HomeMy WebLinkAboutItem 6a. Authorize On-call Engineering Professional Services for the Design of Spillway Wall Offsets RepairCity of San Luis Obispo, Title, Subtitle
Whale Rock Commission Report
Whale Rock Commission Meeting – May 28, 2026
Agenda Item 6a – Authorize On-call Engineering Professional Services for the Design of Spillway Wall Offsets
Repair
FROM: Shawna Scott, Assistant Director of Utilities
PREPARED BY: Noah Evans, Whale Rock Reservoir Supervisor
SUBJECT: AUTHORIZE ON-CALL ENGINEERING PROFESSIONAL
SERVICES FOR THE DESIGN OF SPILLWAY WALL OFFSET
REPAIRS
RECOMMENDATION
Authorize selection of a consultant from the City of San Luis Obispo’s Qualified Civil
Engineering On-Call Consultant List to provide engineering professional services for
the design of the Whale Rock Reservoir Spillway Offset Repairs and issuance of a
purchase order, and any subsequent change orders, in an amount not to exceed the
total authorized budget of $250,000.
DISCUSSION
Background
In July 2025, staff received the Annual
Inspection Report from the Division of Safety
of Dams (DSOD). In this letter, the DSOD
directed the Whale Rock Commission to grind
down the offsets1 on the upper spillway wall
seams to improve water flow and to reduce
pressure that could force water into the
spillway wall seams and cause erosion or
displacement.
The City of San Luis Obispo Utilities
engineering team reviewed the DSOD
direction and recommended further evaluation
based on concerns that grinding down the
concrete could expose reinforcing steel and
weaken the spillway wall. To understand the
impacts of grinding the spillway walls to
reduce the offsets, staff worked with the HDR
Engineering team who was onsite to perform the Stilling Basin condition assessment.
HDR Engineering staff used a Ground Penetrating Radar tool to scan the spillway
1 Spillway wall offsets are structural misalignments or gaps, often causing flow discontinuities that can lead to
cavitation damage. In dams, these offsets are typically surface irregularities, joints, or cracks that trigger
cavitation.
WHALE ROCK SPILLWAY WALL OFFSET
Page 15 of 103
City of San Luis Obispo, Title, Subtitle
Whale Rock Commission Report
Whale Rock Commission Meeting – May 28, 2026
Agenda Item 6a – Authorize On-call Engineering Professional Services for the Design of Spillway Wall Offsets
Repair
wall and determine the thickness of the concrete covering the reinforcing steel. The
results of the scan confirmed that grinding could expose the reinforcing steel or
reduce the material's thickness, leading to cracking or spalling of the concrete. This
finding indicates that grinding the concrete walls is not an acceptable method for
reducing spillway wall offsets.
In place of grinding the offsets, staff proposed adding material that will reduce the
spillway wall offsets, while preserving the designed thickness that protects the
reinforcing steel. To achieve long-term success with the repairs, a firm experienced
in concrete spillway repairs should design the project and specify the products to be
used in the repair.
ENVIRONMENTAL REVIEW
This project is categorically exempt from the California Environmental Quality Act
(CEQA) pursuant to State CEQA Guidelines Sections 15301 (Existing Facilities) and
15302 (Replacement or Reconstruction). The Design of Spillway Wall Offset Repairs
will have the same purpose as the existing spillway walls and will not alter the
Reservoir's capacity or result in an expansion of use.
FISCAL IMPACT
Design of Spillway Wall Offset Repairs
Funding
Category
Contribution
Source
Amount
Budgeted
Amount Spent
Capital Asset
Expense
2026-27 CIP
Contributions
$250,000 $0
ALTERNATIVES
The Commission may deny the staff recommendation and direct staff to make the
spillway wall offset repairs by grinding down the spillway walls. Implementation of this
alternative may be detrimental to the spillway walls' performance and presents public
health and safety risks. Alternatively, the Commission may direct staff not to proceed
with smoothing the spillway wall offsets. Not complying with the DSOD’s request to
smooth the spillway wall offsets could cause the DSOD to impose a reduction in the
volume of water Whale Rock Dam is permitted to impound.
ATTACHMENTS
No attachments.
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