07_-_Vado_Final_Design_Memorandum_w-o_E_20110629.pdf

International Boundary and Water Commission United States Section

Rehabilitation Improvements

For the Vado East Levee Doña Ana County, New Mexico

Contract No. IBM09D0006 Order No. IBM10T0044

Final Design Memorandum

July 29, 2011

TETRA TECH, INC.

17885 Von Karman Ave, Suite 500 Irvine, California 92614

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Vado East Levee Contract No. IBM09D0006 Doña Ana County, New Mexico Order No. IBM10T0044

Rehabilitation Improvements For the Vado East Levee

From Station 636+20 to Station 692+20 Doña Ana County, New Mexico

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 Ave, Suite 500 Irvine, CA 92614 i

TABLE OF CONTENTS

1.0 Project Overview

1.1 Introduction

1.2 Purpose of Project

1.3 Project Description

1.4 Right-of-way Constraints

1.5 Field Reconnaissance

1.6 Comparison of Design Options

2.0 Surveying and Mapping

3.0 Hydrology and Hydraulics

3.1 General

3.2 FLO-2D 2009 Model versus Baseline Model

3.3 FLO-2D Project Conditions Model

3.4 Channel Flow Velocity

4.0 Geotechnical Recommendations

4.1 Foundation Conditions

4.2 Seismic Conditions

4.3 Seepage Conditions

4.4 Embankment and Foundation Stability

4.5 Settlement

4.6 Material Specifications

5.0 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

5.7.1 Hydrologic Analysis

5.7.2 Analysis of Long-Term Aggradation/Degradation

5.7.3 Conclusion

5.7.4 Additional Investigations

5.8 Other Design Criteria – Riverbed Scour

5.8.1 Scour Protection

5.8.2 Conclusion

5.9 Operation Plans

5.10 Maintenance Plans

6.0 Civil Design

6.1 Design Constraints

6.2 Alignment Selection

6.3 Levee Tie-in at Project Limits

6.4 New Levee Construction

6.5 Improvement of Existing Levee

ii

6.6 Riprap Protection

6.6.1 Riprap Sizing

6.6.2 Toedown Depth

6.7 Alignment of Del Rio Culvert Replacement

6.8 Storm Drain and Irrigation Drain Penetrations

7.0 Structural Design

7.1 Reference Documents

7.2 Culvert Sections for Design

7.3 Static Loads

7.4 Live Loads

7.5 Seismic Loads

7.6 Culvert Design

7.7 Culvert Construction

8.0 Construction Issues

8.1 Construction Staging

8.2 BNSF Coordination

8.3 Construction Traffic

8.4 De-Watering and Surface Water Control

8.5 Assess for Local Residences

9.0 Construction Schedule

10.0 Environmental Issues

11.0 Opinion of Probable Cost (OPC)

12.0 References

LIST OF FIGURES

Figure 1.1 – Location Map Figure 1.2 – Typical Existing Section Figure 1.3 – Location of Project Features Figure 3.1 – Surveyed Sections Location Map Figure 3.2 – Profiles of Maximum WSE for 2009 and Baseline Models Figure 3.3 – Profiles of Maximum WSE for Project Conditions Models and Top of Levee

Elevations Figure 5.1 – Computed flood-frequency curve for the Rio Grande at El Paso gage and maximum mean daily flows for the Rio Grande gages below Caballo, Leasburg, and at El Paso

Figure 5.2 – Computed Aggradation/Degradation Depths for Each Subreach for the Annual Flow-duration Curve

Figure 6.1 – Typical New Earthen Levee Embankment Sections Figure 6.2 – Typical Re-Constructed Earthen Levee Embankment Sections Figure 6.3 – Bed Form Prediction as a function of Fr and R/D50 Figure 6.4 – Del Rio Channel Culvert Plan View Figure 6.5 – Del Rio Drain Culvert Figure 6.6 – Storm Drain Alignment (36” diameter RCP) Figure 6.7 – Irrigation Drain (2’X3’ RCB) iii

Figure 7.1 – Del Rio Drain Channel Culvert Figure 9.1 – Conceptual Construction Schedule

LIST OF TABLES

Table 1.1 – Summary of Project Features Table 3.1 – FLO-2D 2009 Model and Baseline Model Comparisons (East Levee Only) Table 3.2 – FLO-2D 2009 Model and Project Conditions Model Comparisons (East Levee Only) Table 3.3 – FLO-2D Baseline Model and Project Conditions Model Comparisons Table 3.4 – FLO-2D Channel Maximum Flow Velocity Comparisons Table 4.1 – Peak Ground Acceleration Table 4.2 – Slope Stability Factors of Safety Table 4.3 – Flex Base Material Requirements Table 5.1 – Minimum Factors of Safety Table 6.1 – Rock Sizing for Riprap Protection (100-year Level Protection)

APPENDICIES

Appendix A – Photographs of Project Features Appendix B – Hydraulic Calculations Appendix C – Geotechnical Report Appendix D – Structural Calculations Appendix E – Cost Engineering Report iv

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1.0 Project Overview

1.1 Introduction

The United States Section of the International Boundary and Water Commission (USIBWC) has recently conducted hydraulic and geotechnical studies to assess the ability of the United States levees of the Rio Grande Canalization Flood Control Project (RGCFCP) to safely contain flood flows in the Rio Grande. From these studies, the USIBWC has determined that the ‘CE1’ reach of the levees require rehabilitation improvements for safe containment of the RGCFCP design flood flows.

The CE1 reach (project reach) is a small part of the Canutillo Levee Segment, located in the vicinity of Vado in Doña Ana County, New Mexico, and extends for a length of approximately

1.08 levee miles. The reach extends approximately from upstream of Del Rio Drain Outlet (upstream) to Three Saints Lateral / Waste Way No.19 (downstream). The existing east levee alignment (Vado East Levee) currently encroaches on the right of way of both the Elephant Butte Irrigation District (EBID) and the Burlington Northern Santa Fe Railroad (BNSF). In fact the current levee alignment follows the BNSF railroad embankment for roughly 888 feet. Recent levee improvements have been completed immediately upstream and downstream of the project limits. These improvements were designed by S&B Infrastructure Ltd. (S&B 2010) and included raising of the levee crest.

The location map of the project reach is shown in Figure 1.1.

1.2 Purpose of Project

The purpose of this project was to first explore three different design alternatives to determine the preferred design approach to provide the required improvements and rehabilitation to the project levee. Following the review of this study by USIBWC, Tetra Tech coordinated with USIBWC to select the preferred design option and then generated construction plans, specifications, and opinion of probable costs for the preferred option as required by the Scope of Work (SOW).

1.3 Project Description

The proposed levee rehabilitation consists of the following: (1) raising the top of the east levee elevations to provide a minimum of 3 feet above the water surface elevations (WSE) for the RGCFCP design flood flows; (2) providing seepage control structures, as required, to control through-seepage and under-seepage; and (3) rehabilitation of existing hydraulic structures and appurtenances located within the levee by modifying them to be in accordance with the raised levee cross-section, repairing any damages as necessary, and adding gates to un-gated structures.

Due to right of way constraints with both BNSF and EBID, the upstream portion of the project will require a re-alignment of the levee and construction of new levee embankment. The downstream portion of the project will involve only rehabilitation of the existing levee.

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Figure 1.1 – Location Map

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1.4 Right-of-way Constraints

Based on the review of the existing USIBWC Right-of-way (ROW) boundaries, the upper half segment of the project levee between the upstream end of the project (Station 636+20) and the north end of an adjacent pecan farm (Station 665+00) is predominantly located outside of the USIBWC ROW. Currently, a combination of the railroad maintenance road (which crosses EBID ROW) and railroad embankment, owned by BNSF, serves as a levee with deficient freeboard along this segment. In order to remain within the USIBWC ROW, a new levee structure in this segment would need to be built at least 100 feet away from the existing railroad embankment to ensure the levee footprints are limited to the USIBWC ROW. The separation from the existing railroad embankment would place the new levee within the Rio Grande, encroaching into the current flow area of the river. Additionally, this new levee would require placing fill material outside of the USIBWC ROW, between the new levee and the existing railroad maintenance road. This fill placement is necessary in order to eliminate sump areas behind the new levee. The fill placement has been designed such that it is limited to USIBWC and EBID ROW. No fill placement will be performed on BNSF ROW.

The typical section showing relative locations of ROW and existing levee is shown in Figure 1.2.

Figure 1.2 – Typical Existing Section

1.5 Field Reconnaissance

Field reconnaissance of the project area was conducted by Tetra Tech on November 1, 2010, and May 3, 2011. The reconnaissance was performed by walking the entire alignment and taking notes and photographs of pertinent project features including existing drainage and irrigation structures, vegetation, survey and right of way monuments, utilities, and other project features.

A summary of pertinent features is presented on Table 1.1. Locations of noted features were approximately located by GPS survey. Feature locations are also shown on Figure 1.3.

Photographs of each feature are presented in Appendix A.

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Table 1.1 – Summary of Project Features

Feature ID No. Photo No Description 1 5 Private Property Adjacent to u/s Portion of the Project 2 13 USIBWC ROW Marker (#82171) 3 21 Survey Marker (8891) 4 30 Existing confluence of Del Rio Drain w/ Rio Grande 5 35 Access gate to BNSF ROW 6 38 Upstream Inlet of Del Rio Drain CMP 7 41 Downstream outlet of Del Rio Drain CMP 8 45 BNSF ROW (rail embankment is current levee alignment) 9 46 Terrain adjacent to BNSF ROW (note tree vegetation adjacent to Rio Grande 10 47 ROW Marker (77186/89300) 11 48 Existing survey control (damaged) 12 51 Typical Tree Vegetation Along Proposed Levee Aligment 13 58 ROW Marker (77129/89278) & unmarked survey control 14 61 Damaged ROW Marker (77124) 15 62 USIBWC ROW Marker 16 64 Overhead Power Lines & Debris Piles 17 66 USIBWC ROW Marker (77169?) & Station Marker (659+03.8) 18 70 Irrigation Ditch Adjacent to USIBWC ROW 19 81 Outlet of Existing Irrigation RCP (landside slope of levee) 20 86 Inlet of Existing Irrigation RCP (riverside slope of levee) 21 88 Irrigation Pump Facility with OH Power Drop and Elec. Box (riverside of levee) 22 95 USIBWC ROW Marker (# not readable) 23 97 USIBWC ROW Marker (# 77174) & Survey Control Marker 24 107 Damaged Survey Control Marker 25 115 Tie-in with Current Construction at Downstream End of Project

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Figure 1.3 – Location of Project Features

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1.6 Comparison of Design Options

As part of the preliminary scope of work Tetra Tech evaluated three design alternatives that meet the project requirements. Details of the comparative study are presented in the Tetra Tech report entitled “Design Options Study, Rehabilitation Project for Vado East Levee” dated January 18, 2011 (Tetra Tech 2011). The findings of this study are briefly discussed as follows.

Various levee design measures were analyzed to determine a preferred design option to rehabilitate the existing Vado East Levee. The rehabilitation of the levee should accomplish the followings:

Provide a minimum of 3 feet freeboard above the water surface elevations (WSE) for the RGCFCP design flood flows within the entire project reach;

Provide seepage control structures, as required, to control through-seepage and under-seepage; and

Rehabilitate existing hydraulic structures and appurtenances located within the levee by modifying them to be in accordance with the raised levee cross-section, repairing any damages as necessary, and adding gates to ungated structures.

Based on the project goals stated above and design requirements specified in the SOW, Tetra Tech prepared preliminary design plans and Opinion of Probable Cost (OPC) of the following design options:

Design Option No.1 – Sheet Pile Wall

Design Option No.2 – Reinforced Concrete Floodwall

Design Option No.3 – Earthen Levee Embankment

The new levee structures in the three design options above would be constructed in the entire upper half segment where the existing levee (existing railroad embankment and maintenance road) does not meet the required freeboard requirement.

In the comparison of the OPCs of different the design options, the earthen levee (Design Option No.3) would require approximately $ 5.3 million less and $ 8.5 million less than the design options Nos. 1 and 2, respectively. However, the earthen levee would require more channel excavation (approximately ~ 130,000 cubic yards) along the west side of Rio Grande to compensate for larger flow conveyance area lost by a larger footprint of earthen levee. Any excavation activities within Rio Grande will require permits from regulatory agencies.

Because all three design options would generate almost the same improvement benefits to the project, Tetra Tech recommended the earthen levee option (Design Option No.3) as a preferred design option for the Vado East Levee, which would require the lowest construction cost.

Additionally, the earthen levee design option is likely to avoid constructional difficulties that may arise from excavating or pile-driving more than 40 feet into the channel bottom to place sheet piles or floodwall foundation piles, respectively. In consultation with USIBWC, the

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Design Option 3 – Earthen Levee Embankment was selected as the design option, and Tetra Tech proceeded to prepare plans and specifications for this option.

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2.0 Surveying and Mapping

Zia Engineering & Environmental Consultants, LLC. (Zia) conducted field surveys along the project levee in November and December, 2010, to complement the USIBWC-provided topographic data (channel cross section surveys (2004) and Light Detection and Ranging (LIDAR) data (2005)). The field survey included performing cross sectional surveys along the levee alignment at a 250-foot interval for the entire project reach. The cross sections and the LIDAR data were processed to generate a 3-dimensional surface and topographic mapping with elevation contours, using Autodesk Civil 3D Software.

The horizontal control for the surveying and mapping were established based on New Mexico State Plane Coordinate Grid System (NMSPCGS) Central Zone North American Datum of 1983 (NAD83) in feet, while the vertical control was established based on the North American Vertical Datum of 1988 (NAVD88) in feet.

Supplemental surveying was performed by Zia in June 2011, and included verifying as-built conditions of the recently re-constructed portions of Vado East Levee immediately upstream and downstream of the current project limits. In addition, a total of five construction survey control points were established along the project alignment.

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3.0 Hydrology and Hydraulics

3.1 General

The hydraulic analysis of the Rio Grande within the project limits was performed using a FLO- 2D software, a two-dimensional flood routing hydraulic model, developed by FLO-2D Software, Inc. A FLO-2D model of the Rio Grande from Caballo Dam to American Dam was developed in October 2005 by Tetra Tech for the U.S. Army Corps of Engineers (USACE) for the RGCFCP.

The model had been evolved and used by the USACE for the river geomorphic study (USACE 2007) and for the conceptual river restoration study (USACE 2009).

The hydraulic results of FLO-2D models were used to analyze the current freeboard availability with existing levee conditions and ensure the project improvements to the existing levee would provide the FEMA-required freeboard for the freeboard deficient areas, under the 100-year level flood condition. In addition, the hydraulic analysis was used to ensure the project improvements would not adversely affect the hydraulic conditions of adjacent levees, such as Vado West Levee and levees upstream and downstream of the project reach.

For this project, the most current FLO-2D hydraulic model (2009 model), provided by USIBWC, was updated and developed into the baseline model (baseline model) by incorporating twenty-five (25) new cross sections within the project limits, surveyed in November and December, 2010. Locations of the surveyed cross sections with respect to the project limits are depicted on Figure 3.1.

Figure 3.1 – Surveyed Sections Location Map

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Graphical cross sections of the FLO 2D analysis are presented in Appendix B. Details of the FLO 2D modeling are contained in the DVD which accompanies this report.

3.2 FLO-2D 2009 Model versus Baseline Model

The computed maximum water surface elevations (WSEs) in the vicinity of the project reach are presented in Table 3.1 and graphically displayed on Figure 3.2 for both the 2009 and baseline models. Top of levee elevations in Table 3.1 were obtained from the levee data file from the baseline FLO-2D model and were used to compute the available freeboard for both 2009 and baseline models.

Table 3.1 – FLO-2D 2009 Model and Baseline Model Comparisons (East Levee Only)

River Mile

Top of Vado East Levee Elevation

(feet)

FLO-2D Maximum WSE (feet) Freeboard (feet)

Model

Baseline Model

Changes from 2009

Model

Model Baseline Model

28.03 3,827.801 3,822.81 3,822.83 0.02 4.99 4.97

27.96 3,827.001 3,822.62 3,822.65 0.03 4.38 4.35

27.90 3,826.701 3,822.42 3,822.45 0.03 4.28 4.25

27.87 3,826.701 3,822.23 3,822.26 0.03 4.47 4.44

27.81 3,826.201 3,822.05 3,822.08 0.03 4.15 4.12

Vado Bridge

27.75 3,824.501 3,821.47 3,821.62 0.15 3.03 2.88

27.69 3,824.401 3,821.44 3,821.62 0.18 2.96 2.78

27.63 3,824.101 3,821.32 3,821.51 0.19 2.78 2.59

27.57 3,824.101 3,821.23 3,821.43 0.20 2.87 2.67

27.51 3,823.901 3,821.12 3,821.33 0.21 2.78 2.57

27.48 3,823.601 3,821.01 3,821.23 0.22 2.59 2.37

27.44 3,823.501 3,820.89 3,821.12 0.23 2.61 2.38

27.38 3,823.201 3,820.77 3,821.01 0.24 2.43 2.19

27.34 3,822.901 3,820.64 3,820.89 0.25 2.26 2.01

27.28 3,822.801 3,820.47 3,820.72 0.25 2.33 2.08

27.24 3,822.501 3,820.28 3,820.52 0.24 2.22 1.98

27.18 3,822.001 3,820.10 3,820.35 0.25 1.90 1.65

27.11 3,822.001 3,819.88 3,820.14 0.26 2.12 1.86

27.05 3,822.901 3,819.61 3,819.86 0.25 3.29 3.04

Upstream Limit of Project Reach

26.99 3822.001/3823.012 3,819.29 3,819.55 0.26 2.71 3.46

26.92 3822.001/3823.002 3,818.98 3,819.28 0.30 3.02 3.72

26.85 3822.901/3819.182 3,818.69 3,819.14 0.45 4.21 0.04

26.79 3823.101/3819.852 3,818.43 3,818.98 0.55 4.67 0.87

26.72 3822.101/3819.082 3,818.18 3,818.68 0.50 3.92 0.40

26.69 3822.001/3818.382 3,817.97 3,818.27 0.30 4.03 0.11

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River Mile

Top of Vado East Levee Elevation

(feet)

FLO-2D Maximum WSE (feet) Freeboard (feet)

Model

Baseline Model

Changes from 2009

Model

Model Baseline Model

26.63 3822.001/3822.042 3,817.77 3,818.02 0.25 4.23 4.02

26.59 3818.901/3821.942 3,817.58 3,817.86 0.28 1.32 4.08

26.54 3819.601/3821.282 3,817.39 3,817.59 0.20 2.21 3.69

26.50 3819.801/3818.872 3,817.20 3,817.38 0.18 2.60 1.49

26.45 3820.001/3820.102 3,817.01 3,817.24 0.23 2.99 2.86

26.40 3820.301/3820.142 3,816.82 3,817.07 0.25 3.48 3.07

26.36 3820.501/3820.362 3,816.65 3,816.94 0.29 3.85 3.42

26.31 3820.401/3820.842 3,816.48 3,816.72 0.24 3.92 4.12

26.27 3820.201/3820.282 3,816.32 3,816.46 0.14 3.88 3.82

26.22 3820.001/3821.032 3,816.14 3,816.31 0.17 3.86 4.72

26.17 3819.701/3820.662 3,815.98 3,816.16 0.18 3.72 4.50

26.11 3819.501/3820.202 3,815.82 3,816.05 0.23 3.68 4.15

26.05 3818.801/3819.792 3,815.64 3,815.92 0.28 3.16 3.87

26.01 3818.701/3819.502 3,815.47 3,815.77 0.30 3.23 3.73

25.94 3818.401/3818.932 3,815.34 3,815.67 0.33 3.06 3.26

25.88 3817.801/3818.862 3,815.20 3,815.48 0.28 2.60 3.38

25.84 3817.801/3818.472 3,815.02 3,815.14 0.12 2.78 3.33

Downstream Limit of Project Reach

25.77 3,817.801 3,814.82 3,814.96 0.14 2.98 2.84

25.71 3,817.501 3,814.66 3,814.81 0.15 2.84 2.69

25.64 3,817.201 3,814.50 3,814.66 0.16 2.70 2.54

25.60 3,816.701 3,814.25 3,814.43 0.18 2.45 2.27

25.53 3,816.601 3,814.01 3,814.21 0.20 2.59 2.39

25.48 3,816.401 3,813.84 3,814.03 0.19 2.56 2.37

25.43 3,816.501 3,813.67 3,813.85 0.18 2.83 2.65

25.37 3,816.001 3,813.51 3,813.67 0.16 2.49 2.33

25.32 3,815.901 3,813.36 3,813.52 0.16 2.54 2.38

25.26 3,815.701 3,813.24 3,813.38 0.14 2.46 2.32

25.21 3,816.001 3,813.08 3,813.22 0.14 2.92 2.78

25.17 3,815.801 3,812.90 3,813.04 0.14 2.90 2.76

25.10 3,815.601 3,812.75 3,812.89 0.14 2.85 2.71

25.06 3,815.501 3,812.66 3,812.80 0.14 2.84 2.70

25.00 3,815.001 3,812.54 3,812.69 0.15 2.46 2.31

24.96 3,815.001 3,812.40 3,812.55 0.15 2.60 2.45

24.91 3,814.401 3,812.24 3,812.40 0.16 2.16 2.00

24.87 3,816.001 3,812.10 3,812.25 0.15 3.90 3.75

24.82 3,815.001 3,811.96 3,812.11 0.15 3.04 2.89

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Top of Vado East Levee Elevation

(feet)

FLO-2D Maximum WSE (feet) Freeboard (feet)

Model

Baseline Model

Changes from 2009

Model

Model Baseline Model

24.77 3,817.501 3,811.81 3,811.97 0.16 5.69 5.53

24.73 3,814.501 3,811.66 3,811.82 0.16 2.84 2.68

24.68 3,814.501 3,811.50 3,811.67 0.17 3.00 2.83

24.63 3,814.301 3,811.31 3,811.49 0.18 2.99 2.81

24.59 3,814.001 3,811.10 3,811.27 0.17 2.90 2.73

24.54 3,814.001 3,810.89 3,811.06 0.17 3.11 2.94

24.49 3,813.501 3,810.69 3,810.86 0.17 2.81 2.64

24.44 3,813.101 3,810.46 3,810.62 0.16 2.64 2.48

24.39 3,813.001 3,810.19 3,810.35 0.16 2.81 2.65

24.35 3,813.001 3,809.93 3,810.08 0.15 3.07 2.92

24.30 3,813.101 3,809.67 3,809.81 0.14 3.43 3.29

24.25 3,812.901 3,809.38 3,809.51 0.13 3.52 3.39

24.21 3,812.201 3,809.05 3,809.17 0.12 3.15 3.03

24.15 3,812.701 3,808.65 3,808.76 0.11 4.05 3.94

24.10 3,812.201 3,808.15 3,808.25 0.10 4.05 3.95

24.05 3,811.301 3,807.92 3,808.01 0.09 3.38 3.29

24.01 3,811.301 3,807.53 3,807.62 0.09 3.77 3.68

23.96 3,811.101 3,807.21 3,807.29 0.08 3.89 3.81

23.91 3,810.801 3,806.92 3,807.00 0.08 3.88 3.80

23.86 3,810.901 3,806.56 3,806.65 0.09 4.34 4.25

23.81 3,810.201 3,806.17 3,806.26 0.09 4.03 3.94

23.77 3,810.201 3,805.83 3,805.90 0.07 4.37 4.30

23.72 3,810.201 3,805.56 3,805.62 0.06 4.64 4.58

23.67 3,810.201 3,805.34 3,805.39 0.05 4.86 4.81

23.62 3,810.101 3,805.14 3,805.19 0.05 4.96 4.91

23.58 3,810.001 3,804.97 3,805.01 0.04 5.03 4.99

23.53 3,809.801 3,804.82 3,804.87 0.05 4.98 4.93

1. Top of levee elevation obtained from FLO-2D 2009 model.

2. Top of levee elevation obtained from November 2010 cross sectional survey data.

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Figure 3.2 – Profiles of Maximum WSE for 2009 and Baseline Models

For the 2009 and baseline models, freeboard deficiencies were found at locations upstream of and beyond the project reach. Within the project reach, freeboard deficiencies occurred in many cross sections and were as large as 2.96 feet at RM 26.85 in the baseline model.

Overall, the computed maximum WSEs from the baseline model were higher than those from the 2009 model. The maximum increase in the WSE, compared to the 2009 model, was 0.55 feet, occurred at River Mile (RM) 26.79 located within the project limits. The increase in WSE was likely caused by incorporation of more surveyed channel cross sections in the baseline model.

Channel modeling for the 2009 model was based on surveyed cross sections that were located far apart and interpolated cross sections between them. In fact, there are only two surveyed cross sections within the project limits (near the upstream and downstream ends, approximately 5,000 feet gap) for the 2009 model, while the baseline model was based on twenty-five (25) individually surveyed cross sections within the project limits with a 250 feet interval.

Incorporation of additional topographical details likely has created differences in the modeling results, including increase in WSEs within the project limits. It should be noted that according to Table 3.1, both the 2009 and baseline models do not meet the FEMA freeboard requirements.

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3.3 FLO-2D Project Conditions Model

The Project Conditions model was developed in FLO-2D by incorporating the relevant aspects of the proposed improvements to the Vado East Levee, including re-alignment of portions of the levee and channel excavation within the Rio Grande floodplain, into the baseline model.

Comparisons of the computed maximum WSEs of the Project Conditions Model to those of the baseline model are presented in Table 3.2 for both the baseline and Project Conditions Models.

Table 3.2 – FLO-2D 2009 Model and Project Conditions Model Comparisons (East Levee Only)

Mile

Top of Vado East Levee Elevation

(feet)

FLO-2D Maximum WSE (feet)

Baseline Model

Project Conditions

Model

Changes from Baseline Model

28.03 3,827.801 3822.83 3822.81 -0.02

27.96 3,827.001 3822.65 3822.62 -0.03

27.90 3,826.701 3822.45 3822.42 -0.03

27.87 3,826.701 3822.26 3822.23 -0.03

27.81 3,826.201 3822.08 3822.05 -0.03

Vado Bridge

27.75 3,824.501 3821.62 3821.31 -0.31

27.69 3,824.401 3821.62 3821.26 -0.36

27.63 3,824.101 3821.51 3821.12 -0.39

27.57 3,824.101 3821.43 3821.02 -0.41

27.51 3,823.901 3821.33 3820.90 -0.43

27.48 3,823.601 3821.23 3820.78 -0.45

27.44 3,823.501 3821.12 3820.65 -0.47

27.38 3,823.201 3821.01 3820.51 -0.50

27.34 3,822.901 3820.89 3820.36 -0.53

27.28 3,822.801 3820.72 3820.15 -0.57

27.24 3,822.501 3820.52 3819.91 -0.61

27.18 3,822.001 3820.35 3819.69 -0.66

27.11 3,822.001 3820.14 3819.42 -0.72

27.05 3823.402 3819.86 3819.05 -0.81

Upstream Limit of Project Reach

26.99 3823.011/3823.163 3819.55 3818.88 -0.67

26.92 3823.001/3823.053 3819.28 3818.81 -0.47

26.85 3819.181/3822.953 3819.14 3818.66 -0.48

26.79 3819.851/3822.843 3818.98 3818.46 -0.52

26.72 3819.081/3822.593 3818.68 3818.23 -0.45

26.69 3818.381/3822.323 3818.27 3818.01 -0.26

26.63 3822.041/3822.093 3818.02 3817.83 -0.19

17 Final Design Memorandum

Top of Vado East Levee Elevation

(feet)

FLO-2D Maximum WSE (feet)

Baseline Model

Project Conditions

Model

Changes from Baseline Model

26.59 3821.941/3821.863 3817.86 3817.70 -0.16

26.54 3821.281/3821.683 3817.59 3817.56 -0.03

26.50 3818.871/3821.443 3817.38 3817.43 0.05

26.45 3820.101/3821.213 3817.24 3817.26 0.02

26.40 3820.141/3820.993 3817.07 3817.06 -0.01

26.36 3820.361/3820.833 3816.94 3816.93 -0.01

26.31 3820.841/3820.833 3816.72 3816.70 -0.02

26.27 3820.281/3820.833 3816.46 3816.45 -0.01

26.22 3821.031/3820.453 3816.31 3816.30 -0.01

26.17 3820.661/3820.123 3816.16 3816.15 -0.01

26.11 3820.201/3819.833 3816.05 3816.04 -0.01

26.05 3819.791/3819.533 3815.92 3815.90 -0.02

26.01 3819.501/3819.233 3815.77 3815.76 -0.01

25.94 3818.931/3819.023 3815.67 3815.66 -0.01

25.88 3818.861/3819.003 3815.48 3815.47 -0.01

25.84 3818.471/3818.983 3815.14 3815.14 0.00

Downstream Limit of Project Reach

25.77 3,817.801 3814.96 3814.95 -0.01

25.71 3,817.501 3814.81 3814.80 -0.01

25.64 3,817.201 3814.66 3814.65 -0.01

25.60 3,816.701 3814.43 3814.42 -0.01

25.53 3,816.601 3814.21 3814.20 -0.01

25.48 3,816.401 3814.03 3814.02 -0.01

25.43 3,816.501 3813.85 3813.84 -0.01

25.37 3,816.001 3813.67 3813.66 -0.01

25.32 3,815.901 3813.52 3813.51 -0.01

25.26 3,815.701 3813.38 3813.37 -0.01

25.21 3,816.001 3813.22 3813.21 -0.01

25.17 3,815.801 3813.04 3813.02 -0.02

25.10 3,815.601 3812.89 3812.88 -0.01

25.06 3,815.501 3812.80 3812.79 -0.01

25.00 3,815.001 3812.69 3812.68 -0.01

24.96 3,815.001 3812.55 3812.55 0.00

24.91 3,814.401 3812.40 3812.39 -0.01

24.87 3,816.001 3812.25 3812.24 -0.01

24.82 3,815.001 3812.11 3812.10 -0.01

24.77 3,817.501 3811.97 3811.96 -0.01

18 Final Design Memorandum

Top of Vado East Levee Elevation

(feet)

FLO-2D Maximum WSE (feet)

Baseline Model

Project Conditions

Model

Changes from Baseline Model

24.73 3,814.501 3811.82 3811.81 -0.01

24.68 3,814.501 3811.67 3811.66 -0.01

24.63 3,814.301 3811.49 3811.48 -0.01

24.59 3,814.001 3811.27 3811.26 -0.01

24.54 3,814.001 3811.06 3811.05 -0.01

24.49 3,813.501 3810.86 3810.85 -0.01

24.44 3,813.101 3810.62 3810.61 -0.01

24.39 3,813.001 3810.35 3810.34 -0.01

24.35 3,813.001 3810.08 3810.07 -0.01

24.30 3,813.101 3809.81 3809.80 -0.01

24.25 3,812.901 3809.51 3809.50 -0.01

24.21 3,812.201 3809.17 3809.16 -0.01

24.15 3,812.701 3808.76 3808.75 -0.01

24.10 3,812.201 3808.25 3808.24 -0.01

24.05 3,811.301 3808.01 3808.01 0.00

24.01 3,811.301 3807.62 3807.61 -0.01

23.96 3,811.101 3807.29 3807.28 -0.01

23.91 3,810.801 3807.00 3807.00 0.00

23.86 3,810.901 3806.65 3806.65 0.00

23.81 3,810.201 3806.26 3806.25 -0.01

23.77 3,810.201 3805.90 3805.90 0.00

23.72 3,810.201 3805.62 3805.62 0.00

23.67 3,810.201 3805.39 3805.39 0.00

23.62 3,810.101 3805.19 3805.18 -0.01

23.58 3,810.001 3805.01 3805.00 -0.01

23.53 3,809.801 3804.87 3804.85 -0.02

1. Top of levee elevation obtained from FLO-2D 2009 model.

2. Top of levee elevation based on June 2011 additional survey data.

3. Top of levee elevation obtained from project conditions model.

Comparisons in Table 3.2 showed that the Project Conditions Model resulted in slightly lower WSEs (as much as a 0.67 feet decrease), compared to the baseline model within the project limits. Beyond the project limits, the Project Conditions Model resulted in either lower WSEs or the same WSEs, compared to the baseline model. It is important to keep the WSEs of the Project Conditions Model at either the same or lower elevations, compared to the baseline conditions, because any increase may adversely affect other levees in the vicinity and cause those levees with adequate freeboard under existing conditions to be deficient in providing the required FEMA freeboard.

19 Final Design Memorandum

Freeboard analysis of the project levee and other adjacent levees, including Vado West Levee, was performed and its results are presented in Table 3.3. In order to determine freeboard, the computed maximum WSEs of the Project Conditions Model were compared to the project top of levee elevations (proposed Vado East Levee), surveyed cross sections in November and December 2010 (existing Vado West Levee), design top of levee elevations from the plans prepared by the S&B Infrastructure, Ltd., in 2010 (existing levees immediately upstream and downstream of the project reach), and levee data file from the 2009 model (existing levees upstream of Vado Bridge). The project top of levee elevations are based on the top of ‘impervious levee’ elevations presented in the Contract Drawings. The top of levee elevations and the maximum WSE profile under project conditions are depicted on Figure 3.3.

Table 3.3 – FLO-2D Baseline Model and Project Conditions Model Comparisons

Mile

Proposed Vado East

Levee Station

Maximum

WSE

(feet)

Required Freeboard

(feet)

Top of East

Levee Elevation

(feet) Freeboard

(feet) +/-

Top of West Levee

Elevation (feet)

Freeboard (feet) +/-

28.03 - 3822.81 3.00 3,827.801 4.99 1.99 3,827.101 4.29 1.29

27.96 - 3822.62 3.00 3,827.001 4.38 1.38 3,826.901 4.28 1.28

27.90 - 3822.42 3.00 3,826.701 4.28 1.28 3,826.001 3.58 0.58

27.87 - 3822.23 3.00 3,826.701 4.47 1.47 3,826.401 4.17 1.17

27.81 - 3822.05 3.00 3,826.201 4.15 1.15 3,826.401 4.35 1.35

Vado Bridge

27.75 - 3821.31 3.00 3,824.932 3.62 0.62 3,826.301 4.99 1.99

27.69 - 3821.26 3.00 3,825.232 3.97 0.97 3,825.801 4.54 1.54

27.63 - 3821.12 3.00 3,824.832 3.71 0.71 3,825.701 4.58 1.58

27.57 - 3821.02 3.00 3,824.882 3.86 0.86 3,825.601 4.58 1.58

27.51 - 3820.90 3.00 3,824.602 3.70 0.70 3,825.001 4.10 1.10

27.48 - 3820.78 3.00 3,824.242 3.46 0.46 3,824.801 4.02 1.02

27.44 - 3820.65 3.00 3,824.072 3.42 0.42 3,824.501 3.85 0.85

27.38 - 3820.51 3.00 3,824.012 3.50 0.50 3,824.401 3.89 0.89

27.34 - 3820.36 3.00 3,823.862 3.50 0.50 3,823.701 3.34 0.34

27.28 - 3820.15 3.00 3,823.682 3.53 0.53 3,823.801 3.65 0.65

27.24 - 3819.91 3.00 3,823.522 3.61 0.61 3,823.601 3.69 0.69

27.18 - 3819.69 3.00 3,823.372 3.68 0.68 3,822.801 3.11 0.11

27.11 - 3819.42 3.00 3,823.252 3.83 0.83 3,822.801 3.38 0.38

27.05 - 3819.05 3.00 3,823.403 4.35 1.35 3,822.301 3.25 0.25

Upstream Limit of Project Reach

26.99 638+15.00 3818.88 3.00 3,823.164 4.28 1.28 3,823.354 4.47 1.47

26.92 640+70.00 3818.81 3.00 3,823.054 4.24 1.24 3,823.184 4.37 1.37

26.85 643+27.50 3818.66 3.00 3,822.954 4.29 1.29 3,822.804 4.14 1.14

26.79 645+84.50 3818.46 3.00 3,822.844 4.38 1.38 3,822.814 4.35 1.35

26.72 647+69.50 3818.23 3.00 3,822.594 4.36 1.36 3,822.574 4.34 1.34

20 Final Design Memorandum

Proposed Vado East

Levee Station

Maximum

WSE

(feet)

Required Freeboard

(feet)

Top of East

Levee Elevation

(feet) Freeboard

(feet) +/-

Top of West Levee

Elevation (feet)

Freeboard (feet) +/-

26.69 650+20.00 3818.01 3.00 3,822.324 4.31 1.31 3,822.704 4.69 1.69

26.63 652+71.00 3817.83 3.00 3,822.094 4.26 1.26 3,822.654 4.82 1.82

26.59 655+21.50 3817.70 3.00 3,821.864 4.16 1.16 3,822.644 4.94 1.94

26.54 657+15.00 3817.56 3.00 3,821.684 4.12 1.12 3,822.754 5.19 2.19

26.50 659+80.30 3817.43 3.00 3,821.444 4.01 1.01 3,822.634 5.20 2.20

26.45 662+32.00 3817.26 3.00 3,821.214 3.95 0.95 3,822.314 5.05 2.05

26.40 664+82.00 3817.06 3.00 3,820.994 3.93 0.93 3,822.384 5.32 2.32

26.36 667+32.00 3816.93 3.00 3,820.834 3.90 0.90 3,822.114 5.18 2.18

26.31 669+83.00 3816.70 3.00 3,820.834 4.13 1.13 3,821.764 5.06 2.06

26.27 672+32.50 3816.45 3.00 3,820.834 4.38 1.38 3,821.344 4.89 1.89

26.22 674+83.50 3816.30 3.00 3,820.454 4.15 1.15 3,820.654 4.35 1.35

26.17 677+33.50 3816.15 3.00 3,820.124 3.97 0.97 3,820.334 4.18 1.18

26.11 679+83.50 3816.04 3.00 3,819.834 3.79 0.79 3,820.334 4.29 1.29

26.05 682+33.70 3815.90 3.00 3,819.534 3.63 0.63 3,820.414 4.51 1.51

26.01 684+83.50 3815.76 3.00 3,819.234 3.47 0.47 3,820.594 4.83 1.83

25.94 687+33.80 3815.66 3.00 3,819.024 3.36 0.36 3,820.314 4.65 1.65

25.88 689+84.00 3815.47 3.00 3,819.004 3.53 0.53 3,819.474 4.00 1.00

25.84 691+12.50 3815.14 3.00 3,818.984 3.84 0.84 3,819.444 4.30 1.30

Downstream Limit of Project Reach

25.77 - 3,814.95 3.00 3,818.802 3.85 0.85 3,818.802 3.85 0.85

25.71 - 3,814.80 3.00 3,818.422 3.62 0.62 3,818.422 3.62 0.62

25.64 - 3,814.65 3.00 3,817.902 3.25 0.25 3,817.902 3.25 0.25

25.60 - 3,814.42 3.00 3,817.902 3.48 0.48 3,817.902 3.48 0.48

25.53 - 3,814.20 3.00 3,817.812 3.61 0.61 3,817.812 3.61 0.61

25.48 - 3,814.02 3.00 3,817.782 3.76 0.76 3,817.782 3.76 0.76

25.43 - 3,813.84 3.00 3,817.652 3.81 0.81 3,817.652 3.81 0.81

25.37 - 3,813.66 3.00 3,817.452 3.79 0.79 3,817.452 3.79 0.79

25.32 - 3,813.51 3.00 3,817.282 3.77 0.77 3,817.282 3.77 0.77

25.26 - 3,813.37 3.00 3,817.082 3.71 0.71 3,817.082 3.71 0.71

25.21 - 3,813.21 3.00 3,816.942 3.73 0.73 3,816.942 3.73 0.73

25.17 - 3,813.02 3.00 3,816.922 3.90 0.90 3,816.922 3.90 0.90

25.10 - 3,812.88 3.00 3,817.002 4.12 1.12 3,817.002 4.12 1.12

25.06 - 3,812.79 3.00 3,816.562 3.77 0.77 3,816.562 3.77 0.77

25.00 - 3,812.68 3.00 3,816.002 3.32 0.32 3,816.002 3.32 0.32

24.96 - 3,812.55 3.00 3,815.762 3.21 0.21 3,815.762 3.21 0.21

24.91 - 3,812.39 3.00 3,815.652 3.26 0.26 3,815.652 3.26 0.26

24.87 - 3,812.24 3.00 3,815.522 3.28 0.28 3,815.522 3.28 0.28

21 Final Design Memorandum

Proposed Vado East

Levee Station

Maximum

WSE

(feet)

Required Freeboard

(feet)

Top of East

Levee Elevation

(feet) Freeboard

(feet) +/-

Top of West Levee

Elevation (feet)

Freeboard (feet) +/-

24.82 - 3,812.10 3.00 3,815.372 3.27 0.27 3,815.372 3.27 0.27

24.77 - 3,811.96 3.00 3,815.302 3.34 0.34 3,815.302 3.34 0.34

24.73 - 3,811.81 3.00 3,815.152 3.34 0.34 3,815.152 3.34 0.34

24.68 - 3,811.66 3.00 3,815.002 3.34 0.34 3,815.002 3.34 0.34

24.63 - 3,811.48 3.00 3,814.792 3.31 0.31 3,814.792 3.31 0.31

24.59 - 3,811.26 3.00 3,814.702 3.44 0.44 3,814.702 3.44 0.44

24.54 - 3,811.05 3.00 3,814.512 3.46 0.46 3,814.512 3.46 0.46

24.49 - 3,810.85 3.00 3,814.302 3.45 0.45 3,814.302 3.45 0.45

24.44 - 3,810.61 3.00 3,814.102 3.49 0.49 3,814.102 3.49 0.49

24.39 - 3,810.34 3.00 3,813.902 3.56 0.56 3,813.902 3.56 0.56

24.35 - 3,810.07 3.00 3,813.712 3.64 0.64 3,813.712 3.64 0.64

24.30 - 3,809.80 3.00 3,813.502 3.70 0.70 3,813.502 3.70 0.70

24.25 - 3,809.50 3.00 3,813.142 3.64 0.64 3,813.142 3.64 0.64

24.21 - 3,809.16 3.00 3,812.782 3.62 0.62 3,812.782 3.62 0.62

24.15 - 3,808.75 3.00 3,812.532 3.78 0.78 3,812.532 3.78 0.78

24.10 - 3,808.24 3.00 3,812.162 3.92 0.92 3,812.162 3.92 0.92

24.05 - 3,808.01 3.00 3,811.832 3.82 0.82 3,811.832 3.82 0.82

24.01 - 3,807.61 3.00 3,812.232 4.62 1.62 3,812.232 4.62 1.62

23.96 - 3,807.28 3.00 3,811.472 4.19 1.19 3,811.472 4.19 1.19

23.91 - 3,807.00 3.00 3,811.302 4.30 1.30 3,811.302 4.30 1.30

23.86 - 3,806.65 3.00 3,810.901 4.25 1.25 3,810.701 4.05 1.05

23.81 - 3,806.25 3.00 3,810.201 3.95 0.95 3,811.001 4.75 1.75

23.77 - 3,805.90 3.00 3,810.201 4.30 1.30 3,810.101 4.20 1.20

23.72 - 3,805.62 3.00 3,810.201 4.58 1.58 3,810.001 4.38 1.38

23.67 - 3,805.39 3.00 3,810.201 4.81 1.81 3,810.101 4.71 1.71

23.62 - 3,805.18 3.00 3,810.101 4.92 1.92 3,809.801 4.62 1.62

23.58 - 3,805.00 3.00 3,810.001 5.00 2.00 3,809.701 4.70 1.70

23.53 - 3,804.85 3.00 3,809.801 4.95 1.95 3,809.301 4.45 1.45

1. Top of levee elevation obtained from FLO-2D 2009 model.

2. Top of levee elevation obtained from drawings prepared by S&B Infrastructure, Ltd.

3. Top of levee elevation based on June 2011 additional survey data.

4. Top of levee elevation obtained from project conditions model.

22 Final Design Memorandum

Figure 3.3 – Profiles of Maximum WSE for Project Conditions Models and Top of Levee Elevations

The minimum freeboard requirement is 3 feet above the computed 100-year WSEs. However, for the portions of the proposed Vado levee which are located in the Rio Grande riverbed (approximately from Proposed Levee Station 640+00 to 658+00), the top of levee needs to be constructed to include an additional 6 inches above the minimum freeboard requirement in order to compensate for possible long-term settlement of the levee embankment over time as recommended by the geotechnical analysis in Section 4.5. Therefore, the freeboard available for the proposed Vado in the Rio Grande Riverbed needs to be a minimum of 3.5 feet to compensate for the settlement.

Based on Table 3.3, the top of the proposed levee elevations would provide the freeboard in the range of 4.12 feet to 4.38 feet where the freeboard requirement is 3.5 feet, while it would provide the freeboard in the range of 3.36 feet to 4.38 feet where the freeboard requirement is 3 feet.

Based on the results, it was concluded that the top of levee elevations in the Proposed Conditions Model, which included top of levee elevations of the project levee (Vado East Levee) and existing Vado West Levee would successfully provide the FEMA-required freeboard for the 100-year level flood condition. It was also concluded that the proposed levee improvement would not adversely affect the freeboard of adjacent existing levees.

It should be noted that FEMA also requires an additional one foot above the minimum within 100 feet in either side of structure (such as bridges) of the levee or where the flow is constricted and an additional one-half foot above the minimum at the upstream end of the levee system, 23 Final Design Memorandum tapering to not less than the minimum at the downstream end of the levee system. However, the USIBWC indicated during the conference call with Tetra Tech on March 11, 2011, that as a federal agency, the USIBWC would coordinate with FEMA in order not to incorporate the additional freeboard requirements near hydraulic structures and ends of the levee system as certification freeboard requirements.

3.4 Channel Flow Velocity

Table 3.4 compares the computed channel maximum flow velocities for the 2009, baseline, and project conditions models.

Table 3.4 – FLO-2D Channel Maximum Flow Velocity Comparisons

River Mile

2009 Model Baseline Model Project Conditions Model Maximum

Flow Velocity (ft/sec)

Maximum Flow

Velocity (ft/sec)

Changes from

Model

Maximum Flow

Velocity (ft/sec)

Changes from

Model

Changes from

Baseline Model

28.03 5.48 5.53 0.05 5.56 0.08 0.03

27.96 5.42 5.47 0.05 5.49 0.07 0.03

27.90 5.37 5.42 0.05 5.44 0.07 0.02

27.87 5.26 5.29 0.03 5.32 0.06 0.03

27.81 5.18 5.20 0.02 5.22 0.04 0.01

Vado Bridge

27.75 5.58 5.58 0.00 5.58 0.00 0.00

27.69 4.13 4.07 -0.06 4.27 0.14 0.20

27.63 4.00 3.92 -0.08 4.12 0.12 0.20

27.57 3.77 3.69 -0.08 3.91 0.14 0.22

27.51 3.77 3.68 -0.09 3.91 0.14 0.23

27.48 3.85 3.75 -0.10 4.00 0.15 0.25

27.44 3.91 3.81 -0.10 4.08 0.17 0.27

27.38 3.98 3.87 -0.11 4.18 0.20 0.31

27.34 4.05 3.95 -0.10 4.41 0.36 0.46

27.28 4.28 4.50 0.22 4.84 0.56 0.34

27.24 4.57 4.69 0.12 5.10 0.53 0.41

27.18 4.73 4.92 0.19 5.38 0.65 0.46

27.11 5.18 5.22 0.04 5.77 0.59 0.55

27.05 5.46 5.08 -0.38 5.07 -0.39 -0.01

Upstream Limit of Project Reach

26.99 5.58 4.72 -0.86 5.07 -0.51 0.35

26.92 5.58 4.53 -1.05 3.90 -1.68 -0.63

26.85 5.45 3.85 -1.60 3.77 -1.68 -0.08

26.79 5.45 4.00 -1.45 3.92 -1.53 -0.08

26.72 5.23 4.49 -0.74 3.99 -1.24 -0.50

24 Final Design Memorandum

2009 Model Baseline Model Project Conditions Model Maximum

Flow Velocity (ft/sec)

Maximum Flow

Velocity (ft/sec)

Changes from

Model

Maximum Flow

Velocity (ft/sec)

Changes from

Model

Changes from

Baseline Model

26.69 5.04 4.49 -0.55 3.99 -1.05 -0.50

26.63 5.05 4.28 -0.77 3.85 -1.20 -0.43

26.59 5.06 4.17 -0.89 3.53 -1.53 -0.64

26.54 5.06 4.17 -0.89 3.41 -1.65 -0.76

26.50 5.11 4.08 -1.03 3.49 -1.62 -0.59

26.45 5.14 3.77 -1.37 3.65 -1.49 -0.12

26.40 5.19 3.67 -1.52 3.65 -1.54 -0.02

26.36 5.19 3.92 -1.27 3.91 -1.28 -0.01

26.31 5.14 4.26 -0.88 4.26 -0.88 0.00

26.27 5.09 4.26 -0.83 4.26 -0.83 0.00

26.22 5.04 3.81 -1.23 3.81 -1.23 0.00

26.17 4.98 3.66 -1.32 3.66 -1.32 0.00

26.11 4.92 3.36 -1.56 3.32 -1.60 -0.04

26.05 4.87 3.17 -1.70 3.14 -1.73 -0.03

26.01 4.82 3.16 -1.66 3.19 -1.63 0.03

25.94 4.73 3.64 -1.09 3.64 -1.09 0.00

25.88 4.71 3.64 -1.07 3.64 -1.07 0.00

25.84 4.75 4.88 0.13 4.87 0.12 -0.01

Downstream Limit of Project Reach

25.77 4.75 4.90 0.15 4.89 0.14 -0.01

25.71 4.69 4.77 0.08 4.76 0.07 -0.01

25.64 4.70 4.79 0.09 4.78 0.08 -0.01

25.60 5.34 5.40 0.06 5.33 -0.01 -0.07

25.53 5.42 5.48 0.06 5.47 0.05 -0.01

25.48 5.49 5.55 0.06 5.53 0.04 -0.02

25.43 5.49 5.55 0.06 5.53 0.04 -0.02

25.37 5.48 5.60 0.12 5.58 0.10 -0.02

25.32 5.32 5.53 0.21 5.35 0.03 -0.18

25.26 5.29 5.33 0.04 5.31 0.02 -0.02

25.21 5.35 5.38 0.03 5.36 0.01 -0.02

25.17 5.20 5.21 0.01 5.19 -0.01 -0.02

25.10 5.13 5.21 0.08 5.19 0.06 -0.02

25.06 4.71 4.76 0.05 4.75 0.04 -0.01

25.00 4.63 4.61 -0.02 4.60 -0.03 -0.01

24.96 4.63 4.64 0.01 4.63 0.00 -0.01

24.91 4.68 4.67 -0.01 4.67 -0.01 0.00

24.87 4.77 4.76 -0.01 4.75 -0.02 -0.01

25 Final Design Memorandum

2009 Model Baseline Model Project Conditions Model Maximum

Flow Velocity (ft/sec)

Maximum Flow

Velocity (ft/sec)

Changes from

Model

Maximum Flow

Velocity (ft/sec)

Changes from

Model

Changes from

Baseline Model

24.82 4.87 4.86 -0.01 4.85 -0.02 -0.01

24.77 4.92 4.91 -0.01 4.90 -0.02 -0.01

24.73 4.95 4.94 -0.01 4.93 -0.02 -0.01

24.68 5.16 5.15 -0.01 5.14 -0.02 -0.01

24.63 5.47 5.46 -0.01 5.46 -0.01 0.00

24.59 5.64 5.64 0.00 5.63 -0.01 -0.01

24.54 5.68 5.68 0.00 5.67 -0.01 -0.01

24.49 5.76 5.75 -0.01 5.75 -0.01 0.00

24.44 6.02 6.01 -0.01 6.00 -0.02 -0.01

24.39 6.21 6.20 -0.01 6.19 -0.02 -0.01

24.35 6.37 6.35 -0.02 6.34 -0.03 -0.01

24.30 6.54 6.50 -0.04 6.50 -0.04 0.00

24.25 6.77 6.69 -0.08 6.69 -0.08 0.00

24.21 7.09 6.97 -0.12 6.97 -0.12 0.00

24.15 7.09 6.97 -0.12 6.97 -0.12 0.00

24.10 7.09 6.87 -0.22 6.87 -0.22 0.00

24.05 6.78 6.85 0.07 6.85 0.07 0.00

24.01 6.75 6.84 0.09 6.83 0.08 -0.01

23.96 6.75 6.84 0.09 6.83 0.08 -0.01

23.91 6.43 6.52 0.09 6.51 0.08 -0.01

23.86 6.12 6.20 0.08 6.20 0.08 0.00

23.81 5.87 5.96 0.09 5.95 0.08 -0.01

23.77 5.87 5.96 0.09 5.95 0.08 -0.01

23.72 5.73 5.83 0.10 5.83 0.10 0.00

23.67 5.45 5.49 0.04 5.49 0.04 0.00

23.62 5.39 5.49 0.10 5.48 0.09 -0.01

23.58 5.19 5.30 0.11 5.30 0.11 0.00

23.53 4.98 5.09 0.11 5.09 0.11 0.00

Results from the Project Conditions Model show there is no significant hydraulic impact to the project reach as well as the reaches immediately upstream and downstream, caused by the proposed improvements to the project levee. When compared to the baseline model, the Project Conditions Model experiences the maximum increase of 0.35 feet per second (fps) near the project upstream limit. Variations of computed maximum water surface elevations and channel flow velocities diminish as the river reach farther away from the project reach.

In addition, based on Table 3.4, the maximum flow velocity of 5.07 fps at RM 26.99 would be used as the design hydraulic parameter for the riprap design in Section 5.6 herein.

26 Final Design Memorandum

27 Design Memorandum

4.0 Geotechnical Recommendations

As part of the geotechnical scope of work, Raba-Kistner Consultants, Inc. (R-K) has completed field exploration at five (5) boring locations within the project limits to characterize subsurface conditions along the Vado East Levee and has prepared a Geotechnical Memorandum (dated May 25, 2011) presenting geotechnical analyses and recommendations for the levee. This document is included with this report as Appendix C. An overview of the geotechnical findings are presented below.

4.1 Foundation Conditions

The levee alignment is underlain predominantly by silty sands, poorly graded sands, and poorly graded sands with silt, with interbedded clay, silt, and gravel layers. Near surface deposits were generally loose to medium dense, becoming medium dense to very dense at depth. The depth to groundwater measured at the time of exploration varied from 7.5 to 11 feet below the riverside toe of the existing levee or existing grade (in areas with no existing levee). Fluctuations in groundwater can occur due to changes in rainfall, river flow, or other hydrologic conditions.

4.2 Seismic Conditions

The peak ground acceleration for various loading conditions was estimated as follows:

Table 4.1 – Peak Ground Acceleration

Design Condition Peak Ground Acceleration Operating Basis Earthquake 0.026g Maximum Design Earthquake 0.081g Maximum Credible Earthquake 0.130g

The potential for liquefaction of foundation soils was found to be minimal for the OBE and MDE events.

4.3 Seepage Conditions

R-K performed seepage analysis of the proposed levee configuration to evaluate potential through seepage and underseepage conditions. It was recommended that a toe drain be constructed within the landside toe of the proposed levee to control potential through seepage.

As a minimum the drain was recommended between Stations 642+00 and 658+00. In order to provide continuity to the drain it was extended to the beginning of the project (Station 637+00).

A toe drain was not necessary down-station of Station 658+00 because the design water surface elevation is below the landside toe of slope, therefore, uplift pressures and seepage will not develop in this area.

Details for the toe drain are included in the Geotechnical Memorandum and included in the construction drawings and specifications. Underseepage was evaluated by R-K and their conclusion was that exit hydraulic gradients would not exceed 0.5, therefore, provision to increase seepage paths, provide pressure relief, or intercept seepage flow were not

28 Design Memorandum recommended. Fairly high seepage rates were estimated within low lying areas behind the proposed levee, therefore it was recommended that the final grade of these areas be raised. This recommendation was incorporated into the project grading design.

4.4 Embankment and Foundation Stability

Stability analysis was performed by R-K to evaluate embankment and foundation stability under various loading conditions. Strength parameters applied to various soils units were based on field Standard Penetration Test (SPT) values, prior experience in the area, and professional judgment. The stability analysis yielded the following minimum factors of safety.

Table 4.2 – Slope Stability Factors of Safety

Condition Minimum Factor of Safety End of Construction 2.4 Sudden Drawdown 1.8 Steady State Seepage 1.8 Earthquake N/A*

*Earthquake loading was not considered applicable because the peak ground acceleration from the MDE event was <0.10g and the potential for liquefaction was considered minimal.

The above minimum factors of safety satisfy the requirements of the EM 1110-2-1913.

4.5 Settlement

The settlement evaluation performed by R-K indicated that total settlement of the proposed levee construction, including foundation settlement and potential shrinkage of the levee fill, would be 6 inches or less. Consequently an embankment overbuild of 6 inches vertically was included in the design of the levee plan and profile.

4.6 Material Specifications

R-K specified several types of soil to be used for various project components.

Non-pervious fill was specified for use for new levee and levee rehabilitation. The material is to have a Unified Soil Classification System (USCS) designation of CL, low plastic clay. The material is to have a Plasticity Index between 20 and 30, and a Liquid Limit of no more than 45.

This type of material is not anticipated to be available within the on-site soil deposits, however it is anticipated that it can be obtained from regional deposits of clay and clayey loam.

Pervious fill was specified for use for re-grading of the terrain on the landside of the proposed new levee. The material is to be free of trash or other deleterious material and have no more than 10 percent fines content (passing the #200 sieve). The maximum allowable particle size will be 3 inches. It is anticipated that this material can be derived from the cleaner sand deposits excavated from the Rio Grande floodplain as part of the project construction.

29 Design Memorandum

Toe drain material was specified as gravel aggregate meeting the requirements of ASTM C33 Type 57 or 357. This type of material is not anticipated to be available within the on-site soil deposits, however it is anticipated that it can be obtained from local vendors of concrete aggregate.

Flex Base material was specified as having the following properties:

Table 4.3 – Flex Base Material Requirements

Property Test Method Grade 3 Master Gradation Sieve Size

ASTM D422-63

% retained 2-1/2 in. 0 1-3/4 in. 0–10 7/8 in. – 3/8 in. – No. 4 45–75

No. 40 50–85

Liquid limit, % max.1

ASTM D4318-05,

AASHTO T-89

Plasticity index, max. 1

ASTM D4318-05

Plasticity index, min. 1 – 1 Determine plastic index in accordance with ASTM D-427 and AASHTO T89.

This type of material is not anticipated to be available within the on-site soil deposits, however it is anticipated that it can be obtained from local vendors of roadway construction materials.

30 Design Memorandum

31 Design Memorandum

5.0 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 that the Federal Emergency Management Agency (FEMA) needs in order to recognize (or “accredit”), on National…