Embed Size (px)
Citation preview
Presentation Developed Prior to Input From 12/17/03 Adobe Collaborative Meeting
Adobe Upper Reach 5Conceptual Plan Issues
December 9, 2003Workshop
Presentation Developed Prior to Input From 12/17/03 Adobe Collaborative Meeting
Modeling of Flows
• At minimum, provide capacity to convey what flows under W. Edith Ave. Bridge
• Downstream of W. Edith Ave. Bridge:– Accommodate Flows A, B1, and B2– Partially accommodate Flows A, B1, B2
and allow for overland flow on Rogez/Astiz property parallel to creek
Presentation Developed Prior to Input From 12/17/03 Adobe Collaborative Meeting
Top of Bank Boundaries
• Before moving forward, there must be agreement on allowable top-of-bank margin for proposed project– Line 1 – twice width of existing creek– Line 2 – matches width of creek d/s of
Robleda Drain– Line 3 – Swanson’s 1% top-of-bank
Presentation Developed Prior to Input From 12/17/03 Adobe Collaborative Meeting
Top-of-Bank Boundaries (cont’d)
• Middle line seems to be good working top-of-bank target
• Can land between Line 2 and Line 3 be potentially used for mitigation planting?
Presentation Developed Prior to Input From 12/17/03 Adobe Collaborative Meeting
Width of Creek Channel
• Upper Reach 5 should not be wider than lower Reach 5, within limits of good channel design
• Can creek be made deeper to minimize channel width w/out compromising downstream and upstream portions or acceptable creek design?
Presentation Developed Prior to Input From 12/17/03 Adobe Collaborative Meeting
Channel Relocation
• Removal of oxbow near Theis property is OK
• Creek channel can be moved 5-10 feet toward LAH side if needed to protect trees on Los Altos side
Presentation Developed Prior to Input From 12/17/03 Adobe Collaborative Meeting
Banks
• ACWG proposal includes gabion or rock rip rap for creek banks to minimize channel width
• Regulatory agencies may have issues with these options and may require mitigation for installing such “hardscape”
Presentation Developed Prior to Input From 12/17/03 Adobe Collaborative Meeting
Mitigation
• Mitigation may be required for:– Adding hardscape to channel – Loss of riparian habitat along top-of-
bank due to channel widening• Ratio of mitigation varies based on value of
lost habitat• Mitigation ratios? 1:1, 2:1, 3:1
Presentation Developed Prior to Input From 12/17/03 Adobe Collaborative Meeting
Mitigation (cont’d)
• Regulatory agencies prefer mitigation to be done at site of impacts
• District has strong interest in mitigating for impacts on site
• Minimize channel width and use portions of Rogez/Astiz properties for mitigation plantings
Presentation Developed Prior to Input From 12/17/03 Adobe Collaborative Meeting
Transplanting Trees
• District will evaluate this work• In the interest of cost-efficiency, this
criterion may be difficult to achieve
Presentation Developed Prior to Input From 12/17/03 Adobe Collaborative Meeting
Proposed Conceptual Approach
• Detailed hydrology to determine Flows A, B1, and B2
• Assume rock rip rap or gabion banks with slopes of 1:1 or 1.5:1
• Develop appropriate channel bottom slope– Match existing downstream invert and desired
invert under W. Edith Bridge– Drop structures to allow for fish passage
Presentation Developed Prior to Input From 12/17/03 Adobe Collaborative Meeting
Proposed Conceptual Approach (cont’d)
• Determine minimum width of channel to convey flow (A) coming under W. Edith Bridge
• Determine minimum width of channel to convey portion or all of overland flows B1 and B2
Presentation Developed Prior to Input From 12/17/03 Adobe Collaborative Meeting
Proposed Conceptual Approach (cont’d)
• Follow CEQA process to determine impacts of project and develop mitigation proposal
• Maintain continual interaction with ACWG and City/Town while developing alternatives
Presentation Developed Prior to Input From 12/17/03 Adobe Collaborative Meeting
NEXT STEPS
• Draft Proposed Project Plan (PPP) – January 28, 2004
• Review, discuss, modify PPP – February 23, 2004
• Prepare for District Board consideration – March 2004
• Present PPP to Board – April 6,2004• Incorporate into Capital Improvement
Program
