HomeMy WebLinkAboutStaff Report 13814
City of Palo Alto (ID # 13814)
City Council Staff Report
Meeting Date: 1/10/2022 Report Type: Consent Calendar
City of Palo Alto Page 1
Title: Adopt a Park Improvement Ordinance for the Replacement of the Palo
Alto Flood Basin Tide Gate Structure in the City's Baylands
From: City Manager
Lead Department: Community Services
Recommendation
Staff and the Parks and Recreation Commission recommend that the City Council:
1. As a responsible agency under CEQA, consider the Mitigated Negative Declaration
(MND) prepared and approved by lead agency Santa Clara Valley Water District (Valley
Water); and
2. Adopt a Park Improvement Ordinance (Attachment A) authorizing Valley Water’s Palo
Alto Flood Basin Tide Gate Structure Replacement Project (Project), which will construct
a new replacement tide gate structure (Structure) within the City’s Baylands.
Background
The levees forming the Palo Alto Flood Basin (Flood Basin) were built by the City of Palo Alto
(City) in the 1940s and the associated tide gate structure (Structure) was constructed in 1957 by
the former Santa Clara County Flood Control and Water Conservation District (now Santa Clara
Valley Water District, also known as Valley Water), Santa Clara County and the City. The
Structure is located along the Bay shoreline in Palo Alto, east of the Palo Alto Municipal Airport
and Palo Alto Baylands Nature Preserve. The floodwaters stored in the Flood Basin are released
to the Bay through eight cells with 16 tide gates (15 passive gates and one motorized sluice
gate) that comprise the overall tide gate structure. The purpose of the passive tide gates is to
regulate water elevation in the Flood Basin such that when the water elevation in the basin is
higher than the tidal elevation of the Bay, the passive tide gates are pushed open by water
pressure and discharge water from the Flood Basin to the Bay. When the water surface
elevation in the Flood Basin is lower than the Bay, the passive tide gates are held shut by water
pressure from the Bay, to prevent full tidal inundation.
In 1977, the City requested to change one of the passive tide gates to a motorized sluice gate
for a mitigation project agreed to by the United States Army Corps of Engineers and the City for
the Palo Alto Refuse Disposal Area. In 1978, the City forwarded the plans and specifications for
the gate modification and Valley Water issued a permit to the City for the gate modification.
City of Palo Alto Page 2
The City operates the motorized sluice gate to improve water quality within the Flood Basin
while considering optimal Flood Basin water elevation.
The Structure has been regularly inspected and maintained by Valley Water. In 2011, Valley
Water discovered that water was flowing beneath the Structure, undermining the function of
the tide gates and potentially its structural stability. In 2012, Valley Water completed
emergency repairs to stop seepage flow beneath the Structure. As part of that effort, Valley
Water staff prepared a post construction report (as required by the United States Army Corps
of Engineers’ Emergency Permit) which detailed the emergency work and recommended
replacement of the Structure.
In 2014, Valley Water retained the services of Mark Thomas & Company (MT) to perform
structural inspections and prepare an assessment report for the Structure. The report
concluded that the Structure was generally in fair condition and recommended minor structural
repairs.
In 2017, Valley Water retained a construction contractor to perform minor repairs. The work
was complicated due to cracks found in the bottom slab and inability to dewater for the repair
work, which resulted in the contract being terminated without completing the work.
Subsequently, a structural assessment was performed by MT in October 2017 which concluded
that the structure would be functional for a couple more years and recommended the Structure
be replaced.
In 2018, after project objectives were changed to replace (rather than repair) the Structure, a
new team was assigned to the Project to commence planning and design of the new Structure.
The new Project team also prepared an Emergency Action Plan in coordination with the City of
Palo Alto in 2019 to provide guidance for potential flooding emergencies in the interim. MT was
engaged to perform additional structural assessments in January 2020 and January 2021, and
both assessments concluded that the Structure would still be functional for another couple of
years.
Project Description
The Project objectives include the following:
• Prevent failure of the existing Structure, which would result in increased risk of coastal
and fluvial flooding;
• Maintain or improve the level of flood protection for Matadero, Adobe, and Barron
Creeks, including during Project construction;
• Construct a new motorized sluice gate on the City’s behalf which will be used to
maintain or improve water quality within the Flood Basin; and
• Upsize the Structure to function with two feet of future sea-level rise.
City of Palo Alto Page 3
The Project would involve construction of a new 132-foot-long tide gate structure slightly
inboard (upstream) and southeast of the existing 113-foot-long deteriorating Structure,
removal of the existing Structure and levee, and construction of a new levee that ties into the
new tide gate structure. The Project would be divided into two phases and constructed in four
construction seasons. The existing Structure would continue to function until the new structure
is completed by the end of second phase. Phase 1 would involve installation of the first
dewatering system; construction of the new tide gate structure and east levee transition; and
removal of the existing levee in front of the new structure. Phase 2 would involve installation of
the second dewatering system; construction of the west levee transition; and removal of the
existing Structure.
The Project would construct a new motorized sluice gate with Supervisory Control And Data
Acquisition (SCADA) system and water elevation sensors which would be monitored and
operated by the City and used to maintain or improve water quality within the Flood Basin. The
existing sluice gate constructed in 1978 is now over 40 years old and shows aging. Some of the
basic operations such as closing the gate must be done by manual physical cranking rather than
use of the motor. Similarly, the existing SCADA system cannot currently be used to automate
opening and closing of the sluice gate. The new sluice gate infrastructure would remove the
existing City owned sluice gate and replace with a new City owned sluice gate and SCADA
system integrated with the replacement tide gate Structure.
Maintenance of the Site
Similar to current operations, the City will monitor, operate, and maintain the sluice gate, water
elevation sensors, communication control system related to sluice gate, and SCADA system.
Similar to current operations, Valley Water staff would continue to support debris removal
from the trash racks and/or tide gates as needed.
Maintenance of the City’s sluice gate should be reduced with the new Structure by installing
trash racks on both the San Francisco Bay (Bay) side as well as the Flood Basin side. The existing
sluice gate only has a trash rack on the Flood Basin side. When the sluice gate is opened, water
from the Bay enters into the Flood Basin through the sluice gate. The incorporation of the
additional trash rack on Bay side of the sluice gate should reduce the risk of debris interference
and subsequential potential damage to the sluice gate system.
Discussion
City of Palo Alto staff and Valley Water staff have been working together on this Project since
2018. This project replaces critical flood, environmental, and recreational infrastructure critical
to the City, Valley Water, wildlife, and the public.
The Project will require temporary closures to portions of the Trail to accommodate
construction of the replacement Structure work. A diagram illustrating anticipated Trail closures
is included in Attachment A. If the replacement Structure is not constructed, future degradation
City of Palo Alto Page 4
of the existing Structure will occur and would eventually require closure of the Trail for an
unknown duration of time.
The replacement Structure will include a dedicated concrete bay with motor driven sluice gate
solely for the City’s use of maintaining water quality within the Flood Basin and controlling
mosquito breeding. This new motor operated sluice gate will replace the existing motor
operated sluice gate which is owned and operated by the City. The Structure will also include
new water level sensors and SCADA system to improve flexibility and efficiency for the City’s
sluice gate operations. The new sluice gate will enable remote operation of the sluice gate.
The replacement Structure, with its improved operations and maintenance features and
improved hydraulic performance, is anticipated to reduce mosquito breeding within the Flood
Basin compared to the existing conditions.
On June 22, 2021, the Parks and Recreation Commission (Commission) reviewed and voted
(7:0) to recommend that City Council adopt a Park Improvement Ordinance for the
improvements to the Palo Alto Flood Basin Tide Gate structure (Staff Report). On July 10, 2021,
Valley Water informed City staff that improvements to the existing levee trail surface, which
was part of the project and included in the Park Improvement Ordinance, were going to be
removed from the scope of work. Because of this change in the scope of the project, the Park
Improvement Ordinance was updated and reviewed again by the Commission. On August 24,
2021, the Commission voted (7:0) to recommend that City Council adopt a Park Improvement
Ordinance for the improvements to the Palo Alto Flood Basin Tide Gate structure (Staff Report).
The proposed trail improvements were intended to smoothen and strengthen the trail surface
as needed based on existing conditions and would be performed by Valley Water’s Operations
& Maintenance staff. However, Valley Water Operations & Maintenance staff are unable to
complete the entire trail stretch within the construction window, thereby reducing the benefit
of the previously proposed trail improvements. Additionally, the outlook for starting the trail
improvement work on time is unlikely due to the anticipated timing of regulatory permits,
further diminishing the benefit of the proposed trail improvements. Valley Water determined
that the proposed trail improvements were no longer justified when comparing the reduced
benefits to the impacts of temporary trail closure and high cost.
While the previously proposed trail surface improvement work would have improved the ability
for the existing levees to facilitate construction equipment loading, it would have also
temporarily closed the trail for at least three months this year. Although omission of the
proposed trail surface improvement work comes with an increased risk for future construction
complications and delays, the planned duration of construction remains unchanged at four
years. In lieu of the proposed trail improvements, there will be an increased need for the
contractor to perform in-kind repairs to the levee trail surface during the normal work seasons.
The contractor can lighten their truck loading to find the optimum balance between number of
truck trips and damage to the levee surface due to heavier loading, thereby minimizing the
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amount levee trail surface repair work required. There are similar South Bay Salt Pond levees
that see high traffic use of haul trucks, and there are provisions that limit the use of loaded haul
trucks on these levees following a significant rain event to prevent damage to the levees. Valley
Water will use similar provisions to mitigate risk of levee damage. The project specifications will
also require that the contractor repair the trail surface to the satisfaction of Valley Water and
the City of Palo Alto at the end of each construction season, prior to opening to trail users.
Timeline
The project construction was originally planned to begin in September 2022, however, due to a
longer than expected permitting process and expanded material procurement lead times,
Valley Water anticipates the following schedule:
September 2023: Start of Year 1 (Season 1) Construction
September 2024: Start of Year 2 (Season 2) Construction
September 2025: Start of Year 3 (Season 3) Construction
September 2026: Start of Year 4 (Season 4) Construction
Resource Impact
Valley Water has requested cost sharing for specific project elements. Discussions for cost
sharing between the City and Valley Water are ongoing. Any funding recommendations
resulting from these discussions will be brought to Council for consideration. Post-construction
operations and maintenance costs are expected to be reduced compared to existing conditions.
Stakeholder Engagement
On February 24, 2020, Valley Water met with stakeholders and members of the public to
discuss the project and collect feedback. On June 24, 2020, Valley Water hosted a virtual
community meeting to discuss the project and collect more community feedback.
The project was discussed with the Parks and Recreation Commission on June 22, 2021, and on
August 24, 2021.
Environmental Review
Valley Water is the Lead Agency under California Environmental Quality Act (CEQA). The CEQA
Final Mitigated Negative Declaration is available at the Valley Water Project website:
https://www.valleywater.org/pafbtidegates. The City is a Responsible Agency under CEQA for
this project and has considered the Final Mitigated Negative Declaration as required by CEQA
regulation 15096.
Attachments:
• Attachment A: Park Improvement Ordinance for Replacement of the Palo Alto Flood
Basin Tide Gate at Baylands
*NOT YET APPROVED*
1
ORDINANCE NO. _____
Ordinance of The Council of The City of Palo Alto Approving
a Plan for Improvements to the
Palo Alto Flood Basin Tide Gate Structure as part of the
Palo Alto Flood Basin Tide Gate Structure Replacement Project
The Council of the City of Palo Alto does ORDAIN as follows:
SECTION 1. Findings. The City Council finds and declares that:
(a) Article VIII of the Charter of the City of Palo Alto and Section 22.08.005 of the Palo Alto
Municipal Code (PAMC) require that, before any substantial building, construction,
reconstruction or development is commenced or approved, upon or with respect to any land
held by the City for park purposes, the Council shall first cause to be prepared and by ordinance
approve and adopt a plan therefor.
(b) The Palo Alto Flood Basin Tide Gate Structure (Structure) is part of the Adobe Creek
Loop Trail (Trail). The Structure is located in the City’s Baylands, which is dedicated parkland
(See PAMC § 22.08.020 et seq.) Based on the Conditional Structural Assessment of the existing
Structure and reduced functionality, the Structure is planned to be replaced.
(c) The City of Palo Alto intends to authorize Santa Clara Valley Water District (Valley
Water) to construct a replacement Structure. The new Structure will replace the existing 1957-
built Structure which has outlived its intended service life and has been recommended for
replacement.
(d) The Plan of improvements shall comprise, as follows:
(1) The Project will construct a replacement Structure near the existing Structure,
and new levees to connect the Trail to the replacement Structure. The project will
re-align a portion of the levees and Trail as required to accommodate the
replacement Structure location. The existing Structure will be removed after the
replacement Structure and levees are constructed. Select plan sheets showing the
in-progress design are attached as Exhibit “A”.
(2) The Project will require temporary closures to portions of the Trail to
accommodate construction of the replacement Structure and connecting levee
work. A diagram illustrating anticipated Trail closures is attached as Exhibit “B”. If
the replacement Structure is not constructed, future degradation of the existing
Structure will occur and would eventually require closure of the Trail for an
unknown duration of time.
(3) The replacement Structure will include a dedicated concrete bay with motor
driven sluice gate solely for the City’s use of maintaining water quality within the
PAFB and controlling mosquito breeding. This new motor operated sluice gate will
replace the existing motor operated sluice gate which is owned and operated by
*NOT YET APPROVED*
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the City. The Structure will also include new water level sensors and Supervisory
Control and Data Acquisition (SCADA) system to improve flexibility and efficiency
for the City’s sluice gate operations. The new sluice gate will enable remote
operation of the sluice gate.
The replacement Structure with its improved operations and maintenance
features and improved hydraulic performance is anticipated to reduce mosquito
breeding within the PAFB compared to the existing conditions.
(e) The Project described above and as otherwise depicted in the attached exhibits is
consistent with recreation and conservation purposes
(f) The Council desires to approve the Plans for the Project described above and as
depicted in Exhibit "A" and Exhibit “B”.
SECTION 2. The Council hereby approves the Plan for construction of the Palo Alto
Flood Basin Tide Gate Structure Replacement Project as described in this Ordinance.
SECTION 3. Valley Water is the Lead Agency for the Project under the California
Environmental Quality Act (CEQA). Valley Water performed an Initial Study and determined
that a Mitigated Negative Declaration (MND) is the appropriate level of review. A resolution
adopting the Final MND (Resolution) was signed by Valley Water’s Board on April 27, 2021. The
Final MND and Resolution are available online from the project website:
https://www.valleywater.org/pafbtidegates. The City Council finds that the City of Palo Alto is
a responsible agency under CEQA for the Project and certifies that it has reviewed and
considered the information contained in Valley Water’s MND.
Valley Water has applied for regulatory permits from six resource agencies and are
currently working with the resource agencies for mitigation requirements and permit
conditions.
SECTION 4. This ordinance shall be effective on the thirty-first day after the date of its
adoption.
INTRODUCED:
PASSED:
AYES:
NOES:
ABSENT:
*NOT YET APPROVED*
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ABSTENTIONS:
ATTEST:
____________________________ ____________________________
City Clerk Mayor
APPROVED AS TO FORM: APPROVED:
____________________________ ____________________________
Deputy City Attorney City Manager
____________________________
Director of Community Services
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EXHIBIT A
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EXHIBIT A
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EXHIBIT A EXHIBIT A
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EXHIBIT A EXHIBIT A
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EXHIBIT B PAGE 1 OF 3
Dates above are tentative target dates subject to change pending project development and acquisition of all required project permits.
Year 1 Construction 9/1/2022 1/31/2023 5 months CLOSED CLOSED CLOSED CLOSED CLOSED
No Construction 2/1/2023 8/31/2023 7 months OPEN OPEN CLOSED OPEN OPEN
Year 2 Construction 9/1/2023 1/31/2024 5 months CLOSED CLOSED CLOSED CLOSED CLOSED
No Construction 2/1/2024 8/31/2024 7 months OPEN OPEN CLOSED OPEN OPEN
Year 3 Construction 9/1/2024 1/31/2025 5 months CLOSED CLOSED CLOSED CLOSED OPEN
No Construction 2/1/2025 8/31/2025 7 months OPEN OPEN OPEN OPEN OPEN
Year 4 Construction 9/1/2025 11/30/2025 3 months CLOSED CLOSED CLOSED CLOSED OPEN
Project completed 12/1/2025 Onward N/A OPEN OPEN OPEN OPEN OPEN
Total Cummulative Trail Closure Duration Per Trail Location = 21.5
months 21.5 months 35.5
months
21.5
months
13.5
months
Target Time Period Trail Location (See Map Below)
Activity Start End Duration Segment #1 Tide Gate Structure Segment #2 Segment #3 Segment #4
3.5
18 months 18 months 32 months 18 months 10 months
OTHER TRAIL
ROUTES & DETOUR
OPEN ALL THE TIME
Byxbee Park
Parking Lot
Emb
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1
Sa
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EXISTING
TIDE GATE
STRUCTURE
TRAIL SEGMENT #1 TRAIL SEGMENT #2
TRAIL SEGMENT #3
TRAIL SEGMENT #4
CONSTRUCTION
SIGN
EXHIBIT B PAGE 2 OF 3
SIGN SIZE
4’ x 4’
48” x 48”
5’ x 3”
DETAIL - (TRUCK AND PEDESTRIAN USE)
12' TO 14'
Construction Sign for Palo Alto Flood Basin Project
EXHIBIT B PAGE 3 OF 3