.15 44.96 4.19 47.96 0.00

67.25 - 44.71 - - -

64.7 47.82 43.15 4.67 46.15 0.00

63.8 - 42.81 - - -

62.5 48.15 42.23 5.92 45.23 0.00

61.3 47.15 41.65 5.50 44.65 0.00

59.9 43.55 40.55 3.00 43.55 0.00 59 43.58 40.15 3.43 43.15 0.00

58.8 44.66 40.11 4.55 43.11 0.00

58.3 43.92 39.83 4.09 42.83 0.00

57.7 43.31 39.59 3.72 42.59 0.00

56.9 42.79 39.26 3.53 42.26 0.00

56.7 43.10 38.95 4.15 41.95 0.00

56.1 42.48 38.22 4.26 41.22 0.00

55.5 - 37.20 - - -

55.25 - 36.91 - - -

55.23 42.73 36.93 5.80 39.93 0.00

55.215 B & M Bridge

55.21 - 36.88 - - -

55.2 - 36.88 - - -

54.5 - 36.61 - - -

54.49 - 36.51 - - -

54.475 Southbound Gateway International Bridge

54.47 - 36.47 - - -

54.46 - 36.47 - - -

54.45 - 36.46 - - -

54.435 Northbound Gateway International Bridge

Note: All elevations are based on NAVD88.

1 Top of levee elevations were provided by USIBWC.

2 USIBWC assume 3 feet below minimum top of levee elevation.

3 Increased top of levee done by USIBWC in 2007, not part of this project.

- = no information available

23 Final Design Report

4.3 Gateway International Bridge

The Gateway International Bridge connects Brownsville, Texas, to Matamoros, Tamaulipas, Mexico. The bridge currently includes a southbound (upstream) span and a northbound span, which cross the Rio Grande at RS 54.475 and RS 54.435, respectively.

USIBWC is responsible for operation and maintenance of the levee along the left bank of the Rio Grande. Since the Rio Grande serves as the border between the United States and Mexico, the U.S. Department of Homeland Security (DHS) constructed a border security fence that is located in the access road along the crown of the levee (Figure 4.2). Per USIBWC, the length of levee in this location is not to be part of the Upper Brownsville Levee design. The fence obstructs access to the levee embankment, possibly limiting access by the USIBWC for flood fighting. The location of the levee embankment along the outside of the bend makes the embankment particularly subject to scour and erosion. To reduce the need for access to the levee during flood events, the USIBWC is considering the construction of an erosion protection along the riverward slope of the levee embankment. Although improvements to this location are not part of the Upper Brownsville Levee design, Tetra Tech prepared an analysis of the existing hydraulic conditions and the risk of embankment erosion. The analysis was documented in a technical memorandum submitted to the USIBWC on March 30, 2011 (Tetra Tech 2011a).

Figure 4.2 – U.S. Levee Embankment, Access Roads, and U.S. Department of Homeland Security

Border Security Fence

-5

0 25 50 75 100 125 150 Distance (feet) from Levee Crown

E le v a ti o n fe e t, N

A V

D

Access Road along Levee Toe

Levee Embankment

Access Road along Levee Crown

DHS Security Fence (approx.)

Rio Grande

24 Final Design Report

An analysis was also performed to determine alternatives that would mitigate erosion as a result of the flow velocity as well as to provide a depth of protection based on the expected scour depth. For several of the alternatives, loose rock revetment was assumed as the erosion protection. Future design phases should consider other options for sloped revetment such as concrete slope paving, Armorflex, and soil cement. The results of this analysis are also presented in the memorandum, which is included as Appendix D.

During the 90% Design Review/ Presentation, USIBWC requested that riprap be placed on the riverside banks from the top of levee to the existing riverside access road. Tetra Tech stated that this would be a temporary solution, as the riprap is not properly toed below the river scour potential. The river may scour and wash out the riverside road and the temporary riprap protection.

25 Final Design Report

5. Compliance with Code of Federal Regulations, Title 44, Section 65.10

The Code of Federal Regulations (44 CFR 65.10) includes a description of the types of information FEMA needs in order to recognize (or “accredit”), on NFIP maps, that a levee system provides protection from the base flood. The following information addresses the design criteria identified in 44 CFR 65.10 and is intended to provide additional information for use by USIBWC in developing the FEMA levee certification package. Tetra Tech’s scope of work does not include developing the information/analyses to support the FEMA levee certification package; however, the following information is provided to aid USIBWC in development of that information and analyses.

Specific design criteria are listed, as well as other criteria as specified on the MT-2 Forms. MT-2 Form 3 (Riverine Structures) includes a description of required sediment transport information.

5.1 Freeboard

According to 44 CFR 65.10, the freeboard requirements are as follows:

A minimum of 3 feet above base flood (100-year) water surface level.

An additional 1 foot above minimum within 100 feet of structures/bridges/constrictions.

An additional 0.5 foot at the upstream end of the levee, tapering to not less than the minimum at the downstream end of the levee.

A comparison of the 100-year water surface elevations from the USIBWC HEC-RAS model of the Rio Grande along Upper Brownsville Levee and the proposed top of levee elevations shown on the drawings of the proposed design (Tetra Tech 2011d) indicates one location where the 3-foot minimum freeboard is not provided. The deficient freeboard is located at the downstream edge of Los Fresnos Pump Canal, where the proposed top of levee elevation is a maximum of

0.88 feet lower than the required height based on the minimum 3 feet of freeboard for a horizontal distance of approximately 115 feet. A strategy for dealing with the deficient freeboard at the canal should be part of the future Los Fresnos Pump Canal closure design.

5.2 Closures

Upper Brownsville Levee includes 58 gatewell structure side drains. Of these gatewells, 33 are operational and 25 have been abandoned. The 33 operational gatewells include working existing sluice gates or will have new sluice gates installed, which meet FEMA’s requirements for a closure device. During construction, the inlet and outlet pipes to the 25 abandoned gatewells will be excavated, and brick and mortar sealed to provide permanent closure. The soil within the existing gatewell structure will be excavated and the steel plates to be removed. The outlet pipe, inlet pipe and cavity of the gatewell structures would be filled with flowable fill. USACE requires that all discharge pipes be inspected using a television camera or other visual inspection at least every 5 years. This is not included specifically as part of FEMA’s requirements for levee certification.

26 Final Design Report

There is one opening along Upper Brownsville Levee where no closure device is provided. This opening is located at the Los Fresnos Pump Canal. The canal does not meet FEMA’s requirement of providing a closure at openings along the levee system. The design of a closure device for the canal is not part of Tetra Tech’s current scope of work, as it will be designed and constructed under a separate future contract.

5.3 Embankment Protection

According to 44 CFR 65.10, engineering analyses must be submitted that demonstrate that no appreciable erosion of the levee embankment can be expected during the base flood and that anticipated erosion will not result in failure of the levee embankment.

To demonstrate that no appreciable erosion of the levee embankment can be expected during the base flood, flow velocities were extracted from the HEC-RAS model of the Rio Grande along Upper Brownsville Levee provided by the USIBWC. No appreciable erosion of the levee embankment is expected during the base flood based on velocities identified in the HEC-RAS model along the left/north bank (maximum of 1.3 feet per second [fps]) or the maximum velocity expected through the bends based on the equation on Plate B-33 in Engineer Manual (EM) 1110- 2-1601, a maximum of 1.7 fps (USACE 1994). Flood waters become erosive at velocities greater than 5 fps for grass-lined earthen channels per EM 1110-2-1601.

The one exception is at the Gateway International Bridge. At this location, the main channel is very close to the levee and the main channel velocity rather than left bank velocity was considered. The channel velocity at this location approaches 5 fps, which is the limit of permissible velocities for earthen embankments. Embankment protection should be considered along this reach as discussed in Section 4.3.

5.4 Embankment and Foundation Stability

According to 44 CFR 65.10, engineering analyses must be submitted that demonstrate that seepage into or through the levee foundation and embankment will not jeopardize embankment or levee stability. The geotechnical evaluation of this reach performed by Raba-Kistner Consultants, Inc. (R-K) indicated that construction of internal drainage was required to mitigate potential seepage conditions during flood stage (R-K 2011b). It was recommended that a toe drain with a minimum base width of 3 feet extending at least 18 inches below the landside toe of the levee be included in the proposed rehabilitation design. Seepage analysis indicated that implementation of the toe drain would control seepage pressures within the levee and foundation soils and would reduce hydraulic exit gradients to less than 0.5. The toe drain detail has been incorporated into the design drawings and specifications. With this condition, seepage associated with the base flood is not expected to jeopardize the embankment or foundation stability.

Slope stability analyses were performed on pertinent cross sections of the proposed rehabilitated levee. The results of the analyses relative to FEMA criteria are provided in Table 5.1.

27 Final Design Report

Table 5.1 – Minimum Factors of Safety

Condition Calculated Minimum Factor of

Safety USACE Required Factor of

Safety End of construction 1.7 1.3 Long-term (steady seepage) 2.1 1.4 Rapid drawdown 1.8 1.0 to 1.2

The results of the analyses indicate that the proposed levee design meets the FEMA levee criteria for embankment and foundation stability.

5.5 Settlement

According to 44 CFR 65.10, engineering analyses must be submitted that assess the potential and magnitude of future losses of freeboard as a result of levee settlement and demonstrate that freeboard will be maintained within the minimum freeboard standards. The geotechnical evaluation for this project indicated that placement of 3 feet of additional fill height could induce total settlement (compression and long-term consolidation) of approximately 3-1/4 inches. The proposed design would not significantly raise the current levee height but rather it would reconstruct portions of the existing levee with engineered fill. As a conservative measure to maintain the required freeboard, the proposed design height of the levee has been increased by 4 inches to mitigate potential settlement.

5.6 Interior Drainage

According to 44 CFR 65.10, joint probability analysis of the sources of flooding landward of the levee and the river itself must be completed and the extent of the flooded area provided. It is expected that this will be a significant effort because of the number of side drains (approximately 58 over Upper Brownsville Levee) and the ownership of these systems outside of USIBWC right-of-way. USIBWC should note that this analysis will be required as part of a levee certification submittal to FEMA. Tetra Tech’s current contract does not include providing any support with regard to the interior drainage analysis.

5.7 Other Design Criteria – Sediment Transport

A sediment transport analysis is required if there is any indication from historical records that scour and deposition can affect the base flood elevation (BFE), or if based on stream morphology, vegetative cover, development of the watershed, and bank conditions, there is a potential for debris and sediment transport to affect the BFE or a structure. If sediment transport will not affect the BFE or any structures, an explanation is required as to why a sediment transport analysis was not performed.

Related to the U.S. (north) levee embankment structure along the Rio Grande between Retamal Dam (south of Donna, Texas) and Brownsville, Texas, the following initial investigations were conducted to identify whether there is potential for sediment transport to affect the BFE or the

28 Final Design Report levee embankment. These investigations focused on the Rio Grande along Upper Brownsville Levee levee but extended upstream as required by the available information.

5.7.1 Analysis of Long-Term Aggradation/Degradation

A trend of long-term aggradation could reduce channel capacity and impact the freeboard of the levee; a trend of degradation could impact channel stability, which could in turn influence the stability of the levee. A review of hydrologic conditions was conducted to characterize the influence of floods on the potential to mobilize, transport, and deposit sediment within the Rio Grande along the Upper Brownsville Levee levee.

USIBWC operates a flow gage on the Rio Grande upstream of the north levee embankment (Gage No. 08-4692.00 below Anzalduas Dam near Reynosa, Tamaulipas, Mexico). Construction of Anzalduas Dam was completed in April 1960 so that floodwaters could be diverted from the Rio Grande into the interior U.S. floodway. Construction of upgrades to Retamal Dam, located approximately 39 miles downstream of Anzalduas Dam, were completed in May 1975 to divert floodwaters to the interior Mexican floodway and to limit floods at Brownsville-Matamoros to the safe capacity of the Rio Grande. According to USIBWC Minute No. 238, the design flood flow below Anzalduas Dam is 20,000 cfs (USIBWC 2003). A review of the average daily discharges recorded between 1960 (when Anzalduas Dam was constructed) and 2010 indicates that floods in excess of the design flow occurred in 9 years. Other than the flooding associated with Hurricane Beulah in September 1967 (maximum average daily discharge of 121,000 cfs), the maximum average daily flow rate was 41,300 cfs in water year 1972 (Figure 5.1). However, considering only the period after 1975 when the upgrades to Retamal Dam were completed, four floods with maximum average daily discharges exceeding 20,000 cfs occurred; the maximum average daily flow of 27,300 cfs occurred in water year 1976. Further investigation of the magnitude of the design flood is warranted to confirm that 20,000 cfs is consistent with the peak flow during the 100-year flood (i.e., the base flood). The current effective FEMA Flood Insurance Study (FIS) indicates that a discharge of 20,000 cfs has a 500-year recurrence level.

29 Final Design Report

Figure 5.1 – Maximum Average Daily Flow by Water Year Recorded at USIBWC Gage No. 04-

4692.00 below Anzalduas Dam

On a long-term basis, most bed material sediment is mobilized, transported, and deposited during flood flows. Since the design flood has been exceeded four times since the upgrades to Retamal Dam were completed in 1975, the system has been tested by major flooding. Assuming the flood regime since 1975 is representative of the future flood regime (due to the regulation of floods by Anzalduas Dam and Retamal Dam), it is expected that future opportunities for floods to transport sediment will be similar. Therefore, any existing trends in long-term aggradation or degradation that are in response to flood hydrology may continue into the future.

Little information was available to evaluate whether long-term aggradation/degradation has the potential to affect the BFE or the Upper Brownsville Levee. Due to the set-back of the levee embankment from the Rio Grande channel, the risk of degradation of the channel and corresponding bank failures appears low; however, this expectation should be confirmed by USIBWC maintenance staff.