presentation developed prior to input from 12/17/03 adobe collaborative meeting adobe upper reach 5...

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