Upper Guadalupe River Final Feasibility Report and Environmental Impact Statement/Report, Part 1 of 2

796 Pages·47.3 MB·English

by  United States. Army. Corps of Engineers. San Francisco District., Santa Clara Valley Water District.

TC
425
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1998
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LIBRARY
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Final
Environmental Impact Report/
Environmental Statement
~mpact
Upper Guadalupe River Feasibility Study
San Francisco
Bay
UPPER GUADALUPE RivER
Los Gatos , FEASIBILITY STUDY AREA
1Cr/ee!>{
'~'\
Ji
c Canoas
Vasona 1 ~ Creek
g::,
R•-'• G-J'-tr, Alamitos
\'A.
Creek Creek
"-., ( \/ Calero I
Guada~upe '"\~reek
I ) /
~.
Reservoir \
l / / """ "- / l J
Calero 1
~\ ,~ /~
1 / ' \ )eservoir
'"-/'\ .,___.- Almaden /
""'~~·
R?ese\o//"
Lake ElsmaTI.
-......._
·"--~/
Prepared for
Santa Clara Valley U.S. Army Corps of Engineers
Water District San Francisco District
State Lead Agency Federal Lead Agency
Prepared by
Science Applications International Corporation
January 1998
Final
Environmental Impact Report/
Environmental Impact Statement
Upper Guadalupe River Feasibility Study
Prepared for
Santa Clara Valley U.S. Army Corps of Engineers
Water District San Francisco District
State Lead Agency Federal Lead Agency
Prepared by
Science Applications International Corporation
January 1998
1
2 TABLE OF CONTENTS
3
4 SUMMARY S-1
5 S.1 INTRODUCTION ..................................... . S-1
6 S.2 MAJOR CONCLUSIONS AND FINDINGS .................... . S-2
7 S.3 AREAS OF CONTROVERSY AND CONCERN ................. . S-3
8 S.4 UNRESOLVED ISSUES ................................ . S-3
9 S.5 RELATIONSHIP TO ENVIRONMENTAL PROTECTION STATUTES
10 AND OTHER ENVIRONMENTAL REQUIREMENTS . . . . . . . . . . . . . . S-3
11
12 1.0 NEED FOR AND OBJECTIVES OF THE ACTION . . . . . . . . . . . . . . . . . . . . . . 1-1
13 1.1 PURPOSE AND NEED . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-1
14 1.2 PROJECT AUTHORITY . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-1
15 1.3 PRIOR STUDIES, REPORTS, AND EXISTING PROJECTS . . . . . . . . . . . 1-1
16 1. 3.1 Pfior to Upper Guadalupe River Feasibility Study . . . . . . . . . . 1-1
17 1.3.2 Upper Guadalupe River Feasibility Study . . . . . . . . . . . . . . . 1-2
18 1.4 PUBLIC CONCERNS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-5
19 1.5 PLANNING OBJECTIVES ................................ 1-7
20 1.6 PLANNING CONSTRAINTS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-8
21
22 2.0 PROPOSED PROJECT AND ALTERNATIVES ......................... 2-1
23 2.1 FEASIBILITY STUDY PLANNING PROCESS ................... 2-1
24 2.2 FORMULATION OF CONCEPTUAL ALTERNATIVE PLANS . . . . . . . . 2-5
25 2.3 FORMULATION AND SCREENING OF COMPREHENSIVE FLOOD
26 PROTECTION ALTERNATIVES ............................ 2-8
27 2.4 ALTERNATIVES CONSIDERED FOR FURTHER STUDY .......... 2-11
28 2.4.1 Channel Widening Plan . . . . . . . . . . . . . . . . . . . . . . . . . 2-11
29 2.4.2 Bypass Channel Plan . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-17
30 2.4.3 No-Action Alternative . . . . . . . . . . . . . . . . . . . . . . . . . . 2-21
31
32 3.0 ENVIRONMENTAL SETTING . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-1
33 3.1 EXISTING SITE CHARACTERISTICS ........................ 3-1
34 3.2 SURROUNDING LAND USES ............................. 3-2
35 3.3 COMPLIANCE WITH ENVIRONMENTAL REQUIREMENTS ......... 3-2
36 3.3.1 Federal Regulations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-2
37 3.3.2 Executive Orders . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-6
38 3.3.3 State Regulations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-7
39 3 .3 .4 Local Regulations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-9
40 3.4 PROJECTS CONSIDERED IN THE CUMULATIVE ANALYSIS ...... 3-13
41
42 4.0 AFFECTED ENVIRONMENT AND ENVIRONMENTAL CONSEQUENCES OF
43 THE PROPOSED ACTION AND ALTERNATIVES ..................... 4.1-1
44 4.1 AIRQUALITY ...................................... 4.1-1
45 4 .1.1 Regulatory Setting . . . . . . . . . . . . . . . . . . . . . . . ·. . . . . . 4.1-1
46 4.1.2 Existing Conditions ............................ 4.1-1
47 4 .1. 3 Environmental Effects . . . . . . . . . . . . . . . . . . . . . . . . . . 4.1-3
48 4.1.4 Mitigation Measures ........................... 4.1-6
49 4.1.5 Unavoidable Significant Adverse Impacts . . . . . . . . . . . . . . 4.1-7
Table of Contents
1 4.2 GEOLOGIC RESOURCES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.2-1
2 4.2.1 Regulatory Setting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.2-1
3 4.2.2 Existing Conditions . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.2-1
4 4.2.3 Environmental Effects .......................... 4.2-7
5 4.2.4 Mitigation Measures . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.2-9
6 4.2.5 Unavoidable Significant Adverse Impacts . . . . . . . . . . . . . . 4.2-9
7 4.3 WATER RESOURCES ................................. 4.3-1
8 4. 3 .1 Regulatory Setting . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4. 3-1
9 4.3.2 Existing Conditions ............................ 4.3-1
10 4.3.3 Enviro:nmental Effects .................. ~ .. ~ .... 4.3-9
11 4.3.4 Mitigation Measures .......................... 4.3-17
12 4.3.5 Unavoidable Significant Adverse Impacts ............. 4.3-17
13 4.4 BIOLOGICAL RESOURCES .............................. 4.4-1
14 4.4 .1 Regulatory Setting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.4-1
15 4.4.2 Existing Conditions . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.4-1
16 4.4.3 Environmental Effects . . . . . . . . . . . . . . . . . . . . . . . . . 4.4-21
17 4.4.4 Mitigation Measures . . . . . . . . . . . . . . . . . . . . . . . . . . 4.4-47
18 4.4.5 Unavoidable Sigrjficant Adverse Impacts ............. 4.4-60
19 4.5 AESTHETICS AND RECREATION ......................... 4.5-1
20 4. 5.1 Regulatory Setting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4. 5-1
21 4.5.2 Existing Conditions ............................ 4.5-1
22 4.5.3 Environmental Effects ......................... 4.5-14
23 4.5.4 Mitigation Measures . . . . . . . . . . . . . . . . . . . . . . . . . . 4.5-28
24 4.5.5 Unavoidable Significant Adverse Impacts ............. 4.5-30
25 4.6 NOISE ............................................ 4.6-1
26 4.6.1 Regulatory Setting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.6-1
27 4.6.2 Existing Conditions . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.6-2
28 4.6.3 Environmental Effects .......................... 4.6-2
29 4.6.4 Mitigation Measures ........................... 4.6-5
30 4.6.5 Unavoidable Significant Adverse Impacts . . . . . . . . . . . . . . 4.6-7
31 4.7 TRANSPORTATION ................................... 4.7-1
32 4.7.1 Regulatory Setting ............................. 4.7-1
33 4.7.2 Existing Conditions ............................ 4.7-1
34 4. 7. 3 Environmental Effects . . . . . . . . . . . . . . . . . . . . . . . . . . 4. 7-6
35 4.7.4 Mitigation Measures .......................... 4.7-12
36 4.7.5 Unavoidable Significant Adverse Impacts ............. 4.7-13
37 4.8 LAND USE ......................................... 4.8-1
38 4.8.1 Reguiatory Setting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.8-1
39 4.8.2 Existing Conditions 4.8-1
40 4. 8. 3 Environmental Effects . . . . . . . . . . . . . . . . . . . . . . . . . . 4.8-3
41 4.8.4 Mitigation Measures .......................... . 4.8-5
42 4.8.5 Unavoidable Significant Adverse Impacts ............. . 4.8-6
43 4.9 PUBLIC SERVICES AND UTILITIES ....................... . 4.9-1
44 4.9.1 Regulatory Setting ............................ . 4.9-1
45 4.9.2 Existing Conditions ........................... . 4.9-1
46 4.9.3 Environmental Effects . ~ G ~ ~ ~ ~ ~ 4 • e • • • • • • 4 • • • • • • • • £A+ .)r1\' -.'4"', ,,
47 4.9.4 Mitigation Measures . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.9-4
48 4.9.5 Unavoidable Significant Adverse Impacts . . . . . . . . . . . . . . 4.9-5
ii
Table of Contents
1 4.10 CULTURAL RESOURCES ...............· ............... 4.10-1
2 4.10 .1 Regulatory Setting . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.10-1
3 4.10.2 Existing Conditions . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.10-2
4 4.10.3 Environmental Effects ......................... 4.10-6
5 4.10.4 Mitigation Measures . . . . . . . . . . . . . . . . . . . . . . . . . . 4.10-9
6 4.10.5 Unavoidable Significant Impacts . . . . . . . . . . . . . . . . . . 4.10-10
7 4.11 HAZARDOUS MATERIALS ............................. 4.11-1
8 4.11.1 Regulatory Setting . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.11-1
9 4.11.2 Existing Conditions . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.11-2
10 4 .11. 3 Environmental Effects . . . . . . . . . . . . . . . . . . . . . . . . . 4.11-3
11 4.11.4 Mitigation Measures . . . . . . . . . . . . . . . . . . . . . . . . . . 4.11-4
12 4.11.5 Unavoidable Significant Adverse Impacts . . . . . . . . . . . . . 4.11-5
13 4.12 PUBLIC SAFETY ................................... 4.12-1
14 4.12.1 Regulatory Setting ............................ 4.12-1
15 4.12.2 Existing Conditions . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.12-1
16 4.12.3 Environmental Effects . . . . . . . . . . . . . . . . . . . . . . . . . 4.12-1
17 4.12.4 Mitigation Measures . . . . . . . . . . . . . . . . . . . . . . . . . . 4.12-3
18 4.12.5 Unavoidable Significant Adverse Impacts . . . . . . . . . . . . . 4.12-3
19 4.13 SOCIOECONOMICS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.13-1
20 4.13.1 Regulatory Setting ............................ 4.13-1
21 4.13.2 Existing Conditions ........................... 4.13-1
22 4.13.3 Environmental Effects . . . . . . . . . . . . . . . . . . . . . . . . . 4.13-2
23 4.13.4 Mitigation Measures . . . . . . . . . . . . . . . . . . . . . . . . . . 4.13-5
24 4.13.5 Unavoidable Significant Adverse Impacts . . . . . . . . . . . . . 4.13-5
25
26 5.0 RECOMMENDATIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-1
27 5.1 Environmentally Preferred Alternative . . . . . . . . . . . . . . . . . . . . . . . . . 5-1
28 5.2 Recommended Alternative . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-1
29
30 6.0 CUMULATIVE IMPACTS ...................................... 6-1
31 6.1 OTHER PROJECTS IN THE VICINITY OF THE GUADALUPE
32 RIVER CORRIDOR . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-1
33 6.1.1 Guadalupe River Flood Control Project from I-880 to I-280 . . . . 6-1
34 6.1.2 Guadalupe River Park . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-1
35 6.1.3 Guadalupe River Park South Corridor Master Plan (I-280 to
36 Coleman Avenue) ............................. . 6-2
37 6.1.4 SR 87 Freeway Upgrade Project (Highway 101 to Julian
38 Street) .................................... . 6-2
39 6.1.5 SR 85 Transportation Corridor Project . . . . . . . . . . . . . . . . . 6-2
40 6.1.6 San Jose International Airport Expansion Plan ........... . 6-2
41 6.1.7 San Jose Riparian Corridor Policy Study . . . . . . . . . . . . . . . . 6-3
42 6.1.8 Santa Clara Valley Water District Upper Guadalupe River
43 Flood Control Project ................ ." .......... . 6-3
44 6.1.9 Almaden Road Widening ......................... . 6-3
45 6.2 CUMULATIVE IMPACTS AND MITIGATION MEASURES ......... . 6-4
46
iii
Table of Contents
1 7.0 THE RELATIONSHIP BETWEEN LOCAL SHORT-TERM USES OF MAN'S
2 ENVIRONMENT AND THE MAINTENANCE AND ENHANCEMENT OF
3 LONG-TER.t\1 PRODUCTIVITY . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-1
4
5 8.0 GROWTH-INDUCING IMPACTS ................................. 8-1
6
7 9.0 IRREVERSIBLE AND IRRETRIEVABLE COMMITMENTS OF RESOURCES . . . . . 9-1
8
9 10.0 PUBLIC INVOLVEMENT AND INTERAGENCY COORDINATION . . . . . . . . . . 10-1
10 10.1 PUBLIC INVOLVEMENT PROGP~l\.l\.1 . ~ ~ . ~ ...... ~ . . . . . . . . . . . 10~1
11 10.2 REQUIRED COORDINATION . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-1
12 10.3 AGENCIES, ORGANIZATIONS, AND INDIVIDUALS RECEIVING
13 THIS EIR/S . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-1
14
15 11.0 REFERENCES. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11-1
16
17 12.0 PERSONS AND AGENCIES CONTACTED ......................... . !• L,.,.- 11
18
19 13.0 LIST OF PREPARERS AND CONTRIBUTORS ....................... 13-1
20
21 14.0 ACRONYMS ............................................. . 14-1
22
23 15.0 INDEX 15-1
24
25 APPENDICES
26 A. AIR QUALITY REGULATIONS
27 Federal Regulations
28 State Regulations
29 Local Regulations
30 B. AIR QUALITY EMISSION CALCULATIONS
31 C. AIR QUALITY CONFORMITY DETERMINATION
32 D. USFWS COORDINATION ACT REPORT AND CORPS RESPONSES
33 E. VEGETATION IMPACTS AND MITIGATIONS FOR
34 THE BYPASS CHANNEL PLAN
35 F. BIOLOGICAL DATA
36 G. CLEAN WATER ACT SECTION 404(b)(l) DETERMINATION
37 H. WATER RESOURCES DATA
38 I. TRANSPORTATION LEVEL OF SERVICE DEFINITIONS
39 J. HAZAFOOUS MATERI<'i~LS DATA
40 K. DRAFT BIOLOGICAL ASSESSMENT
41 L. MITIGATION MONITORING AND REPORTING PLAN
42 M. COMMENTS AND RESPONSES TO COMMENTS ON THE DRAFT EIR/S
iv
Table of Contents
1 FIGURES
2
3 2-1 Regional Project Site Location . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-2
4 2-2 Upper Guadalupe River Feasibility Study Limits, Reaches 7 to 12 . . . . . . . . . . . . 2-3
5 2-3 Guadalupe River Watershed . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-4
6 2-4 Conceptual Widened Earth Channel Plan Design . . . . . . . . . . . . . . . . . . . . . . . 2-7
7 2-5 Conceptual Earth Bypass Channel Plan Design . . . . . . . . . . . . . . . . . . . . . . . . 2-9
8 2-6 Conceptual Floodwall Plan Design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-10
9 2-7 Bypass Channel Plan Recreational Trail . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-22
10 2-8 Recreational Trail on Reach 7, Looking Downstream . . . . . . . . . . . . . . . . . . . 2-23
11 4.2-1 Geologic Map ............................................ 4.2-3
12 4.2-2 Soil Associations Located in the Area ............................. 4.2-4
13 4.2-3 Regional Active and Potentially Active Faults ........................ 4.2-6
14 4.3-1 Guadalupe River Watershed and 100-Year Flood Event .................. 4.3-3
15 4.3-2 Upper Guadalupe River 50-Year Floodplain ......................... 4.3-6
16 4.3-3 Upper Guadalupe River 100-Year Floodplain ........................ 4.3-7
17 4.3-4 Upper Guadalupe River Residual Floodplains 50-Year Project on Guadalupe
18 River and 20-Year Project on Canoas Creek . . . . . . . . . . . . . . . . . . . . . . . 4.3-11
19 4.3-5 Upper Guadalupe River Residual Floodplains 100-Year Project on Guadalupe
20 River and 20-Year Project on Canoas Creek ........................ 4.3-15
21 4.4-1 Identified Barriers to Fish Migration on Alamitos, Guadalupe, and Arroyo
22 Calero Creeks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.4-11
23 4.5-1 Reach 7 Existing Visual Setting ................................. 4.5-3
24 4.5-2 Reach 8 Existing Visual Setting ................................. 4.5-5
25 4.5-3 Reach 9 Existing Visual Setting ................................. 4.5-7
26 4.5-4 Reach lOA Existing Visual Setting ............................... 4.5-9
27 4.5-5 Reach lOB Existing Visual Setting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.5-11
28 4.5-6 Reach lOC Existing Visual Setting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.5-15
29 4.5-7 Reach 11A Existing Visual Setting .............................. 4.5-17
30 4.5-8 Reach 11 B and 11 C Existing Visual Setting . . . . . . . . . . . . . . . . . . . . . . . . 4. 5-19
31 4.5-9 Reach 12 Existing Visual Setting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.5-21
32
v
Table of Contents
1 TABLES
2
3 S-1 Summary of Environmental Consequences . . . . . . . . . S-4
4 S-2 Comparison of Flood Control Alternatives . . . . . . . S-14
5 S-3 Project Compliance with Environmental Requirements S-15
6 2-1 Comparison of Channel Widening Plan and Bypass Channel
'i Plan Alternatives . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-13
i
8 4.1-1 1995 Emission Inventory for the San Francisco Bay Area Air Basin . . . . . . . . . . 4.1-4
9 4.2-1 Characteristics of Faults in the Guadalupe River Region .................. 4.2-7
ill 4.3-1 Drainage Area Data for the Guadalupe River ........................ 4.3-2
.LV
11 4.6-1 Typical Noise Data for Construction Equipment ....................... 4.6-4
12 4.6~2 Overall Construction Noise Levels . . . . . . 4.6-4
13 4.6-3 Revised Construction Noise Levels ............................... 4.6-7
14 4.7-1 Existing Traffic Voiumes ..................................... 4.7-5
15 4.7-2 Bridge Construction for the Bypass Channel Plan ...................... 4.7-9
16 4.7-3 Affected Traffic Arteries . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4. 7-9
1"7 4.13-1 Population Growth in San Jose (1950 to 1990) ....................... 4.13-1
.L I
18 4.13-2 Employment Distribution in the San Jose Metropolitan Area (1990) . . . . . . . . . 4.13-2
19 6-1 Stream Segments included in the Cumulative lmpact Assessment
20 for Biotic Resources . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-7
21 6-2 Historical Projects that have Affected the Nature, Extent, and Distribution of
22 Riparian Habitat in the Guadalupe River System . . . . . . . . . . . . . . . . . . . . . . . 6-8
23 6-3 Sunm1ary of Fish Habitat Accessible by Removal of Fish Barriers on the
24 Guadalupe River and Alamitos, Calero, and Guadalupe Creeks . . . . . . . . . . . . . 6-11
25
26
vi
1 SUMMARY
2
3 S.l INTRODUCTION
4
5 This Environmental Impact Report/Environmental Impact Statement (EIR/S) analyzes the impacts
6 associated with proposed flood control measures for the upper Guadalupe River in San Jose, California.
7 The EIR/S fulfills regulations of the National Environmental Policy Act (NEPA) and the California
8 Environmental Quality Act (CEQA) that require agencies sponsoring these federal civil works projects
9 to prepare a document that explains the consequences of the action on the environment. This feasibility
10 study evaluates the extent and nature of the flood control problem. It investigates several different levels
11 of protection, and identifies a flood control protection plan, called the National Economic Development
12 Plan, that optimizes the size of the project from an economical point view. The cost of the NED plan
13 determines to what extent the federal government is able to fund the construction of the project, or share
14 funding with a local sponsor. The Corps of Engineers, San Francisco District (Corps), is the federal lead
15 agency for the project and the Santa Clara Valley Water District (SCVWD) is the non-federal (local)
16 sponsor. The feasibility study of flood control needs along the upper Guadalupe River is authorized by
17 Section 205 of the Flood Control Act of 1948 (33 U.S.C. 701s), as amended.
18
19 The feasibility study area includes a 5.5-mile segment of the Guadalupe River in the City of San Jose.
20 For flood control engineering descriptive purposes, the river has been divided into a number of "reaches,"
21 . segments distinguished by major street and railroad crossings. The feasibility study area contains Reaches
22 7 through 12, extending from the Southern Pacific Railroad bridge just south of 1-280, upstream 5.5 miles
23 to the Blossom Hill Road bridge. The feasibility study area also includes areas of Ross Creek extending
24 5,200 feet upstream from its confluence with the Guadalupe River, and Canoas Creek extending 2,800
25 feet upstream from its confluence with the Guadalupe River. This part of the river, including Reaches
26 7 through 12, has flooded on several occasions in the past, with major episodes occurring in 1986 and
27 1995.
28
29 The principal objective of the proposed flood control work is to protect homes and businesses in this
30 portion of the Guadalupe River drainage from flooding damage. Other flood control projects on areas
31 of the river downstream (northward) have been analyzed and are under construction (i.e., the downtown
32 Guadalupe River project, providing flood protection from Interstate 880 to Interstate 280), or are in the
33 planning stages (including the upper Guadalupe River project improvements proposed by the SCVWD
34 extending from U.S 101, two miles north and downstream of the feasibility study area, through Reach
35 12).
36
37 The Corps feasibility study evaluated a number of potential flood control alternative plans. Two
38 alternative plans for providing flood protection on the upper Guadalupe River with the greatest net
39 benefits are analyzed in detail in this document: a Channel Widening Plan, and a Bypass Channel Plan.
40
41 The Channel Widening Plan would provide protection from all floods up to an approximate 50-year flood
42 event (a flood that occurs on the average of once every 50 years, or has a 2 percent chance of occurring
43 in any one year). The major components of the plan include widening and benching along portions of
44 the river to provide an expanded area for floodwaters, and a maintenance road and access points.
45
46 The Bypass Channel Plan would provide protection from all floods up to an approximate 100-year flood
47 event (a flood that occurs on the average of once every 100 years, or has a 1 percent chance of occurring
48 in any one year). Major components of the Bypass Channel Plan include a secondary channel located
49 adjacent to much of the existing river that would not require removing important riparian vegetation on
S-1