FIO-LSAR_R9P5B_DDR_Geotech_Appendix_Post_ATR_080116_with_figures_and_plates_(reduced).pdf

Los Angeles District Geotechnical Branch

GEOTECHNICAL STUDY REPORT (100% DRAFT)

Reach 9 Phase 5B Lower Santa Ana River, Orange County, California

U.S. Army Corps of Engineers, Los Angeles District, Engineering Division, Geotechnical Branch 915 Wilshire Blvd, Los Angeles, CA 90017

June 2016

(THIS PAGE LEFT INTENTIONALLY BLANK)

Geotechnical Appendix, Design Documentation Report

Lower Santa Ana River: Reach 9 – Phase 5B Orange County, California

Report Prepared by:

Michael Lau, P.E.

Civil Engineer Soils Design & Materials Section Geotechnical Branch, Engineering Division, Los Angeles District, USACE

David Tran, P.E.

Civil Engineer Soils Design & Materials Section Geotechnical Branch, Engineering Division, Los Angeles District, USACE

Anabel Pho, P.E.

Civil Engineer Soils Design & Materials Section Geotechnical Branch, Engineering Division, Los Angeles District, USACE

Julia Yang, P.E.

Civil Engineer Soils Design & Materials Section Geotechnical Branch, Engineering Division, Los Angeles District, USACE

Scott Kerwin, P.G., C.E.G Senior Associate Engineering Geologist Amec Foster Wheeler

Stephen Chickey, P.E., G.E.

Senior Geotechnical Engineer Soils Design & Materials Section Geotechnical Branch, Engineering Division, Los Angeles District, USACE

Douglas Dahncke, P.E., G.E.

Chief, Soils Design & Materials Section Geotechnical Branch, Engineering Division, Los Angeles District, USACE

TABLE OF CONTENTS

LIST OF FIGURES ..................................................................................................................... iii LIST OF ATTACHMENTS ....................................................................................................... iv LIST OF ACRONYMS ................................................................................................................ v

1.0 INTRODUCTION

1.1 Project Description

1.2 Available Project References

1.3 Scope of Work

2.0 FIELD AND LABORATORY STUDY

2.1 Soils and Laboratory Investigations in 2014-2015

2.2 Engineering Geologic Review of Existing Rip-Rap Conditions

2.3 Soils Investigation and Laboratory Testing by Leighton Consulting

3.0 SITE CONDITIONS AND GEOLOGY

3.1 Surface Conditions and Topography

3.2 Regional Geology

3.3 Local Geology and Subsurface Conditions

3.3.1 Artificial Fill (af & Caf)

3.3.2 Alluvium (Qal)

3.3.3 Older Alluvium (Qao)

3.3.4 Topanga Formation Bedrock (Tt)

3.3.5 Vaqueros-Sespe Formation Bedrock (Tvs)

3.4 Groundwater Conditions

4.0 SEISMIC HAZARDS

4.1 Regional Seismology

4.2 Local Faulting and Earthquake Zone

4.3 Seismic Hazard and Earthquake Fault Zone Map

4.4 Seismic Hazard Analysis

4.4.1 Hazard Potential Classification

4.4.2 OBE

4.4.3 MDE

4.4.4 MCE

4.5 Seismic Loading Parameters

4.6 Soil Liquefaction Potential

5.0 GEOTECHNICAL ANALYSIS AND DISCUSSIONS

5.1 Shear Strength Parameters

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5.2 Adopted Design Shear Strengths

5.3 Stability of Slopes Protected by Grouted Stone

5.3.1 Load Cases for Slope Stability Analysis

5.3.2 Results of Slope Stability Analysis

5.4 Lateral Spreading and Seismic Slope Deformation Analysis

5.5 Settlement

5.6 Seepage

5.7 Soil Corrosivity

5.8 Soil Shrinkage Potential and Borrow Source Requirements

5.9 Structural Design of Side Drain Extensions

5.10 Salvage and Reuse of Existing Stone

5.11 Engineering Geologic Assessment of Existing Stone Protection

5.12 Erosion Protection from Surface Runoff

5.13 Subdrain System

5.14 Bike Path, Horse Trail, Maintenance Road, and Concrete Pavement

5.14.1 Bike Path

5.14.2 Horse Trail

5.14.3 Maintenance Road

5.14.4 Concrete Pavement

6.0 CONSTRUCTION RECOMMENDATIONS

6.1 Site Preparation

6.2 Temporary Excavation

6.3 Excavation and Subgrade Preparation

6.4 Fill Placement and Compaction

6.4.1 Compacted Fill

6.4.2 Compacted Backfill

6.5 Dewatering

6.6 Soil Corrosivity, Concrete/Grout Proportioning, and Materials

6.7 Side Drain Extensions

6.8 Stone Protection

6.9 Staging Area Limitations

6.10 Geotechnical Instrumentation and Monitoring

6.11 Summary of General Grading Recommendations

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7.0 REFERENCES

LIST OF FIGURES

Figure 1: Site Location Map

Figure 2: Geomorphic Provinces and Some Principal Faults of California

Figure 3: Regional Geology Map

Figure 3A: Regional Geologic Map Legend USGS 420-B

Figure 3B: Regional Geologic Map Legend USGS 420-D

Figure 4: LOTB Gypsum Canyon Bridge

Figure 5: Well Construction Detail MW15-P5B-01

Figure 6: Well Construction Detail MW15-P5B-02

Figure 7: Well Construction Detail MW15-P5B-03

Figure 8: Well Construction Detail MW15-P5B-04

Figure 9: Seismic Hazard Zones Map

Figure 10: Earthquake Fault Zones Map

LIST OF TABLES

Table 1: Summary of Hollow Stem Auger Test Holes

Table 2: Summary of Resonant Sonic Test Holes

Table 3: Summary of Becker Hammer Test Holes

Table 4: Summary of CPT Soundings

Table 5: Summary of Leighton Consulting Borings and Monitoring Wells

Table 6: Summary of CPT Pore Pressure Dissipation Data

Table 7: Interactive Deaggregation Tool Input

Table 8: Seismic Design Parameters

Table 9: Summary of LPI Calculations for OBE and MDE Events

Table 10: Summary of Adopted Design Shear Strengths and Material Properties

Table 11: Slope Stability Load Cases and Factors of Safety

Table 12: Estimated Seismic Slope Deformations

Table 13: Settlements Due to Earthquake Shaking

Table 14: Summary of Corrosivity Test Results

Table 15: Geotechnical Design Parameters for Side Drain Extensions

Table 16: Existing Rip Rap Gradation

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Table 17: Existing Derrick Stone Gradation

Table 18: Existing Filter Material Gradation

Table 19: Recommended Rip Rap Gradation

Table 20: Recommended Bedding Material Gradation

Table 21: Drain Material Gradation

Table 22: Summary of R-Value Test Results

PLATES

G-01 through G-77

Plate 1: Boring Location Plan

Plate 2: Boring Location Plan

Plate 3A: Typical Embankment Section & Geologic Cross Section A-A'

Plate 3B: Geologic Cross Sections B-B' & C-C'

Plate 3C: Geologic Cross Sections D-D' & E-E'

Plate 4A: Bedrock Profile

Plate 4B: Bedrock Profile

Plate 4C: Bedrock Profile

LIST OF ATTACHMENTS

Attachment A: Subsurface Explorations and Laboratory Test Results by USACE

Attachment B: Measurements and Analysis on Becker Penetration Tests

Attachment C: Subsurface Explorations and Laboratory Test Results by Leighton Consulting

Attachment D: Seismic Hazard Analysis

Attachment E: Results of Soil Liquefaction Analysis

Attachment F: Development of Design Shear Strength Parameters

Attachment G: Slope Stability Analysis

Attachment H: Seismic Slope Deformation Analysis

Attachment J: Seismic Settlement Analysis

Attachment K: Spring Modulus Calculations for Side Drain Extensions

Attachment L: Exposed Rock Exploration and Petrographic Analysis Results

Attachment M: Pavement Design Calculations

Attachment N: Geotextile Filter Design

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Attachment O: Bedding Material Design

Attachment P: Lower Santa Ana River Reach 9 Phase 5A Construction Photographs

Attachment Q: Determination criteria for levee condition by the Los Angeles District (SPL) Levee Safety Program

LIST OF ACRONYMS

ABC Aggregate Base Coarse AC Asphalt Concrete ACI American Concrete Institute ASCE American Society of Civil Engineers ASTM American Society for Testing and Materials bgs below ground surface BPT Becker Penetration Test CAPWAP CAse Pile Wave Analysis Program CBR California Bearing Ratio CPT Cone Penetration Test CQC Construction Quality Control CRR Cyclic Resistance Ratio CSR Cyclic Stress Ratio DDR Design Documentation Report DG Decomposed Granite DM Design Memorandum DSHA Deterministic Seismic Hazard Analysis EM Engineering Manual ER Engineering Regulation FS Factor of Safety GDM General Design Memorandum GE Gravel Equivalent GRMHP Green River Mobile Home Park HDPE High Density Polyethylene LPI Liquefaction Potential Index MCE Maximum Credible Earthquake MDE Maximum Design Earthquake NCEER National Center for Earthquake Engineering Research

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NGVD National Geodetic Vertical Datum NSF National Science Foundation NSHMP National Seismic Hazard Mapping Project OBE Operating Basis Earthquake OSHA Occupational Safety and Health Administration PCA Portland Cement Association PDA Pile Driving Analyzer PGA Peak Ground Acceleration PHGA Peak Horizontal Ground Acceleration PL Public Law PSHA Probabilistic Seismic Hazard Analysis PVC Polyvinyl Chloride QA Quality Assurance R9P5B Reach 9 Phase 5B SAR Santa Ana River SARI Santa Ana Regional Interceptor SPF Standard Project Flood SPT Standard Penetration Test USACE United States Army Corps of Engineers USCS Unified Soil Classification System USGS United States Geological Sur

Geotechnical Study Report Santa Ana River Mainstem, Reach 9 Phase 5B

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1.0 INTRODUCTION

This study report presents an evaluation of the geotechnical and geologic conditions for the Lower Santa Ana River Reach 9 Phase 5B (R9P5B) project, and provides recommendations for design and construction.

Authorization for construction of this project is contained in the Water Resources Development Act of 1986 (99th Congress 2nd Session, Public Law [PL] 99-662). The project authorization for flood control is contained in the Report of the Chief of Engineers for the Santa Ana River (SAR) Mainstem, Including the Santiago Creek, California, dated January 15, 1982, except that, in lieu of the Mentone Dam feature of the project, the Secretary is authorized to plan, design, and construct a flood control storage dam on the upper Santa Ana River. The full authorization language is presented in the Main Report of Design Memorandum (DM) No. 1 entitled, Phase 2 (GDM) on the Santa Ana River Mainstem, Including Santiago Creek, Volume 3, dated August 1988.

The purpose of the Santa Ana River Mainstem project is to provide adequate flood control to the communities in Orange, Riverside, and San Bernardino Counties in conjunction with the modifications at Prado Dam, which include the raising of its main embankment and spillway, and increasing the capacity of the outlet works structure. The area designated as Lower Santa Ana River Reach 9 is situated between Prado Dam and Weir Canyon Road, in the City of Yorba Linda.

Currently, the Reach 9 project is divided into phases: Phase 1, 2A, 2B, 3, 4, 5A, 5B, and the Green River Mobile Home Park Levee (GRMHP), which is a component of Phase 2A. Phase 5A is located along the north bank of the Santa Ana River, parallel to East La Palma Avenue and just upstream of Yorba Linda Boulevard, and is approximately 4,150 feet in length. The Phase 5A project includes construction of a 2:1 (H:V) grouted stone revetment and an anchored sheet pile wall. The Phase 5B project is an upstream extension of the Reach 9 Phase 5A project consisting of 2:1 grouted stone revetment. The site location is called out on the ESRI World Street Map presented as Figure 1.

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Approximate Scale in Feet

00 800' 1600'

Sources: Background from ESRI World imagery &

ESRI World Steet Map

Coordinate System: State Plane California

Datum: NAD 27, Zone 6

SANTA ANA RIVER MAINSTEM

LOWER SANTA ANA RIVER CHANNEL REACH 9 - PHASE 5B

ORANGE COUNTY, CALIFORNIA

SITE LOCATION PLAN

US Army Corps of Engineers

Los Angeles District

CKD BY: STK\SC

DWN BY: JBD

FIGURE

PRADO DAM

DATE: March 2016

P l o t

D a t e

A

M

P l o t t e d b y l e d j b d

F i l e

N a m e

R

B

S

I T

E

L O

C A

T I O

N D

W G

F i g u r e

S i t e

L o c a t i o n U

S G

S

END PROJECT

STA. 1399+60

BEGIN PROJECT

STA. 1274+43

PROJECT

SITE

SARI LINE

PROJECT

SITE

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1.1 Project Description

The purpose of the Reach 9 Phase 5B project is to mitigate erosion in a reach of the north bank of the Santa Ana River. The project extends from Stations 1274+43 to 1399+60, a distance of approximately 12,800 feet. The Phase 5B project is an upstream extension of the Reach 9 Phase 5A project. The Phase 5B project includes construction of a 24 inch thick grouted stone revetment extending from the 100 year flood elevation down to one foot below the anticipated scour elevation. Above the grouted stone will be 12 inch rip rap to the top of the current slope. The maximum height of the grouted and ungrouted stone revetment will be about 40 feet. The proposed finish slope gradient will be 2:1 (horizontal: vertical [H:V]). Other project features include:

Extending seventeen existing storm drain outlets through the grouted stone revetment;

Installing subdrain system with weep holes, spaced at 100 foot on center, to provide hydrostatic pressure relief behind the grouted stone revetment;

Protection of the Santa Ana Regional Interceptor – Yorba Linda Spur (SARI-YLS) sewer siphon pipeline and manholes;

Modification of the Santa Ana River Trail Bikeway and Horse Trail; and

Constructing a maintenance road.

1.2 Available Project References

United States Army Corps of Engineers (USACE), Los Angeles District (August 1988).

Santa Ana River Mainstem – Phase II General Design Memorandum.

USACE, Los Angeles District (July 2011). Lower Santa Ana River Mainstem – Reach 9 DDR, Hydrology, Hydraulics, & Sedimentation Appendix.

Leighton Consultants (May 2010). Final Geotechnical Data Report for the Santa Ana Regional Interceptor (SARI) Replacement Project.

URS (July 2015). Geotechnical Appendix to Design Documentation Report, Geotechnical Investigation for the Lower Santa Ana River, Reach 9 Phase 5A

1.3 Scope of Work

This Geotechnical Study Report was prepared by personnel from USACE Los Angeles District, Engineering Division, Geotechnical Branch. The study included review of existing subsurface information, geotechnical explorations, laboratory testing, engineering analysis, development of design recommendations, and preparation of this report. The scope of the report included the following tasks:

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1. Review available reports and data pertaining to the geotechnical conditions at the site and vicinity;

2. Perform subsurface investigations at the project site by drilling twenty-six (26) hollow stem auger test borings; ten (10) sonic test holes; twenty-three (23) Becker hammer test holes:

converting four (4) of the Becker hammer test holes into groundwater monitoring wells, advancing nineteen (19) Cone Penetration Test (CPT) soundings; and excavating twenty four (24) test pits along the project alignment;

3. Classify and log soils encountered during the subsurface investigations;

4. Obtain in-situ samples of substrata;

5. Observation of groundwater conditions encountered during the subsurface investigation;

6. Perform laboratory tests on selected soil samples;

7. Engineering geologic review and evaluation of the existing rip-rap conditions to assess the potential for reuse of the existing stone in the planned project;

8. Analyze and interpretation of field data and laboratory test results;

9. Evaluate seismic hazards such as liquefaction potential and seismic slope deformation;

10. Evaluate seepage, settlement, and slope stability;

11. Flexible pavement design and recommendations for structural sections;

12. Develop geotechnical parameters for structural design of side drain extensions;

13. Prepare grading and geotechnical instrumentation recommendations; and

14. Prepare this report documenting the site conditions, and geotechnical and geologic constraints with design and construction recommendations.

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2.0 FIELD AND LABORATORY STUDY

The Reach 9 Phase 5B Plan of Exploration, geologic contacts and profile sheets, geologic cross sections, and all of the exploration logs are presented in Plates G-01 through G-77. Laboratory test reports on samples collected during the USACE Los Angeles District explorations are presented in Attachment A. A detailed description of all field activity is presented in the following sections. Except as otherwise indicated, all explorations were continuously logged and samples classified in general accordance with the Unified Soil Classification Systems (American Society for Testing and Materials [ASTM] D2487).

2.1 Soils and Laboratory Investigations in 2014-2015

Foundation conditions along the proposed alignment of the project were initially investigated by USACE Los Angeles District from October of 2014 to February of 2015. The exploration effort consisted of advancing twenty-six (26) hollow stem auger test borings, advancing ten (10) resonant sonic test holes, drilling twenty-three (23) Becker hammer test holes: ten (10) closed bit drill casing instrumented with a Pile Driver Analyzer, two (2) closed bit without instrumentation, eleven (11) open bit drill casing(four (4) of the open bit Becker hammer test holes were converted into groundwater monitoring wells), advancing nineteen (19) Cone Penetration Test (CPT) soundings, and excavating twenty four (24) test pits along the project alignment.

Twenty-six (26) hollow stem auger test holes identified as TH14-P5B-01 through TH14-P5B-21A were drilled between 17 November and 22 December 2014. At some stations two borings were taken, one near the centerline at the top of slope and the companion boring designated with an “A” was advanced in the river bed. Samples were collected with a 2.4 inch inside diameter (3.0 inch outside diameter) modified California split-barrel sampler lined with brass rings and a standard split spoon penetrometer with dimensions in accordance with ASTM D3550 and D1586, respectively. Both samplers were driven with a 140-pound automatic trip hammer falling 30 inches. Alternating disturbed samples (SPT) and relatively intact ring samples (California Modified Sampler) were collected at 5-foot depth intervals. Drilling mud was added after encountering ground water to release hydrostatic pressure. The hollow stem auger test holes were advanced to depths ranging from 29 to 51.5 feet bgs employing a DR-10K drill rig. USACE soil engineers supervised the drilling and logged the boreholes. Samples collected were tested for grain size distribution and plasticity index in general accordance with ASTM D422 or D4318 respectively. Table 1 summarizes the test hole number, ground surface elevation, depth to groundwater, depth to bedrock (if encountered), and total depth for each hollow stem auger test hole.

Ten (10) Resonant Sonic test holes identified as SH15-P5B-02 through SH15-P5B-08 and SH15- P5B-11 through SH15-P5B-13 were drilled from 2–3 February 2015 and ranged in depth from 15 to 47 feet bgs. Continuous 4-inch diameter cores were collected employing a SC-500 truck-mounted sonic drill rig. The cores were extruded into clear plastic liners and stored in wooden

Page | 8 core boxes to facilitate transport to the laboratory. The continuous cores were spread out for display at the laboratory in stratigraphic depth sequence on 2x12 inch wooden planks supported on folding stands. The wooden planks provided a comfortable platform to facilitate visual classification, logging, photographs, and samples selected for laboratory index testing of each material type encountered. Representative soil samples were tested for grain size distribution and plasticity index in general accordance with ASTM D422 or D4318 respectively. The tests performed are indicated at discrete depths on the test hole logs where the samples were collected.

Table 2 summarizes the test hole number, ground surface elevation, depth to groundwater, depth to bedrock (if encountered), and total depth for each Resonant Sonic test hole.

Twenty-three (23) Becker hammer test holes were advanced between 13–20 October 2015 and 5– 13 January 2016 to depths of 75 feet bgs. The becker hammer tests holes are not sequentially numbered; they were named to match the corresponding adjacent bore hole. Four (4) of the test holes were converted to groundwater monitoring wells. Becker hammer penetration blow counts were manually recorded for every foot of depth by USACE soil engineers. The Becker Penetration Test (BPT) is used for determining the penetration resistance for coarse-grained soils with particles that are too coarse for split spoon samplers to collect accurate blow counts. The BPT consists of recording the number of blows required to drive a closed bit casing 1 foot into the ground while recording bounce chamber pressures. By counting blows for each foot of penetration, a continuous record of penetration resistance can be obtained for the entire soil profile. “Becker and Standard Penetration Test (BPT-SPT) Correlations with Consideration of Casing Friction,” developed by Sy and Campanella (1994), was used to convert the BPT blow counts to equivalent SPT N60 blow counts (blow count corrected for a hammer efficiency of 60 percent). The Sy and Campanella approach involves instrumenting the Becker hammer drill with a Pile Driving Analyzer and selecting representative blows for input in the Case Pile Wave Analysis Program (CAPWAP).

Further discussion on the Becker hammer drill instrumentation and CAPWAP analysis is presented in the report prepared by GRL Engineers in Attachment B: Measurement and Analysis on Becker Penetration Tests. Ten (10) of the test holes were advanced with a closed bit drill casing instrumented with a pile driving analyzer, two (2) of the test holes employed the closed bit without instrumentation. Eleven (11) of the Becker hammer test holes were advanced using an open bit casing to facilitate the collection of soil and bedrock samples. Table 3 summarizes the bit type, test hole number, ground surface elevation, depth to groundwater, depth to bedrock (if encountered), and total depth for each Becker hammer test hole..

Nineteen (19) Cone Penetration Tests (CPTs) soundings were advanced from 20–22 January 2015.

USACE contracted Gregg Drilling to advance the CPTs using a 30-ton truck-mounted CPT rig.

The CPTs encountered refusal conditions ranging from 28 to 60 feet below the ground surface (bgs). Pore pressure dissipation tests were conducted at every sounding to evaluate the groundwater condition. Table 4 summarizes the ground surface elevation, termination depth, and depth of pore pressure dissipation tests for each CPT sounding.

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Twenty-four (24) shallow test pits were excavated from 9–10 February 2015 with a backhoe.

Shallow test pits, ranging in depth from 8 to 12 feet bgs, were excavated along the toe of the existing bank protection to evaluate the suitability of the in situ material to be used as a soil cement aggregate. USACE staff supervised the test pit excavations, bulk samples were collected from each test pit excavation and the materials were composited and stockpiled at the Prado Dam materials laboratory to develop a mix design. Detailed field logs were not generated since the test pits were excavated in artificial fill soils and the intent of the exploration program was to collect a representative bulk quantity of material for a soil cement study. The soil cement alternative was abandoned during the value engineering study so the soil cement study was never conducted.

2.2 Engineering Geologic Review of Existing Rip-Rap Conditions Plans provided by the City of Yorba Linda dated 1981 indicate the entire length of the project alignment was originally constructed as a levee. These plans indicate the subject river-side slope area along the southerly side of the levee was originally constructed at a gradient of 2.5:1 (H:V) and included an approximately 18-foot wide bench for a maintenance road that is generally consistent with the existing Santa Ana Trail configuration. The plans also specify installation of rip-rap erosion protection on the lower portion of the river-side slope below the maintenance road that are similar to the existing slope configuration/conditions. Engineering geologic review of the full length of the exposed rip-rap section was performed on 4 March 2016 with the purpose of verifying the suitability of the existing exposed rock for use as grouted rip-rap. This review and assessment also included collection of representative samples and petrographic evaluation of the suitability of the existing stone for use as grouted rip-rap. The general conditions and overall configuration the existing rip-rap are presented and discussed below under Section 3.3.1 and are illustrated on Plates 3A through 3C. Information, evaluations and recommendations regarding design and construction considerations associated with reuse of the existing rip-rap are presented and discussed in Sections 5.10 to 5.11 and 6.8 to 6.9.

2.3 Soils Investigation and Laboratory Testing by Leighton Consulting Leighton Consulting conducted a geotechnical investigation between May to July of 2009 and in March of 2010 along the proposed Santa Ana River Interceptor (SARI) realignment located on the south bank of the Santa Ana River between the Green River Golf Course and Weir Canyon Road.

Seven (7) hollow stem auger borings and two (2) groundwater monitoring wells were drilled within the limits of the Reach 9 Phase 5B project alignment as part of their investigation. The test holes were drilled using an 8-inch diameter truck-mounted hollow stem auger drill rig and a 24-inch diameter truck-mounted bucket-auger drill rig. Disturbed soil samples were collected using the SPT sampler and relatively undisturbed samples were collected using a Modified-California ring sampler at selected intervals within the test holes.

Soil samples collected during drilling were tested at the Leighton Group Laboratory for moisture content, dry unit weight, grain size distribution, sand equivalent, R-Value, shear strength (direct

Page | 10 shear), modified proctor compaction, and corrosion potential. The locations of the borings and monitoring wells are identified on the USACE Plan of Exploration presented on Plates G-01 and G-02. The geotechnical boring logs produced by Leighton Consulting are presented on Plates G- 62 through G-72. Tables summarizing the explorations and plates presenting the laboratory test results are included in Attachment C: Subsurface Explorations and Laboratory Testing by Leighton Consultants.

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Table 1: Summary of Hollow Stem Auger Test Holes

Test Hole Number Date Drilled Northing Easting

Ground Surface

Elevation (ft)(2)

Depth to Groundwater

(ft-bgs) (1)

Depth to Bedrock (ft-bgs)(1)

Total Depth (ft)(1)

TH14-P5B-01 11/17/14 624911.63 1550866.63 360.45 24.0 -- 50.5

TH14-P5B-02 11/19/14 624297.21 1551183.42 365.33 27.10 -- 51.5

TH14-P5B-02A 12/15/14 624126.38 1550935.89 354.37 14.50 -- 51.5

TH14-P5B-03 11/20/14 623666.30 1551665.30 368.73 27.30 -- 51.5

TH14-P5B-03A 12/15/14 623492.98 1551350.30 357.14 12.40 -- 51.5

TH14-P5B-04 11/20/14 623437.26 1552024.67 370.92 28.02 -- 32.0

TH14-P5B-05 11/21/14 623288.95 1552556.55 373.28 30.94 -- 49.5

TH14-P5B-05A 12/18/14 622984.04 1552778.08 353.89 5.30 49.0 51.5

TH14-P5B-06 11/24/14 623318.33 1553157.24 375.91 26.17 40.3 51.3

TH14-P5B-07 11/25/14 623553.47 1553884.19 377.08 22.20 -- 35.5

TH14-P5B-08 11/25/14 623914.50 1554857.28 376.65 16.70 -- 35.8

TH14-P5B-09 11/26/14 624053.89 1555269.25 379.67 21.30 -- 34.50

TH14-P5B-10 11/26/14 624122.53 1555537.65 381.89 22.50 -- 29.0

TH14-P5B-12 12/1/14 624128.63 1556294.50 371.31 9.85 32.0 35.5

TH14-P5B-13 12/1/14 624234.49 1557113.09 386.46 23.80 43.0 50.3

TH14-P5B-13A 12/19/14 623820.27 1557318.14 375.88 8.10 25.5 37.0

TH14-P5B-14 12/2/14 624206.71 1557525.60 390.51 26.45 -- 32.6

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Test Hole Number Date Drilled Northing Easting

Ground Surface

Elevation (ft)(2)

Depth to Groundwater

(ft-bgs) (1)

Depth to Bedrock (ft-bgs)(1)

Total Depth (ft)(1)

TH14-P5B-15 12/8/14 624205.59 1558128.88 389.58 19.40 -- 51.5

TH14-P5B-15A 12/18/14 623980.11 1558215.15 381.41 9.20 -- 51.5

TH14-P5B-16 12/8/14 624324.33 1558691.55 390.57 16.74 -- 51.5

TH14-P5B-17 12/9/14 624557.38 1559292.33 395.43 21.80 -- 51.5

TH14-P5B-17A 12/19/14 624307.27 1559380.19 384.66 8.85 -- 51.5

TH14-P5B-18 12/9/14 624787.15 1559895.57 397.54 20.40 -- 51.5

TH14-P5B-19 12/10/14 625001.41 1560564.20 404.15 26.0 35.5 51.5

TH14-P5B-20 12/14/14 625340.71 1560785.98 404.75 24.60 -- 29.0

TH14-P5B-21A 12/22/14 625630.74 1550237.11 345.43 11.10 -- 51.5

Notes:

(1) (ft-bgs) = feet below ground surface

(2) Elevation Datum – NGVD 1929

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Table 2: Summary of Resonant Sonic Test Holes

Resonant Sonic Test Hole Number

Date Excavated Northing Easting

Ground Surface Elevation

(ft)(2)

Depth to Groundwater

(ft-bgs) (1)

Depth to Bedrock (ft-bgs)(1)

Total Depth (ft)(1)

SH15-P5B-02 2/2/15 624733.00 1559748.50 393.00 20.0 -- 37.0

SH15-P5B-03 2/3/15 625032.29 1560621.25 402.71 26.0 29.0 39.0

SH15-P5B-04 2/2/15 625298.68 1560751.82 404.65 27.0 -- 37.0

SH15-P5B-05 2/4/15 624116.57 1555740.6 370.39 -- -- 15.0

SH15-P5B-06 2/3/15 623765.20 1554520.98 365.91 20.0 36.5 47.0

SH15-P5B-07 2/4/15 623235.88 1552831.83 359.87 -- -- 15.0

SH15-P5B-08 2/4/15 624003.26 1551307.15 355.57 -- -- 15.0

SH15-P5B-11 2/2/15 625511.46 1560888.29 406.30 27.0 -- 36.0

SH15-P5B-12 2/3/15 624869.03 1560106.37 401.32 22.0 40.0 42.0

SH15-P5B-13 2/3/15 624687.32 1559626.84 393.32 -- -- 15.0

Notes:

(1) (ft-bgs) = feet below ground surface

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Table 3: Summary of Becker Hammer Test Holes

Test Hole Number

Date Drilled Northing Easting

Ground Surface

Elevation (ft)(2)

Depth to Groundwater

(ft-bgs)(1)

Depth to Bedrock (ft-bgs)(1)

Pullback Test

Depth (ft-bgs)(1)

Total Depth (ft)

Closed Bit Drill Casing with PDA Instrumentation(3)

BH15-P5B-01 1/7/15 624915.94 1550863.85 360.55 -- -- 40 75.0

BH15-P5B-02A 1/15/15 624129.91 1550923.04 354.38 -- -- 20 75.0

BH15-P5B-03 1/8/15 623668.88 1551663.24 368.79 -- -- 30 75.0

BH15-P5B-05A 1/15/15 623000.81 1552785.86 354.45 -- -- 30 43.6

BH15-P5B-08 1/8/15 623912.91 1554851.46 376.70 -- -- 10 51.5

BH15-P5B-13 1/9/15 624236.00 1557109.88 386.51 -- -- 20 40.0

BH15-P5B-13A 1/13/15 623821.41 1557311.18 375.94 -- -- 20 28.1

BH15-P5B-15 1/9/15 624206.59 1558123.26 389.66 -- -- 30 75.0

BH15-P5B-17A 1/12/15 624322.62 1559334.26 385.19 -- -- 20 64.5

BH15-P5B-18 1/12/15 624786.90 1559888.19 397.24 -- -- 30 69.5

Closed Bit Drill Casing without PDA Instrumentation(3)

BH15-P5B-07 1/5/15 623554.16 1553882.48 377.18 -- -- 49.0

BH15-P5B-10 1/6/15 624123.99 1555536.24 382.16 -- -- 54.0

Open Bit Drill Casing

BH15-P5B-04 1/5/15 623439.20 1552020.65 370.50 28.0 69.0 75.0

BH15-P5B-09 1/6/15 624055.27 1555267.64 379.82 21.0 58.0 75.0

BH15-P5B-14 1/14/15 624208.64 1557518.76 390.42 27.50 36.0 41.5

BH15-P5B-20 1/14/15 625353.21 1560785.31 406.10 25.0 45.0 50.2

BH15-P5B-22A 1/13/15 625299.00 1562166.08 402.28 14.0 23.0 35.8

BH15-P5B-23 10/19/15 624781.44 1559881.18 395 26.0 71.0 75.5

Page | 15

Test Hole Number

Date Drilled Northing Easting

Ground Surface

Elevation (ft)(2)

Depth to Groundwater

(ft-bgs)(1)

Depth to Bedrock (ft-bgs)(1)

Pullback Test

Depth (ft-bgs)(1)

Total Depth (ft)

BH15-P5B-24 10/20/15 624781.42 1559876.18 395 26.0 -- 52.0

MW15-P5B-01 10/16/15 625047.61 1550734.89 347.03 12.50 67.0 70.0

MW15-P5B-02 10/15/15 623218.20 1553162.50 358.49 12.80 23.0 30.0

MW15-P5B-03 10/14/15 624133.50 1556347.89 369.67 8.30 30.5 35.0

MW15-P5B-04 10/13/15 624781.42 1559886.18 394.63 19.48 -- 35.0

Notes:

(1) (ft-bgs) = feet below ground surface

(3) No soil samples collected, no logs created

Page | 16

Table 4: Summary of CPT Soundings

CPT Date Drilled Northing Easting Ground Surface Elevation (ft)(2)

Depth of Pore Pressure Dissipation Tests (ft-bgs)(1)

Termination Depth (ft-bgs)(1)

CPT-01 1/20/15 624907.70 1550868.80 360.63 42.49 50.52

CPT-02 1/20/15 624300.81 1551181.95 365.30 45.11 55.28

CPT-03 1/20/15 623667.01 1551666.52 368.59 50.36 50.36

CPT-04 1/23/15 623438.33 1552023.71 370.90 48.39 50.20

CPT-05 1/20/15 623289.42 1552557.94 373.40 44.46 46.10

CPT-06 1/20/15 623318.78 1553153.93 375.85 35.60 35.60

CPT-07 1/20/15 623555.11 1553887.21 376.96 29.86 29.86

CPT-08 1/21/15 623917.00 1554862.38 376.81 20.34 29.03

CPT-09 1/21/15 624056.07 1555277.32 379.56 27.72 28.05

CPT-10 1/21/15 624123.57 1555541.28 381.95 52.33 52.33

CPT-12 1/21/15 624128.78 1556299.03 371.45 28.54 29.03

CPT-13 1/21/15 624229.14 1557110.25 386.08 31.66 31.66

CPT-14 1/22/15 624201.78 1557521.67 390.56 28.38 29.20

CPT-15 1/22/15 624206.47 1558133.42 389.60 31.82 50.52

CPT-16 1/22/15 624327.71 1558701.73 390.51 28.38 50.52

CPT-17 1/22/15 624534.0148 1559309.079 386.25 31.50 51.34

CPT-18 1/22/15 624760.4498 1559910.738 386.5 56.43 58.73

CPT-19 1/22/15 624991.8153 1560583.888 398.25 30.68 60.04

CPT-20 1/22/15 625374.3736 1560789.316 404 29.86 40.68

Note: (1) ft-bgs = feet below ground surface (2) Elevation Datum – NGVD 1929

Page | 17

Table 5: Summary of Leighton Consulting Borings and Monitoring Wells

Log Identification Number (1) Date Drilled Ground Surface

Elevation (ft)

Depth to Groundwater

(ft-bgs)(2)

Depth to Bedrock (ft-bgs)(2)

Total Depth (feet)

B-24+40 06/04/09 365 31.0 -- 41.5

B-37+50 07/29/09 365 26.2 40.0 41.5

B-44+50 06/04/09 372 28.5 -- 36.5

B-54+00 07/29/09 374 -- 11.0 40.5

B-63+40 06/03/09 376 25.5 -- 40.9

B-66+70 07/29/09 378 22.5 -- 32.0

B-69+60 07/29/09 377 21.8 40.0 41.5

MW-40+50 06/03/09 368 26.5 -- 36.5

MW-60+20 06/03/09 378 27.0 -- 41.5

Note:

(1) The naming convention for the log identification numbers represents the station along the SARI line where the boring or monitoring well is located

(2) ft-bgs = feet below ground surface

Page | 18

Page | 19

3.0 SITE CONDITIONS AND GEOLOGY

3.1 Surface Conditions and Topography

The project area is located in Santa Ana Canyon about 6 to 8 miles to the east of the Los Angeles physiographic basin, a broad alluvial lowland or coastal plain that comprises much or most of the urban areas of Los Angeles and Orange Counties. Alluvial deposition in this physiographic basin still continues to a limited extent in the present day, primarily during storm flow of the major rivers in the area, including the Los Angeles, San Gabriel, and Santa Ana Rivers. The Santa Ana River flows through Santa Ana Canyon and relatively young alluvium deposited by the river comprises much or most of the foundation soils beneath the project area. The Santa Ana River has its headwaters in the San Bernardino Mountains and flows across the upper Santa Ana Valley in a southwesterly direction to Prado Dam, which is located about 4 to 5 miles upstream from the project site.

Downstream from Prado Dam, the Santa Ana River flows through the relatively narrow, steep-sided Santa Ana Canyon, and then across the Los Angeles basin before entering the Pacific Ocean. In the area downstream from Prado Dam, the Santa Ana River meanders across the bottom of the canyon between the Chino Hills and the Santa Ana Mountains.

The north side of the canyon is bounded by the rolling topography of the Chino Hills, which in geological publications for the area are referred to as the eastern Puente Hills. The relatively high, rugged relief of the Santa Ana Mountains forms the southerly side of the canyon.

The meandering course of the Santa Ana River in the bottom of the canyon is about 12 to 13 miles long. The elevation of the modern floodplain ranges from about 470 feet on the downstream side of Prado Dam to about elevation 230 feet near the mouth of Santa Ana Canyon, which is equivalent to an average gradient of about 18 to 20 feet per mile. The relatively steep terrain on the southerly side near the head of the canyon ranges up to an elevation of about 2,000 feet, decreasing to elevations of about 600 to 700 feet near the mouth of the canyon. The more subdued topography on the northerly side of the canyon ranges up to an elevation of about 700 to 800 feet in the headward portion of the canyon and diminishes to elevations of about 300 to 400 feet in the low rolling hills that form the northerly side of the canyon near the mouth. Local small canyons and washes drain into the Santa Ana River from both sides of Santa Ana Canyon, and although most of this drainage is controlled by storm drain improvements, in at least a few areas these drainages still appear to be contributing small amounts of alluvial sediments to the river floodplain area. Through most of the canyon area, manmade fills and associated development now cover the edges of the original floodplain, even in areas where the river has not been channelized.

Page | 20

The project site/alignment is approximately 2.4 miles long and is located along the northerly side or edge of the current river floodplain (Figure 1). In the vicinity of the project site, construction of relatively high embankment fills for the SR-91 Freeway has encroached on the southerly side of the river floodplain. Along the northerly side of the subject alignment, construction of East La Palma Avenue and the adjoining commercial/residential areas have included placement of manmade fills that similarly encroach on the original natural floodplain of the river.

Typical elevations of the current/remaining floodplain adjoining the alignment range from about 395 feet near the upstream end, to about 340 feet at the downstream end (National Geodetic Vertical Datum [NGVD] of 1929, refer to the recently prepared topographic base for the project, Plates 1 and 2). Review of the recently prepared topographic base map for the project indicates the active or recently active river channel is typically more than about 400 feet southerly of the existing revetment slope that is being replaced, and at its closest approach near the westerly terminus of the planned project alignment, is about 100 feet from the existing slope. The elevation of the active or recently active river channel in the vicinity of the project ranges from about 374 feet near the upstream end to about 325 feet at the downstream end. Review of the topographic base at several locations indicates the elevation of the active channel ranges from about 9 to 21 feet lower than the adjacent edge of the floodplain along the project alignment, more typically ranging from about 12 to 19 feet lower.

3.2 Regional Geology

The subject area is located in the northern portion of the Peninsular Ranges geomorphic province, one of eleven naturally defined geologic regions that have been delineated in the state of California (refer to Figure 2). Each of these provinces exhibits a unique set of defining geomorphic characteristics that are closely associated with the underlying geologic conditions, geologic history, topographic relief, and climate. The Peninsular Ranges province is characterized by a series of steep, elongated valleys, basins, mountain ranges, and associated major fault zones that trend northwestward across southwestern California. The Santa Ana Mountains, the adjoining Elsinore Valley to the east, and the associated Whittier-Elsinore fault zone extend to the southeast from the subject area and are prominent examples of the northwesterly trending geologic structure that is characteristic of the Peninsular Ranges province. The westerly trending Transverse Ranges province (San Bernardino Mountains, San Gabriel Mountains, Santa Monica Mountains, etc.) forms the northerly boundary of the province. The Peninsular Ranges province includes the Los Angeles basin/coastal plain and also several northwesterly trending offshore valleys and ranges with local peaks that form the islands of San Clemente, Santa Catalina, Santa Barbara, and San Nicholas along the southern California coast.

Page | 21

The coastal plain and physiographic bowl that forms the Los Angeles basin is the modern counterpart of a much larger structural basin that has been receiving discontinuous deposition since late Cretaceous time (approximately 60 to 70 million years b.p., USGS, 1965). Essentially continuous subsidence of this structural basin and chiefly marine deposition of sediments began in the middle Miocene time (about 15 to 20 million years b.p.), forming extremely thick sections of Miocene– and Pliocene–age bedrock, semi-consolidated Pleistocene sediments, and also an extensive mantle of unconsolidated Recent– or Holocene–age alluvium beneath the central portion of the modern physiographic basin. The bedrock forming the flanks of Santa Ana Canyon and underlying the project site was deposited in the much larger structural basin, which was subsequently uplifted by tectonic forces at the periphery of the Los Angeles basin, including displacements along the Whittier fault, which projects beneath the easterly portion of the project site (refer to Regional Geologic Map, Figure 3). Regional uplift and associated cones of alluvial deposition from the San Bernardino and eastern San Gabriel Mountains during the mid-Pleistocene (about 1 million years b.p.) apparently deflected or redirected flow of the upper Santa Ana River to the southwest away from those mountain fronts and towards the Santa Ana Mountains. The redirected flow cut down through older Pleistocene alluvial sediments shed from the northerly end of the Santa Ana Mountains, and also ultimately into the underlying bedrock in the vicinity of the Whittier fault, forming the modern Santa Ana Canyon drainage.

The principal geologic references for the subject area are USGS Professional Paper 420- B: “Geology and Oil Resources of the Eastern Puente Hills, Southern California” (1964), and USGS Professional Paper 420-D: “Geology of the Northern Santa Ana Mountains, California” (1981). The geologic maps from these publications respectively cover the northerly and southerly sides of Santa Ana Canyon, and excerpts of these regional maps have been combined on Figure 3 to illustrate the regional geologic conditions in the vicinity of the project site.

The dominant geologic feature in the vicinity of the subject site is the Whittier fault zone that trends to the west northwest (i.e., ~N65W) beneath the easterly portion of the planned alignment (Figure 3). The Whittier fault is a west-northwesterly extension or splay of the Elsinore fault that parallels the steep easterly side of the Santa Ana Mountains. The combined fault segments are sometimes referred to as the Whittier-Elsinore fault zone.

This combined fault zone bifurcates in the area south of Corona, and an apparently less active extension or splay of the Elsinore fault identified as the Chino fault (trending ~N35W) extends along the easterly side of the Chino/Puente Hills, passing near the location of Prado Dam.

Near the head of Santa Ana Canyon, a combination of right-lateral strike-slip and oblique dip-slip displacement along the Whittier fault has juxtaposed Tertiary-age sedimentary

Page | 22 rocks on the north side of the canyon with much older Cretaceous-age sedimentary rocks on the south side of the fault/canyon (USGS, 1964 and USGS, 1981). Similarly, in the vicinity of the subject site, the Whittier fault separates sedimentary bedrock of the Puente formation on the northerly side of the fault from older sedimentary bedrock of the Topanga and Vaqueros-Sespe formations on the southerly side of the fault (USGS, 1964; Figure 3).

Consistent with tectonic uplift and general westerly tilting of the Santa Ana Mountains, sedimentary strata exposed on the southerly side of Santa Ana Canyon become progressively older to the east (Figure 3). The regional mapping indicates this overall westerly tilting of the bedrock is limited to the southerly side of the Whittier fault and appears to persist to some degree in the vicinity of the subject site (i.e., the older Vaqueros- Sespe formation has been encountered to the east of the Topanga formation on the southerly side of the fault).

SOURCE: BASE MAP FROM CALIFORNIA

GEOLOGY, SEPTEMBER 1984. CALIFORNIA

DIVISION OF MINES AND GEOLOGY

PROJECT

SITE

SANTA ANA RIVER MAINSTEM

LOWER SANTA ANA RIVER CHANNEL REACH 9 - PHASE 5B

ORANGE COUNTY, CALIFORNIA

GEOMORPHIC PROVINCES AND SOME

PRINCIPAL FAULTS OF CALFORNIA

US Army Corps of Engineers

Los Angeles District

FIGURECKD BY: STK\SC

DWN BY: JBD

DATE: May 2016

P l o t

D a t

A

M

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F i l e

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Page | 24

SANTA ANA RIVER MAINSTEM

LOWER SANTA ANA RIVER CHANNEL REACH 9 - PHASE 5B

ORANGE COUNTY, CALIFORNIA

REGIONAL GEOLOGIC MAP

US Army Corps of Engineers

Los Angeles District

FIGURE

00 2000' 4000'

PROJECT

SITE

420-D

420-B

420-D

420-B

Sources: Portions of the GEOLOGIC MAP OF THE NORTHERN SANTA

ANA MOUNTAINS, CALIFORNIA; U.S.G.S. Professional Paper 420-D, Plate 1 and the GEOLOGIC MAP OF THE PRADO DAM AND YORBA

LINDA QUADRANGLES, LOS ANGELES, ORANGE, RIVERSIDE AND

SAN BERNARDINO COUNTIES, CALIFORNIA; U.S.G.S. Professional

Paper 420-B, Plate 1

Coordinate System: State Plane California

Datum: NAD 27, Zone 6

CKD BY: STK\SC

DWN BY: JBD

DATE: May 2016

P l o t

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D a t u m

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Page | 29

3.3 Local Geology and Subsurface Conditions

Foundation materials along the Phase 5B alignment can be divided into five primary geologic units. In generally increasing age and depth they are: 1) artificial or manmade fill (af); 2) alluvium (Qal); 3) older alluvium (Qao); 4) Topanga formation bedrock (Tt); and 5) Vaqueros-Sespe formation bedrock (Tvs). Stratigraphic nomenclature for the project is taken primarily from USGS Professional Paper 420-B (USGS, 1964; refer to Figure 3). The geologic map symbols referenced above and shown on Figure 3 follow standard geologic practice wherein naturally deposited Quaternary-age geologic units (i.e., from the present to about 2.6 million years old [USGS, 2010]) are labeled with a capital “Q”, including appropriate subscripts, and Tertiary-age geologic units/bedrock (i.e., from about 2.6 million to 65 million years old [USGS, 2010]) are labeled with a capital “T”. Manmade or artificial fill is not labeled with a time period and is identified only with appropriate subscripts. Brief summary descriptions of each of these units are provided below.

3.3.1 Artificial Fill (af & Caf)

As briefly discussed above under Section 3.1, manmade/artificial fill has been constructed over the Santa Ana River floodplain along the entire length of the planned project. This fill has been placed for construction of East La Palma Avenue that adjoins the northerly side of the alignment along most of its length and also for construction of the adjacent/adjoining commercial and residential developments (Figure 1). Reference to available topographic maps from other projects indicates the elevation of the street and pad grades adjoining the existing descending slope along the alignment ranges from approximately elevation 358 feet near the westerly end of the project, up to about elevation 404 feet near the easterly end. Comparison of these elevations to those of the adjacent floodplain at several locations indicates the existing fill slope that comprises the project area has an exposed height that ranges from about 10 to 30 feet, but more typically ranges from about 12 to 18 feet in height. The highest portion of the descending fill slope occurs near the intersection of East La Palma Avenue and Via Lomas de Yorba East (near about Station 1324 +00) where the exposed slope height is about 30 feet.

Plans provided by the City of Yorba Linda dated 1981 entitled, “Plans for Construction of Lomas de Yorba-Sur Levee, from 3,000 feet Upstream of Weir Canyon Road to 3,000 feet Downstream from Coal Canyon Road”, indicate the entire length of the subject slope was originally constructed as a levee. The last revision shown on the plans is dated 4 November 1981 and the plans are not marked “As-Built”. As shown on the plans, this levee included a 3:1 (H:V) northerly land-side slope, and in the westerly portion of the alignment also included an approximately 84-foot-wide roadway surface on the top of the levee embankment that was apparently constructed for East La Palma Avenue. These plans indicate the subject river-side slope area along the southerly side of the levee was originally constructed at a gradient of 2.5:1 (H:V) and included an approximately 18-foot-wide bench for a maintenance road that is generally consistent with the existing Santa Ana Trail configuration. The plans also specify installation of rip-rap erosion protection on the lower portion of the river-side slope below the maintenance road, similar to the existing slope

Page | 30 configuration/conditions (refer to Typical Embankment Section [1981], Plate 3A and Geologic Cross-Sections, Plates 3A through 3C).

The plan and profile sheets for the levee structure in the subject area (Yorba Linda, 1981) specify a rip-rap revetment with a thickness of 33 inches and an overall height that ranges from about 15 to 20 feet (i.e., from a buried toe elevation beneath the river floodplain to a top elevation that is below the planned maintenance road). The planned revetment section also includes a 3-foot-wide toe-key of larger derrick stone that extends approximately 3 feet below the planned toe elevation of the revetment slope (the typical section detail shown on Sheet 10 of the plans indicates that larger stone comprising the toe-key would extend up to about 9 feet beyond the planned toe of the revetment). The rip-rap gradation shown on the plans specifies stone ranging from 100 to 1,000 lbs. for the revetment slope and 100 to 2,500 lbs. for the toe-key. The revetment section also includes a bedding or filter layer consisting of a 9-inch thick graded mineral filter or, as an alternative, a layer of filter fabric covered with a 6-inch layer of gravel beneath the rip-rap (Plate 3A).

The elevations of the existing grade along the toe of the planned revetment slope are shown on the 1981 plan profiles. Comparison of these elevations to those shown on the current topographic base for the project indicate similar elevations for the alluvial floodplain along the toe of the existing slope (i.e., ranging from about elevation 395 feet near the upstream end, to about 340 feet at the downstream end).