Monday, April 9, 2018

Sea Level Rise : Please Read

How about we start with a moratorium on impervious surfaces and work to incorporate more green infrastructure into future building ?  

Regardless of any well meaning proposed solutions, the last thing we need around here is another top down, one size fits all approach that imposes more taxes on people who can barely afford to stay here as it is. That is my opinion.

Besides, any funding should go to an area of greatest need. This is how all projects should be decided. Residents of Marin City to travel to and from the 94941 area code for work and school. 

---------- Forwarded message ---------
From: Curry Eckelhoff
Date: Mon, Apr 9, 2018, 12:22 PM
Subject: Think piece on our SLR problem...

Good Morning all,

Chuck Oldenburg is a long time resident of Homestead Valley just over the hill from Tam Valley which is also part  of the Tamalpais Planning Area. He is currently a member of Flood Control Board for Zone 3. He is very interested in Sea Level Rise and its impact on the 94941 area. His think piece is very interesting and presents a solution that could and should be considered. There are studies underway for a broader area than just 94941 but maybe 94941 should push for a solution for us to start now or in the near future. What do you think? This will be expensive and is it worth it to you who live here in our little slice of Paradise?

Curry & TVIC

Mill Valley Tidal District

The sea level is expected to rise 3 ft. by the year 2100.  If nothing is done, San Francisco Bay will flood adjacent marshes and developed properties. Billions of dollars are required to construct tidal barriers that would prevent such disastrous inundations. Bay area agencies will seek federal funding.

Marin City, a low-income community with federal-owned public housing is currently considering a possible FEMA grant to fund of a flood control project. Success is likely.

Mill Valley 94941, a much more affluent community, stands little chance of receiving federal funding. Funding for a tidal barrier near the Richardson Bay Bridge that will eliminate flooding can come from bond issues.

The boundaries of a Mill Valley Tidal District (MVTD) would be almost the same as those of the Zip code 94941 area. Voters in the Mill Valley School District (MVSD) have recently passed large bond issues and parcel taxes to meet school needs.  Voters in the MVTD will likely meet the flood control needs.

Expected Milestones

Accomplishments before 2030: established the Mill Valley Tide District; passed a $10 million bond issue; significant progress made on tidal barrier design, engineering, environmental and economic studies; acquired all permits; constructed a rock, dirt and concrete levee with two gates; demonstrated routine operation of normally open gates, closed at low tide before a king tide.  Accepted risk of flooding when a king tide and a major storm coincide.

Accomplishments before 2050: passed a second $10 million bond issue; increased levee height; installed pumps; demonstrated routine operation of pumps and gates; prevented all flooding including when a king tide coincides with a major storm; increased level of highway 101 and on and off ramps.

Accomplishments before 2100: increased tidal barrier height; demonstrated routine prevention of flooding of Mill Valley 94941 area.

Tidal Barrier 94941

Tidal Barrier 94941 would extend from Seminary Drive to Highway 101 next to the heliport. It would comprise a dam (or levee) about 2200 ft. long, several fish-friendly floodgates, and a pump station.

Adapt to sea level rise in Tamalpais Valley, Almonte, Mill Valley, Alto, and Strawberry in zone 94941.
Protect wetlands and developed properties from king tides and storm flooding.
Eliminate tides higher than 5.5 ft in the tidal basin of Coyote Creek and Arroyo Corte Madera del Presidio watersheds.
Provide a low water level in the tidal basin to accommodate runoff when a storm is expected.

Operations When Sea Level Rise is 3 ft. (in 2100?)
Richardson Bay sea level would typically range from 3 ft. to 8 ft. i.e., 3 ft. above current levels. Operation of the gates would limit the corresponding sea level in the 94941 basin to 3 ft. to 5 ft. Pumps are required to lower the sea level to below 3 ft. When a storm is expected, pumps could establish a low sea level at any time during the normal tidal cycle to receive and pump out storm runoff.

Tidal Barrier 94941 would preserve historic tidal conditions in the 94941 tidal basin.
Current flooding at Manzanita and Tam Junction would be eliminated.
Bothin Marsh, Bay Front Park, and the Shared-use Path would be unaffected by sea level rise.

Construction Progress
Tidal Barrier 94941 could initially be built for adaptation to a 1 ft. sea level rise. It could then periodically be made higher as the sea level rises to 3 ft.  Adaptation to larger sea level rises would call for further heightening and lengthening of the barrier. Maximum length of the barrier extending from the cliffs on each end would be about 2300 ft.

Satellite photo showing Tidal Barrier 94941 (yellow) and the wetland and developed area it protects.

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