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Alviso Dock Feasibility Study

Published on: 1/9/2019 9:19 AM
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Alviso Dock 


Project Planner: Cherise Orange

Contact: cherise.orange@prk.sccgov.org​; 408-335-2228

 



Background

At the August 2015, community members in attendance of a Housing, Land Use, Environment, and Transportation (HLUET) Committee meeting suggested that the County pursue replacing and operating the existing Alviso Slough boat dock located at the South Bay Yacht Club (SBYC) near Alviso Marina County Park as a public dock. HLUET directed the County of Santa Clara Department of Parks and Recreation (County Parks) to undertake a feasibility study that would assess the possibility of replacing the dock and the potential costs to operate the new public facility.
The Study was completed in 3 phases and accepted by HLUET on November 15, 2018.
  

Location

The potential project site is located in close proximity to the intersection of Hope Street and N. Taylor Street in the Alviso community. The existing dock is located in the Alviso Slough 0.2 miles south of the County Park and is currently operated by the SBYC; a private entity. The Slough itself is bordered by Santa Clara Valley Water District (SCVWD) Flood protection levees and wetlands that are part of the Don Edwards Wildlife Refuge.


 

Study Scope 

 
The project scope accessed by the Feasibility Study includes replacement of 128 feet of the existing dock to provide three (3) berths, and construction of approximately 600 feet of additional dock to provide approximately 15 berths, for a total of 18 berths. The scope also includes compliance with Americans with Disabilities Act (ADA) standards and other utility and landside amenities as a public-serving dock.
 
 
Phase I: Alviso Dock Feasibility Study
 
The Feasibility Study was based on a review of background documents, site analysis, financial analysis of project alternatives, and interviews with the following key stakeholders:
·         U.S. Army Corps of Engineers (USACE)
·         State Lands Commission (SLC)
·         San Francisco Bay Conservation and Development Commission (BCDC)
·         SCVWD
·         SBYC
The study elevated critical challenges to implementing the dock replacement project under three (3) potential courses of action (referred to as alternatives) and further refined the analysis into feasibility findings. The Feasibility Study concluded that dock construction appeared feasible from an engineering standpoint; however, environmental and cost constraints were significant and potentially prohibitive. The Study’s resulting conclusion was based on the assumption that there was a high potential that initial dredging and long-term maintenance dredging would be necessary to facilitate the Project.
To address the uncertainties relating to dredging, that remained after completion of the Feasibility Study, HLUET requested further analysis to assess the need for dredging, including sediment stability and existing limitations to waterway navigability along the slough and at the proposed Project location.
 

Phase II: Alviso Slough Bathymetric Survey
 
The Department hired consultants to conduct a bathymetric data to characterize the slough, the Project area, and the County Park launch ramp area. Once compiled, the bathymetric data and overall Survey Report confirmed that development of a public dock facility in Alviso Slough merited some level of dredging. The report identified the most appropriate potential solution to dredge to a depth of -6.8 feet(ft.) Mean Lower Low Water (MLLW- the average lower low water height of each tidal day; measured twice a day, in the morning and afternoon) and width of 50ft. to provide adequate room for vessel maneuvering and passing; this was based on Guidelines from the California Department of Boating and Waterways (DBAW). However, the width of 50ft. does not meet the DBAW Guidelines of 75ft. minimum width.
The Survey findings reinforced that Alternative 2B (Dock Replacement, Dredging Near Potential Dock, and Slough Dredging) from the Feasibility Study Phase I report was the most appropriate scenario to allow less restricted public boating access from the dock to the San Francisco Bay. The Consultant team determined the estimated capital cost of the potential dock project to be $21.4M with a net annual cost for dredging at $1.7M - $5M.
To address the significant project cost, HLUET requested further analysis of a lesser project.
 
DISCLAIMER: The Alviso Dock Feasibility Study Phase II Bathymetric Survey represents a snapshot in time of the channel depth and shape of the Alviso Slough. The Bathymetric Survey findings should not be used as a definitive guide or substitute for protocols of boting navigation and safety.  

Phase II: Alviso Slough Bathymetric Survey Follow Up
 
At the June 2018 meeting, the HLUET Committee directed the Department to report back and address the following questions:
 
  1. Is dredging necessary to allow the construction of the potential public dock, and if so what is the minimum level of dredging necessary and what costs would be associated?
  2. What quantity and cost would be associated with dredging to -4.0ft. MLLW, in comparison to the -6.8ft. MLLW Project in the Bathymetric Survey?
  3. How often would tides limit access to the potential dock facility for both the -4.0ft. MLLW and -6.8ft. MLLW scenarios?
To answer the questions above, the consultant produced additional estimates and the Department performed additional review and refinement of the work carried out in Phases I and II of the Feasibility Study. The resulting findings confirmed that dredging for both construction of the proposed public dock and to provide access from the dock to the Bay provides the broadest range of access throughout tidal conditions and skill-level of boaters. Dredging the slough to a depth of -6.8ft. MLLW and width of 50-ft. is the most suitable option to make Alviso a fully accessible destination for recreational and emergency use.
 
On Thursday, November 18, 2018 the HLUET Committee accepted the full report.

 
 

 

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