Lower Sleepy Hollow Creek Improvements (Morningside Neighborhood Area)

 

Residents check high creek flows at Broadmoor Avenue during the December 2014 storm

 

About the Project

The Lower Sleepy Hollow Creek Project Improvements are a portion of the Ross Valley Flood Protection & Watershed Program (Program). They were first described in the Capital Improvement Plan Study for Flood Damage Reduction and Creek Maintenance for Flood Control Zone 9/Ross Valley (Study) by Stetson Engineers dated May 2011. Most of the improvements are proposed along Sleepy Hollow Creek from Broadmoor Avenue Bridge down to the Taylor Street Bridge as shown on the overview map. The goal of all the improvements is to create additional creek flow capacity. Conceptual improvements include bridge replacements, retaining wall replacements, bank stabilization, building relocation or removal, creek channel enlargement, concrete removal from the creek bed, and flood barriers along the top of bank as shown on the three detailed maps below. The Study indicated that further study is needed to refine the conceptual improvement options. The Study also indicated that detention basins are not needed along Sleepy Hollow Creek to provide 100 year flow capacity if all elements of the Program are constructed as described in the Study.

In 2016, Stetson Engineers started work on further study of this portion of lower Sleepy Hollow Creek.

Status & Next Steps

As of July 2016, Stetson Engineers is working on the “Lower Sleepy Hollow Creek Feasibility Study” which includes:

  • Acquiring new topographic data from LiDAR.
  • Obtaining new creek channel topographic data by field survey.
  • Detailed hydraulic modeling using the existing HEC-RAS model with the new topographic data added to prioritize the conceptual improvements for 25 year flow capacity and to identify downstream adverse impacts.
  • Preparation of a report describing the methods and results of the study.

At the same time, Oberkamper & Associates is performing field surveying of existing front door threshold elevations of approximately 300 homes in the 100 Year FEMA Flood Zone within the limits of the study area. Post cards were sent in June 2016 to all homes where the survey will occur. The door threshold elevations will be used in cost/benefit analysis of the proposed conceptual improvements to obtain grant funding for design and construction of the improvements.

The field survey work began in June and continued through August 2016. Contact Assistant Engineer Felix Meneau at 415-473-3223 or fmeneau@marincounty.org with any questions. A neighborhood meeting was held on July 7, 2016 and a second meeting on November 15, 2016 to describe the survey, preliminary model results and to answer any questions.

The next steps after the study are:

  • Apply for applicable grant funding when they are announced.
  • Prepare the environmental review for the Program.

Preliminary Schedule (Pending Funding & Project Approval)

A timeline (below) has been prepared for the Lower Sleepy Hollow Creek Feasibility Study. As the timeline indicates, we expect to have a draft report complete in October 2016 and hold a Neighborhood Meeting in October or November 2016 to discuss the results and to get feedback.

Click for larger image:

 

The schedule for the project implementation is difficult to estimate because it is dependent upon obtaining grant funding. It is possible that the grant funds awarded to the Memorial Park Project may be transferred to this project and that would help clarify the schedule. At this time, the project schedule is estimated to be:

Project Phase

Typical Duration

Feasibility Study

4-5 months

Program Environmental Review

12-18 months

Project Environmental Review

6-9 months

Selection of Preferred Alternative

1-3 months

Design Development & Final Design

18-24 months

Construction of Preferred Alternative

18-24 months

Total Project Duration

4-7 Years

 

A community based participatory planning and design process would be used to engage residents and stakeholders, seek their input, and provide a pathway for them to help shape the project prior to its implementation.

Upcoming Public Meetings

No upcoming meetnigs are currently scheduled specific to this project, but please check RossValleyWatershed.org homepage for other upcoming project and program meetings.

Past Public Meetings

November 15, 2016: A neighbhorhood meeting was held on November 15 at 7:00p in the Mt. Tam Room of the Isabel Cook Community Center to discuss the study results of the front door threshold (March 2017 Update: front door threshold elevation data of surveyed properties is now available by clicking here) and creek bank surveying and to discuss next steps. View the meeting flyer, presentation, videos shown in presentation, and the Exhibits (shown below) of three options achieving 25-year level of flood protection. All three options identified as achieving 25-year level of flood prtection require a combination of one or two bridge removals/replacements, new low-lying flood barriers and/or flood fences against Sleepy Hollow Creek along private properties, and a Detention Basin upstream to mitigate the increased creek flow sent downstream.

July 7, 2016: Community members gathered at Isabel Cook Community Center to learn about the front door threshold and creek bank surveying and hear an update on the status of the Program. Attendees asked several questions, shared ideas & concerns, and learned how to be part of the community engagement process. View the meeting flyer, presentation, meeting notes and Exhibits.

Background Documents

Some of these documents and concept plans may be outdated and superceded. Please contact the project manager to confirm the most current plans for this project.

Morningside/Lower Sleepy Hollow Creek Area Map Overview

Detail Maps showing three Creek & Bridge Improvement Options:

 

 

Cost & Funding

The project is preliminarily estimated to cost $9.1 million (per the 2011 Capital Improvement Plan Study for Flood Damage Reduction and Creek Management for Flood Control Zone 9/Ross Valley). Further development of the project details and project feasibility may result in increased estimated cost. Possible funding sources include the Ross Valley Flood Control Zone 9 Storm Drainage Fee and other potential grant funding sources. Other potential grant funding sources include the possible transfer of the Memorial Park grant funds to this project.

In April 2016, a technical memorandum entitled “Analysis of Project Alternatives for DWR Grant” was prepared to examine the transfer of the Memorial Park grant funds to other projects. The Sleepy Hollow Creek Alternative in the technical memorandum included only creek channel improvements and the replacement of the Morningside Bridge. The cost of these improvements was preliminarily estimated to cost $5.5 million.

Implementing Agency & Partners

Marin County Flood Control & Water Conservation District in cooperation with the Town of San Anselmo.

Contact

The project manager for this project is Felix Meneau, P.E., Assistant Engineer (fmeneau@marincounty.org).

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