Alviso Dock Feasibility Study Phase II: Follow-Up HOUSIN G, LAND - - PowerPoint PPT Presentation

Alviso Dock Feasibility Study Phase II: Follow-Up

HOUSIN G, LAND USE, ENVIR ON MENT & TRANSPOR TATI ON (HLUET) COMMIT TE E

COU NTY OF SA NTA CLARA

NOVEMBER 15, 2018

1

Background

• Apr. 2015 Public asks County to

consider replacing dock at SBYC

• Jun. 2016: Funding approved to

perform study

• Apr. 2017: Alviso Dock Feasibility

Study Phase (I) presented at HLUET

Dredging is a core issue. HLUET requests additional study

• 6.8ft. Mean Lower Low Water(MLLW)

Scenario presented costing $21M HLUET requests a lower cost analysis

• Jun. 2018: Bathymetric Survey &

Report (Phase II)

• Nov. 2018

County Parks presents

• 4.0 MLLW Scenario at

HLUET

2

Comparison of Dock Construction Costs

*Soft Costs include design, contingency, environmental and permits, engineering, etc.

3

Comparison of Scenarios

4

Comparison of -4 MLLW and -6.8MLLW Scenarios

Mean Lower Low Water (MLLW) The average height of low tide each

• day. Measured twice a day, in the

morning and afternoon Draft The draft determines the minimum depth of water a boat can safely sail Dredge Zone Location of sediment needed to be removed above -4.0 and -6.8 Scenarios respectively

5

Number of Days per Month where Accessis Impacted by Tides within AlvisoSlough

10% 7% 10% 100% 100% 82% 81% 90% 100% 93% 77% 81% 90% 100% 100% March February 18% January 19% June May April August 23% July 19% December November October September 0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100% % of Days Not Affected % of Days Affected

• 4.0 MLLW SCENARIO
• 6.8 MLLW SCENARIO

December 100% November 100% October 100% September 100% August 100% July 100% June 100% May 100% April 100% March 100% February 100% January 0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100% % of Days Not Affected % of Days Affected

6

100%

Number of Mornings and Afternoons per Monthwhere Access is Impacted by Tides within AlvisoSlough

20% 10% 0% 30% 40% 50% 90% 80% 70% 60% % of Mornings Affected % of Afternoons Affected

• 4.0 MLLW SCENARIO
• 6.8 MLLW SCENARIO

ACCESS WILL NOT BE IMPACTED BY TIDES.

7

Summary

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• If the proposed public dock were to be developed, dredging is recommended
• Relative to the -6.8ft. MLLW scenario costs can be reduced by dredging to
• 4.0ft. MLLW, but access is significantly impacted
• Both scenarios involve high initial capital expenditure and significant ongoing

maintenance costs and staff time for permitting

Questions

9