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 Apr. 2017: Alviso Dock Feasibility consider replacing dock at SBYC Study Phase (I) presented at HLUET Dredging is a core issue. HLUET requests additional study Nov. 2018 County Parks presents -4.0 MLLW Scenario at HLUET -6.8ft. Mean Lower Low Water(MLLW) Scenario presented costing $21M HLUET requests a lower cost analysis Jun. 2016: Funding approved to Jun. 2018: Bathymetric Survey & perform study Report (Phase II) 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 -4.0 MLLW SCENARIO -6.8 MLLW SCENARIO December 10% 90% December 100% November 100% November 100% October 100% October 100% September 7% 93% September 100% August 23% 77% August 100% July 19% 81% July 100% June 10% 90% June 100% May 100% May 100% April 100% April 100% March 100% March 100% February 18% 82% February 100% January 19% 81% January 100% 0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100% 0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100% % of Days Not Affected % of Days Affected % of Days Not Affected % of Days Affected 6

Number of Mornings and Afternoons per Monthwhere Access is Impacted by Tides within AlvisoSlough -4.0 MLLW SCENARIO -6.8 MLLW SCENARIO 90% 80% 70% 60% ACCESS WILL NOT BE IMPACTED 50% 40% BY TIDES. 30% 20% 10% 0% % of Mornings Affected % of Afternoons Affected 7

Summary o If the proposed public dock were to be developed, dredging is recommended o Relative to the -6.8ft. MLLW scenario costs can be reduced by dredging to -4.0ft. MLLW, but access is significantly impacted o Both scenarios involve high initial capital expenditure and significant ongoing maintenance costs and staff time for permitting 8

Questions 9