COMMITTEE AGENDA MEMORANDUM
Capital Improvement Program Committee
Government Code § 84308 Applies: Yes ☐ No ☒
(If “YES” Complete Attachment A - Gov. Code § 84308)
SUBJECT: title
Receive Moffett Fish Ladder Improvement Project Update.
End
RECOMMENDATION: Recommendation
Receive information on the feasibility analysis and preliminary Staff-Recommended Alternative for the Moffett Fish Ladder Improvement Project.
Body
SUMMARY:
The Moffett fish ladder is a fish passage facility located adjacent to a drop structure on Stevens Creek approximately three miles upstream from the San Francisco Bay, in the City of Mountain View. The goal of the Moffett Fish Ladder Improvement Project (Project) is to improve steelhead passage through the facility. The Project is included in Valley Water’s Capital Improvement Program (referred to as Safe Clean Water D4.3 Fish Passage Improvements [Moffett]) and funded through construction.
The Moffett drop structure was originally constructed in the 1960s as a grade control where the streambed drops six feet in elevation over a distance of ten feet. A Denil-style fish ladder was constructed in 1985 by cutting into the concrete drop structure. The fish ladder slope creates high velocity flows which fail to meet all adult and juvenile salmonid passage and attractant flow criteria. In addition, the placement and design of the ladder traps debris within the ladder and encourages sediment deposition at the ladder’s upstream exit that restricts fish access to the ladder. These issues are common with Denil fishways, and most experts now favor different approaches to fish passage that take into account the needs of multiple species and life stages.
The Project was identified as one of four priority barriers to fish passage on Stevens Creek by the Fisheries Aquatic Habitat Collaborative Effort (FAHCE) Draft Settlement Agreement. To identify the recommended approach for improving fish passage at the Moffett drop structure, Valley Water has undertaken a Planning Study. A Planning Study identifies the problems, project objectives, feasible alternatives, and a staff-recommended alternative.
The following planning phase milestones have been completed:
• Problem Definition and Refined Objectives Report
• Conceptual Alternatives Report
• Stakeholder and public outreach
• Feasibility Evaluation
• Selection of the Preliminary Staff-Recommended Alternative
This memorandum summarizes the Project’s Feasible Alternatives Analysis and the Preliminary Staff-Recommended Alternative.
Feasible Alternatives Analysis
The feasible alternatives analysis supports the selection of a Staff-Recommended Alternative that will be further developed to complete the Planning Study and serve as the basis for project design.
Project objectives (PO) include:
PO-1: Remediate the FAHCE Priority Barrier at the Moffett Drop Structure to improve fish passage.
PO-2: Construct or improve a fishway with minimal operation and maintenance requirements.
PO-3: Minimize impacts to Stevens Creek Trail users.
Staff developed four conceptual alternatives (CA) that address the project objectives:
CA-1: Retain the Moffett Avenue fish ladder and increase maintenance efforts.
CA-2: Improve the existing drop structure and fish ladder.
CA-3: Remove existing fish ladder and construct a rock roughened channel fishway.
CA-4: Remove existing fish ladder and construct a Concrete Vortex Weir Pool and Chute Fishway.
CA-1 and CA-2 both retain the existing drop structure and only provide limited improvements to fish passage. CA-3 enhances passage by creating a roughened channel composed of a series of boulder riffles and pools, which improves fish passage and provides grade control. CA-4 replaces the existing structure with a series of channel-spanning concrete weirs and pools that allow fish to pass effectively and requires the least amount of long-term maintenance.
Each alternative is evaluated against feasibility metrics based on the project objectives, as well as other factors, which are developed through an internal stakeholder process. Each metric is assigned a weight so that more important metrics have a greater weight. Attachment 1 summarizes the criteria and their scores; the higher the score, the better the alternative meets project objectives.
Preliminary Staff-Recommended Alternative
Staff recommend moving CA-4, Concrete Vortex Weir Pool and Chute Fishway, into design. This alternative would replace the existing concrete drop structure and fish ladder at Moffett Avenue with a series of engineered concrete vortex weirs designed to provide continuous and hydraulically suitable fish passage. The proposed configuration would accommodate passage of both adult and juvenile salmonids across a range of flow conditions while reducing long-term operation and maintenance requirements relative to the existing facility. Construction sequencing and site access would be designed to minimize temporary impacts to the Stevens Creek Trail.
Next Steps
After receiving and incorporating input from the Committee, staff will finalize the Planning Study and transmit the Planning Study Report to the Board of Directors. The project will then transition to the design phase. Design is anticipated to be complete and construction to begin in 2028.
ENVIRONMENTAL JUSTICE IMPACT:
The Project is not anticipated to result in disproportionate adverse impacts to any specific community relative to the general population. No environmental justice impacts are anticipated.
ATTACHMENTS:
Attachment 1: Feasibility Alternatives Comparison
Attachment 2: PowerPoint
UNCLASSIFIED MANAGER:
Manager
Lisa Bankosh, 408-630-2618